| Page 2 of 2 | 1 | 2 |
|
|
On Mon, 28 Jul 2003 07:02:53 GMT, (John Crighton)
wrote: On Sun, 27 Jul 2003 22:33:48 +0100, Paul Burridge wrote: How did you go with Win's soft start motor controller? Currently under construction... -- Hello Paul, you are dragging the anchor a bit. That was months ago! :-) Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf This also looks a possibility: http://w1.859.telia.com/~u85920178/use/rc-prop.htm Might be a contender for the next 'bot, possibly? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Mon, 28 Jul 2003 07:02:53 GMT, (John Crighton)
wrote: On Sun, 27 Jul 2003 22:33:48 +0100, Paul Burridge wrote: How did you go with Win's soft start motor controller? Currently under construction... -- Hello Paul, you are dragging the anchor a bit. That was months ago! :-) Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf This also looks a possibility: http://w1.859.telia.com/~u85920178/use/rc-prop.htm Might be a contender for the next 'bot, possibly? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
"Paul Burridge" wrote in message
... On Mon, 28 Jul 2003 13:20:27 GMT, (John Crighton) wrote: The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. John, what in your experience causes this 'servo-twitching'? I've observed it myself at close hand many times. The last time it happened, we cured it by isolating the die-cast box the rx was mounted in from the chassis. I still can't figure out why this worked, as I'd have thought grounding it *ought* to solve the problem. But in this instance, grounding it *created* the problem and isolating it solved it! Sometimes when I see those servos behaving like they've got a mind of their own it almost makes me believe in the supernatural. R/C servos are EXTREMELY sensitive to trash on the power supply leads. Grounding the box probably coupled some trash into the ground lead to the servo. I don't know what you have in your system, but I'd start by investing in a few small 250 uF (nominal) capacitors and put them directly across the servo supply leads. Use Y-harnesses to hook them in if you don't feel like modifying a cable. |
"Paul Burridge" wrote in message
... On Mon, 28 Jul 2003 13:20:27 GMT, (John Crighton) wrote: The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. John, what in your experience causes this 'servo-twitching'? I've observed it myself at close hand many times. The last time it happened, we cured it by isolating the die-cast box the rx was mounted in from the chassis. I still can't figure out why this worked, as I'd have thought grounding it *ought* to solve the problem. But in this instance, grounding it *created* the problem and isolating it solved it! Sometimes when I see those servos behaving like they've got a mind of their own it almost makes me believe in the supernatural. R/C servos are EXTREMELY sensitive to trash on the power supply leads. Grounding the box probably coupled some trash into the ground lead to the servo. I don't know what you have in your system, but I'd start by investing in a few small 250 uF (nominal) capacitors and put them directly across the servo supply leads. Use Y-harnesses to hook them in if you don't feel like modifying a cable. |
On Mon, 28 Jul 2003 22:24:11 +0100, Paul Burridge
wrote: On Mon, 28 Jul 2003 13:20:27 GMT, (John Crighton) wrote: The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. John, what in your experience causes this 'servo-twitching'? In that incident with the rich guy, he was a few hundred yards away from his model and my transmitter, only 20 feet away. even though it was on a different channel upset his signal. Therefore his servos twitched and his model crashed. I've observed it myself at close hand many times. Waving a transmitter with a fully extended antenna beside the model will cause a bit of servo twitching. The signal is too strong. That is why you see people doing close range testing with the antenna retracted. The last time it happened, we cured it by isolating the die-cast box the rx was mounted in from the chassis. I still can't figure out why this worked, as I'd have thought grounding it *ought* to solve the problem. I would have thought that grounding the RX to the box would be good practice also. Not having a circuit to guide you, maybe you were grounding a spot on the PCB that should not be grounded. But in this instance, grounding it *created* the problem and isolating it solved it! Sometimes when I see those servos behaving like they've got a mind of their own it almost makes me believe in the supernatural. You got some good advice from John R Strohm in regards to fitting decoupling capacitors across the servo supply leads. I am assuming that your R/C gear is operating from its own battery supply not the main driving motor supply. Using the same battery for the radio and main driving motors could cause servo twitching. Pity there isn't one of these fighting robot clubs here in Sydney. I would like to have a go. Paul you will have to put some pictures up somewhere so we can have a look. Regards, John Crighton Sydney |
On Mon, 28 Jul 2003 22:24:11 +0100, Paul Burridge
wrote: On Mon, 28 Jul 2003 13:20:27 GMT, (John Crighton) wrote: The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. John, what in your experience causes this 'servo-twitching'? In that incident with the rich guy, he was a few hundred yards away from his model and my transmitter, only 20 feet away. even though it was on a different channel upset his signal. Therefore his servos twitched and his model crashed. I've observed it myself at close hand many times. Waving a transmitter with a fully extended antenna beside the model will cause a bit of servo twitching. The signal is too strong. That is why you see people doing close range testing with the antenna retracted. The last time it happened, we cured it by isolating the die-cast box the rx was mounted in from the chassis. I still can't figure out why this worked, as I'd have thought grounding it *ought* to solve the problem. I would have thought that grounding the RX to the box would be good practice also. Not having a circuit to guide you, maybe you were grounding a spot on the PCB that should not be grounded. But in this instance, grounding it *created* the problem and isolating it solved it! Sometimes when I see those servos behaving like they've got a mind of their own it almost makes me believe in the supernatural. You got some good advice from John R Strohm in regards to fitting decoupling capacitors across the servo supply leads. I am assuming that your R/C gear is operating from its own battery supply not the main driving motor supply. Using the same battery for the radio and main driving motors could cause servo twitching. Pity there isn't one of these fighting robot clubs here in Sydney. I would like to have a go. Paul you will have to put some pictures up somewhere so we can have a look. Regards, John Crighton Sydney |
On Mon, 28 Jul 2003 22:52:21 +0100, Paul Burridge
wrote: Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf You'll have to forgive me here, John, as i'm battling with a duff display on the computer I'm using at the moment and I was only able to glimpse the data for a few seconds, but this chip doesn't seem to be suitable for 40Mhz FM, does it? I'm sure your general solution to the problem is an excellent one, though, if a suitable chip can be found. -- Hello Paul, under Features on page 1 it says 50KHz to 72 MHz but not FM. I forgot about that. My mistake. OK we'll keep looking for something that suits your FM transmitter. Or find, beg, borrow, "buy used," or build an ordinary AM R/C transmitter. Ten quid should get you an old style metal cased Futaba transmitter. A model shop gave me the circuit diagram decades ago of an old JR brand transmitter that I bought off them in dud condition, cheap. Keep looking. That model shop/sanwa agency are a bit mean that is why I said dump their product. Stick with brands that will offer support and circuits. There is plenty of info with that LM1872 chip, that is what makes it attractive to use. Have Fun, John Crighton Sydney |
On Mon, 28 Jul 2003 22:52:21 +0100, Paul Burridge
wrote: Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf You'll have to forgive me here, John, as i'm battling with a duff display on the computer I'm using at the moment and I was only able to glimpse the data for a few seconds, but this chip doesn't seem to be suitable for 40Mhz FM, does it? I'm sure your general solution to the problem is an excellent one, though, if a suitable chip can be found. -- Hello Paul, under Features on page 1 it says 50KHz to 72 MHz but not FM. I forgot about that. My mistake. OK we'll keep looking for something that suits your FM transmitter. Or find, beg, borrow, "buy used," or build an ordinary AM R/C transmitter. Ten quid should get you an old style metal cased Futaba transmitter. A model shop gave me the circuit diagram decades ago of an old JR brand transmitter that I bought off them in dud condition, cheap. Keep looking. That model shop/sanwa agency are a bit mean that is why I said dump their product. Stick with brands that will offer support and circuits. There is plenty of info with that LM1872 chip, that is what makes it attractive to use. Have Fun, John Crighton Sydney |
On Mon, 28 Jul 2003 23:07:59 +0100, Paul Burridge
wrote: Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf This also looks a possibility: http://w1.859.telia.com/~u85920178/use/rc-prop.htm Might be a contender for the next 'bot, possibly? -- Hello Paul, yes it does. That is a great site. Harry gives you the circuit, the artwork and tells you how he makes his printed circuit boards. Harry explains that he has managed to use that little AM Rx on FM also. I think you plenty of info now Paul. Have Fun, John Crighton Sydney |
On Mon, 28 Jul 2003 23:07:59 +0100, Paul Burridge
wrote: Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf This also looks a possibility: http://w1.859.telia.com/~u85920178/use/rc-prop.htm Might be a contender for the next 'bot, possibly? -- Hello Paul, yes it does. That is a great site. Harry gives you the circuit, the artwork and tells you how he makes his printed circuit boards. Harry explains that he has managed to use that little AM Rx on FM also. I think you plenty of info now Paul. Have Fun, John Crighton Sydney |
"John Crighton" wrote in message ... On Mon, 28 Jul 2003 10:19:13 +0100, "Hans Summers" wrote: Back to your interference problem. Is your operating channel frequency smack in the middle of the 40 Mhz band? If so, maybe you could try a different set of crystals, so that you operate as far away from everyone else as possible. Or simply just borrow a different set of crystals in case there is a weird mix going on, just to eliminate that possibility. We've recently got wise to that one and I've ordered a pair of xtals from the *last* channel of the band. That's what we'll be running with come the last week in August, when we're due up for the next filming. Not necessarily the solution, I got bitten by that one once some 9 or 10 years ago when I used to fly radio controlled aircraft (in the UK on 35MHz). It bothered me when someone else at the flying field had the same crystal as I did and I had to wait for them to finish flying before I could fly. So bought another pair of crystals, the highest I could find, if I recall that was channel 83 (35.230MHz). Everything was fine for a while but a few weeks later I crashed after losing radio contact with my plane. A little investigation (in between gluing the aircraft bits back together) found the cause. A channel vs frequency listing, compared with the MHz printed on the crystal case revealed that the receivers were single conversion superhets with 110KHz IF. Channel separation was 10KHz. Clearly with that setup, image rejection is practically negligible. So someone transmitting on channel 61, 220KHz away, interferes with channel 83. After that I went back to my crystals on 76 smack in the middle of everyone elses, learnt to be patient if someone was already using the channel, and had no more problems ;-) Hans G0UPL http://www.HansSummers.com Hello Hans, what brand/make was that R/C set that you had? It was a Futaba, I don't recall which one. Very old and battered but worked great. I've been away from aero-modelling for 9 years or so and don't know what's new now - but at that time, the latest control sets were dual conversion (avoiding that image problem) and PCM (Pulse Code Modulation) compared to the old PPM like mine (Pulse Position Modulation). It always seemed to me (perhaps somewhat subjectively) that the PCM tranceivers, which were supposed to be more reliable, were in fact more prone to interference. In the presence of interference the flyer seemed to have no control, presumably because the incoming code was scrambled and the receiver couldn't make head or tail of it. With the old fashioned PPM sets it seemed that often even if interference was causing your servos to twitch a little you still had some degree of control over it, often enough to turn it round and bring it in closer whereupon full control would return and permit a hasty landing. You have reminded me of a silly incident at my model flying club decades ago. One of the wealthier club members was having all sorts of trouble with his model, engine and radio gear so he flung heaps of money at a ready made, ready to fly model with an expensive four stroke engine, and a new expensive all singing and dancing radio control set. First day out with the new model and everything is going well for him, he was doing stunts all over the sky. My models were el cheapo sticks and tissue construction, I couldn't afford nice covering film/material. I was more interested in home built radio control gear. Radio assisted free flight was more my style. When the fuel ran out in my models I didn't mind walking a few hundred yards if necessary to retrieve my model. So I am off for a long walk with my transmitter still switched on as one would. (The receiver gets switched off first then the transmitter.) The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. Ha Ha, similar story here. I was a student at the time, had very little money. Serves that rich fellow right for flying so low near you, sounds dangerous. I used to have a Hi-Boy 4-channel trainer with 0.40 cu inch 2-stroke OS engine. When it came to me it had spent at least a decade in a damp garage and required an almost complete fuselage rebuild to clear the rot. Quite likely therefore that by the time I finally flew it, the original dimensions weren't adhered to any longer. A particular weakness seemed to be the nosewheel which was endlessly breaking up during my bad landings. Solution to that one was just to remove it and fly the thing as a taildragger. The OS40 engine worked a treat, perhaps slightly overpowering the model: I used to be able to take off and fly vertically immediately like the jet fighters at air shows. Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. Happy days ;-) Hans http://www.HansSummers.com Fun and games, eh! :-) Regards, John Crighton Sydney |
"John Crighton" wrote in message ... On Mon, 28 Jul 2003 10:19:13 +0100, "Hans Summers" wrote: Back to your interference problem. Is your operating channel frequency smack in the middle of the 40 Mhz band? If so, maybe you could try a different set of crystals, so that you operate as far away from everyone else as possible. Or simply just borrow a different set of crystals in case there is a weird mix going on, just to eliminate that possibility. We've recently got wise to that one and I've ordered a pair of xtals from the *last* channel of the band. That's what we'll be running with come the last week in August, when we're due up for the next filming. Not necessarily the solution, I got bitten by that one once some 9 or 10 years ago when I used to fly radio controlled aircraft (in the UK on 35MHz). It bothered me when someone else at the flying field had the same crystal as I did and I had to wait for them to finish flying before I could fly. So bought another pair of crystals, the highest I could find, if I recall that was channel 83 (35.230MHz). Everything was fine for a while but a few weeks later I crashed after losing radio contact with my plane. A little investigation (in between gluing the aircraft bits back together) found the cause. A channel vs frequency listing, compared with the MHz printed on the crystal case revealed that the receivers were single conversion superhets with 110KHz IF. Channel separation was 10KHz. Clearly with that setup, image rejection is practically negligible. So someone transmitting on channel 61, 220KHz away, interferes with channel 83. After that I went back to my crystals on 76 smack in the middle of everyone elses, learnt to be patient if someone was already using the channel, and had no more problems ;-) Hans G0UPL http://www.HansSummers.com Hello Hans, what brand/make was that R/C set that you had? It was a Futaba, I don't recall which one. Very old and battered but worked great. I've been away from aero-modelling for 9 years or so and don't know what's new now - but at that time, the latest control sets were dual conversion (avoiding that image problem) and PCM (Pulse Code Modulation) compared to the old PPM like mine (Pulse Position Modulation). It always seemed to me (perhaps somewhat subjectively) that the PCM tranceivers, which were supposed to be more reliable, were in fact more prone to interference. In the presence of interference the flyer seemed to have no control, presumably because the incoming code was scrambled and the receiver couldn't make head or tail of it. With the old fashioned PPM sets it seemed that often even if interference was causing your servos to twitch a little you still had some degree of control over it, often enough to turn it round and bring it in closer whereupon full control would return and permit a hasty landing. You have reminded me of a silly incident at my model flying club decades ago. One of the wealthier club members was having all sorts of trouble with his model, engine and radio gear so he flung heaps of money at a ready made, ready to fly model with an expensive four stroke engine, and a new expensive all singing and dancing radio control set. First day out with the new model and everything is going well for him, he was doing stunts all over the sky. My models were el cheapo sticks and tissue construction, I couldn't afford nice covering film/material. I was more interested in home built radio control gear. Radio assisted free flight was more my style. When the fuel ran out in my models I didn't mind walking a few hundred yards if necessary to retrieve my model. So I am off for a long walk with my transmitter still switched on as one would. (The receiver gets switched off first then the transmitter.) The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. Ha Ha, similar story here. I was a student at the time, had very little money. Serves that rich fellow right for flying so low near you, sounds dangerous. I used to have a Hi-Boy 4-channel trainer with 0.40 cu inch 2-stroke OS engine. When it came to me it had spent at least a decade in a damp garage and required an almost complete fuselage rebuild to clear the rot. Quite likely therefore that by the time I finally flew it, the original dimensions weren't adhered to any longer. A particular weakness seemed to be the nosewheel which was endlessly breaking up during my bad landings. Solution to that one was just to remove it and fly the thing as a taildragger. The OS40 engine worked a treat, perhaps slightly overpowering the model: I used to be able to take off and fly vertically immediately like the jet fighters at air shows. Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. Happy days ;-) Hans http://www.HansSummers.com Fun and games, eh! :-) Regards, John Crighton Sydney |
In (rec.radio.amateur.homebrew), Hans Summers wrote:
Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. From RFC 1925: "(3) With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead." -- Mike Andrews Tired old sysadmin since 1964 |
In (rec.radio.amateur.homebrew), Hans Summers wrote:
Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. From RFC 1925: "(3) With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead." -- Mike Andrews Tired old sysadmin since 1964 |
Watson A.Name - 'Watt Sun' wrote in message ...
.... How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. I think that's a popular misconception. The resonator Q is essentially the same as the Q of the same part used as a shielded inductor, and the shield actually lowers the Q from what it is with an inductor in free air (so long as it's not large enough to radiate significantly). They're tunable, but I'm not sure how much. They're certainly easily tunable over a few percent, if you need that... But the problem as originally stated implies a filter of fairly high order and low in-band attenuation, which in turn implies resonators of very high unloaded Q. 20kHz bandwidth at 40MHz in a single tank is a loaded Q of 2000, and to keep attenuation low, the unloaded resonator Q should be perhaps 5 times that much. It would be worse for a multi-pole filter. All this tells me it's silly to even think of an LC filter. Add to that the extreme difficulty of getting a set of resonators to tune together. (To get Qu=10000 in a coaxial resonator at 40MHz would take an air-dielectric line nearly half a meter in diameter! Just plain silly.) I'd opt for a front end with very high dynamic range (esp. low third-order intermod products), into a good IF filter, etc., and a communications protocol that optimized whatever performance measure I needed. Talk to the people who build RF communications sytems that go on aircraft carriers. Or talk with hams who design receivers with third order intercepts up in the +50dBm region and higher. By the way, you may do well by putting an ATTENUATOR on the front end, if interference (distortion products), and not desired-signal-strength, is the problem. Distortion products will go down faster than the inserted attenuation. Cheers, Tom |
Watson A.Name - 'Watt Sun' wrote in message ...
.... How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. I think that's a popular misconception. The resonator Q is essentially the same as the Q of the same part used as a shielded inductor, and the shield actually lowers the Q from what it is with an inductor in free air (so long as it's not large enough to radiate significantly). They're tunable, but I'm not sure how much. They're certainly easily tunable over a few percent, if you need that... But the problem as originally stated implies a filter of fairly high order and low in-band attenuation, which in turn implies resonators of very high unloaded Q. 20kHz bandwidth at 40MHz in a single tank is a loaded Q of 2000, and to keep attenuation low, the unloaded resonator Q should be perhaps 5 times that much. It would be worse for a multi-pole filter. All this tells me it's silly to even think of an LC filter. Add to that the extreme difficulty of getting a set of resonators to tune together. (To get Qu=10000 in a coaxial resonator at 40MHz would take an air-dielectric line nearly half a meter in diameter! Just plain silly.) I'd opt for a front end with very high dynamic range (esp. low third-order intermod products), into a good IF filter, etc., and a communications protocol that optimized whatever performance measure I needed. Talk to the people who build RF communications sytems that go on aircraft carriers. Or talk with hams who design receivers with third order intercepts up in the +50dBm region and higher. By the way, you may do well by putting an ATTENUATOR on the front end, if interference (distortion products), and not desired-signal-strength, is the problem. Distortion products will go down faster than the inserted attenuation. Cheers, Tom |
|
|
On Tue, 29 Jul 2003 23:04:00 +0100, Paul Burridge
wrote: On Tue, 29 Jul 2003 04:12:43 GMT, (John Crighton) wrote: Or find, beg, borrow, "buy used," or build an ordinary AM R/C transmitter. Ten quid should get you an old style metal cased Futaba transmitter. Hi John, I've already got an AM tx and rx set-up, but am loathed to use it due to the much increased risk of interference from the speed controllers, motors, etc., which as you will know, is far more likely with an AM system. Keep thinking! -- Hello Paul, I would try out your old AM set for sure. You never know your luck. If the servo connections are compatible it will only take a short time. What brand/model? I agree with you that the AM set has an increased risk of interference from your own motors but you said some time ago that your robot works fine at your place but at the venue with other competitors and their transmitters around, the interference is bad for you with your present Sanwa FM set. Even if you do not fit the AM set to the robot, take the working AM set in a box to the venue and see if the servos misbehave in that electrical noisy environment. Regards, John Crighton. Sydney |
On Tue, 29 Jul 2003 23:04:00 +0100, Paul Burridge
wrote: On Tue, 29 Jul 2003 04:12:43 GMT, (John Crighton) wrote: Or find, beg, borrow, "buy used," or build an ordinary AM R/C transmitter. Ten quid should get you an old style metal cased Futaba transmitter. Hi John, I've already got an AM tx and rx set-up, but am loathed to use it due to the much increased risk of interference from the speed controllers, motors, etc., which as you will know, is far more likely with an AM system. Keep thinking! -- Hello Paul, I would try out your old AM set for sure. You never know your luck. If the servo connections are compatible it will only take a short time. What brand/model? I agree with you that the AM set has an increased risk of interference from your own motors but you said some time ago that your robot works fine at your place but at the venue with other competitors and their transmitters around, the interference is bad for you with your present Sanwa FM set. Even if you do not fit the AM set to the robot, take the working AM set in a box to the venue and see if the servos misbehave in that electrical noisy environment. Regards, John Crighton. Sydney |
|
|
On Wed, 30 Jul 2003 21:28:29 +0100, Paul Burridge
wrote: Even if you do not fit the AM set to the robot, take the working AM set in a box to the venue and see if the servos misbehave in that electrical noisy environment. See above. We won't be using that set-up ever again for this application! -- Hello Paul, I think you are missing my point when you said, "We won't be using that set-up ever again for this application!" My point is this. If the radio control set works OK, while just sitting in its own cardboard box , at the noisy Venue, meaning, the servos work nice and smooth. If you then install that same Rx and servo set into your metal box robot and the servos play up, that is now an " installation problem." You cannot blame the gear. Let's try and sort this out with some basic checks. Using a field strength meter (which is just a simple crystal set with a large moving coil meter as discussed months ago, I assume you have made one already), are both the Sanwa and Futaba transmitters producing similar output power when compared to a known good working transmitter? Yes or No? At your place, are range checks of both the Sanwa and Futaba R/C sets, on there own, not installed in anything, over 100 yards . Yes or No? At your place, are range checks of both the Sanwa and Futaba R/C sets installed in the robot or metal test box with "no" drive motors connected still over 100 yards. Yes or No? At your place, are range checks of both Sanwa and Futaba with drive motors being controlled and running nicely, still over 100 yards. Yes or No? At the noisy Venue, while doing a range check of less than 30 yards with all other competitors absent or their transmitters switched off in the Tx compound, do both your Sanwa and Futaba R/C sets play up? Yes or no? At The Venue, do other competitor's radio control sets play up like yours Yes or No? At the Venue have you scanned the band with a simple crystal set type radio or fancy scanner for some ******* with a transmitter who is determined to give you, personally, a hard time? One last thought, I take it that you have sorted your aerial out so that you do not have a long dangly piece of wire as an antenna lead-in, inside the metal robot body from the base of your whip antenna mounting bracket to the Rx input. If you do have a long wire lead-in, that is bad as it will pick up local motor noise very nicely. If your Rx is a long way away from your antenna base, use coax for the lead-in as explained here. http://homepages.which.net/~paul.hills/Radio/Radio.html If after all that basic stuff has been checked and still no joy then consider a dual conversion superhet Rx. like this one. http://www.norcim.fsnet.co.uk/Index.htm#U You could scratch build from the given circuit and the description of how it works on that web site. Or buy the kit from Micron for 32 quid. If you are still having problems after all that, sorry Paul, I give up. Regards, John Crighton Sydney |
On Wed, 30 Jul 2003 21:28:29 +0100, Paul Burridge
wrote: Even if you do not fit the AM set to the robot, take the working AM set in a box to the venue and see if the servos misbehave in that electrical noisy environment. See above. We won't be using that set-up ever again for this application! -- Hello Paul, I think you are missing my point when you said, "We won't be using that set-up ever again for this application!" My point is this. If the radio control set works OK, while just sitting in its own cardboard box , at the noisy Venue, meaning, the servos work nice and smooth. If you then install that same Rx and servo set into your metal box robot and the servos play up, that is now an " installation problem." You cannot blame the gear. Let's try and sort this out with some basic checks. Using a field strength meter (which is just a simple crystal set with a large moving coil meter as discussed months ago, I assume you have made one already), are both the Sanwa and Futaba transmitters producing similar output power when compared to a known good working transmitter? Yes or No? At your place, are range checks of both the Sanwa and Futaba R/C sets, on there own, not installed in anything, over 100 yards . Yes or No? At your place, are range checks of both the Sanwa and Futaba R/C sets installed in the robot or metal test box with "no" drive motors connected still over 100 yards. Yes or No? At your place, are range checks of both Sanwa and Futaba with drive motors being controlled and running nicely, still over 100 yards. Yes or No? At the noisy Venue, while doing a range check of less than 30 yards with all other competitors absent or their transmitters switched off in the Tx compound, do both your Sanwa and Futaba R/C sets play up? Yes or no? At The Venue, do other competitor's radio control sets play up like yours Yes or No? At the Venue have you scanned the band with a simple crystal set type radio or fancy scanner for some ******* with a transmitter who is determined to give you, personally, a hard time? One last thought, I take it that you have sorted your aerial out so that you do not have a long dangly piece of wire as an antenna lead-in, inside the metal robot body from the base of your whip antenna mounting bracket to the Rx input. If you do have a long wire lead-in, that is bad as it will pick up local motor noise very nicely. If your Rx is a long way away from your antenna base, use coax for the lead-in as explained here. http://homepages.which.net/~paul.hills/Radio/Radio.html If after all that basic stuff has been checked and still no joy then consider a dual conversion superhet Rx. like this one. http://www.norcim.fsnet.co.uk/Index.htm#U You could scratch build from the given circuit and the description of how it works on that web site. Or buy the kit from Micron for 32 quid. If you are still having problems after all that, sorry Paul, I give up. Regards, John Crighton Sydney |
In article ,
says... Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill i just read this thread and had a few thoughts. i don't know what kind of interference you're dealing with, nor do i know what restrictions are placed on your competitions. i was thinking about front end overload, also. the types of interference vary in different countries, but those paging towers and, taxis, etc. all play hell on a front end. you really need a spectrum analyser to figure out what you're deaaling with. as for those ceramic resonators, they're ok, but in the better receivers, they're followed by if xfmrs to get rid of the spurious response of the ceramic filter. since you are thinking of just starting from scratch, here's what i'd do if you're not bound by rules. http://www.aerocomm.com http://www.radiometrix.com cost? i dunno. i figure if you can afford one, good. then you can spend more time on the robotics and weaponry. if you can use these, the question becomes a matter of whether you can retrofit one of these in time. i'm not ready to look into using them yet and therefore haven't gotten into the details. so i don't know what you'd have to do to get a PWM signal in and out, but since they handle a higher data rate (1 Mbps) than std R/C PWM, you could bust the PWM signal up into little "chips" and reconstruct it on the receiving end. maybe an integrator/LPF would be all you need. on the other hand, maybe you can just send" the PWM directly. I'm sure the applications engineers could help. hope this helps. mike |
In article ,
says... Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill i just read this thread and had a few thoughts. i don't know what kind of interference you're dealing with, nor do i know what restrictions are placed on your competitions. i was thinking about front end overload, also. the types of interference vary in different countries, but those paging towers and, taxis, etc. all play hell on a front end. you really need a spectrum analyser to figure out what you're deaaling with. as for those ceramic resonators, they're ok, but in the better receivers, they're followed by if xfmrs to get rid of the spurious response of the ceramic filter. since you are thinking of just starting from scratch, here's what i'd do if you're not bound by rules. http://www.aerocomm.com http://www.radiometrix.com cost? i dunno. i figure if you can afford one, good. then you can spend more time on the robotics and weaponry. if you can use these, the question becomes a matter of whether you can retrofit one of these in time. i'm not ready to look into using them yet and therefore haven't gotten into the details. so i don't know what you'd have to do to get a PWM signal in and out, but since they handle a higher data rate (1 Mbps) than std R/C PWM, you could bust the PWM signal up into little "chips" and reconstruct it on the receiving end. maybe an integrator/LPF would be all you need. on the other hand, maybe you can just send" the PWM directly. I'm sure the applications engineers could help. hope this helps. mike |
sorry, i did mean PPM, not PWM a link was provided earlier. might be this, or it may link to this. there're links to radios for robot wars. according to this page there are 2 bands allowed, so maybe those 2.4GHz radios are verbotten. that sucks! it's a robot competition, not a ham competition. http://homepages.which.net/~paul.hills/Radio/Radio.html mike |
sorry, i did mean PPM, not PWM a link was provided earlier. might be this, or it may link to this. there're links to radios for robot wars. according to this page there are 2 bands allowed, so maybe those 2.4GHz radios are verbotten. that sucks! it's a robot competition, not a ham competition. http://homepages.which.net/~paul.hills/Radio/Radio.html mike |
|
|
| All times are GMT +1. The time now is 09:15 PM. |
|
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com