On Sat, 02 Aug 2003 11:11:31 +0100, Paul Burridge hath writ:
Paul Burridge wrote:

Can anyone suggest a suitable material from which to make an
ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need
something that can be bent to 90 degrees at a very small radius and
still return to reasonable straightness.

Yeah, sorry chaps, I should have better defined what I meant by 'very
small radius'. I compete in radio-controlled model battles, so the
model stands to get fipped upside down from time to time in a very
bruising environment and it already has a very low ground-clearance,
so using a spring as a base mounting won't help much, I'm afraid.
We're talking about radiuses of as little as 5mm! How about the
specific grade of stainless steel in wire form that springs are made
from? I know where I can get hold of some of that....

You might try a section from a steel tape measure.
(Just don't select one of the cheap, Made-In-China plastic/mylar
ones. HI!HI!)
Additionally, try to mount the antenna in a "well" on the robot.
Even a well of 5-10 mm will help out.

HTH,
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | OS/2
| Gunnison, Colorado | @ | Jonesy | linux __
| 7,703' -- 2,345m | config.com | DM68mn SK

In article ,
says...
On Sat, 02 Aug 2003 03:25:47 GMT, Active8
wrote:

In article vKBWa.20717$KF1.308575@amstwist00, lid says...
Paul Burridge wrote:
Hi chaps,

Can anyone suggest a suitable material from which to make an
ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need
something that can be bent to 90 degrees at a very small radius and
still return to reasonable straightness.

I think thin piano wire will give the best results. Place a lot of them
in a flexible tube to gain some thickness and have them silvered for
conductivity - or add a stranded copper wire.

Spring metal strip may also work, especially if you can manage some type
of hinge at the base that allows it to turn when sideways force is
exerted, or if the force is in one plane.


Thomas

what is a tight bend? music wire comes in diff sizes and the number in
the tube and how tightly the tube conforms to it will have an effect on
the flexibility.

Yeah, sorry chaps, I should have better defined what I meant by 'very
small radius'. I compete in radio-controlled model battles, so the
model stands to get fipped upside down from time to time in a very
bruising environment and it already has a very low ground-clearance,
so using a spring as a base mounting won't help much, I'm afraid.
We're talking about radiuses of as little as 5mm! How about the
specific grade of stainless steel in wire form that springs are made
from? I know where I can get hold of some of that....
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

oh, hi. it's the battle bot guy. i should have caught that, duh!

mike

In article ,
says...
On Sat, 02 Aug 2003 03:25:47 GMT, Active8
wrote:

In article vKBWa.20717$KF1.308575@amstwist00, lid says...
Paul Burridge wrote:
Hi chaps,

Can anyone suggest a suitable material from which to make an
ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need
something that can be bent to 90 degrees at a very small radius and
still return to reasonable straightness.

I think thin piano wire will give the best results. Place a lot of them
in a flexible tube to gain some thickness and have them silvered for
conductivity - or add a stranded copper wire.

Spring metal strip may also work, especially if you can manage some type
of hinge at the base that allows it to turn when sideways force is
exerted, or if the force is in one plane.


Thomas

what is a tight bend? music wire comes in diff sizes and the number in
the tube and how tightly the tube conforms to it will have an effect on
the flexibility.

Yeah, sorry chaps, I should have better defined what I meant by 'very
small radius'. I compete in radio-controlled model battles, so the
model stands to get fipped upside down from time to time in a very
bruising environment and it already has a very low ground-clearance,
so using a spring as a base mounting won't help much, I'm afraid.
We're talking about radiuses of as little as 5mm! How about the
specific grade of stainless steel in wire form that springs are made
from? I know where I can get hold of some of that....
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

oh, hi. it's the battle bot guy. i should have caught that, duh!

mike

On Sat, 2 Aug 2003 16:40:43 +0100, "cpemma"
wrote:

The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn
wire, or even better is a 17/7PH (precipitation hardening) grade that our
firm once produced for tank aerials, that also may take a few knocks.

Both (especially the PH grade) need a final heat-treatment (420C for a few
minutes IIRC) for ultimate spring properties, but to get such a tight bend
you'd need quite a thin wire. It's a matter of the proof strain or limit of
proportionality, how much the outer skin can stretch without taking a
permanent set, compared to the neutral central axis, on the bend.

There speaks a man who obviously knows what he's talking about. Yes, I
believe we can order 301 from our guy in N. London who's very
accommodating on such matters. Thanks for a valuable steer!
Just one point, though: is stainless steel a reasonable radiator of RF
energy?

--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Sat, 2 Aug 2003 16:40:43 +0100, "cpemma"
wrote:

The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn
wire, or even better is a 17/7PH (precipitation hardening) grade that our
firm once produced for tank aerials, that also may take a few knocks.

Both (especially the PH grade) need a final heat-treatment (420C for a few
minutes IIRC) for ultimate spring properties, but to get such a tight bend
you'd need quite a thin wire. It's a matter of the proof strain or limit of
proportionality, how much the outer skin can stretch without taking a
permanent set, compared to the neutral central axis, on the bend.

There speaks a man who obviously knows what he's talking about. Yes, I
believe we can order 301 from our guy in N. London who's very
accommodating on such matters. Thanks for a valuable steer!
Just one point, though: is stainless steel a reasonable radiator of RF
energy?

--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia
wrote:

You might try a section from a steel tape measure.
(Just don't select one of the cheap, Made-In-China plastic/mylar
ones. HI!HI!)
Additionally, try to mount the antenna in a "well" on the robot.
Even a well of 5-10 mm will help out.

Not sure about the tape measure suggestion, but mounting in a well is
something I'd not considered and am most grateful for the idea of!
Thanks...
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia
wrote:

You might try a section from a steel tape measure.
(Just don't select one of the cheap, Made-In-China plastic/mylar
ones. HI!HI!)
Additionally, try to mount the antenna in a "well" on the robot.
Even a well of 5-10 mm will help out.

Not sure about the tape measure suggestion, but mounting in a well is
something I'd not considered and am most grateful for the idea of!
Thanks...
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

:

The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard
drawn
wire, or even better is a 17/7PH (precipitation hardening) grade that our
firm once produced for tank aerials, that also may take a few knocks.

Both (especially the PH grade) need a final heat-treatment (420C for a
few
minutes IIRC) for ultimate spring properties, but to get such a tight
bend
you'd need quite a thin wire. It's a matter of the proof strain or limit
of
proportionality, how much the outer skin can stretch without taking a
permanent set, compared to the neutral central axis, on the bend.

There speaks a man who obviously knows what he's talking about. Yes, I
believe we can order 301 from our guy in N. London who's very
accommodating on such matters. Thanks for a valuable steer!
Just one point, though: is stainless steel a reasonable radiator of RF
energy?

Back years ago (30 or so) there was an ad in a magazine about either a
loaded CB or 5/8 two meter whip about 36 inches long bent in a circle made
of the 17/7 material. Not sure what the whips are actually made of but
most are some kind of steel .

:

The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard
drawn
wire, or even better is a 17/7PH (precipitation hardening) grade that our
firm once produced for tank aerials, that also may take a few knocks.

Both (especially the PH grade) need a final heat-treatment (420C for a
few
minutes IIRC) for ultimate spring properties, but to get such a tight
bend
you'd need quite a thin wire. It's a matter of the proof strain or limit
of
proportionality, how much the outer skin can stretch without taking a
permanent set, compared to the neutral central axis, on the bend.

There speaks a man who obviously knows what he's talking about. Yes, I
believe we can order 301 from our guy in N. London who's very
accommodating on such matters. Thanks for a valuable steer!
Just one point, though: is stainless steel a reasonable radiator of RF
energy?

Back years ago (30 or so) there was an ad in a magazine about either a
loaded CB or 5/8 two meter whip about 36 inches long bent in a circle made
of the 17/7 material. Not sure what the whips are actually made of but
most are some kind of steel .

"Paul Burridge" wrote in message
...
On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia
wrote:

You might try a section from a steel tape measure.
(Just don't select one of the cheap, Made-In-China plastic/mylar
ones. HI!HI!)
Additionally, try to mount the antenna in a "well" on the robot.
Even a well of 5-10 mm will help out.

Not sure about the tape measure suggestion, but mounting in a well is
something I'd not considered and am most grateful for the idea of!
Thanks...

Does it have to be a whip antenna? Why not try a horizontal circular loop?
Since you are working line of sight to the robot, the signal loss from going
from vertical to horizontal shouldn't matter much unless your transmitter is
extremely low power. A loop could be mounted inside a wooden or fiberglas
body and be pretty safe from attack.

Is there anything in the rules forbidding your installing a jammer
transmitter to cause the other bot to lose its command channel? Probobly a
poor use of what little electrical capacity the onboard battery holds, but
it would be one way of causing the other bot to freeze in place and become
like a deer in the headlights.
thanks, John.
KC5DWD