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RC Radio antenna (special application)

Old 03-25-2004, 01:54 AM
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grmckauge
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Default RC Radio antenna (special application)

I have constructed a highly miniaturised device which fits into a 'lawn bowl' (not so common in the USA) to apply radio control for coaching purposes. It employs a Hitec Feather receiver with HS-55 servo controlled by a Hitec Ranger 3 Sky FM transmitter on 36Mhz.

No conventional wire antenna is possible as nothing must protrude from the bowl surface and the bowl material has an insulation effect. Reliable reception at 150' would be acceptable instead of the possible 1000'.

Solid aluminium end caps of 2' diameter wired to the receiver give only 50'. The supplied 40' wire coiled flat and mounted on the endcap gives about 60'. Lots of options such as a modified 'loaded antenna' but my knowledge is very limited.

Any suggestions on how this problem could be approached would be greatly appreciated by an isolated Aussie.
Old 03-25-2004, 04:48 AM
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Lynx
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Default RE: RC Radio antenna (special application)

Like you said, use a Deans. Just search for Dean's Antenna on the forums here, there's a hundred links to them.
Old 03-25-2004, 05:44 AM
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Default RE: RC Radio antenna (special application)

go to [link]http://www.iroquois.free-online.co.uk/aerial.htm[/link] for a DIY base loaded antenna. it's designed for 35MHz but should be just fine with 36. cheap too.

and just what is this "lawn bowl"?? pics? links?


dave
Old 03-25-2004, 05:20 PM
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XJet
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Default RE: RC Radio antenna (special application)

I expect you don't want to spend the extra money, but switching to a full-range receiver such as the Hitec 555 or FMA M5 (both very small) would significantly increase your range.

I gather you don't want any of the aerial extending outside the circumference of the bowl itself?

Another option would be to *neatly* coil the antenna wire tightly by winding around a dowel or whatever, but make absolutely sure that there is as much of a straight section between the receiver and the start of that coil as possible. This will effectively top-load the receiver antenna and produce more range than just a random coiling of the wire.
Old 03-25-2004, 05:42 PM
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grmckauge
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Default RE: RC Radio antenna (special application)

Thanks for the suggestions. Dave, bowls is a very popular game here in Australia and elsewhere; thousands of greens in this country.
A good link is www.bowls-australia.com.au

The RFChoke seems the way to go but I will need to wind the 7" of exposed arial inside a non-conductive cap to replace the aluminium cap.

Shortage of space precludes the luxury of 4" of straight wire from the receiver, and it will be encased in the insulating bowl material but I can experiment with this. The choke will also be very close to the receiver and the servo; this I cannot avoid.

Space is so scarce that the Feather receiver has thousanths of an inch to spare so no other more powerful receiver would be possible.

I will be happy to get 150' range as that exceeds the length of a bowling green.
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Old 03-25-2004, 05:56 PM
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macgyver22
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Default RE: RC Radio antenna (special application)

Forgive my ignorance -

What does the servo do? Does it move the ball? I think it is cool, but have no idea what the radio and servo are doing???
Old 03-25-2004, 06:30 PM
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grmckauge
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Default RE: RC Radio antenna (special application)

The bowls depend upon the bias and when bowled, turn towards the heavy side to get as close as possible to the kitty. Their curved trajectory is highly predictable and the skill is in using speed, weight of throw and direction to win.

This unique 'animal' has a sliding counter-weight controlled by the servo motor and linkeage to change the centre of gravity when the bowl is moving towards its target, making it change direction according to the joystick on the transmitter.

Its a fun thing that will turn a lot of heads when it is launched.

My first model has a reversable geared motor (not a stepper motor) with ownly two wires and it is on hold until I acquire some IC which can go between the receiver and the motor to allow the signal wire to change the polarity

Many problems have been overcome and the last seems to be a suitable antenna. I am grateful for the interest and advice.
Old 03-25-2004, 08:00 PM
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XJet
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Default RE: RC Radio antenna (special application)

ORIGINAL: grmckauge
bowls is a very popular game here in Australia and elsewhere; thousands of greens in this country.
happy to get 150' range as that exceeds the length of a bowling green.
Yeah, I saw the movie Crackerjack -- excellent!
Old 03-26-2004, 06:55 AM
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Default RE: RC Radio antenna (special application)

ORIGINAL: grmckauge


My first model has a reversable geared motor (not a stepper motor) with ownly two wires and it is on hold until I acquire some IC which can go between the receiver and the motor to allow the signal wire to change the polarity
for this you could just use the little circuit board found in any servo. once you disconnect the feedback pot from the circuit the motor will continuously turn in either direction depending on stick position. the motor speed is also dependent on stick position.

there are also some very tiny, full range receivers on the market. [link]http://www.bergent.net/[/link] has a very small 4 channel but i don't know about availability on the 36MHz band.

dave
Old 03-26-2004, 12:59 PM
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Default RE: RC Radio antenna (special application)

I'd say connect the antenna wire to one aluminum end cap and connect any ground wire from the receiver or battery to the other end cap. It would help to place inductors in series with each wire. It's hard to guess a good value for the inductors, but try 10 turns of antenna-size wire close wound around a 1/2 inch to 1 inch diameter hollow plastic tube for starters. I have cut inductor tubes from the bodies of old felt tip markers.
Old 03-26-2004, 04:56 PM
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grmckauge
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Default RE: RC Radio antenna (special application)

Thanks Dave for the method of controlling the reversible motor. I assume the feedback pot is the one attached to the bottow of the gear train. Not very familiar with the terminology.

I have fabricated and tested the loaded antenna which was recommended earlier with improved but unsatifactory results. I am curious about the potential for interference with the radio signal within the bowl itself.

I currently have the first three inches of antenna wire packed in the cavity with the servo wires and the power wires from the battery pack, all alongside the servo and the battery pack. Could you confirm that this would cause jittering and strange servo operation at about 80 feet. I can reverse the receiver and run an antenna straight out of the cavity without contact with the other wires and intend to try this next.

Additionally, it would help to know what the experts use for sheilding an antenna wire where it passes through hostile territory.

I will certainly also try the method with the existing aluminium end caps. Thanks JPMacG. I assume there is no connecting wire between the endcaps, only the negative power wire to one and the antenna to the other, both via the inductors. Would end caps turned from brass be more effective than aluminium?
Old 03-27-2004, 08:35 AM
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JPMacG
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Default RE: RC Radio antenna (special application)

That is right, no connecting wire between the endcaps. Just connect the antenna wire to one end cap and a ground wire to the other, both through inductors. There is no advantage to brass over aluminum from an RF standpoint, except that you can solder to brass and not to aluminum.

I think the more you can keep the antenna wire and the other wiring separated the better. Good luck!

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