RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

Y harness

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Old 05-28-2003, 06:45 AM
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ManicMechanic
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Default Y harness

Hi guys, I drive a monster truck and have had some steering probs so I bit the bullet and bought a hitec 945 servo for it.
I'm still having probs. This servo is supposed to have 144oz of torque at 6v, and yet it wont turn the wheels when the truck is still. I've checked the steering and there's no binding so I'm wondering if its a power thing.
I'm going to switch from alkaline batteries to NiCd's and in the servo instructions it mentions something about using a Y harness between the power pack, Rx and servo. I assume the idea is that only a signal voltage goes through the rx, and the bulk of the power gets drawn straight from the battery pack, is this right and will it help?
Maybe some of you large scale guys have a suggestion as in mt steering you need loads of torque.
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Old 05-29-2003, 03:54 PM
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strato911
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I'm not into ground based RC, but I have a theory...

Don't RC cars / trucks incorporate springs into the steering mechanism to prevent stripping the servo if the wheels hit a hard bump? I'm not talking about the suspension springs. The weight of the truck may provide enough friction on the wheels to cause the steering springs to compress instead of turning the wheels. Since turning the wheels while the truck is standing still serves no purpose, this sholdn't be a problem, as long as the steering turns as soon as the truck starts rolling. If they don't, try installing stiffer springs.
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Old 05-30-2003, 06:02 AM
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Yeah, its called a servo saver, its a spring loaded mechanism that helps to dampen shocks transmitted through the steering to the servo and so avoid stripping gears etc. I need to have a play with the settings on that. But what about the y harness though. Have you ever heard of it or of anyone who's employed it? I'm especially thinking of high drain applications like the rudder on large scale planes etc.
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Old 05-30-2003, 08:16 AM
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Servo savers can also be used in planes eg for nosewheel or tailwheel. Dubro carries them.
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Old 05-30-2003, 08:19 AM
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Erm yeah, I already have one, this thread is about Y harness' I don't need to buy a servo saver
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Old 05-30-2003, 03:57 PM
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The receiver can route several amps to the servos without damage (at least for short bursts). There is no harm in using a Y-harness to connect the battery. Many receivers with 8 or 9 channels actually require it if you want to use the last channel.

However, this won't help the steering issue when standing still.
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Old 05-30-2003, 07:53 PM
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To check wheel movement, get a big block of wood or a proper stand to sit the truck chassis on with wheels clear of the ground surface. Those huge tyres create to much friction to allow the wheel to turn whilst truck is staionary. DO NOT fit heavier duty springs as they ones supplied are more than adequate fir the job which is to protect the servo from shock - heavier springs will lead to damaged gears, broken or burnt pc board or gear pins in the servo.
With regard to the Y lead, yes this is recommended in the instructions for all the heavy duty servos mounted in trucks, boats and aircraft especially when, as one would expect you use a 2 ch RX in the truck, a receievr which has "BEC" clearly printed on the top = Battery Eliminator Circuit". These usuall 2 but a number of 4ch RX incorporate a regulator to allow the use of the 6 & 7 HD power packs in electric cars in lieu of a separate RX pack - similar to ESC in E/flight. MAX volt out is usually 5V at about 1A.
For full detail on servos refer to http://homepages.ihug.co.nz/~atong/ and scroll down to "Radio Systems, Accessories, Alterations and FAQ" then sub section =
"Servo & TX alterations, calculators, clonepacs, make an ESC or winch, FAQ."

see also http://www.hitecrcd.com/Support/Faqs/Faq_Genservo_.htm

regards

Alan T.
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Old 06-02-2003, 06:27 AM
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A.T, Strato, Thanks for all your help. I'll have a good look at those links today, and have another go of the truck when I get back of vacation. Once again, thanks, your help is appreciated
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