does anyone know anything about 4 wire servos

Sybil

I am trying to interface a bs2 with a team losi mini t 1/18 scale rc car but have run into a small hitch. this car has a tiny little servo with a 4wire lead and I am not sure how to controll it.
Has anyone written any code for a 4 wire servo, or have any beta on how they work

Bruce Bates

Sybil -

With only the information provided available, I'd have to guess that what you're looking at may be a stepper motor, and not an R/C servo. I supppose in its normal mode of operation you could check each wire looking for .5 --> 2 mS pulsed signal while it's moving. If found, then one might presume it's an R/C servo, rather than a stepper. Where to go at that juncture is anyones guess.

Regards,

Bruce Bates

Jim Richey

The servo you have does not have the amplifier on board ,like most others.The reason for four wires is because the amplifier circuit is contained in the matching receiver.You would be better off to use a more conventional servo.

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Thanks, Parallax!

Sybil

thanks, i was afraid of that. guess i will have to do some mechanical engineering instead of programming.

thanks again
sybil

LoopyByteloose

Is this really a servo? Or something completely non-standard?

If it really looks like a R/C servo from the outside, consider the following:

It may be that the servo has been modified with a Solarbotics H-bridge inside. That might explain the four wires- two for power and two for directional control. Take a look inside.

Anyway, you could always cannabalize the interior and put in such an H-bridge. The gears and the motor are pretty straight foward without the PWM circuitry, just two motor wires.

In my opinion, it seems a bit inefficent to use the PWM [noparse][[/noparse]which was useful for R/C transmission] when an H-bridge is less demanding of the microcontroller's resources.

It also seems odd, that you must hack a perfectly good servo and adapt it to H-bridge use to gain this efficency in a standard chassis.

It seems that the servo manufactures are reluctant to provide internal H-bridge controlled servos as a genuine product.

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The the above does not apply, take your VOM and try to figure out the purposes of those 4 wires by measuring their continuity, their resistance, and their ability to create a voltage when the wheels are spun.· If you are going to tear the motor out of the car, you might as well try running it from a battery at first.· If you burn it up, it was only going to become garbage anyway.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Post Edited (Kramer) : 11/27/2005 5:11:48 PM GMT

Oper8r Al

If your looking for a replacement servo to be controlled by your stamp look for a steering servo from a Traxxas revo. I found one on e-bay for less than a dollar minus shipping. It is about the same size as the servo in the mini-t but is only three wires, and can be controlled like a full size servo.·It may not·be a direct repalcement but·it should be close in size. ·I'm not sure how it would inerface with the original Losi remote control if your planing to still use it.

Alan