Re: speed controller help [TANKS]

[Jim Neifert <jneifert-at-shaw.ca>]

Just as a note here, I have made a RC Switch up on a PC Board. It will 
control one relay to do,,hmm something anyway. Its much like the one Joe 
sells for 15.00, not as nice looking and with all the smoke I let escape 
from several components cost me more than double what his would have. The 
plus side to this is I learned about making a PC Board, and had great fun 
doing it. Next is a simple controller with BEC to control my turret, and 
then mayby on to an ESC. More for the fun and to say I made it,,,at least 
will say that if it works...
Thanks Frank and to all the others that keep giving me ideas to work on and 
learn. Who says an old dog can't learn new things.

Jim
Abbotsford, BC

----- Original Message ----- 
From: "Frank Pittelli" <frank-at-rctankcombat.com>
To: <tanks-at-rctankcombat.com>
Sent: Sunday, November 13, 2005 11:36 PM
Subject: Re: speed controller help [TANKS]


> Pete Curran wrote:
>> Just did a quick search and came up with
>> http://www.rc-airplane-advisor.com/electronic-speed-controller.html
>>
>> Uses and old servo and power amp,
>
> Yep. Forgot about that approach.  Servo ICs use PWM to control the servo 
> motor and that signal can be used to control power FETs to control a 
> larger load.  But, keep one thing in mind:  Airplane motors only turn in 
> one direction ... tank motors need to go forward and reverse.  I think the 
> circuit referenced above only provides proportional speed in one direction 
> (it only taps one of the servo motor wires).
>
> The two wires between the servo IC and the motor carry a PWM signal in 
> both directions, switching the polarity.  That is, in forward the signal 
> is a square wave between 0 and +X volts, while in reverse the signal is a 
> square wave between 0 and -X volts.  If you pass these signals through 
> some discrete logic (good ole fashion NAND gates), they can be used to 
> drive the motors in both directions using an H-Bridge arrangement of FETs.
>
> You'll also want to isolate the power and control sides of the circuit, so 
> that large power spikes from the motors don't blast into the ICs.
>
> Frank P.
>