Last update: 3:21 PM 6/17/2008
Robot Combat ESC.
The purpose of a speed controller is to take the small signal coming from the receiver and amplify it to
drive much bigger motors/relays/squirt guns than the receiver itself ever could.
First, we'll start with a cheap R/C toy car motor controller.
All we do is take the wires that normally go straight to the motors, and hook them up to the signal wires
of a circuit called an H-bridge. The signals go in the H-bridge, are amplified using voltage and current
from the main battery, and are spat out at the motor.
Schematic A shows normal operation of the toy, and B shows our H-bridge hooked up with a separate battery
for supplying the motor, with both "minuses" of the batteries connected, but not the "pluses"(You
can use just one battery for everything, just make sure that the receiver does not get too much
voltage. A voltage regulator will help there).
[The H-bridge circuit itself is shown as a "black box". Schematics for it's many thousands of variants can
be found at Robotroom and Solarbotics.net]
Now, the next type of ESC will be a little tricky-er-est. Let's say we have a higher quality radio
receiver that is meant to plug into servos. How do we control our macho motor with this? Well, the answer
lies in the servo itself. I know, other people can tell you lots more about the inner workings and uses of
servos, but guess who's webpage you're on right now? That's right; mine. So here goes.
The servo has three wires going into it: Usually a red one for 4.5 to 6V, a black one (for ground,
hereafter referred to as GND), and a white, brown, or other color for signals. The order for these wires
vary, so you need to double check with the manufacturer.
Normally, the receiver sends the pulses through the signal wire and a little circuit board inside of the
servo watches the pulse properties, and decides where the output of the motor shaft needs to be. Attached
to the motor output (hereafter referred to as servo horn, or just horn) is a potentiometer, or pot for
short. This pot tells the servo where it is now, and how far away it is from where it needs to be. The
circuit board reacts by sending the motor power in whatever direction or speed is needed to get
there.
Also, realize that this servo cannot rotate continuously. There is a plastic or metal stopper on one of
the gears attached to the motor to prevent it from being forced far enough to damage the pot. Now, if you
remove the pot from the servo case, set it (the pot) to it's middle position and take out the stub on one
of the gears, the servo can rotate continuously without damaging anything. The pot is now immobilised so
that the servo now always thinks it's in center position. This setup also gives the advantage of
proprotional speed control over the servo(fast/slow/medium). Know that this will wear out the gears
inside the servo. They weren't designed for constant, medium duty use as a convenient robot gear
motor.
The procedure I have just described is called "Continuous Rotation Servo Modification" or somesuch.
other people have done fantastic how-to's on this. But a little servo gearmotor ain't good enough. We want
to power our macho motor!
Well, hold your horses for a minute. Look at what this servo can do for us. It's now converting the
receiver pulses to regular motor signals. All we have to do is take the circuit board out of the servo
(with the pot, or suitable equivalent), leaving a gearmotor and our board. Now, plug the servo guts into
the receiver, and take the two motor wires, and plug them up into our H-bridge that we used for our toy
motor receiver.
Hey, HEY, HEEEY! we got our macho motor goin'! See schematic C for how I plan on implementing the
receiver, ESC, servo guts, and power supply in my battlebot. [We'll need one set of guts for each motor.]
