Homemade parts

I am thinking about buying other servos (hitec), not the ones that are the vex brand, and using the vex “brain” to control them. My fear is that I will fry the darn thing. I have other parts that are also PWM, do you guys think it will break the robots “brain” if I were to use it? :confused: what regulations are there?

You should be able to use many different servos provided that they do not exceed 1 ampere of current draw. The vex motor output ports are only rated at 1 ampere continuous draw. So I wouldn’t recommend trying to drive some of the monster high inch/oz torque servos that are available, but I’d definitely look at the newer micro and mini servos.

You mentioned other pwm devices. Again if they’re some sort of driven device like an actuator, relay, stepper motor with driver circuit, or solenoid, keep the 1 ampere output limit in mind and they must be driven by standard hobby servo pwm signal. If you’re looking at devices driven by the digital/analog ports as outputs, sensors using the analog/digital ports as inputs, or devices using the interrupt ports, please check the specifications here.

Mechanical components can certainly be fabricated or purchased that are compatible with vex. Watch for a post from Artdutra04 soon on some of this info on other commercial parts that will work with vex. Some of these parts FIRSTers are already likely to own, and they’re items that have shown up on the vex wish list. That’s all I’ll say, I don’t want to steal his thunder. :wink:

pins 2, 3 and 4 of the motor section are brought out from three of the hardware pwm pins on the 18f8520 and can e programmed to generate pwm signals at frequencies and duty cycles other than those used to drive hobby servos. with a couple of hours of head scratching i was ale to control the brightness of a couple of leds based on the positions of the joysticks on the controller. more usefully, these pins could drive an h-bridge or something.

for more current you could connect the power and ground to multiple outputs in the motors section, or directly to the battery.

Hobby ESC’s can be used for RC car and truck motors. The PWM is the same. Spike relays can also be used off of the PWM outputs. To build your own H bridge controller is complicated. You can fry the vex very easily when interfacing to high voltage electronics. That said, there are allot of resources on the International Rectifier website under automotive applications. One interesting class of devices are fully protected low and high side switches. I used an 8 output one to control 2 servo motors.

Yes, It will work. Keep in mind the 1 amp rating though as previously mentioned.

You can run ESC’s for cars and other task off it too, just make a Y harness for the battery so the ESC gets power from the battery.

I actually have a Traxxas R/C car that I’ve stripped down and made autonomous with a vex controller so I know firsthand this will work.

there’s lots of places online to get ESC’s…

If you want to drive a heavier load servo, just make sure you follow the BEC (battery eliminating circuit) specifications. I THINK you just need to connect the ground wire of the cable from the pic to the ground of the battery you use together (reference same ground), signal wire goes to servo, and the positive lead from the battery goes to the positive lead of the servo, thus not using the vex to power the servo. JUST MAKE SURE that the battery you use is NOT more than the input voltage of whatever you are driving. There are also optocouplers that you could use to drive the servo off if you want.

I would just be safe and get a cheap ESC, i have one if you want it, send me $10 and shipping costs and its yours. Its a novak.

here’s a good site too, for drivers:


One more thing to note about ESC and the VEX controller. Certain ESC designs can put damaging voltage and current back into the micro controller signal lines frying the micro. When all the grounds are connected, a loss of ground can cause magic smoke. One way to protect against these conditions is to put a 1000 to 10000 ohm resister in line on the control signal. Adding this resistor can have an effect on the ESC. The IR web site has some app notes on motor control and micros and protections.