How to Integrate a Non-VEX Motor to the VEX Kit
The purpose of this document is to tell you how to extract a speed controller from a VEX motor module and use to power non-VEX motors
-There is a risk with soldering around the speed controller that the heat could damage or destroy it.
-A VEX motor module (not done with a servo module: unsure if it works the same way)
-A standard (non-VEX) DC motor
Materials not needed but may be useful
The VEX motors are controlled by a PWM signal from the microcontroller. This signal will not drive a motor by itself: it needs an intermediary to convert the data signal to electrical pulses. It needs a speed controller. What this means is that every VEX motor has a speed controller inside of the plastic enclosure. We can use this speed controller to control any motor we want!
(1) Using a small screw driver, remove the 4 screws from the back (the green part that has “motor module” silk screened on it) of a VEX motor module. You should see a PCB exposed. DO NOT ATTEMPT TO PRY IT UP JUST YET! It is still connected to the motor. Removing it now could cause damage to this motor: making this process irreversible.
(2) Locate the two pads marked with a positive (+) and negative (-) symbol. There should be one for each symbol, and it should be towards the end of the PCB opposite the PWM cable.
(3) Using the de-soldering equipment, remove the solder from those 2 pads.
(4) There should now be nothing holding the PCB down. Using the knife, carefully pry the PCB up from the rest of the motor assembly.
(5) Solder a couple of wire to the pads that the motor was attached to.
(6) Solder the other end of the wires to the DC motor (or the terminal, just remember to connect the DC motor to it).
(7) Plug the PWM cable into the VEX microcontroller.
(8) Program it like it’s a normal VEX motor.
If you have any questions, comments, additions, or advice regarding this tutorial: please post them. I will update this post as new information becomes available.
On the contrary, it is very useful. Speed controllers usually cost much more than the cost of a hobby servo. If you don’t want to spend money on a new speed controller, you can simply use the vEx motor’s speed controller. I’m gonna have to try this sometime.
Thanks for the post, underdark.
wow, that is a really nice solution to the lack of power from current vex motors. i would never have thought of that. and although you might destroy (but not permanently) a vex motor for $20 and regular VICTOR 884 will cost you $130 to do the same thing. so i say well done, underdark:D
This is very useful but the I imagine the VEX speed controllers put out only a tiny amount of current (I’d say 15 amps max). Most motors of a truly useful size will require more current than that. But for smaller motors this is a great trick.
I must point out here that the normal stall current on the motors is around 1 amp. I would doubt that the motor driver transistors are rated much more than that. Also, the robot controller is only rated to put out a maximum of 4 amps from all the motor ports combined.
The point is that it would be easy to fry the driver if you put too big a load on it.
How about posting some pics of the motor controller? I’d love to see what parts they used, but I don’t want to risk one of my motors. I’m wondering about replacing their H-Bridge with something that can handle more current.
Thanks, for the info. According to the Infineon data sheet, the H-Bridge chip can handle up to 9 amps peak, plenty of supply voltage, and has thermal overload protection. It looks to me like you can indeed drive a more powerful motor than the vex motors without too much fear of smoking the controller.
Great to see this procedure well documented, nice work!
Here’s a link to a Vexfan thread from a while back, showing much the same thing as discussed in this thread. The Vex Motor speed controller works very well with Lego motors, which I find to be much quieter and stronger than the vex ones.
I included a few pictures of the motor interface and other details of a VEX/ Lego hybrid project.
i was wondering how do u tell if an rc cars motor is pwm
cause i wanted to try to use back from rc car with vex and it has 3 wires and a couple capacitors but im not sure if it might just b extra ground wire and if it is pwm how do u find which is which cause theres a blue wire black wire and some other color
hey i have been looking into intergrating a non vex motor in by using the method of turning and current motor into a speed controller only im not quite sure if the amps will be enough and if it will actually work this is the motor i hope to use. feedback would be nice