Brushless Motors

Hello VEX Community,

I am new to VEX, and am really excited to be learning what VEX can do. And please forgive me if I am posting in the wrong part of the forum. (I wonder if there needs to be one for running NON-VEX parts and NON VEX competitions?)

I have a group looking to use a VEX Cortex for an Underwater Robot. It will be tethered to the cortex and battery, which will be safely waterproofed and protected on the pool deck.

Our question is this: Can we run Brushless motors off of a Cortex controller? We want to run hobby sized brushless motors, the kind you fine on RC cars, boats, and such.

I assume we would need some sort of speed controller, something like:

And this type of motor:

We will most likely be looking at other vendors, and ebay, as well, but I just wanted to get a link (which I cannot seem to get the link function to work correctly) to show you the size and scale we were thinking of.

If you have seen the movie Spare Parts, or looked at, you get the idea of what we are trying to do. Has anyone here run brushless motors off of a VEX Cortex?](

If the speed controller has an RC pwm type input (which the one you linked does) then yes, you could use the cortex to control it (disconnect the red wire on the receiver cable though). You will need an external battery, don’t try and use the cortex battery to run these high current motors. The particular motor you linked isn’t compatible with that speed controller.

Thanks for the input.

I have yet to really research and price out our ESC and motor combo. I am not really that sure what to look for in compatibility, but clearly that is important.

I just picked the cheapest ones that Hobby King had when I looked them up.

If any of you have any suggestions, I am all ears. We are looking at running maybe 1.5-2" propellers, underwater.


In terms of compatibility, make sure the ESC can provide enough current for the motor. For the parts you linked, the ESC has a max continuous current of 10A, the motor probably needs 2 or 3 times that under normal loads and its stall current is 10x.

I have never worked on underwater robots, however, motor size will depend on the mass you are trying to propel and how fast you want it to move.

Would this type of ESC work with the VEX Cortex:

In the past we have used little brushed DC motors, the $3.00 versions, hobby motors. We really do not need a ton of torque, I know that is vague at best, sorry.

I am really just looking for something to try, to see if we can get a prototype up and running, to see if we want to go this route.

You would want around a 100 amp ESC for a motor of that size. Like this one here
Generally speaking you don’t have to get a higher rated ESC for your max amperage draw (which is 115) so a 100 amp esc should allow you to run your motor at around ~75% throttle comfortably. Like jpearman said, you would want to get a lipo battery to power that individual motor.

I recommend using this motor combo sold on ebay since you know the two will work together and there is free shipping.

If you are looking for more power try this, free shipping included

After that all you need to do is hook up a 2-3s lipo battery to the ESC, and plug the 3pin connector on the ESC to the cortex

Thank you all for your help.

OK, here is where we are at: Decided to not go brushless, but just plain old brushed 12 volt motors. Like the Jameco 232022


We have 1 Victor SP controller, which works great, but they are $60. We are trying to find another cheaper alternative, as we may need to use 4 motor controllers for this project.

We also need nowhere near 60 amps, I think at full load these 12 volt motors pull less than 5 amps.

Any ideas of cheaper 12 volt motor controllers?

out of curiosity, why do you want to use the VEX Cortex? if it’s not VRC there’s a lot less expensive options available (your VEX Forum name is one of them).

Great question about why we want to use a VEX Cortex. Two basic answers, really.

One, we already have them for classroom use, so they are “Free” for this project, we can just take one off of a clawbot, and hook it up, when we are done, we just put it back. There no cost in using it, and there is no point in leaving it in a cabinet if it is not being used, we have a couple back ups that we can use.

Two, we had tried using Arduino Uno’s in the past, with limited success. We still need to use motor controllers with them, and we found them to be glitchy when we ever had 2-3 motors running at a time.

Also, as a bonus, the VEX joystick just seems to be well designed, and is really easy to use. Not only is it ergonomically well designed, it just sync’s easily with the cortex, and is very reliable. We have had more hit and miss results with a joystick set up with arduino micro controllers.

(we do currently have a Talon motor controller running a large 12 volt motor off of an uno for another project, and it has been perfectly reliable. But that is just one motor, not 4 of them like we are hoping for with this project.)

The VEX MC29 would probably work (need to check on the 12V part), otherwise, have a look at what Pololu offers (for example, this)