3-wire 393 motor and no 2-wire ports on the cortex.

Here is what I think:

-no more motor controller 29s

-more simple wiring


But, what do you think? Tell me, please, using the poll or post it please.

So you want the motor controller to be inside of the 393s? I do dislike having to fit large grey boxes inside of c-channels to make the wiring look nice and clean.

but there are a few problems

  1. You would no longer be able to reverse motors by flipping the connections around. Yes, you can reverse the motors in the code,but sometimes flipping the wires is nice.

  2. The product page says that we should not use more than 1 3-wire extension cable between the cortex and a motor controller. With 3 wire 393s we would have to use several 3 wire extension cables in order to connect intake (and probably lift) motors.

  3. Having motor controllers and motors separate allows for them to be replaced individually when they break–which happens fairly often. If they are combined, both would have to be replaced, and that would be more expensive.

  4. I’m not sure if there’s room inside a 393 case for a motor controller, and I don’t think anyone wants the motor cases to get larger.

Bad idea, and this is why I think so.

  1. More expensive motor (if motor and MC29 are combined) making replacement parts higher.

  2. Motors will not work at long distances from the cortex unless the motor controller section is redesigned. Large voltage drops due to wire resistance and high current occur when the motor starts, this tends to cause any logic (ie. the MC29) to reset if it is placed at more than say 5 feet from the cortex. This is currently circumvented by keeping the MC29 close to the cortex and running 2 wire extensions to the motors.

  3. The built-in 2 wire ports work much better in PID applications due to the (much) higher update rate for the motors (approx 600Hz vs 60Hz).

Another problem arises when your motor wires short and you motor controllers catch fire. I know this might not seem like the most common occurrence, but it’s happened to me twice. With all the motor controllers inside the motors or cortex, this problem becomes far more expensive.

I’d like to see a hybrid approach; I’ll call it the MC429. Basically, it is like a combination of the Power Expander and four MC29s.

It would be a smallish mountable box powered by its own battery. It would have four (or more?) 2-wire motor ports with retaining clips just like the Cortex ports. It would attach to the cortex via the I²C bus, which could allow for much faster updates for better PID.

For bonus points it could have inputs for limit switches that are enforced even when no software is running on the Cortex (though I’d hate to drive the price up too much).

Power Expander + four MC-29s runs about $90, so it would need to cost less than that - ideally around $80?


  • Dean

I second this

That’s a better idea than mine.

I have found pins and replacement sleeves for most of my bad motors, but I can’t find the female end connectors for the Motor controllers. I bought my pins etc from Karlsson Robotics but cant find the female ends. Any help would be appreciated.

I found the solution:

SKU Product Item price Quantity Total
1930 Female Crimp Pins for 0.1" Housings 100-Pack $5.95 1 $5.95
From Karlsson Robotics

can someone tell me why we don’t have only 2 wire motor ports on the cortex, what is the benefit of the 3 wire ports?

It seems to me that someone specifically asked VEX what their rationale for this was recently. Basically it would be more expensive all around for several reasons