393 Motor Reversed Polarity

We also have motors with reverse polarity. (Could not respond to you Blake because you posted from the official forum.) We have 1 motor from lot#2202AA where the connector is keyed correctly - red wire close to the tab that sticks out, and 6 from lot #3082AA where the connector is keyed reversed also - black wire close to the tab that sticks out. These were all purchased in 2013 (the 6 arrived in Aug). All our older motors & some of our new motors turn the opposite way & have the red wire close to the tab. Have notified Eli.


You and I are making different assumptions about which of the two polarities is “correct”. Are you basing your assumption on some documentation?

I was/am assuming that the black wire should be close to the connector tab.

You are assuming that the red wire should be close to the connector tab.

We need to wait to hear from the official Q&A folks before jumping the gun.


We never really pay attention to the polarity. For 8 of the motor ports, you can just reverse the direction it’s plugged into the motor controller and for the others it takes 60 seconds to change it in the code. I don’t think we would ever bother sending motors back over something trivial like this, but that’s my opinion.

Sorry Blake. You are right about making assumptions. There is no documentation but we pulled out all our 393 motors from the past 3 years and compared the first reversed one that we found. We ran every motor we could find. All of those were like the one with the red tape that you had in your picture. Only the 6 new ones that had reversed polarity were like the motor with the yellow tape in your picture. Talked to Eli & they want to see those motors. Just wanted you to be aware that your motor was not the only fluke.

I checked several motors, they are all the same and I don’t ever remember seeing a different orientation, if I had I would probably have just fixed it. This is what I consider correct.


Which when plugged into the cortex as follows;


causes the motor to rotate in the same direction as motors connected to the three wire ports via MC29’s. Red wire to center of cortex, same for ports 1 and 10.

That is what we consider correct also.

Not sure if anyone can help me with this question, but how can you control additional motors with the controller? We have added 2 additional motors to control the front 2 wheels of our robot, as well as the original ones in the back of the robot next to the Vexnet “Brain” I guess you could call it, but when I tried to connect the 4 motor’s to the “brain”, only the 2 back motor’s worked. So, how do I get the other 2 motors to connect to the “Brain” So that all 4 of the motors are controlled by the controller?

Rick R.


It sounds like perhaps you are running with the default code.

The answer is to use ROBOTC or EasyC to create your own program that controls the motors how you want to.

Please start a new thread with questions on another topic in future, it gets confusing when the thread title does not relate to the thread content.

Well buddy - You aren’t using your imagination enough.

A problem requiring a company to expend several expensive labor-hours to ensure that several robots being used in an industrial setting actually do contain interchangeable parts, can all use identical software, and can be recreated at will just by reordering the same part numbers used in the original design; is not a trivial matter.

John and the other VEX employees know this. That is why they are so focused on dealing with situations like this quickly and effectively.

I understand that you might think that I was building a one of a kind VRC competition robot, but even then it is a mistake to call this “trivial”. Imagine having to quickly swap a motor during a tournament time-out, immediately placing the robot on the field for the match, and then finding out (too late) that the new motor is spinning backwards…


I believe all Daniel is saying is that he isn’t going to wait 4 weeks to get the motor changed. Instead he would just invert that one motors port. This isn’t a factory with dozens of identical robots or team 12 :slight_smile: :slight_smile: :slight_smile: :slight_smile: :slight_smile:

I understand - And all I am saying (in what I hope comes across positively) is that calling the reversed polarity “trivial” is a poor choice of words.

I am letting him know why it isn’t trivial. Learning that part of the bigger picture is part of learning to be a good robot builder or parts-supplier.


I just came across a motor of ours that has reversed polarity and I had this problem as well.

Upon wire being slightly moved the motor would cut out. Would this be from the soldering on the inside being lose. Would this have anything in common with the reversed polarity of the motor?

How did you determine that the motor’s polarity is inverted? We have run thorough tests and found that motor controllers can also cause motors to run backwards, or in a number of strange other ways. For example, with 2 different known working codes on 2 different known working cortexes and a known working port, one of our motor controllers caused known working motors to run at -127 when they were supposed to be at 0, ~-30 when they were supposed to be at 127, and at 0 when they were supposed to be at -127.

You can use a small screwdriver and remove the wires. Then you can flip them around if you are really that worried about it. Otherwise, just change the direction in your code.

or if you are using an extension, plug it in backwards and then to the motor controller

You could read the thread. See were people decided which wire configuration was correct and which was inverted.

To clarify, I believe you can do this with 2 wire extensions, but not with 3 wire extensions.
Does anyone know for sure?

If you are using 3-wire motors, make sure that they are plugged in correctly. I haven’t used one in a few years, but if I remember correctly, a 3-wire motor plugged in backwards will run constantly at a single speed. In any event, it will not work the way you want it to.

nope (meaning you are correct ed.), I remember the novelty of being able to put the wires ‘backwards’ with the ‘new’ motors when they first came out.

I was talking about a 2 wire motor, with a motor controller.
Am I correct in believing that the 3-wire cord on a motor controller has to be keyed correctly (colors match the 3-wire extension)?
Am I also correct in believing that the motor’s 2-wire cord can be plugged into the motor controller either way, and flipping it will reverse it?