motor wiring

[Armando]

our motors are driving opposite ways when we move the joystick forward. i need to know what to do.

[woody]

Just figure out which motor is driving in reverse, then swap its leads on your Victor motor (Red to M- and black to M+).

[Armando]

ok, i'll try it now.

[Armando]

my instructor doesn't want to do that...

[woody]

Why not? When you reverse the motors with the joystick, the Victor does the exact same thing internally. Thats just the way motors work; they are not polarity sensitive. This is the simplest solution and is perfectly safe.

[Armando]

fyi our instructor is really stupid, all team members quit. All that is left is three ppl. i'm near quitting as well...

[woody]

I'm sure your instructor isnt stupid, and I'm sorry your teammates quit. Stick with it, and you'll have a great time and learn/teach plenty.
As far as the motors go, just explain that it won't hurt anything, its just changing the way the motor turns.

[Armando]

you have no clue... even the other instructors quit!

[woody]

Well, I think the best thing to do is try to work through it and make the best of your situation. I wish you and what is left of your team the best of luck this season!

[Armando]

thanks

[imax48236]

The inspection team at the regional event may not approve of reversing the polarity on the victors. They like + voltage to be red, and ground to be black.

[Kims Robot]

M+ and M- are simply the outputs of the victor speed controllers. Motors can be given polarity in either direction, it just causes a reverse in the motor. This is a proper way to do it and GOOD PRACTICE. It allows your programmers to give equal control to the motors when they are running the opposite directions.

If you are interested, read up on motors:
http://www.howstuffworks.com/motor1.htm

This will explain that it is OK to reverse the polarity on a motor, and in fact the ONLY way to drive it in the other direction.

Another way to do it is through the programming, but switching your leads is the easiest and gives you the most even control.

[Jim E]

The programming of 1 motor in a forward direction(right side) to match the programming of another motor in the reverse direction(left side) is impossible to do with the FIRST supplied code. Autonomous maybe, but in telematic mode, that would mean one joystick forward and 1 in reverse just to drive straight. Your robot must be spinning in circles literally.

As far as the victors, they don't care what is attached to the M+,M- terminals. The V+,V- terminals are the ones to be concerned about. Yes, attach the wires reversed there and you will have learned a very expensive lesson and see some magic smoke.

Good luck this season. And as the losing NFL team fans always say: There is always next year. TIP: Find a another close by team to come in and mentor whats left. Maybe the instructor will come around with more experienced input.

[Ari Allyn-Feuer]

I'm terribly sorry about the mentoring situation, but if they won't agree (which they should, no questions) there is an easy way around it which will solve the problem pretty well.

In the drive, where you're having code like

pwm03 = p1_y;

if that causes the motor to go backwards and you can't switch the leads (which is the best way to do it), you can effectively do the same thing by saying

pwm03 = 255 - p1_y;

which will map pulling the joystick back to the "forward" pwm ranges and vice versa. Neutral is still neutral of course.

This will be almost the same as switching it. Good luck with your mentor issues. Where are you and what regionals are you going to?

Ari.