Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 3 down vote favorite

I am a mentor on a US First FTC team. We have had some motors start to smoke a couple of times. How can I test the motors we have to find out if they are good?

I have the data sheet for the motors here:

http://www.tetrixrobotics.com/Building_System/Downloads/default.aspx?moid=721

share|improve this question

2 Answers

up vote 3 down vote accepted

Measure the resistance between the motor terminals and compare it with a known good motor (or the datasheet). If the coils have melted, they will have shorted and you'll see a lower resistance. Or they will have broken altogether, and you'll read infinite resistance.

Turn the axle of the motor with your fingers and compare it to a known good motor. A bad motor can sometimes stick, or feel like it's got a lot of friction.

Finally, connect a known good motor to a variable voltage power supply. Turn the voltage up slowly from zero, up to the motor's rated voltage. See how the motor behaves. Do the same for the suspect motor. Compare them.

share|improve this answer
up vote 3 down vote

Jon,

I was on a FTC team for 4 years. What I have learned about the motors, is that when you see the "Magical Smoke", it is actually a resistor inside of the motor, and can be fixed by opening up the motor and replacing the resistor.

These motors are extremely susceptible to burning out when they are over driven. Take care not to use two motors on the same gear set, use the "big" gears with the "little" gears in a high torque situation, or to drive the motors under high torque for a long period of time (running into a wall, and keeping the wheels moving).

Our team just used some wire to hook up the motor directly to the battery (just be careful not to touch + and - together) to test them. It will not hurt the motors in any way.

Once you see smoke, the resistor inside has already been destroyed, and the motor is no longer going to operate like new. It may not be what you want to hear, but you are better off only using the "smoked" motors for testing components, and replacing the "smoked" motors on your competition robot.

share|improve this answer
The motors still turn, I just wonder if they still operate at 100%. Well, I assume they don't, but I wonder how much they have been damages – Jon Apr 17 '12 at 0:47
They will not operate at 100%. Depending on how long the the motors "smoked", will effect at what percentage the motors will work. There are ways to test the output of the motor, but it is tough and expensive. As I said above, my team and I aired on the side of Caution, and although it cost more money in the long run, our robot functioned well. – Reid Apr 17 '12 at 0:51
Also use some graphite based grease to reduce friction in the gears, and allow the motors to handle a greater load. – Reid Apr 17 '12 at 0:53
I just got in contact with my old team to look up our old notebook where we compared the "smoked" motors to new motors. We found that under no load they were nearly 100%, however under a "high load" they dropped down to about 50% of the speed, and had a higher tendency to smoke again. – Reid Apr 17 '12 at 1:48

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.