Testing Motors, Jags, Batteries

[tsaksa]

Originally Posted by avanboekel

We were looking for something that we can do with what we already have.

Well here is my attempt at suggesting something that can be done without specialized testing equipment. Please have someone who is knowledgeable in electrical safety look these suggestions over and help you implement the tests if you chose to do something similar to this. The ideas are not tested.

Do you have any motors, Jags, or batteries that are new, or that you trust enough to use for comparison? If so, you might get some idea of how good the unknown ones perform by doing a simple side by side comparison. Set up your old robot with only one CIM motor and one Jaguar on each side. The known good ones on one side, and the ones you want to test on the other. Then drive the robot straight forward and backwards several times. If the robot tracks reasonably straight each time, the Jags and CIMs are probably working correctly at least to a first level approximation.

If the robot will not track straight you will need to find out the real cause. It could be just mechanical binding or poor alignment. Look for excess friction and also try switching sides with the motors and controllers. Also swap the motors between the controllers so that you discover if the behavior is due to the Jag or the CIM. Doing enough side by side comparisons should eventually give you some amount of confidence that there is nothing seriously wrong with these components, or help to pinpoint the damaged ones.

Testing the battery without a real battery tester is not complicated, it just takes a while. Completely charge the batteries you want to test. Then select a load to use to drain the battery. Something like a car headlight might work. Connect a volt meter across the battery and add the load. Have a student monitor the voltage once every five minutes. You might want to take readings more often if you have a higher current load. When the voltage starts to dip below some voltage (say 10 volts) stop and plot the results. It might take quite a while to drain the battery with a low current load, but it should produce good results.

The area under the curve should be approximately proportional to battery capacity. This is not really true, because you were measuring voltage and not current, but it is close enough to get a comparison between batteries if you use the same load for each test. If you collect this information for a new battery, you will have something to compare against in the future. Not the fastest or most accurate way to test a battery, but it does not require a dedicated tester.