Needed: suggestions for a meter to measure currents

I would like to measure the currents that the Vex Cortex and motors consume. For example, I would like to measure the current being consumed by a single motor, and, in other cases, the current being consumed by or directed through the Cortex when multiple motors are in use, etc.

I have a multimeter and I know it’s possible to measure the currents in series but that requires breaking into the wires, and I would like to avoid using that approach. I would like the kids to be able to make measurements on their system after they have assembled it so they can see what is consuming what. I’m guessing a clamp-on current meter could do that, but I don’t know what to shop for in a meter that would be used for Vex-level currents and voltages.

Can anybody suggest a clamp-on style meter that works well with Vex or some other approach? Thanks. :slight_smile:

Excellent point! I had forgotten about that. Thanks very much for reminding me about that. I suppose there could be a little separation done to allow for measurements where needed, then “repair” the separation with tape when finished. What I wanted to avoid was actually cutting the wires.

Thanks again. :slight_smile:

You don’t need to separate the wires on all your motors, just on one extension cord. then you can plug that extension cord in between the motor controller and the motor you want to measure.

Or if you have an ordinarly probe multimeter:

Then you can turn one extension cord into a connection point for your multimeter. Cut through one wire of the extension cord and solder alligator clips onto the cut ends so that you can attach a multimeter to measure current. Then move that extension cord to whatever part of the circuit you’re interested in.

Yes it does. Thanks so much! :slight_smile:

That’s a great idea! And now that there are (or soon will be) battery extension cables, I guess I could use that, too. You guys are great! Thank you! :):):slight_smile:

There are a couple of problems in measuring motor current.

  1. The current has lots of transients making measurement difficult unless the motor is running at constant speed, and then you can pretty much calculate what it is.

  2. The robot generally has to be driving around (well I guess not if measuring a lift system) and you end up running around after it trying to hold the meter.

You could try this approach.
https://vexforum.com/showpost.php?p=318273&postcount=1

Okay, I’ll have to ponder that one. I am mostly worried about the kids running everything to the point where they will start tripping their motors and/or Cortex. I also want to teach them more about torque/speed/current relations and about optimizing the power they can get out of a motor, motor efficiency, etc.

At least one of the kids has an iPhone, and they video everything. That gives me an idea. :slight_smile:

Thanks as always for the in-depth analysis. Looks like I’ve got my work cut out for me trying to absorb all of this. Good thing they are starting to work already. I guess.