DC Brushless Motor Testing Question


I have a question regarding whether a Neo Motor can be used as a generator, as described in the attached PDF. I want to test and evaluate the health of my motors using a simple setup. My idea involves connecting a DC brushless motor to an input, and then connecting another DC brushless motor to act as a generator. As shown in the schematic, I have included a variable resistor to apply load to the motor and test its performance. I have also included sensors to measure voltage and current, which will help me determine the motor’s power output and efficiency.

Will this setup work for testing the motor’s health? Are there any other cost-effective methods for testing motor health? Can a DC brushless motor function as a generator? If not, are there any generators compatible with the Neo Motor? Any input would be greatly appreciated.

Thank you.
Neo Motor Testing Device.pdf (24.4 KB)

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Yes, it will work as a generator but your diagram somewhat over simplifies it. A NEO would be a multi-phase generator so you need to handle voltages and currents across the set of what are now “output” wires.

If you want to characterize a motor, this approach will get you a lot of data. If you want to go / no-go test a motor, running it off of a SparkMAX against a known force can help there (I’ve used a gearbox / winch combo lifting a known weight and measured the time it took to do it). That will get you enough information to determine whether a motor is out of spec with your other motors in a pretty straight forward way.

I recently built yet another version of a PWM-based motor driver for mechanism prototyping and motor testing that will drive all of the current brushless motor controllers - code and other details at Utility/hardware/motor_testing/ardiuno_pwm_brushless_driver at main · Team-2151-Progrraming-Room/Utility · GitHub

It’s about as simple as you think it would be - this is actually simplified from a 4 motor version which took like 3 people to operate if you wanted to drive 4 motors at once.

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First: Yes, if you spin a NEO it will act as a generator.

You will need a brushless motor driver between your power supply and your drive NEO. And a pretty beefy power supply if you aren’t using a FRC battery.

The generator NEO will make three phase power. If you really want to know something about the windings, you might want to measure the AC Voltage and current across the windings and use three resistors. You need to think about how much power you want to push across , and choose your resistors appropriately. They will get HOT if you put real power in them, so plan for it. Use power resistors and a heat sink+fan. Or do a short test… The maximum power transfer would be where the load resistors equal the phase resistance (about 11 milli-Ohms), but that’s going to be VERY low and you will generate large currents. I would avoid going to full stall current…

Alternatively, you could use a three phase rectifier on the windings and a single load resistor.

You should take a look at this long thread where I developed my NEO tester board and also a power drill type device that runs a NEO when you pull the trigger.

NEO data from the same thread:

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If you spin these boards, I would love to buy two :slight_smile:
I hate those PWM testers for servos. Soooo easy to turn things on and have the motor spin like mad :frowning:

They’re designed through pin choices to work with an UNO-based Arduino in a way that things are easy to connect and don’t need a lot of cross-wiring. As an example, for the pot connections, I do it all from the pin set associated with A0-A5; 3 are configured as analog in, and one each of the remaining are set as digital outputs to provide the GND and 5V levels for the pots. For things like the pots or the direction switches, the pins in digital mode can sink / source enough current to make things work and you don’t have reach all over the board for simple high and low logic level sources.

I’ve built several versions of these over the years and this is probably the best thought out variant in terms of simplified connections. I’ll throw up a few pics when I have a chance.

I agree that the typical servo testers can be a little surprising on start up - one of the goals from the get go was a way to positively get things in a place so you can start up in a nice and controlled manner.

Look for some pics shortly.