Has anyone got plans or a link to a tutorial on how to build a PWM circuit that would allow a person to spin a motor at variable speeds.  I am looking to setup a rig for testing motors, so when i get new motors I can do a couple of things. The rig will consist of a single ESC of say 30-40A, a variable PWM generator that will allow motor speed to be varied using a POT and probably two connection methods for the motor, one using a JST connector and one using croc clips.

Aim of the testing rig:

1) Test they actually work
2) Test thrust on a given prop (by applying force to a weighing scale)

And if it fails, well, it shall be a learning experience.

You can get yourself a servo tester, that is probably the easiest. Or otherwise just attach a MCU/dev board, preferably one that runs on 5v if that will be your power source. A 5v arduino will do nicely, you can just download the servo library, and either program it to step through a preset PWM range, or attach a pot or other input device of choice to set the frequency. And you should be able to run 4 separate PWM signals without any issue. Plenty of online tutorials on using an Arduino to drive a servo.

Here is one built using an Arduino nano from back in the day.


Edit: If you're doing a test rig, you can program the throttle to automatically step through a predefined sequence, and there are electronic balances that have digital output which you can interface directly to your MCU and have it log the thrust at the same time. If you plan to test a lot of motors you will get better repeatability and more comparable data. You could probably use dshot protocol as well if you are testing drone ESCs, that would remove the range calibration factor of PWM.

If going the arduino route, you may be able to connect up the scales / load cell also and log the thrust values for you.

However it may be easier to keep it simple depending how many measurements you're doing

Nice setup there mstc.  I went the shortcut route and just used an old FC: Home made motor tester | IntoFPV Forum

Simple is what I want. I'm after something initially I can connect a motor to just to test it spins, but I have a couple of sets of those digital scales, so thought, why not build a mounting system so I could strap/fix the motor down then I can throw a prop on and spin it up to 25/50/75/100% and get thrust values. Also throw an ammeter/voltmeter on and I can get amp draw and voltage sag. But it's going to be pen and paper level for recording values.

Thanks for the replies.

If you don't mind being tethered to your PC/laptop, then an old FC is probably the easiest. Surely you must have an old AIO where just a single ESC is dead (I've been saving mine for a tricopter... but never got around to it). Then you can use bi-d d-shot, get ESC rpm reading, and if your FC has a calibrated current meter get the amp draw at the same time.

Or if you have an old school receiver (like for planes or cars), those have PWM output, just connect the motor signal to one of the channels and use your radio.

(24-Mar-2024, 06:04 PM)mstc Wrote: Surely you must have an old AIO where just a single ESC is dead

So far, no.  Been really lucky or really careful and not torched any esc.  Two fatalities, but both were entire AIO, ie no longer work from USB full stop.

I gave my voltcraft battery checker to a buddys motor test bench.
Some chargers and battery testers does support pwm signal. I would use that.

I might just buy a cheap (Aliexpress) FC, I already have a spare 30A ESC which should work. Most of what I will test will use far less than 30A.

Unless you have other uses for the FC, maybe getting a dev board with integrated OLED display would serve you better and save you some $ (they cost only a few dollars).

PWM would be very easy to setup, here is a quick overview, and just a few more lines to send data to the display.
https://nnarain.github.io/2023/01/29/Int...-ESCs.html

Of course bi-d dshot is even better, and someone has already written the library for ESP32
https://github.com/Carbon225/esp32-dshot
https://github.com/derdoktor667/DShotRMT

Looks like a fun project.

Following with interest, curious with what you end up doing.

No cheap but it does even show kv!...

SK-500020-01 Brushless LCD Display 3 Mode Motor Analyzer Monitor Tester for Hobby Remote Control Car Motor Testing with Connectors and Manual - $109.99
https://www.amazon.com/SKYRC-Brushless-A...SKY-500020

...hmmm, just saw this one:

Brushless Motor Analyzer: Motor KV, RPM, Timing Measurement, Hall Sensor Check, Brushless Motor Tester with 2x16 Characters LCD - Ideal for RC Hobby
$86.69 with 13 percent savings-13% $86.69
https://www.amazon.com/SkyRC-Brushless-M...B00UMV606U

same as first one?

skads more at Amazonal

...edit to add:

Brushless motor thrust stand with Arduino - this may be closer to what you were looking for?:
https://www.pcbway.com/project/shareproj...duino.html
https://www.instructables.com/Brushless-...ust-Stand/

erm, richly appointed version:
https://www.tytorobotics.com/pages/series-1580-1585