I have an idea. Get an old LP record turntable and replace the motor with a small 3 phase motor(low kv) with a controller that can be set to RPM mode. Turn table has rotational inertia due to its mass, their job is to run steady. You also have a big platter to attach test subject and equipment to, just keep it balanced. Control the PWM to the motor contoller using an Arduino controller and calibrate it. I wrote a motor controller for testing motor thrust and it works very well. I used a serial display from Sparkfun and a few switches for setting output. I can give you the code after I add the calibration setting you will probably want.
Now where to find a small 3 ph motor and RPM contoller with PWM inputs?????
Or were to get a good turn table cheap that you can hack.
Pat from Invensense was using a turntable and a USB slip ring.