The controller is an obsolete board that’s over 20 years old made by Mclennan in the UK.
It’s pure analog using 741 op amps running a load of power transistors. The board has two parts depending on whether you want velocity or positional feedback. I could pm you the circuit if you were interested.
In this case, the input to the op amps are the joystick on one side and the scaled tacho feedback on the other.
The main problem is that it’s quite big, very thirsty, dual polarity and doesn’t have a deadband for the joystick.
However, as you saw it can run very slowly. If I tried to stop it spinning at that very slow speed it would still fight me.
I agree with you about gearing but the dilemma I have is that one moment the shot is very slow and smooth with the motor hardly moving, perhaps to adjust the framing slightly or to follow an actor from the rear of the theatre, and the next moment it’s whipping round to get a shot of a racing car passing within metres of the camera.
Now, these two events are unlikely to be side by side but if I use gearing to make the changes then I’d be forever opening up the mechanics.
I’d prefer to have these differences in software only.
Sorry, got carried away with the controller board.
I bought 4 of the motors from eBay in the States and had a friend ship them over to the UK for me. They are still there and the motor details are on the page. Search for item no. 370127976736.
I’ll see if I can find anything about them in the meantime.
I’ll be interested to see how you get on with this motor.
I found that it oscillated/buzzed at very low speed when I tried to fight it. That’s with the old analog board I was talking about earlier.
It could be the controller or or could be the motor. It could even be that the motor is completely crap, in which case I’ve been wasting everybody’s time
This leads me onto another theme: Are some motors better suited for straight DC control and others are ok with pulses? This motor was designed quite a few years ago, perhaps when pulsing wasn’t the norm.
The motor is long and thin. Would short and fat motors be better suited for pulsed control?
I don’t really know, but I think it shouldn’t matter. Most speed control gets done with some kind of PWM, and the current through the motor is typically not discontinuous. If the PWM frequency is low, you can hear it, but what you’re describing is probably a function of the feedback causing some oscillation at a lower frequency.
