Servo speed (both movement and PWM frequency)

[Hove]

I'm musing about using a couple of servos and a laser diode to draw a picture on a wall (not cut, just draw in red light). For the whole picture to be seen, the servos would need the laser diode to scan around the picture at roughly 24 frames per second (which is the rate old black and white films ran at and is the slowest tolerable by the eye / brain image processing). So if the picture contains a simple outline of a Christmas tree made up of say 15 lines to be drawn by the laser, then there needs to be 15 changes to the servo PWM with each frame, so the PWM carrier needs to be running at at least (24 * 15) = 360Hz.

I've only heard of servos running at 50Hz carrier PWM, so I think this musing probably flies like a lead balloon, but I thought I better ask the servo users out there.

I realise there are many other problems to be solved also, such as just the physical speed the servo can rotate the laser diode at, and the fact long lines need to take longer to draw to achieve that same brightness for each line. But solutions to those are simply in software as long as a fast moving, high PWM carrier frequency input is available.

Do such servos with these requirements exist?

Thanks

[joan]

Some ESCs can be driven up to circa 500Hz. It seems a bit pointless to do so unless the attached servo can benefit from the update rate. I think you'll need to look at so called digital servos.

[Hove]

Thanks Joan, I take it these are not driven by PWM, but more directly? I'll go digging. Certainly the ESCs for my quadcopter can only go to 450Hz and 500Hz is the absolute maximum for PWM pulses ranging between 1 - 2 ms (which seems to be the arbitrary standard). I presume servo's have in-built ESCs with similar rating as far as PWM is cycle / pulse rate is concerned - the external wiring matches the ESC input wiring for my quad.

For the moment, I'm only musing on this as a concept for a winter project as the nights get darker and the wind gets windier and the rain gets wetter. Not conditions for quad test flights!

Cheers.

[joan]

Thanks Joan, I take it these are not driven by PWM, but more directly? I'll go digging. Certainly the ESCs for my quadcopter can only go to 450Hz and 500Hz is the absolute maximum for PWM pulses ranging between 1 - 2 ms (which seems to be the arbitrary standard). I presume servo's have in-built ESCs with similar rating as far as PWM is cycle / pulse rate is concerned - the external wiring matches the ESC input wiring for my quad.

For the moment, I'm only musing on this as a concept for a winter project as the nights get darker and the wind gets windier and the rain gets wetter. Not conditions for quad test flights!

Cheers.

Hobby servos tend to use a 50Hz PWM with the dutycycle constrained to be 5-10% (1-2 ms every 20 ms).