Great Job. Quick Question re; multiple Servo's

[TimRosener]

How do you recommend handling multiple servos? I have a project with 16 servos with different PWM limits and velocity profiles for smoothing.

[joshua-8]

Hi @TimRosener,
Thank you for your interest in this library!

You can make as many instances of Derivs_Limiter as you want. You can have one Derivs_Limiter per servo and have separate velocity and range limits for each servo. This library doesn't help with actually sending control signals to many servos, it only provides the smoothed angle to send to the servo.

Do you have independent control of all 16 of your servos working? (without velocity profiles)
Controlling 16 servos is a challenge for a standard Arduino. The standard library has a limit of 12 servos https://www.arduino.cc/reference/en/libraries/servo/
If you haven't already found a way to control 16 servos, here are some suggestions:

• There might be a library that supports more servos.
• While I have no experience with this, if you search for arduino servo driver board there are results for boards that can connect to your Arduino and provide more servo outputs.

Thanks to you, I realized that I didn't have an easy way to handle an array of Derivs_Limiter objects.
I made a fix for that, and added an example for using multiple copies of Derivs_Limiter.

Please update the library to 3.1.0 or newer and let me know how it works for you.

For some reason the new library version isn't showing up in Arduino's library manager, so you may have to download the updated library from here: https://github.com/joshua-8/Derivs_Limiter/releases/tag/v3.1.1

Here is an image showing 4 independent Derivs_Limiters running at once (it's the output of the Multi example).

It sounds like you're working on a very cool project! Good luck, and feel free to ask any other questions you might have.

-- joshua-8

[joshua-8]

I'm happy to hear that!

[TimRosener]

Another quick question, your documents talk about velocity in terms of intervals per second; I assume that the Acceleration parameters are intervals/Sec Squared. working with hobby servo, I have ranges of 0-180 or 0-270 degrees that I am operating in. can you give more insight on how you calculate movement per second? I have had to increase values by a factor of 50 to get some of the profiles I need, for instance, a value of 12,500 (256 DMX Channel max range * 50) to get the desired response to match the input response. A value of 250 gives me a very slow response compared to the input position. If we were working with degrees (Intervals) per second, it would seem my working ranges would be more in the 0-200 range for velocity and acceleration parameters.

One of the reasons I am asking is that I want to calculate the right max parameters based on the Servo specs; many times, those values are given in the time it takes a servo to move 60 degrees. Then allow the velocity and acceleration limits to operate within those ranges. BTW I am dynamically adjusting those acceleration parameters on the fly.

Thanks again for this great library!

[joshua-8]

If you are controlling the servos by sending an angle in degrees, then I think DL.getPosition() is degrees, DL.getVelocity() is degrees per second and DL.getAcceleration() has units of degrees per second per second.

You might need to use a small fraction of a servo's max rated speed to make sure that the servo moves smoothly, since otherwise the servo might lag behind the position that you're trying to set it to.

A value of 12500 for acceleration or velocity sounds really large to me, I'm not sure why you're needing that. Are you able to make a graph of position, velocity, and acceleration?

As a point of reference, here is a video of a servo moving between 0 and 180 degrees, with a maximum velocity of 500 degrees per second and an acceleration of 2000 degrees per second per second.

ezgif.com-gif-maker.mp4

[TimRosener]

Thanks for looking into this. I took a step back and went through some of my code. I was able to get it working as you described. I had an error when I was dealing with acceleration. Your note helped a lot. Thank you.

You had asked about getting 16 servos working on the RP2040. The only way I could get that to work was by taking advantage of the State Machines. RP2040 has 8 of them each can control twp PWM pins. There is a great library that allows you to drive the state machines. This has the added advantage of freeing up the core from all of the PWM management. I just had to build a servo control layer on top of it.

Thanks again, cheers and happy holidays!

[joshua-8]

I'm happy to hear that it's working for you now.
Thanks for pointing out the library for PWM state machines!
Best of luck with all your projects.
Cheers and happy holidays!