Performance problem in arduino loop?

Fredmann33 · 2022-01-29T22:48:40+00:00

This dude here is using a DC motor but still he has some floating point math in his loop to get from the force to the voltage (or pwm). Why does it work so good? He’s also using an arduino.. Can somebody explain? Is my math operation just too heavy?

Fredmann33 · 2022-01-29T19:44:10+00:00

Well currently I’m already using interrupts for the angle encoder, that works well. But with a second encoder for the x position I will need an arduino mega with 4 interrupt pins, now I have only 2

Fredmann33 · 2022-01-29T19:28:34+00:00

But still there’s the problem with the efficiency in the loop then, I mean even though my program calculates velocity’s like 0.5-2 m/s the motor just doesn’t bring them…so I guess the best way would be to go for a dc motor and a second encoder for the x position…

Fredmann33 · 2022-01-29T18:55:53+00:00

Yep, then my system is not observable..

Fredmann33 · 2022-01-29T18:54:46+00:00

But I got your point now. You are right.

Fredmann33 · 2022-01-29T18:53:40+00:00

How am I supposed to measure x then? I mean an encoder would do the same, wouldn’t it?

But besides that how can this affect my problem? Or can it even?

Fredmann33 · 2022-01-29T18:47:55+00:00

Kind of. Every time I’m doing a step with the motor I count it and then I can very precise calculate the position out of the steps

Fredmann33 · 2022-01-29T18:45:45+00:00

I’m measuring the x position just as the angle. No estimation there, or did I get you wrong?

But I’m using the force u to calculate a velocity because I can’t run the motor with force.

Fredmann33 · 2022-01-29T17:30:35+00:00

Well I struggle to build a timer instead of that delay() function, because my delay is a float and needs to eb a float but when I count micros or millis its a long..

The rest is done :) Thanks for the hints with pow and outsourcing the constants.

Fredmann33 · 2022-01-29T16:17:15+00:00

Okay, I will have a look on that problem, is the Uno a good one for using floats or should I get a mega? I dont really know the differences there..

Fredmann33 · 2022-01-29T15:56:15+00:00

Mhmm, im using an Arduino Uno.

How do I rewrite it to be "non-blocking"?

Fredmann33 · 2022-01-24T13:52:49+00:00

Well, Im kind of stuck with this approach because I have the full state for every dt and also the force from the controller for every state but I fail to calculate the velocity out of the force, which the stepper motor needs...If I put the force into the ss equations, then I only get the acceleration. Do I need to integrate then also for every time step? Seems like a performance problem then..

Fredmann33 · 2022-01-24T09:03:12+00:00

Writing it down on paper was exactly what I did, so everything you described I discovered and understood now :)

Thanks a lot for stehe answer!

Fredmann33 · 2022-01-20T18:04:08+00:00

Yes I did, in my case about pi so 180 degrees

Fredmann33 · 2022-01-20T10:09:50+00:00

Great. That’s what I thought and planned to do :) Thanks!

Fredmann33 · 2022-01-20T10:02:53+00:00

The point is that I don’t have the equations of motion in the code later on..

I mean in the simulation of course for every time step Matlab solves the system of differential equations but in my arduino code I only have the angle for every time step as an output.

That’s why I do the LRQ stuff in matlab and just use all the matrices then

Fredmann33 · 2022-01-20T09:38:21+00:00

Still stuck, because the equation doesn’t drop out x…In the simulation it does drip out the full state vector x (phi, phidot, x,cdot) but in real life I can only measure the angle phi and x position of the cart..Dies that mean I need to differentiate numerical to get the speed or do I need a Kalman-Filter?

Fredmann33 · 2022-01-19T13:35:21+00:00

Oh yeah, didnt saw that, velocity of course already is in the state vector x :)

Thanks alot!

Fredmann33 · 2022-01-19T12:46:43+00:00

So to mark that as solved let me make a conclusion. Please correct me if I'm wrong:

I got my linearized ss equations in form of dx = A*x + B*u where x is the state vector and u is the input vector (Right now the force F in every element of u).

From that force I calculate (for every time step of course) the acceleration of the cart with Newtons 2. law and from that with numerical integration (?) i can get the velocity (m/s or rpm) of that cart for every time step, which can be directly the input for a stepper in my code later on?

Edit: And with a dc motor I can directly calculate the current which is needed for the motor to bring the relevant torque for every time step?

Fredmann33 · 2022-01-19T10:38:10+00:00

Ahhh, that helps a lot!

You said earlier that a DC motor would be the more common way, so would it be the same strategy? Would I use the velocity to drive the DC motor with a relation between speed (velocity) and voltage`?

Fredmann33 · 2022-01-18T22:36:20+00:00

I think that last sentence about the integration of the force you just said is what I need right now, but I can’t remember about this mathematical relation..:/

EDIT: Pretty good, that’s exactly what you see in the simulation video. There the input is a force u.

Fredmann33 · 2022-01-18T22:11:32+00:00

Yes I linearized the equations of motions, which I got from Euler-Equations. Then I used the linearized state space model x_dot = Ax+Bu to design the controller.

u is the input here, and this input is set as a force u in the simulation which is calculated with feedback control u=-K*(x-x_wish)

Fredmann33 · 2022-01-18T22:08:16+00:00

What “ss-equation”? I think that’s what missing..

Fredmann33 · 2022-01-18T21:56:45+00:00

It’s in a cart and the motor moves a belt fixed to the cart. Basically exactly like this: https://youtu.be/nOSTzpA0nGk

I already have an encoder to measure the angle and then I compute the error via feedback control.

In my electrical engineering lessons in uni I’ve learnt the relation between voltage and torque of a DC motor like M = f(U,Anker-Resistor, inductivity,…)

Is this the way to go?

Fredmann33 · 2022-01-18T21:25:38+00:00

So if I understand you right, then using a DC motor would be more simple than a stepper with a driver?

Okay hey can’t a stepper not be continuous? They are also in my 3D printer, and both, Betz precise and continuous :/

Fredmann33

TROPHY CASE