Enccoder output does not match motor input

[petercohen]

Hi, I need some help. I created an input data file for the MX-28 and recorded the output from the encoder. The resulting curves are included. The top one is input data and the bottom one is output from the encoder. Can anybody explan the differences in shape and amplitude?

P.S. How do I attach a photo? Don't see that option anymore.

[petercohen]

Hi, anybody knows the answer? Perhaps I should change the question. Anybody managed to make the MX motor turns in the same way as the input data? Thank

[MarcoP]

Hi Peter

For images i suggest you upload them to a free image hosting site such as Flickr and then use the link here to share them.

Should help people to help you.

Rgds

[petercohen]

Thanks MarcoP. Can you view the image?

[img]
http://www.flickr.com/photos/96719207@N06/
[/img]

At first, I thought I did not give the motor enough time to reach the desired position as usleep was set to 10000. However, from the curves, it does not seem to be the reason.

[MarcoP]

Yes i can.

Do you have a load applied on the servo?
It looks like you have to play around with your PID values.

Rgds

[petercohen]

Yes i can.

Do you have a load applied on the servo?
It looks like you have to play around with your PID values.

Rgds

Thanks. Just a small load. What values do you recommend? It was worse when I set the P_P_GAIN to 8. When I increased it to 50, I got the results posted. So, even on the same robot, depending on the load, I need to adjust the PID values? Sounds a bit inconvenience. Is there a set of values that does well in general?

[MarcoP]

Hi

I do not have a lot of experience with that but from the images you Integral term seems low.

There are no ideal values (otherwise the servos would come pre-programmed with them).

It's all about compromises depending on what you want.
You will have to read about PID control and tweak the values to suit your needs.

Regards