encoder PIDController and set

[bmfrc]

Originally Posted by ollien

I'm sorry for any confusion I caused. It's late at night over here and I forgot to check over my work. Haha. If you know the number of pulses per revolution, you therefore know the number of radians per pulse.

RPP = 2*pi/PPR.

Knowing this, combined with d = Θr, we know that each pulse will travel us a linear distance of RPP * r. In your case, this would be (2 * pi)/(1440) * 10 cm, for a 10 cm radiused wheel.

In other words its circumference/ppr :-)

[ollien]

Originally Posted by bmfrc

In other words its circumference/ppr :-)

You know, I never noticed that relationship. I always thought it through as a calculation of distance with radians per tick.

I'll let someone else answer this. I think I've successfully talked myself into a circle here.

[bmfrc]

Originally Posted by ollien

You know, I never noticed that relationship. I always thought it through as a calculation of distance with radians per tick.

I'll let someone else answer this. I think I've successfully talked myself into a circle here.

lol thanks man!!!

[Joe Ross]

1x and 4x decoding affect which edges the FPGA counts, but not the reported distance. When you select 4x, WPILib scales the output to be the same as 1x, ie if DistancePerPulse is 1, in 4x you would get values of 1.0, 1.25, 1.50, 1.75, 2.0, and in 1x you would just get 1.0, 2.0, etc.

The FPGA measures rate by timing successive pulses. In 4x decoding, the next pulse is from the opposite channel, which means that you will see a lot of noise. If you look phase relation specs for the the E4T, the relationship can vary by up to 60 degrees, which means you could get 2/3 of the measurement as noise. It's much better to use 1x decoding for rate, so the same edge is always being counted. It's also better to use a lower resolution encoder, so that there is a longer time period between pulses.

This is based on using the roboRIO for decoding the encoder. If using the Talon SRX, the opposite applies, it's rate algorithm wants a very high resolution encoder (although this might not be an issue with the 2.22 firmware).

[bmfrc]

Thanks Joe!
I'm really new to this stuff..

Originally Posted by Joe Ross

1x and 4x decoding affect which edges the FPGA counts, but not the reported distance. When you select 4x, WPILib scales the output to be the same as 1x, ie if DistancePerPulse is 1, in 4x you would get values of 1.0, 1.25, 1.50, 1.75, 2.0, and in 1x you would just get 1.0, 2.0, etc.

Im not sure i understand the scaling thing.
if 4X output higher resolution to 1.25, 1.50 VS 1, 2 of the 1x, where is the scaling?
Does it affect the DistancePerPulse calculation from our side? we devide the circumference by 360 or 1440?

Originally Posted by Joe Ross

It's much better to use 1x decoding for rate, so the same edge is always being counted. It's also better to use a lower resolution encoder, so that there is a longer time period between pulses.

What about measuring distance? should we use 4x decoding?