Is it true that 80 % velocity is goes the same speed as 100 % velocity for iq motors?

VEX IQ General Discussion
1

I’ve been wanting to ask this question because it seems like my robot doesn’t turn when I set one velocity to 90% and one to one hundred. I heard this on a video, I wanted to make sure that this was actually true.

2

They are different rates,

The standard VEX IQ wheels are 200 mm circumference. So with every revolution they go 200 mm. The wheel running at 90% will go 180 MM, a 20 MM difference. A 8’ field is 2400 mm distance, so it takes 12 revolutions of the wheel to go across. On the slower wheel it will go 12*20mm=240mm less. A highly simplistic look would be that you have a triangle with one side 2400 mm and a second side of 2160. Assuming a small angle at the start, the distance at the end will be about 300 mm .

So given some friction with standard wheels, I’d expect across a full field for the robot to “turn” about 180-240 mm, which isn’t very much across that distance.

Is that what your experiments show?

2 Likes
3

Yes, I’m trying to code a pid system to make sure my robot stays straight, but it doesn’t correct it while its driving, and I suspected that it might be because of the velocity. Am I correct ?

4

But, I also want the robot to go as fast as possible

5

don’t forget that a motor under load will not reach 100% of it’s unloaded free speed. Perhaps your motors have a maximum actual speed of 60-70%, you can determine this from testing, ask for 100% and measure actual velocity. 100% and 90% requested speed may end up being the same actual velocity.

7 Likes
6

Oh ! Okay, yes, when I get home I’ll make sure to test the maximum speed, so that my robot will make sure to turn during my pid rather than turning after, because now my robot turns after because its at 100 % velocity for most of the time. I think that the problem I’m facing now.

7

So, this must be the reason that my robot isn’t turning as it goes for my drive straight pid right ?

8

I have seen the same video, I just put my motors to 80% and it worked fine, the way to test it is to start really slow, then go up until it has a negative effect on the adjustment

2 Likes
9

What do you mean by until it has a negative effect on the adjustment

10

You can use a testing code to explore it for each motor:

3 Likes
11

It does not work anymore

12

our team tried 127% and it was faster. is this the same for everyone else?

13

That may be 127 RPM.