Omni-drive autonomous questions
 

Our design meeting tonight settled on four omni-wheel drive system. Since there is significant scrub when driving forward, optical shaft encoders can't reliably calculate distance traveled. Correct ;)

I would then think that one would have to use some combination of the gyro chip and acceleration sensors and an integral function to keep track of robot displacement. :confused:

This will be a new venture for our programming team this year. I'd appretiate any suggestions for code resources. :yikes:

Thanks,

APS

Re: Omni-drive autonomous questions
 

http://kevin.org/frc/

Use these sensors to keep track of your location on a virtual grid.
Keep the calculations to the basic right triangle trig calculations.
I am still thinking about it but the best way i think is to know the angle <90 of the robot direction to parallel of the field. This is done by adding and subtracting the gyro values. Then use sin and cos to calulate the change in x and y based on the distance you traveled in that direction. The accelerometer will help you with this.

Re: Omni-drive autonomous questions
 

There are many sensors listed on Kevin's site. Which are you referring to?

6600gt,
I'm not sure can follow your explanation. Could you please elaborate? I see a few key words but not a clear picture of what is to be done and what each component is used for.

Thanks,
-Joe

Re: Omni-drive autonomous questions
 

In my experience, an inertial measurements unit is difficult to keep accurate if you integrate over a long period without a Kalman filter. Also, keeping track of the inertial measurements will consume a lot of your processing time, so depending on what else you plan to do, it may not be worth it. This year's challenge seems like it is far less necessary to know exactly where you are. It should be sufficient to be able to see your target and at least keep facing toward the correct end of the field. ;)

Best of luck!
-Joe

Re: Omni-drive autonomous questions
 

Thanks Joe,

Thinking as I type, closed loop control of sorts via visioncam if going for center goal and then maybe some proximity sensor for closed loop control if going for a dump into the low goal. :cool:

APS

Re: Omni-drive autonomous questions
 

We built a 4-wheel omni two years ago. We placed a small pair of free-wheeling omni-wheels (~2" dia) underneath the center of the chassis pan, and oriented them at 90deg. Each omni had a Grayhill optical encoder. This gave us local x and y movement of the chassis. Using an additional Analog Devices yaw rate sensor and integrating the yaw rate for yaw angle, we had the info we needed for field position. Any binding or slippage in the wheels, of course, led to error, but it worked OK for us.

Good Luck!
Eric

Re: Omni-drive autonomous questions
 

The gyro and accelerometer, that they asked for.

\ x |
\ | y
\ 0 |
\ |

The y axis should be kept parallel to partiquar side of the field. The gyro will give you theta(0) and the hypotenuse is the distance traveled, the accelerometer will give you this value or more accurately you have to calculate it. Form these two values you can calculate the change in x and y.
Then if you know your point on the field, you can calculate your distance away form the target.

There is more to it which has to modified based on the direcition you are facing. I am still trying to figure it out. This will keep getting more inaccurate as the match goes on.

This is for a tank dirve. For the omni drive, if you don't want to turn, all you need the accelerometer to keep track of you position. The angle you traveled and the ammount you traveled.

I thought this up a couple days ago. Still have no cule how to impliement the code. The picture is mess up becaues it dosen't keep the spacing.