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-   -   pic: OMNI Drive (http://www.chiefdelphi.com/forums/showthread.php?t=153454)

pribusin 11-01-2017 12:01
pic: OMNI Drive
 

The Doctor 11-01-2017 12:03
Re: pic: OMNI Drive
 
Though I've never had direct experience with this, I'm sure it would have many of the main problems associated with mecanum wheels, though probably a bit worse. The main concern is that you'll get pushed around, since omniwheels have so little traction.

If there was no chance of defense, it might be a good idea. However, I get the idea that there will be a lot of pushing this year.

Taylor 11-01-2017 12:08
Re: pic: OMNI Drive
 
Disclosure: I have never personally worked with this type of system, but I have seen it used both in person and in video.

When the omniwheels are centered on the frame like this, the robot tends to get tippy in the corners when turning. A way to overcome this is to make the frame low to the ground or 'wheelie bars' in the corners.

Ether 11-01-2017 12:19
Re: pic: OMNI Drive
 
Quote:
Originally Posted by pribusin (Post 1629259)
They thought it could give fast straight drive speeds along the two main axes of the wheels
Kinematically, it will be faster along the diagonals.

pribusin 11-01-2017 12:28
Re: pic: OMNI Drive
 
Quote:
Originally Posted by Ether (Post 1629282)
Kinematically, it will be faster along the diagonals.
How do you figure? Aren't you always losing some forward vector from all four wheels due to all rollers being angled and only part of the rotational vector getting translated into forward motion? I'll give you that you have four wheels propelling rather than two.

mr_yes 11-01-2017 12:30
Re: pic: OMNI Drive
 
Like with a mechanum drive system, one key to this being a viable drive train is lots of practice with it under realistic conditions. Because omniwheel systems drive differently than tank-style, the driver's brain has to be re-trained.

JamesCH95 11-01-2017 12:34
Re: pic: OMNI Drive
 
Quote:
Originally Posted by pribusin (Post 1629292)
How do you figure? Aren't you always losing some forward vector from all four wheels due to all rollers being angled and only part of the rotational vector getting translated into forward motion? I'll give you that you have four wheels propelling rather than two.
You get v1/(2)^1/2 + v2/(2)^1/2=vd, assuming v1=v2, then vd=sqrt(2)*v1

That is to say: the diagonal speed will be ~140% of either pair of wheels' speed.

See:



I imagine that this drive base would be quite tippy given the small base of support. The setup below is more common because the base of support is larger, and the fastest drive speeds are now aligned with the major faces of the chassis.

Boltman 11-01-2017 12:42
Re: pic: OMNI Drive
 
Wheres you Fuel intake? hope you are not relying on Hoppers. I suspect many games within first 30 secs will have all fuel on floor...and going to loading station is a slow process.

Ether 11-01-2017 12:54
Re: pic: OMNI Drive
 
Quote:
Originally Posted by pribusin (Post 1629292)
How do you figure? Aren't you always losing some forward vector from all four wheels due to all rollers being angled and only part of the rotational vector getting translated into forward motion?
Using your argument, how is it possible for a sailboat's speed to exceed the wind speed that is propelling it?

GeeTwo 11-01-2017 13:16
Re: pic: OMNI Drive
 
If you keep the wheels in the same locations but rotate the chassis 45 degrees (or vice versa), you get what is sometimes referred to as Killough Drive (edit: pictured in post#7). This eliminates (or at least greatly reduces the "tippiness" at the corners. It is also kinematically the same as mecanum.

Ether 11-01-2017 13:30
Re: pic: OMNI Drive
 
Quote:
Originally Posted by GeeTwo (Post 1629325)
It is also kinematically the same as mecanum.
Not.

Mec fwd/reverse kinematics is same as standard wheel.

GeeTwo 11-01-2017 13:49
Re: pic: OMNI Drive
 
Quote:
Originally Posted by Ether (Post 1629336)
Not.
You do have to gear the Killough Mecanum ~40% faster to get the same behavior. I should have said similar (same shape, different scale).

Quote:
Originally Posted by Ether (Post 1629336)
Mec fwd/reverse kinematics is same as standard wheel.
I'm not sure what you're saying here. What sort of standard wheel?

Ether 11-01-2017 16:53
Re: pic: OMNI Drive
 

omni vs mecanum vs standard wheel chart

Lil' Lavery 11-01-2017 17:21
Re: pic: OMNI Drive
 
While each wheel has different kinematics between Omni and mecnanum, as a 4-wheeled system they behave the same. You just swap the "diagonal" behavior in one system for the cardinal directions in the other.

Quote:
Originally Posted by GeeTwo (Post 1629360)
You do have to gear the Killough ~40% faster to get the same behavior. I should have said similar (same shape, different scale).
How do you figure.

jaweth12@gmail 11-01-2017 18:09
Re: pic: OMNI Drive
 
Check this pdf on page 12
http://www.simbotics.org/files/pdf/drivetraindesign.pdf


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