11-01-2017 12:03

The Doctor

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.

11-01-2017 12:08

Taylor

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.

11-01-2017 12:19

Ether

Re: pic: OMNI Drive

Kinematically, it will be faster along the diagonals.

11-01-2017 12:28

pribusin

Re: pic: OMNI Drive

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.

11-01-2017 12:30

mr_yes

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.

11-01-2017 12:34

JamesCH95

Re: pic: OMNI Drive

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.

11-01-2017 12:42

Boltman

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.

11-01-2017 12:54

Ether

Re: pic: OMNI Drive

Using your argument, how is it possible for a sailboat's speed to exceed the wind speed that is propelling it?

11-01-2017 13:16

GeeTwo

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.

11-01-2017 13:30

Ether

Re: pic: OMNI Drive

Not.

Mec fwd/reverse kinematics is same as standard wheel.

11-01-2017 13:49

GeeTwo

Re: pic: OMNI Drive

You do have to gear the Killough Mecanum ~40% faster to get the same behavior. I should have said similar (same shape, different scale).

I'm not sure what you're saying here. What sort of standard wheel?

11-01-2017 16:53

Ether

Re: pic: OMNI Drive

omni vs mecanum vs standard wheel chart

11-01-2017 17:21

Lil' Lavery

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.

How do you figure.

11-01-2017 18:09

jaweth12@gmail

Re: pic: OMNI Drive

Check this pdf on page 12
http://www.simbotics.org/files/pdf/drivetraindesign.pdf

11-01-2017 22:04

OZ_341

Re: pic: OMNI Drive

Team 341 did a variation of this in 2007 and 2008.
However, we placed the wheels at the corners.
Our nickname for this configuration was "Z-drive".

If you do this, you have to be resigned to the fact that everyone can push you around at will.

We were OK playing a "run and gun" game in 2007. It allowed us to always face the goal with the tubes and just drive sideways. Then in 2008 you were not allowed to contact each other, so we did not have to worry about defenders.

We won the Philly Regional with this drive configuration in those two years.
That being said, it has a limited range of uses for most games.

12-01-2017 09:09

GeeTwo

Re: pic: OMNI Drive

Ether answered in the previous post. √2 - 1 =~ 40%.

Edit: As I look at Ether's chart, mecanum should be 40% faster, or omni 30% slower.

And thanks for keeping us honest, Ether!

13-01-2017 01:31

pmattin5459

Re: pic: OMNI Drive

If you haven't built a holonomic drivetrain before, don't design one in the middle of build season. Just use a tank drive. If you're really set on it, then i would suggest mecanums, which can be added to a standard chassis fairly easily, or, if you really want the omnis, put them in the corners diagonally.