An interesting approach to an omni drive

http://blog.makezine.com/2012/02/27/robot-with-four-wheel-steering/
^ This came up in my RSS reader today…

Only 3 motors, yet still as maneuverable as any omnidrive…

This would be an interesting application of the lexan allotment.

//Andrew

Do a search on “swerve drive”. VEX makes a swerve drive kit that is even competition-legal.

AH! I knew that the “real” name was eluding me… :slight_smile:

I thought that this was an intriguing design due to its method of rotating the wheel sub-assemblies. Instead of requiring an independent motor for each assembly, or requiring elaborate chain configuration, it uses a linkage, powered by (I think) a center motor (either that, or it’s on one of the wheel assemblies). For teams that are “motor-strapped” by their lift/arm, I thought this would be an interesting way of attaining omni-directional motion…

//Andrew

I can see how it spins and moves forward/back and side to side. But how does it strafe (at 45 degree angles to the wheels)? Without omniwheels, it seems that it would have a lot of drag.

It appears that if you want to move at a 45 degree angle (or non-right angle), you are forced to rotate the wheels (and base), rather than strafing, which introduces complications if you have a lift/delivery that you want to hold in a fixed position.

It would be interesting to see how easy/difficult it is to drive this contraption, say compared to an X-holonomic.

But does a swerve drive save on motors? I’m envisioning a minimum of 5 motors: 4 to drive each of the 4 wheels, one coupled to the 4 wheels for direction, and realistically, 2 motors for direction gives better sensitivity than 1.

I’ve never actually constructed one, but the thought of a swerve drive with unpowered “drag” wheels does not sound pretty.

I have seen a swerve drive without that kit. It has three motors. Two of them are in the front like normal and the other is in the back, perpendicular to the other two motors. Your base will look like a triangle most likely. The back wheel needs to be an omniwheel and you could expirement with the other two.

The referenced picture shows 4 wheel crab steer setup.
If one motor is for the crabbing, then the other two must be left wheels and right wheels.
The crab range looks like it might be -90 for left, 0 for straight, +90 degrees for right.
In that case, strafing at + or - 45 degrees without rotating the base should be easy.

The base has 3 degrees of freedom, just like X, +, or H holo, the degrees are just different.
Anytime the base is rotating, there will be wheel scrub like any other squarebot.

Its a cool drive. However I would never put it on any system of mine. It lacks to much. I wouldn’t quite consider it fully omni-directional as well.

Its not really a swerve, and its not really a crab (yes they are different) its just sorta a pseudo-swerve I guess.

  • Andrew