Kiwi Drive Concept

[marshall]

Kinda reminds me of the poor pit lighting from Palmetto this year...

On a more serious note, I remember 116 from 2005 in Annapolis. That was a cool concept then and this a cool concept now.

[Richard Wallace]

Originally Posted by marshall

..., I remember 116 from 2005 in Annapolis. That was a cool concept then and this a cool concept now.

Thanks for reminding me about 116's drive way back when. It inspired me to build a dual omniwheel and a holonomic demonstration chassis.

Thinking about these past efforts makes me really grateful for AndyMark and VexPro/WCP. Today's FRC teams can spend more time on tweaking and practice, because we have access to good COTS components.

[marshall]

Originally Posted by Richard Wallace

Thinking about these past efforts makes me really grateful for AndyMark and VexPro/WCP. Today's FRC teams can spend more time on tweaking and practice, because we have access to good COTS components.

Yeah, back in my day, we did it up hill both ways in the snow with drill motors! And we had to remove anti-backdrive pins from gearboxes to do it! And we didn't complain about it!

[Wayne Doenges]

Here's another working Kiwi drive:
http://www.chiefdelphi.com/media/photos/35176
This was our robot for the 2011 game. Breakaway

I would be a little worried about mounting Omni's sideways like that. Especially if the game is rough. In Breakaway we were constantly being hit. This would lift the corner of our robot and then slam it back down.

[billbo911]

We are planning on experimenting with a Kiwi bot this off season as well. If next years game doesn't lend it's self to an omni drive robot, at least we learned something!

The way you have those three drives angled in, there is no need for the second wheel. It will never touch the floor. If it does, you have bigger issues to deal with!

[Ginger Power]

Originally Posted by billbo911

We are planning on experimenting with a Kiwi bot this off season as well. If next years game doesn't lend it's self to an omni drive robot, at least we learned something!

The way you have those three drives angled in, there is no need for the second wheel. It will never touch the floor. If it does, you have bigger issues to deal with!

Obviously some years are better than others for kiwi drives but I think 1425 and 1501 proved that a well built kiwi drive can compete amidst heavy defensive pressure. My initial thought process for having dualie omni wheels was that I was worried about a single omni wheel not being strong enough. Now that you've pointed that out, my logic doesn't make a whole lot of sense!

[Monochron]

What is the benefit of putting the wheels at such an angle? I wouldn't assume omnis are designed to handle that much loading at that angle. And it looks like it would add a lot more difficulty for the machining?
Is it a shock system to help guarantee that all wheels are touching the floor?

[Alan Anderson]

In general, three wheels will always be touching the floor no matter what angle they are at. The two reasons I see for using the nearly flat angle are 1) it lowers the center of mass, and 2) it moves the contact point outward just a little more from the center of the robot.

[GeeTwo]

Originally Posted by Alan Anderson

In general, three wheels will always be touching the floor no matter what angle they are at. The two reasons I see for using the nearly flat angle are 1) it lowers the center of mass, and 2) it moves the contact point outward just a little more from the center of the robot.

I believe that the motors are moving upward as much as the wheels and gearbox move down, so I'm not sure about #1.

For #2, this could also be done by putting the motors inboard of the wheels; the wheels could be just a fraction of an inch from the outer frame.

[Ginger Power]

Originally Posted by GeeTwo

I believe that the motors are moving upward as much as the wheels and gearbox move down, so I'm not sure about #1.

For #2, this could also be done by putting the motors inboard of the wheels; the wheels could be just a fraction of an inch from the outer frame.

The entire frame is riding lower when the omni wheels are sideways. Also there are more omni rollers in contact with the ground when they are sideways as opposed to when the ground is tangent to the wheel.

[GeeTwo]

Originally Posted by Ginger Power

The entire frame is riding lower when the omni wheels are sideways.

This could also be achieved by raising the axles relative to the chassis while keeping them horizontal.

Originally Posted by Ginger Power

Also there are more omni rollers in contact with the ground when they are sideways as opposed to when the ground is tangent to the wheel.

This is the point of dualies - there is always a roller in contact with the carpet, provided that they're mounted on a horizontal axis. Having multiple rollers in contact with the carpet at that angle will also introduce some additional friction as the rollers point in different directions.

The biggest issue is the one Wayne presented - wheels weren't meant to be loaded that direction. Omnis probably even more so - the whole point of omnis is that they don't exert a force parallel to the shaft. As a result, sound engineering would tend to reduce the sustainable force parallel to the shaft in favor of other requirements.

[Ginger Power]

Originally Posted by GeeTwo

This could also be achieved by raising the axles relative to the chassis while keeping them horizontal.



This is the point of dualies - there is always a roller in contact with the carpet, provided that they're mounted on a horizontal axis. Having multiple rollers in contact with the carpet at that angle will also introduce some additional friction as the rollers point in different directions.

The biggest issue is the one Wayne presented - wheels weren't meant to be loaded that direction. Omnis probably even more so - the whole point of omnis is that they don't exert a force parallel to the shaft. As a result, sound engineering would tend to reduce the sustainable force parallel to the shaft in favor of other requirements.

Both of these points make sense. The same functionality behind the "kizzy drive" can be achieved with wheels that are tangent to the ground. Thanks for the comments!

[GeeTwo]

Originally Posted by Ginger Power

Both of these points make sense. The same functionality behind the "kizzy drive" can be achieved with wheels that are tangent to the ground. Thanks for the comments!

Also, it would require a lot less machining to mount the feet on pneumatic cylinders (though you'd still have to harden them against lateral forces, perhaps with a pipe-within-a-pipe), and hard-mount the wheels. Whichever you actuate, moving the feet close to the where the wheels contact the carpet will decrease the vertical travel required to reliably switch.

[GeeTwo]

Looking a little closer - what are those cans inboard of the gearboxes (one of them is partially obscured by the signal light)? If those are pneumatic cylinders, perhaps these raise the robot and lower the wheels to the floor?

Hmm, and there seems to be a foot midway along the short face of the frame. Is there some reason that you want to "raise the landing gear" and be stationary?

Thinking up names for that - how about a kizzy drive? It sounds close enough to kiwi, and those of you who remember the Roots miniseries a few decades ago may recall that kizzy means "stay put".

[Ginger Power]

Originally Posted by Alan Anderson

In general, three wheels will always be touching the floor no matter what angle they are at. The two reasons I see for using the nearly flat angle are 1) it lowers the center of mass, and 2) it moves the contact point outward just a little more from the center of the robot.

Both were design considerations. A third consideration was that the geometry of a sideways omni wheel made it easy to "retract" the omni wheel using the pneumatic cylinders shown. When the omni wheels are retracted the robot rests on a singular contact point extending down from the frame presumably covered in rough top tread.

The idea is that each omni wheel can be retracted independently, giving the robot the ability to change its center of rotation about each pivot point. There's also the advantage of retracting all omni wheels when in scoring position so the robot becomes difficult to move.