Hex Kiwi Drive

[caume]

Over the past few weeks, I have been working on a hex kiwi drive train. It is a six-sided drive, with an omni wheel on each side. This allows for nearly identical speed and pushing power in every direction. A rough weight estimate of this is ~35lb, without bumpers, battery, or electronics.

Specs:

• 12:64 Drive Ratio
• 4 inch Omni Wheels
• Theoretical Speed: 17 ft/s
• Stall Force: 196-227 lb, depending on direction

If you see any mistakes after looking at this, please let me know! Thanks!

[Jay O'Donnell]

i would definitely work on adding some gussets or other type of support between the drive rails and the upper frame. Looks like it only held on by 6 standoffs right now. Keep in mind all of the force of a defense hit goes into the bumpers, so you want that connection to be really strong.

Also, keep in mind pushing with omnis isn't very efficient. The major point of an omni directional drivetrain is to avoid collisions.

[caume]

Originally Posted by Jay O'Donnell

i would definitely work on adding some gussets or other type of support between the drive rails and the upper frame. Looks like it only held on by 6 standoffs right now. Keep in mind all of the force of a defense hit goes into the bumpers, so you want that connection to be really strong.

Also, keep in mind pushing with omnis isn't very efficient. The major point of an omni directional drivetrain is to avoid collisions.

I was thinking the same thing about the bumpers.

For the omnis, shouldn't coefficient of friction be high in the direction of the wheel? The added pressure from the sides of the rollers should help, no? The reason omnis are used to get away is because they are more maneuverable, but if the rollers aren't consistent in every direction, they should be good for pushing, I thought.

[Jay O'Donnell]

Originally Posted by caume

I was thinking the same thing about the bumpers.

For the omnis, shouldn't coefficient of friction be high in the direction of the wheel? The added pressure from the sides of the rollers should help, no? The reason omnis are used to get away is because they are more maneuverable, but if the rollers aren't consistent in every direction, they should be good for pushing, I thought.

Not sure what you mean by added pressure from the sides of the rollers, so forgive me if my thoughts don't make sense with yours.

The main issue is that most collisions are directly applied to a bumper side. This means that only two of your wheels will be driving directly against the pushing robot, and you're not using all of the power that you have efficiently since the driving vectors are at an angle.

Edit: other problem with omni directional drivetrains like this is that it is easier to get pushed from the side and be moved. A good driver can get out of it, but usually it ends up not being worth it.

[asid61]

That might be a tad fast even for 6 CIMs, because of brownouts. Apart from that, I really love this implementation.
Your CIMs appear to be bleeding into the bellypan.
Have you thought about using the Vex clamping gearboxes instead of custom? I like your implementation as it keeps this low to the ground, but it's something to think about.

EDIT: Missed the upper fame. As Jay said, adding some 2x1s or something with cuts to that they fit into the main rail and upper rail would be much more secure.

[caume]

Originally Posted by asid61

Your CIMs appear to be bleeding into the bellypan.
Have you thought about using the Vex clamping gearboxes instead of custom? I like your implementation as it keeps this low to the ground, but it's something to think about.

My original version of the cad actually used the vex clamping gearboxes. My team has had problems with motors sagging down, so I went on to make the motors lower, with cutouts in the bottom plate. The idea was the bottom plate would support the motors a bit. I attached the other images.

[messer5740]

So I have difficulty seeing what previous game a hex chassis would be effective for. Would someone care to enlighten me on what benefits there are for having a hex chassis? I feel that an H drive or mecanum is a more efficient way of driving for you still have the omnidirectional movement. Also, with the electronics that would need to be added, I do not see how attachments could go onto the robot without having a tangled mess of wire and electronics on the belly pan. Perhaps even an additional pan would be good for adding attachments... I know Simbotics used a kiwi drive in 2015 in a non defensive game, but their chassis was not a hex like the one shown above. So why Hex and why kiwi?

EDIT: can you send me the CAD so I can review it some more?

[caume]

Originally Posted by messer5740

So I have difficulty seeing what previous game a hex chassis would be effective for. Would someone care to enlighten me on what benefits there are for having a hex chassis? I feel that an H drive or mecanum is a more efficient way of driving for you still have the omnidirectional movement. Also, with the electronics that would need to be added, I do not see how attachments could go onto the robot without having a tangled mess of wire and electronics on the belly pan. Perhaps even an additional pan would be good for adding attachments... I know Simbotics used a kiwi drive in 2015 in a non defensive game, but their chassis was not a hex like the one shown above. So why Hex and why kiwi?

Hex kiwi could be really good 2014, or any flat field really, because it can be so fast and maneuverable

[messer5740]

So how would you be able to get a shooter or kicker on the robot?

[CalTran]

Originally Posted by messer5740

So I have difficulty seeing what previous game a hex chassis would be effective for. Would someone care to enlighten me on what benefits there are for having a hex chassis? I feel that an H drive or mecanum is a more efficient way of driving for you still have the omnidirectional movement. Also, with the electronics that would need to be added, I do not see how attachments could go onto the robot without having a tangled mess of wire and electronics on the belly pan. Perhaps even an additional pan would be good for adding attachments... I know Simbotics used a kiwi drive in 2015 in a non defensive game, but their chassis was not a hex like the one shown above. So why Hex and why kiwi?

EDIT: can you send me the CAD so I can review it some more?

To be fair, 148 won a Championship with a nonagon chassis.

[Alan Anderson]

Originally Posted by CalTran

To be fair, 148 won a Championship with a nonagon chassis.

The frame had nine sides, true. Count the wheels, though.

[messer5740]

Originally Posted by Alan Anderson

The frame had nine sides, true. Count the wheels, though.

Most likely not 6...

[caume]

Originally Posted by messer5740

Most likely not 6...

To counter that argument, look at like 90% of the robotics this year, 6WD. This is just a fancy 6WD if you think about it

[messer5740]

Originally Posted by caume

To counter that argument, look at like 90% of the robotics this year, 6WD. This is just a fancy 6WD if you think about it

True true didn't think about our own robot

[ThaddeusMaximus]

Originally Posted by caume

To counter that argument, look at like 90% of the robotics this year, 6WD. This is just a fancy 6WD if you think about it

6 wheels? yep. fancy? You betcha. Same thing? Heavens no.

6wd gives you maximum pushing force (for both motor and traction) in the direction of orientation. Omniwheels currently available are less grippy than solid wheels currently available, and having 2/3s of your wheels basically inactive when in a straight line reduces motor power. These are not perks...

Not to mention the normal force on any set of wheels is half of that in a kiwi. I'd think for this reason that a kiwi would beat this in a pushing match, which would proceed to get dominated by a 6wd with good solid wheels.