Hex Kiwi Drive

[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.

[caume]

Originally Posted by ThaddeusMaximus

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.

I was mostly joking when I said it's a 6WD. Obviously, the only real similarity is the number of wheels. Where did you get the information about omnis being less grippy? I'm not doubting it at all, I just haven't been able to find info about the CoF when I've looked.

[EricH]

Originally Posted by caume

I was mostly joking when I said it's a 6WD. Obviously, the only real similarity is the number of wheels. Where did you get the information about omnis being less grippy? I'm not doubting it at all, I just haven't been able to find info about the CoF when I've looked.

0.8-0.88 for an AM 6" aluminum omni (AM site)
A 6" "normal" wheel (rubber tread, not high grip) is 0.9 (AM site).
"HiGrip" wheels are 0.95.

That's going to be a 10%-20% increase in grippiness when using non-omni wheels instead of omniwheels.

[Jonny_Jee]

Originally Posted by messer5740

Most likely not 6...

148 had a three wheel swerve drive that year.

[Cash4587]

The programming on this would be very very tricky. Figuring out how much power to give each motor in the "Forward" direction would take some playing with and tuning because two wheels are pointed "Forward" and the other four are angled.

Although this is a cool idea and looks interesting it probably is not very practical. In most cases it would make the most sense to just do a 3 wheel kiwi or an H-Drive. For that matter, even a swerve would probably make more sense.

[ThaddeusMaximus]

Originally Posted by Cash4587

The programming on this would be very very tricky. Figuring out how much power to give each motor in the "Forward" direction would take some playing with and tuning because two wheels are pointed "Forward" and the other four are angled.

Unsure why this would be any more confusing than kiwi drive inverse kinematics. Just do the geometry what with the velocity vectors.

[Cash4587]

Only thing I would be worried about is that it probably will act a bit weird when trying to go forward since the side wheels would not be at the 30 degree angle like the other 4. As long is the math is done out right though it probably would be fine.

[Ether]

Originally Posted by Cash4587

The programming on this would be very very tricky.

wheel1 =   STR + ωR
wheel2 = - FWDcos30  + STRcos60 + ωR
wheel3 = - FWDcos30  - STRcos60 + ωR
wheel4 = - STR + ωR
wheel5 =   FWDcos30  - STRcos60 + ωR
wheel6 =   FWDcos30  + STRcos60 + ωR

(Then divide all wheel speeds by the maximum one if any one exceeds the maximum achievable wheel speed)

[Cash4587]

Originally Posted by Ether

wheel1 =   STR + ωR
wheel2 = - FWDcos30  + STRcos60 + ωR
wheel3 = - FWDcos30  - STRcos60 + ωR
wheel4 = - STR + ωR
wheel5 =   FWDcos30  - STRcos60 + ωR
wheel6 =   FWDcos30  + STRcos60 + ωR

(Then divide all wheel speeds by the maximum one if any one exceeds the maximum achievable wheel speed)

I hadn't thought of doing it this way. I had just assumed that "Forward" would be a point of the hexagon moving forward utilizing all six wheels when going forward, instead of just four using this setup. Even still, this all makes more sense now.

[Ether]

Originally Posted by Cash4587

I hadn't thought of doing it this way. I had just assumed that "Forward" would be a point of the hexagon moving forward utilizing all six wheels when going forward, instead of just four using this setup. Even still, this all makes more sense now.

If you want FWD to be a point on the hexagon, just change the inverse kinematics like so:

wheel1 = - FWDcos60  + STRcos30 + ωR
wheel2 = - FWD + ωR
wheel3 = - FWDcos60  - STRcos30 + ωR
wheel4 =   FWDcos60  - STRcos30 + ωR
wheel5 =   FWD + ωR
wheel6 =   FWDcos60  + STRcos30 + ωR

(Then divide all wheel speeds by the maximum one if any one exceeds the maximum achievable wheel speed)