pic: FRC488 - Six Wheel Drive Chassis

[MikeDubreuil]

Can you explain why you chose not to have a cross brace? I'm not a mech-e but I would guess you need one.

[Madison]

Originally Posted by dhoizner

A couple of questions:

Does that have any rocker in it? And is that 25 or 35 chain?

The wheels are all in line -- there's no 'rock' at all. The chain is #25.

Originally Posted by Joel J.

Why omniwheels on a 6WD?

Because the center wheel is not lowered at all, at least one outside set of wheels should be omniwheels to alleviate friction while turning. I chose to put a set on each end because there's no penalty to in line pushing force, generally, and I like to subtley encourage our drivers to avoid conflict.

Originally Posted by Gdeaver

If the bumpers are back and the design is like 2006, then the next step is to add mounting to this frame that would allow the bumpers to be a structural element. If the rules allow forget home center plywood. Baltic birch "wood" be a good choice.

I'm now looking at a mounting scheme that will accept bumpers and protect the wheels from impact. I've never put bumpers on a robot before, so I'm looking at examples of others' work to get an idea how to best accomodate the additional weight of the bumper assembly.

Originally Posted by Cody C

Not necessarily more maneuverable, But I bet it is nice to have the 'bot spin around it's center set of wheels instead of whichever four happen to be touching the ground

Our 2005 robot had a lowered center wheel and the tipping action drove me and our drivers crazy. It's an impact to the system each time the robot's inertia shifts and that starts to lead to annoying things like loosened bolts and the like. Practically, it's cheaper and easier for me to make omniwheels than it is to make traction wheels and it's certainly cheaper than buying them.

Originally Posted by s_forbes

Wow, looks light! Do you have an estimated weight for the entire drive base?

And on the subject of omniwheels: It looks like with the setup you have it would be very easy to swap them for traction wheels if they are needed. I guess that would be decided in testing.

As shown -- which includes everything but stiffening gussets and a base upon which to mount electronics, it's 29.5 lbs.

The omniwheels are riding on 5/8" keyed shaft, while the AndyMark performance wheel is broached for a 1/2" hex shaft. It'd be relatively easy to change out a set of omniwheels for a set of traction wheels with a little bit of forethought. Namely, I'd need to make some shafts that are 5/8" diameter with keyway on one end and 1/2" hex on the other.

Originally Posted by MikeDubreuil

Can you explain why you chose not to have a cross brace? I'm not a mech-e but I would guess you need one.

I'm waiting on the game before adding cross-bracing since I'm not sure if I'll need a scoop or something on one or both ends. I'd like to, if weight allows, put an aluminum plate (1/16" or so) across the bottom to add rigidity.

[foundbobby]

Originally Posted by M. Krass

The wheels are all in line -- there's no 'rock' at all. The chain is #25.



Because the center wheel is not lowered at all, at least one outside set of wheels should be omniwheels to alleviate friction while turning. I chose to put a set on each end because there's no penalty to in line pushing force, generally, and I like to subtley encourage our drivers to avoid conflict.



I'm now looking at a mounting scheme that will accept bumpers and protect the wheels from impact. I've never put bumpers on a robot before, so I'm looking at examples of others' work to get an idea how to best accomodate the additional weight of the bumper assembly.



Our 2005 robot had a lowered center wheel and the tipping action drove me and our drivers crazy. It's an impact to the system each time the robot's inertia shifts and that starts to lead to annoying things like loosened bolts and the like. Practically, it's cheaper and easier for me to make omniwheels than it is to make traction wheels and it's certainly cheaper than buying them.



As shown -- which includes everything but stiffening gussets and a base upon which to mount electronics, it's 29.5 lbs.

The omniwheels are riding on 5/8" keyed shaft, while the AndyMark performance wheel is broached for a 1/2" hex shaft. It'd be relatively easy to change out a set of omniwheels for a set of traction wheels with a little bit of forethought. Namely, I'd need to make some shafts that are 5/8" diameter with keyway on one end and 1/2" hex on the other.



I'm waiting on the game before adding cross-bracing since I'm not sure if I'll need a scoop or something on one or both ends. I'd like to, if weight allows, put an aluminum plate (1/16" or so) across the bottom to add rigidity.

Nice design. What about having the wheels on the outside? Don't they need be protected some to avoid bent shafts and broken wheels?

[Gdeaver]

I noticed that the front and rear c channels are notched for the drive rails on top and bottom. This could be a weak point. Shouldn't the drive rails fit inside the c channel leaving the channel uncut ?

[dlavery]

M -

Looks quite nice, and you have obviously put a lot of work and thought into the design. The efforts to minimize the total weight are obvious. The biggest concern you may have is strength in the event of an impact or collision. You might consider making the frame members out of rectangular tube instead of channel. Given the amount of material you are removing, the additional weight from the fourth side of the tube will be minimal, but there will a considerable increase in stiffness of the frame assembly.

Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?

-dave

[Cody Carey]

Oh goodness.

[ChuckDickerson]

Here we go again...

[Madison]

Originally Posted by dlavery

Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?

-dave

[Jeff K.]

Originally Posted by dlavery

Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?

-dave

Any crocs?

CRIKEY!

[DanDon]

WATCH OUT!!! WE'VE GOT A DAVE ON THE LOOSE!!! SOS...SOS...SOS

[dfukuba]

That looks very nice and pretty well engineered. My suggestions are that you only use one set of omni wheels. You have to admit that you will be getting in to conflict no matter what you do.
The frame does look pretty sound, but with all that material taken out, are you worried about bending at all? these bots go through some pretty hard hits.
But i am very impressed by your design and i look forward to seeing the end product after the next hectic 6 weeks =)
--Dan

[Rich Kressly]

Originally Posted by dlavery

M -
Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?
-dave

Who keeps letting him in? Security!!!

I love the simple approach to the 6-wheel drive. I'll be follwing up later if you use this to see what additional stiffening was used/needed. Good luck.

[Madison]

Originally Posted by Rich Kressly

Who keeps letting him in? Security!!!

I love the simple approach to the 6-wheel drive. I'll be follwing up later if you use this to see what additional stiffening was used/needed. Good luck.

I took Dave's advice and added the fourth wall to the front and rear cross members as a start. Because these drivetrains are almost never operating absent some additional mechanism or superstructure, I try to incorporate those future additions into the design and allow for them to be used as support for the drive in the same way that the drive supports the mechanisms, if that makes sense. I try to design such that the finished robot appears organic -- not as if it was designed in pieces that were smashed together later.

Because of the holidays primarly, we haven't really done much of anything with our mecanum drive prototype. It still has no feedback system installed and remains difficult to drive. Most of the team agrees that, unless it appears to be a perfect solution for the new game, we'll stick with something more traditional like this drive, so there's a good chance you'll be seeing it somewhere.

[Andrew Blair]

Madison, I know that you have no broach capability, so I'm curious- where do you buy your #25 sprockets? I can't find any finished ones online, or in the Browning catalog.

[Madison]

Originally Posted by Andrew Blair

Madison, I know that you have no broach capability, so I'm curious- where do you buy your #25 sprockets? I can't find any finished ones online, or in the Browning catalog.

For this, we'll be ordering from McMaster-Carr -- part no. 2737T123. 5/8" bore was the smallest I found with a keyway for this particular sprocket. I didn't take a comprehensive look at many teeth counts, though, so I'm not sure how consistent the keyways are in 5/8" bore sprockets -- but I can't imagine why they all don't have one.