09-04-2006 14:04

Adam Richards

Re: pic: What else has Billfred been doing?

Kiwi drive?

09-04-2006 14:05

Greg Needel

Re: pic: What else has Billfred been doing?

i hope you are going to have some ball casters or skids under the corners of the triangle or it might be unsteady.

09-04-2006 14:33

Stuart

Re: pic: What else has Billfred been doing?

I personaly would move the wheels to the corners instead

09-04-2006 14:36

Billfred

Re: pic: What else has Billfred been doing?

Man, I thought they didn't post these things until after I finished the description! (insert anime-style sweat drop here)

Yes, it is indeed a kiwi drive. I've been working on it as part of a research grant from Preston Residential College here at USC for the better part of the semester. (Preston offered grants up to $500 to research a topic with a faculty member. It was a good excuse to learn to CAD, among other things.)

The idea is to create a kiwi drive that a team with limited resources and fabrication abilities can create. The only thing that you'd have to add on top of the list of tools needed to fabricate the Kitbot is a power drill. A center punch and/or scribe wouldn't hurt either, but you can live without them. (You can get fancier with this design--if you could find an appropriate sprocket, you could substitute an AndyMark Gearbox for the third IFI transmission and possibly shave a few bucks off of the cost. But since I couldn't find the right sprocket for the job without having one custom-machined, I kept with three IFIs.)

Most of my time has been spent just learning the finer points of Pro/ENGINEER (what USC uses) and designing those corner brackets. (You can cut two from a Kitbot's top plate. You can't really use it for its intended purpose in this setup anyway, so you might as well get something from it, right?)

We're hoping to get this thing together for Discovery Day (USC's annual undergraduate research shin-dig) in a couple of weeks. It should be fun.

Something will be going under there. I'm thinking PVC, since I already had to buy some to make spacers with.

It could be done like that, but one of the first things I learned from my mentor (Dr. Philip Voglewede, if anyone was at the Palmetto team social) was that the wheels's axes needed to converge in the middle for things to work out smoothly. To get them in the corners would take, at least in my judgement, a lot more trouble than it's worth. (But if someone has an idea, I'm all ears.)

09-04-2006 14:53

Stuart

Re: pic: What else has Billfred been doing?

it is an equilateral triangle isn't it? . . . cause if it is just moving the wheels to the coroners would keep the axises centered. . . then for the kit drives just move them above the wheels instead of to the side of them. . . . this is all of course assuming that it is an equilateral triangle

09-04-2006 15:01

Tristan Lall

Re: pic: What else has Billfred been doing?

Billfred, I think that people are suggesting that the wheels be mounted to the triangular brackets, with their axes perpendicular to the long edge of the brackets. That allows the robot to be fully supported on its wheels, rather than causing some of the weight to rest on undriven wheels/casters/skids (which would reduce the amount of force that the robot could exert in a pushing match).

Also, why not consider a quadrilateral version of the Kiwi drive? Like what 854, 931 and others used this year? It seems even simpler to build, and a little more powerful (provided that the extra CIM wasn't needed elsewhere).

A note on the kitbot sprocket. I just realized that we ought to be looking for ISO 04 and ISO 06 sprockets, not #25 and #35. They're functionally equivalent to ANSI roller chain sprockets, if I'm not mistaken, but they do come in 16 mm bore sizes. In fact, SDP/SI has some, in larger tooth sizes for ISO 04/#25. And Martin sells a few ISO 06/#35 ones with 16 mm bores. Search GlobalSpec for "Sprockets, Roller Chain, Metric", for more sources.

09-04-2006 15:02

supermosquito69

Re: pic: What else has Billfred been doing?

Nice job on the 3-D Modeling man!!

Actually, the "steady" factor depends on the center of gravity of robot. So, if the robot is as tall as it can be but the center of gravity is very low then the robot will have no problem. Otherwise the skids are the way to go since the casters need a direction on their axis while the skids don't need any directionality, they just stand there.

09-04-2006 15:05

Tim Delles

Re: pic: What else has Billfred been doing?

Billfred, here is a video of our kiwi drive. (Looking for the pictures still. Will post when i find. and the other picture i posted was actually teams 857's design) Hope it gives you some ideas.

Edit:// Also don't run it on any hard floor, only use carpet. If you run it on a hard floor it makes the most horrible sound in the world. Well close to it

09-04-2006 15:34

Rohan_DHS

Re: pic: What else has Billfred been doing?

<noob>
how exactly does this type of drive system work, and what are the advantages of using such a drive system over a normal type of drive system?
</noob>

09-04-2006 15:39

pakrat

Re: pic: What else has Billfred been doing?

one awesome thing about these kinds of drives is that they can have increased maneuverability without having to build a complex swerve drive system (having motors to rotate the wheels. You can spin very easily and many teams use a 4 wheel configuration of this idea. I know we did, and about 5 or 6 or the Waterloo teams did too.

I think This is 229's version with wheels at the corners. Billfreds is simpler i think, but it may need casters or whatnot. I think this is a solid design by the way.

09-04-2006 15:42

sanddrag

Re: pic: What else has Billfred been doing?

If those were 6" wheels (they look like 8" right now, are they?) you could get away with putting them right on the gearbox output shafts. Although you'd need a custom hub, which is not desired in this project I guess.

09-04-2006 15:54

Billfred

Re: pic: What else has Billfred been doing?

The angle of the drawing (and my comments) might be unintentionally tricking folks--it does rest solely on the omniwheels. Any skids I might add to the corners would be just for some extra insurance--a wheelie bar of sorts. (Though don't most kiwis attempt to avoid pushing matches anyway?)

Why not quadrilateral? Good question. Besides a desire to do something a little different (I only know of 857's in 2002 and 229's prototype kiwis in FIRST, but there have been many more quadrilateral ones), a three-wheeled version has an additional thing going for it: cost. You don't have to buy or make the fourth omniwheel/transmission/etc. (Besides, that also frees up a CIM motor for other things, which I'll leave to the reader's imagination.)

Simplicity shouldn't be too much of an issue--those corner brackets are the sole part you have to custom-fabricate, and that's just a matter of lining up your hacksaw correctly. Everything else is just assembling the Kitbot with the low-rider configuration (although you could go the traditional way if you desired--I just went low-rider for the center of gravity benefits.)

Interesting. I'll have to check it out.

Something to keep in mind--luckily, the halls of both 300 Main (the mechanical engineering building) and Preston are carpeted. Fwahaahaa.

It is an equilateral triangle--the corner brackets only took me about 47 tries to get right. The wheels are mounted where they are for simplicity and durability (how many decently-constructed kitbots have you seen smashed to pieces?). This setup is basically just the lowrider configuration with some interesting corners. I haven't fully investigated mounting them on the corners, but I can't picture it being done in a cheap-and-easy fashion.

Those are 6" AM omniwheels. I didn't plan on traversing anything other than flat carpet, so I didn't see a benefit to spending $12 more for 8" wheels all around. You're right, though--the hub was undesired.

I appreciate the feedback--it's good to hear it from a lot of folks.

09-04-2006 17:22

JVN

Re: pic: What else has Billfred been doing?

The 229 version that was linked in this thread was designed primarily by Chris Carnevale.

Chris' design consisted of designing a simple "Omni-Module" which was a solid unit consisting of one AM omni-wheel, 1 gearbox (he used the Bosch Drill+Gearbox, but a kitbot gearbox could easily be substituted), and all the mounting/framing that comes with it.

Chris then built 3 of these simple omni-modules, and bolted them onto a big triagular piece of plywood. Simple, and easy; this design can definitely be built by low-resource teams.

-JV