Maybe on a perfectly 4-way symmetrical robot, but in My team’s experience, It stays on 4 wheels and rocks back and forth… Whichever four wheels happen to be touching are the ones the bot spins around. Kinda messes up high-speed maneuvering.
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.
Ah, I see. We were going to be using 1/2" bore, and for some reason, no one on earth carries broached 1/2" bore sprockets. Thanks though!
The last two years I worked on center-drive, 6-wheel robots and both times we purposely loaded one end of the 'bot with a LOT more weight for game reasons. This also had the effect of having the same four wheels on the ground most of the time. We had little fore-and-aft rocking and the robot wasn’t tricky to steer at all. Having said that, Madison makes nice chassises – er, chasses – er, chassisses – what IS the plural of chassis anyway? I’d hire her to consult on our chassis, but since I’m now on a VEX-only team, I think we’d be wasting her skills.
I agree wiht what dave said about strenght, but on the contrary our team used aluminum channel for our frame and we didnt seem to have and problem with strength, and our frame took quite a beating during aim high this year
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
team 1783, which is my schools team, used a different drivetrain set up, we had designed a setup where each side had indepent suspension, and two wheels for each side. and this year (depending on the game) i have designed a three speed gear box that would be incorperated into our original design. also i was thinking about trying out a four whee drive design that would be built by me and a local shop. how many of you guys know about the xmods remote control cars at radio shack? well i got one for christmas (god only knows why) but i was looking at upgrades for it and i saw that they have a four wheel drive kit for them. and after hours of configuring, and designing i think that i can build the 4 wheel drive suspension and drivetrain for our robot.
And you of course, are welcome to come consult on our team any time 
Stop by if you feel you are missing out on the hectic 6 weeks that is FRC this season!
chassis, singular = chassis, plural
the plural would have a wee different pronunciation though
One chass-ee, two chass-ease.
Ah, jeez, I know that the plural of chassis is chassis, I was just funnin’ around.
For the record, in 2005 our bot had six wheels with 2WD, but last year our very heavy, very strong chassis had six wheels with 6WD. In case anyone cared.
I AM going through FRC withdrawal now that kickoff is near, but I also fell asleep last night thinking about softballs, so maybe I’m becoming a VEXer, too.
I would like to bring our new, nearly-all-rookie team to visit an FRC team during build, so maybe I will take 488 up on their offer. We also have had friendly comments from team members at 1318 and 492. I think the “F” in FIRST really stands for “friendly.”
One can only venerate the intrinsic quagmires of the lexicon of the English language.
Nice design. What about having the wheels on the outside? Don’t they need be protected some to avoid bent shafts and broken wheels?
Nice picture! We’ll see you at SVR
Based on pictures in another thread I think this is probably FRC Team 488’s robot. Madison is a member of that team, and her team role is mentor.
Maybe I didn’t understand your question?
uhh did you just say suspension, as in springs and dampners suspension??
this is a carpeted field were talking about
Do you guys have a shaft coming out of the tranny for the middle wheel as well as 2 sprockets on the inside leading to the front and rear wheels? Are the sprockets inline? Wouldn’t you need gears on the same axle as the sprocket to drive the sprockets in that case? Are the sprockets on the same axle? In that case how can your wheels be inline? Are the sprockets on the wheels on an offset?
Alright no more questions 
just curious.
Teams have had success with similar designs in the past and our experience with the completed chassis yesterday indicates that, though we may want to protect the wheels, it’s not a paramount concern given our strategy and design. In another game, or on another robot, it may be very important that the wheels are protected from damage and from the sort of wedging effect impedes motion that other teams with similar drives have seen in past seasons.
We hope you’ll take a minute and stop by our pit to talk to the team. I’d be happy to talk more about our robot and answer any questions you might have – as would anyone else on our team. We’re proud of the work we do.
The gearbox at the center of each side has an output shaft that drives the center wheel. Two 18 tooth sprockets are coupled to that shaft and, via chain, drive the wheels at the front and back of the robot. Those sprockets are not in line – they are offset 1/4". Our wheels remain in line because the sprockets on either end mimic the offset of their corresponding center sprocket.
Attached to this post is a cross-section of the gearbox that may help make the gearing arrangement a bit more clear. Excuse that the gears aren’t meshed properly, please. 
My favorite part about this design, something that no one has mentioned yet supprisingly, is the way that you extended your front and rear rails in order to protect the cantilevered wheels. Excellent design all around!