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Building a Non-kitbot chassis & Some info on drivetrains

Otaku

By: Otaku
New: 12-09-2007 20:20
Updated: 12-09-2007 20:39
Total downloads: 2 times


Just a little whitepaper to help out teams who might need it.

Alright. I've seen some people ask how to make drivetrains, how to organize electronics, etc, so I think the CD community as a whole should help them out.

First off:

Building a Non-Kitbot chassis:

To build a very robust, non-kitbot chassis, you want the outside of the frame to be the largest part of your robot, then you want to make sure that there are plenty of supports and good fasteners. 675 uses 3/8ths inch Grade 8 bolts with a shoulder on them, and a washer on each side of the bolt. Gloria Machina, 675's bot, is layed out like this.



The thin black lines are vertically-mounted peices of quarter-inch thick, 3 inch tall aluminium.
The maroon rectangles are the wheels.
The dark blue strips are the same type of aluminium, but bolted on top of our gearboxes to support the chassis and gearboxes.
The thick black strips are some other sort of material, and hold the stump of our arm, along with our ramp bracket and battery.

Not to scale.

[Add-in: As well as basic chassis layouts like Gloria's, one could build variants of a similar style (For instance, Cthulhu, 675's '06 'bot had an open front with a support in the middle) that will also work. I warn, however, about getting rid of supports. Cthulhu took one nasty hit and the whole frame bent. If you do get rid of supports, think about all the different angles you might get hit from (or hit somebody from) and what effects it might have on the chassis. For instance, if you get hit in a less-supported corner your frame will take more damage than if you get hit in a more-supported corner. On top of this, for teams that can afford it, you should always have extra chassis parts. It will help if one or more gets bent.]



Building a good Drivetrain:

First off, unless you want insane traction and a hard time turning with tank drive, steer clear of the KOP wheels. They're very grippy and to lose traction, teams have had to cover them in plastic or zipties.

[Add-in: I've read through the original thread and would like to amend this. Apparently the KOP wheels actually offer LESS traction than the new IFI Traction V2's. Our team has never used IFI Traction V2's after our bad experience with V1's, instead we CNC Mill out our own custom wheels and use the blue nitrile tread for it.

Also, one of the other posters mentioned that a good way to see if you've got too much traction is to get your bot working and whatnot, then to drive it up to and against the wall. If the wheels spin when you try to go forward, you're good. If the wheels don't spin and the motors seize, you've got to get less traction.]

There are several different kinds of drivetrains you can do. You can do a direct-drive system with all wheels powered by their own motor (4 or 6 wheels works best for this), a chain-drive system with all wheels powered with their own motor/gearbox (again, 4-6 wheels), chain-drive for each side (2 motors generally, 4/6 wheels total), or some other interesting systems (like a 6-CIM drive system, or a 12-wheel system, not recommended for rookie or less experienced teams. It could be a fun off-season project however, and I suggest doing it if you want. The more you learn in the off-season, the more of an edge you may gain during competition.).

There are also several different types of wheels. Traction, Omniwheel, and Mecanum are the three most well known. Traction wheels have a grippy tread that gives, as the name implies, traction. The design on the tread can be all sorts of things, from a crisscross pattern, to a pseudo-car-tire design, to the kind of stuff that comes on IFI Traction wheels.

IFI Traction V2 wheels:



Not the two different types of tread. The kind on the left is called "Roughtop", and the type on the right is called "wedge".


Omnidrive wheels are cool. They are normal wheels in the sense that they are round and give you traction, but only forward and backwards. A common design for omniwheel useage is traction wheels in the center of a 6-wheel chassis, and omniwheels at the corners. This improves turning speed greatly over an all-traction wheel chassis.

AndyMark Omnidrive Wheels, 6in Diameter:



Mecanum wheels are probably the coolest, however. The wheel design is similar to Omnidrive, however different in such a manner that the robot using them can move in any direction and rotate easily, allowing it to slide around much like a hockey puck. There is a special way of mounting them, however, and that is so that the 4 wheels form an X when looked at from the top down.

Mecanum Wheel, 8in diameter:


Notice the staggered rollers.

Thanks to AndyMark.biz and InnovationFIRST.com for the pictures, and making good prodoucts.

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