pic: SimpleChassis



CAD at: https://drive.google.com/file/d/0B4KOM49Q5ksGR3BUMHNTdXNTVkE/edit?usp=sharing

This chassis is designed to be built in very little time by teams with few resources. It features a plywood board as the majority of the chassis’s structure. Normally, a chassis like this would tear itself apart just by driving around, but this chassis draws it’s strength from it’s bumpers. A similar setup was run by team 3958 in 2012 and held up pretty well.

Specs:
23.75in x 32in
6WD with 1/8 Center Drop
Hi-Grip KOP wheels
4 CIMs
AM Shifter Gearbox (with 15 tooth output sprockets instead of 12)
13.64fps High Gear (assuming 90% efficiency)
5.33fps Low Gear (assuming 90% efficiency)

Designed by Chris Johnson, with help from Paul Terrasi, and inspired by FRC3958’s 2013 chassis.

If this is for low resource teams, what advantage does this have over the kitbot, or any of the other COTS drivebases out there?

I don’t wanna speak for the designer, but one of the immediate ‘advantages’ I see of this, not necessarily as opposed to the kitbot, but other COTS drivebases, is that I’m sure, aside from transmissions/motors/wheels, this could be built for <$75 with stuff that can be bought on a single trip to Home Depot

The brackets used for the eyebolt tensioning system are a little funky. Where would you source those?

I think the CAD rendering is a little funky. Double images on the outside wheels and the eyebolts.

I’m looking more at the slots that need to be machined and precise manual hole drilling that most low resource teams won’t be able to do.

Yep, and gearboxes etc can be recycled. You could even say it has this advantage over the kitbot, because you could just get the $450 Andymark voucher instead.

Also, some teams may have opted out of the kitbot, and since then realized that they really needed it. I know that my team thought we were going to be a lot better off this than we actually are, especially in terms of CAD resources.

And, some people may just not like the kitbot. Especially this year when we don’t know what to expect. So this would be a good alternative for those people, just like the COTs drivebases.

Last year we machined a very similar chassis with mainly a band saw and a drill press. The slots were made with a dremel and worked fine (although this year we are probably going to make them with our manual mill that we finally learned how to use).

Those are just 2 1in piece of angle aluminum.

The wheels aren’t a problem with the render. We had double wheels, 1 on either extreme of the chain tensioning, and I forgot to hide one.

What precise drilling? There’s slots in the L-bracket for the wheels which can easily be done on any mill, and everything else seems quite doable by hand. No exact centers or anything here. Looks super cheap to make and uses the bumpers for strength. I don’t see this drivetrain as something you can easily dismiss as inferior to COTS options.

Ah. This is a time when including hardware in your model would be helpful. :slight_smile:

Yeah. After my post I realized that you probably were showing both the ‘tensioned’ and the ‘un-tensioned’ positions. Thanks for sharing this design.

Very nice design. Looks like an afternoon project for 1 or 2 people. The chain tensioning set up I have used for many projects and while it does looks crude it works great. GRT has used eye bolts many times. I would add a cross brace at the top but that is my preference. This design would give a team a cheap practice chassis and one to test mechanisms on and save the kit chassis for later if they wanted to. Good work.:slight_smile:

Quick Question - Where is the cross strength going to come from? If all of the force is going to that wooden board, where the electronics are ideally mounted, that might not make a pretty sight.

Looks nice though, great way to practice CAD!

Their team name fits this very well :smiley: .

Also, when the new rules come out, check if those corners are compliant with the bumper rules. Other than that it looks great.

The bumpers! While the plywood board gives the chassis strength again parallelograming and other stresses parallel to the ground, the bumbers provide great resistance to any forces perpendicular to the ground.

When we first built our chassis last year, we tried driving it around without bumpers. Like you said, it was not a pretty sight.

What exactly might be wrong with the bumper corners? I don’t see anything wrong.

Offset the transmission closer together. The main shaft needs to extend so a pulley can be attached outside the plate. This makes it easier to attach a belt without having to take the transmission apart to install/replace the belt.

Sorry I thought you guys were using a belt

After finding last years rules I think I mixed up the “you must have at least 1 inch supported on the bumper corners” with another number (very sorry about that). The bumpers should be fine.

One question, how heavy is it? (just so I can compare it to all the cots drives)

Here is a link to a $8 mill](http://www.lowes.com/pd_152677-930-324CP9_4294857572__?productId=1018541&Ns=p_product_qty_sales_dollar|1&pl=1&currentURL=%3FNs%3Dp_product_qty_sales_dollar|1&facetInfo=) for cutting slots in angle. The amazing thin about a mill like this is it uses no electricity and can fit in pretty much any tool box. It is significantly less danergous that a vertical mill, and can actually do more precise cuts. I took a jewelry and metal smithing calss at Purdue. One of the first assignments was to cut out the profile of Lincoln out of a penny. It was pretty cheap practice and helped showcase the tools skills.
While I couldn’t find a picture of a penny, I did find this picture of something similar done to a quarter (much harder metal):
While some might think it would take a long time to do such a thing, the lincoln profile took about 35 minutes with a beginner skill level. Sawing a couple straight lines after dilling 2 holes would likely require less time than locating edges in a mill.