pic: WCD Sheet Metal Concept Chassis



Here is a cool little concept idea that I decided to CAD.
Yes I do realize that there are a few issues here and there with the cad itself, this is mainly to show the concept of the drive.

So here are the specs!
-All 0.09 Sheet Metal chassis
-Its back wheels a direct driven by a pair of modified AndyMark Super Shifters (standard gearing for now)
-4" wheels (Donated to my CAD by FormerlyFamous, AKA Rion)
-1/16th Center Dropped 6WD
It’s designed to be sturdy and rugged, while still being somewhat streamlined.
The big thing that separates this from most WCD’s is that the chain and drive sprockets for the wheels are all enclosed within the chassis side rails. Protecting the chain from debris (a problem my team had this season) but still allowing it to be fixed if need be (via the bottom opening).
Also, I’m considering making the whole side be even more modular, so it can be taken off between matches for repairs (similar to team 25’s drive modules).
All in all this is just a concept idea that I have been thinking a lot about lately.

Looks sharp, where are the wheels from and what cad did u use, the render looks sharp

Very very nice! I’ve got a design that’s quite similar to this brewing.

Out of curiosity, why drive the rear wheel, instead of the middle wheel? I’ve always found that it’s easier to distribute the weight of the base when it’s centered.

I really dig this design. Keep plugging at it!

if you are going to do this make sure that the chain is not going through a tube, my team did something exactly like that for 2008 and it ended a very badly, we dremeled at least 5 holes in the cover at competition in order to fix it. also, be sure to leave a lot of space between the chain and its cover, otherwise when in operation the chain vibrates just a little bit and hits the cover. as long as you dont have those issues, that drive looks fantastic.

How would you tension the chains? Will you just CAD them to be the right distance apart?

I have a question in general about the WCD system, are you using generic bearings/bushings int he sheet metal for the axles, or are there some special ones?

I CADed the wheels a few weeks back, the entire thing was done in SolidWorks.

The tensioning system will be spring powered so that we wont really have to check on the chain too much.

When you say don’t take the chain through a tube, what do you mean? Would the in side the side channel there count as your tube?

Because WCD are done with live hex axles most of the time, teams use bearing blocks and then hex bearings. I can’t remember who right now sells the bearing blocks(AndyMark?), but I do remember that AndyMark sells the bearings.

Garrett, it looks awesome. :wink:

Thanks Craig!

I have a few reasons for going with the rear direct drive.
-I wanted to start off with a good majority of weight behind the middle wheels in order to
reduce the amount of rock the chassis experiences while driving.
-I also wanted the maximum amount of open mounting space for electronics without the gearboxes getting in the way.
-With this design I’m able to put the battery closer to the center of the chassis, which
helps a lot in balancing things out, and since the battery weighs more than the shifters, its
placement on the chassis is more critical (at least in my opinion).
-And of course… because it looks cooler :stuck_out_tongue:

I already took this into account. The chain is fully accessible from the bottom of the robot, there
is more than enough distance from the chain to the rail, and my chain tensioner (coming soon)
will help hold the chain away from the rail itself just for added protection.

Thanks for the advice though :smiley:

Thanks buddy!
Though most teams make their own bearing blocks for their chassis, team221 sells them, and yes the hex bearings I used are AM’s.

Spring loaded tensioners are notoriously unreliable. I would suggest the “traditional” west coast tensioning method of sliding bearing blocks, or possibly a nylon / delrin sliding standoff for each chain section.

When you say don’t take the chain through a tube, what do you mean? Would the in side the side channel there count as your tube?

I would prototype a scale version of this drive and figure out how serviceable the chain is through the completely open bottom hole.

I like this drivetrain… reminds me a lot of Vex. :slight_smile:

Now for my design questions… I have no experience, so these comments are worthless. Would it make sense to add some fillets to the triangular cutouts in the sheet? What if you had the inner flange bend in toward the chassis, so you could rivet the belly pan to it? This would also increase the serviceability of the drivetrain by giving you more access to the chain.

I would think that most FRC spring loaded tensioners are unreliable due to lack of understanding in the design. A standard bicycle has used spring loaded tension for who knows how many years how, even with a shifting drive system. Yet teams who put them in on a 2-way torque transferring system must account for both directions, whereas a bike tensioner only has to deal with one. Thus, a team could easily make a spring loaded tensioner reliable so long as the design is sound. The mini-bike motor belt tensioners from 2006 would be a good place to start experimenting.

As for the CAD render: if the side rails are open on the bottom for chain accessibility, are there supports on the inside of the rail to keep it from buckling in on itself? The channel shown in the reflection of the render makes be believe the side rails are very prone to torsion.

I also like the rear-wheel drive; Drop-center drive train designs are TOO easily turned if the weight is close to the middle, so putting most of the drive train/electronics weight towards the back allows for more flexibility in weight distribution when designing manipulators. The tradeoff is less maneuverability if a chain comes off or breaks.

I started a thread on here about spring chain tensioners. We decided through it that with some good designing and testing we would be able to make a decent chain tensioner that would work both ways.

Looks good! I like your design. I would, however, encourage you to put the transmissions in the middle. It will help the chassis’ ability to turn both from an inertia standpoint and from a “reducing scrub” standpoint.

How are the sections fastened together?
O’all weight?

Just a thought: some nuts like these fastened on the inside of your drive modules might be a great way to tie components/chassis elements together.

http://www.aircraftspruce.com/menus/ha/nut_anchor.html

I realize Aircraft Spruce isn’t the cheapest place to buy things, but it’s the first source that came to mind.

A properly designed and CNC machined drive train shouldn’t need chain adjustment once the chain stretches. If careful attention is paid to ensure the sprockets are well aligned with an easy to use chain tensioner, then there should never be any broken/popped chains as long as you aren’t exceeding the maximum force of the weakest link in the roller chain. A master link is only 60% of the strength of a regular link, but you can eliminate the need for master link if you use a tool like the DarkSoul chain breaker.

Also, you really should put the transmission on the center wheel, and drive the front and rear wheels via roller chains. It all comes down to reliability. In the odd chance a chain does fail, losing the chain between the rear wheel and center wheel would also take out the front wheel from the picture as well. By moving the transmission to direct-driving the center wheel, losing a single chain means only losing a single wheel. And because the center wheel can never lose power if a chain breaks, you’ll still be able to drive whether you’re tipped to the front or back.

PEM nuts are simpler and can be pressed in at the sheet metal shop.

Certainly a valid option, but if you get one over-zealous person (think finals match 5-minute repairs) who spins or strips a pressed-in nut you could find yourself totally hosed. If the nut is riveted in then the rivets can be drilled out and a new nut riveted in very quickly. I work with an ex-A&P mechanic and we’ve used these nuts with great success.

Very good point about the 6wd reliability. I would keep chain tensioners as an option, check out the AndyMark floating tensioners as a simple and cheap option.

Care to explain the DarkSoul chain breaker? And how it eliminates the need of the master link? I looked around and couldn’t find anything but the words “out of stock” and “this item no longer available”.

I know about those chain tensioners very well. In fact, I’ve used them in ways R.C. never intended them to be used.(I’m assuming) :slight_smile: It’s always a good idea to keep spare parts just in case. Tensioners would be one more part to add.

#8-32 and #10-32 PEM nuts both use a .25 or smaller hole that they are pressed into. If there is ever an issue where they get stripped/pushed out, they can be replaced with a 1/4-20 bolt and nut. We’ve been using them for two years now on critical drive train/chassis sheet metal components, and as far as I know have yet to have one strip or fail.

Instead of using a master link, the DarkSoul chain break is used is used to drive the pins [partially] out of the roller chain, put two ends of the chain together, and then drive the pin back in. There is no master link because any link can be the ‘master link’.

It’s too bad about the out of stock issues; the one we picked up back in December has proven to be one of our most useful tools. If the DarkSoul chain breaks are no longer in production, it’s not a very difficult device to reverse engineer and machine yourself on a milling machine.

Ack! Don’t buy things from Aircraft Spruce, they have awful customer service, and habit of messing up orders. A good friend responsible for maintenance on 30 antique airplanes has had them screw up more than one large (>1k) order. On the other hand, he’s never had a problem with Wicks.

I’ve never had a problem with Aircraft Spruce, nor has my co-worker who is an ex-A&P mechanic. =shrug=

I’m not entirely certain. But I have a feeling businesses don’t care what peoples jobs are when their orders get messed up. :wink:

An A&P mechanic (Airframe and Powerplant) is an aircraft mechanic, I was merely implying that he ordered from Aircraft Spruce frequently.