Integrated WCD "Warp drive" chassis
 

I'm working on a off-season drive train project for our team. It takes some cues from the WCD.

It's made from 3 X 3" .120" box tube and uses the VEX ball shifter with a modified 3 stage with 34:50 gearing. The rear VersaWheel is directly driven and then chained to the middle VersaWheel with two sprockets, This wheel is then chained to the 3rd.

The top of the chain runs inside the tube on and outside on the bottom chain for easy tensioning.

Has anyone done anything similar to this? Any comments?

Re: Integrated WCD "Warp drive" chassis
 

This reminds me of the Rock Box Chassis Rail from 221 Systems. The Rock Box has a very nice solution to chain tensioning in this case that you could draw inspiration from in your own projects.

Re: Integrated WCD "Warp drive" chassis
 

chain inside box tube is a pain in the @$$ to work with. unless you have access holes that i'm not seeing, its going to be really hard to get chain on the sprockets.

i was not really impressed with the versa wheels. in my experience they wear down really fast. my team ran them for about an hour of practice driving and 10 matches before they pretty much balded. picture (i understand that other teams have not had the same issues with the versa wheels wearing down that fast)

Re: Integrated WCD "Warp drive" chassis
 

Wouldn't it be better to run the chain on the outside over the top, and on the inside on the bottom? Might make it easier to tension, rather than having to get under the robot. And also might avoid any issues with the chain damaging field elements/game pieces?

Oh, and yes, similar things have been made before, Andymark has been selling these for a couple years now.

Re: Integrated WCD "Warp drive" chassis
 

Wow that wear is staggering, how was the traction when they were balded?

The Chain runs outside the tube for half it's run so it shouldn't be two hard. I'll be adding more lightening holes soon so it should make it easier to access.

Re: Integrated WCD "Warp drive" chassis
 

The wheels are too small to do that sadly but the chain height would be the same as putting the versawheels on the vexpro chassis

Re: Integrated WCD "Warp drive" chassis
 

what is the advantage of this over cantilevering wheels?

Re: Integrated WCD "Warp drive" chassis
 

Might i suggest adapting this for eight wheels? Also, I think Plaction Wheels (or the VexPro Equivalent) with roughtop would be much better suited to this. We have roughtop tread on our wheels and the traction is tremendous.

Re: Integrated WCD "Warp drive" chassis
 

its lighter as you don't need the blocks and it leaves a little more space inside the robot. You also don't have to worry about wires getting caught in it as much.

Re: Integrated WCD "Warp drive" chassis
 

You might want to consider some way of tensioning chain

Re: Integrated WCD "Warp drive" chassis
 

I noticed that the vexpro chassis doesn't have any way of tensioning the chain and I'm hoping the relatively large sprocket surface will prevent the chain from slipping. If it becomes a big issue I will probably add a sliding delrin slider or implement something like the rockbox.

Re: Integrated WCD "Warp drive" chassis
 

While definitions of WCDs vary, virtually all include cantilevered wheel shafts and sliding bearing blocks for chain tensioning.

Re: Integrated WCD "Warp drive" chassis
 

I designed a similar system (technical term/name for this style of drive is 'nested tube', see notes about WCD above) in 2011 when I was on 816 and it worked reasonably well, although servicing it was a complete pain - or at least when servicing anything out of the norm. Here are some pictures:

Frame: http://www.chiefdelphi.com/media/photos/36107

Completed Chassis: http://www.chiefdelphi.com/media/photos/36163

Some general specs:

Drop Center 6WD
6" AM Plaction Wheels, Roughtop Tread
AM Super Shifters, Standard Gearing
Direct Drive Center Wheel, #35 Chain to outer wheels.

That drive didn't have any method of tensioning* and we never had any issues with the chain tension through two regionals and the off season. The drive only ever had one major failure that I can remember - the tread on one of the wheels came off and lodged itself in between the wheel and the tube.... Other wise, aside from needing to swap out the roll pins in the Super Shifters for 4-40 screws (or the other way around, it's been a while) the drive was solid.

* The Chains were 'dead spaced' meaning that they were spaced on exact center to center distances. #35 chain is really easy to dead space as it's a bit more forgiving to misalignment and weird tensions, #25 is a little more difficult, primarily due the tighter tolerances on tension and misalignment. (341's drive this year has a total of 6 #25 chain spans that have been dead spaced, no issues yet *knock on wood*)

Another note on dead spacing in drive applications, I only recommend doing so if one of the wheels is direct driven from a transmission. If one wheel is direct driven and all other wheels are chain driven a lost chain shouldn't render the entire drive useless for the rest of the match.

Re: Integrated WCD "Warp drive" chassis
 

WCDs also typically direct drive the center wheel off the transmission. This means that both chains must fail to lose both additional wheels. Will you able to quickly replace wheels on this chassis? (WCD cantilevering speeds up wheel replacements).

Re: Integrated WCD "Warp drive" chassis
 

Each module is only about 60$ of parts without the shifter and we can machine it in our school so if we were to implement it in a comp bot we could just build backup modules. The wheels shouldn't be that tricky to replace, once the chain is removed you just slide it out of the bottom.

Re: Integrated WCD "Warp drive" chassis
 

wow, could you explain more about how to dead space the chain?

Re: Integrated WCD "Warp drive" chassis
 

You can use a calculator like this one to figure out exactly how far apart your sprockets should be to perfectly take up the slack in the chain.

Re: Integrated WCD "Warp drive" chassis
 

With a CNC Plasma, I would consider doing drivetrains similar to 610. They have very nifty flat plate drivetrains, and is probably much easier to access and service. They cut their's on a CNC router.

http://www.chiefdelphi.com/forums/sh...&highlight=610
http://www.chiefdelphi.com/forums/sh...&highlight=610

Re: Integrated WCD "Warp drive" chassis
 

+1 on this. I really really really want to get a CNC router for 1306 so we can make stuff like this.

Re: Integrated WCD "Warp drive" chassis
 

I would but sheet metal is really expensive, I'm not sure if its just Canada but two 6061 6x37 .125 sheets would be double what the 3x3x37 .120 box tube costs. Plasma cut metal also takes a long time to finish and isn't as precise. Does anyone know how 610 hold's there sheetmetal in place on there router? I cant think of a way to do it without using wood as a relief material but it looks like there using something else in there pictures.

Re: Integrated WCD "Warp drive" chassis
 

Can you link to the photos of them cutting it?

A wood panel under the workpiece is one of the easiest ways to do it, plastic is a good substitute, but a bit more expensive. For accuracy, it's common to have the router face a small amount of material off of the top to true it to the spindle.

You can also get a vacuum table, but that is also more expensive.

Re: Integrated WCD "Warp drive" chassis
 

You can see it in one of the images of there pdf http://team610.com/wordpress/wp-cont...-Edition-4.pdf it's a small picture though. It looks like some sort of a vacuum table with plastic relief?

Re: Integrated WCD "Warp drive" chassis
 

Not a vacuum table, those strap clamps are definitely doing the holding. I think they just have a sheet of plastic (the black part) as a backing.

Re: Integrated WCD "Warp drive" chassis
 

The team I was on had a CNC router. We used a big piece of plywood and wood screws to hold the metal down.

At Metal Supermarkets a 6x37 sheet of 6061 0.125 would be $30, and a 6x37 sheet of 5052 would be $24. That is pretty cheap to me, considering you only need 4 sheets. Why 37", and what is your source?

Re: Integrated WCD "Warp drive" chassis
 

The more I think about it the more I want to build it that way.. Anyway It still doubles the metal cost. I'll see if I can get the funding, my teachers are picky. I'm building it off of 2011 size specs

Re: Integrated WCD "Warp drive" chassis
 

You can use a calculator like centurion posted, or if you're using two sprockets of equal Pitch Diameter/Tooth Count/Etc, just make sure that the center spacing between the two axles is divisible by the pitch and comes out to a whole number and you'll be good to go.

It's worth noting that the chain will wear in (stretch) after some use, so depending on how well your critical tolerances were held, this may or may not cause problems...

Re: Integrated WCD "Warp drive" chassis
 

This makes me think of these

Way more heavy duty than is needed, but lots of good engineering and explanations for it on the website. Could be helpful.

Re: Integrated WCD "Warp drive" chassis
 

Any particular reason you are extending the driven wheel hex shaft outside the frame?:) :)

Re: Integrated WCD "Warp drive" chassis
 

Well we are thinking of putting spikes on it to attack other robots:D

I'm just lazy, I'm redoing the cad so it can be built in a plate configuration and fixing up the references

Re: Integrated WCD "Warp drive" chassis
 

We use hold-down setup clamps, step blocks, studs and t-nuts. Similar to this set found on McMaster: http://www.mcmaster.com/#fixture-clamps/=mc62a5

The top of our router's table has t-slots running down the length.

In between the t-slots, the top surface has black Sintra strips glued to the surface. These came with our router, and we replace them around once a year. When we replace the strips, we face them down with the router to make sure the working surface is level.

Whenever we cut a part on the router, the cutter goes through the part, and barely scratches the surface of the Sintra strips beneath. This does leave scratch marks on the Sintra, but not enough to warrant replacing them more than once a year.

In hindsight, a vacuum hold-down table would've been a nice addition, but we've been able to do without. Cutting COMPLETELY THROUGH plate is easy. Cutting partially through thinner plate is an issue, because the middle section tends to lift off the surface of the table when clamped using the hardware above.

Re: Integrated WCD "Warp drive" chassis
 

Thanks, is there any advantage using the sintra over wood and other plastics?

Re: Integrated WCD "Warp drive" chassis
 

Yes. Because our router has a Unist mister on it, the coolant it sprays could absorb into wood. Depending on the wood you use, it could maybe even cause it to swell? I'm not 100% sure as I've never let coolant sit around on wood to see if this happens, but I would be concerned.

Over other plastics - yes - it turns out Sintra can be had for quite cheap, and we've started using it for some of our in-class projects and prototypes. Its surface properties are grippy enough to provide a nice clamping surface.

Now we don't see the Sintra as a "sacrificial material" as we barely scratch the surface of it when we cut parts. As I mentioned before, these strips last us about a year before they get scratched up badly enough to be replaced.

If you were considering using it for a true sacrificial material, where you're trashing the Sintra sheet every time you cut parts, then it's probably not going to be very cost-effective.

Re: Integrated WCD "Warp drive" chassis
 

IIRC, a good hardwood impregnated with oil actually gets harder and stronger, but I'm no carpenter.

Re: Integrated WCD "Warp drive" chassis
 

Wow, I never thought about that. Are "brute force" coolant pump would destroy the wood. I'll have to see if I can get my hands on some sintra.

Re: Integrated WCD "Warp drive" chassis
 

We've definitely had this issue. Especially with very long pieces (eg long tubing), if the piece is being clamped with MDF underneath, swelling from absorbed coolent can cause some misalignment in the part. Plywood is even worse; because it isn't informally packed like MDF, it doesn't swell evenly and is very often not flat to begin with.

I can't remember any specific issues with sacrificial backing swelling, but I'm pretty sure we've had issues with it in the past. Don't read this the wrong way, coolant (especially mist coolant) is awesome, just swelling in the MDF backing can sometimes mess up milled parts.

Also, that film of MDF dust and coolant mixed together that forms after a long day of milling is really gross...

Re: Integrated WCD "Warp drive" chassis
 

Kind of reminds me of some 233 drivetrains of the past.

http://www.chiefdelphi.com/media/photos/33366

http://www.chiefdelphi.com/media/photos/31472

(The second one doesn't have wheels, but you can see from the bearings where they'd go).

Re: Integrated WCD "Warp drive" chassis
 

I've been a little busy lately but here is the latest update:

I've modified the modules to the plate design with 4 wheels. It is properly dead spaced now (Thanks, that saved me a lot of headache). Unfortunately there is not a lot of room for spacers but hopefully the addition of a tire will add some rigidity. I could always add some plasma cut spacers if strength becomes a issue.

We also learned how to use our bridgeport CNC with CAM software. Are last team "wave" didn't like using any computerized tools. Now we just have to buy endmills that aren't 0.02" off :) (It might have been a non standard endmill but we rarely buy those)

If someone is interested I will post the CAD files here.

Re: Integrated WCD "Warp drive" chassis
 

Very nice! Looks like it will be a lot easier to work with the chains now.

I assume you're going to be adding some lightening in there?

Also, why can't you add more spacers in there? It looks like there's plenty of room

Re: Integrated WCD "Warp drive" chassis
 

This design is actually very similar to our chassis layout this year and the one we used in 2011, except that we drove the center wheel of the chassis and had chain running from that to front and back.

You can see an exploded view here:

http://www.youtube.com/watch?v=uIpXitkiu7U

Re: Integrated WCD "Warp drive" chassis
 

Yup, I'm waiting for are team to decide on a standard lightening pattern.

You're right, now that a look at it there's a bunch of space.