Questions about building a West Coast Drive with VersaChassis

I will be leading our team in an offseason project to build this summer to build our first (and my first) non-KOP drivetrain. I decided to base most everything on VexPro’s VersaChassis as we have very little machining capabilities and to use the Toughbox Minis that came in last year’s (2013) KOP.

When I started to look into what parts specifically I would need to order I realized I still had quite a few questions as to what exactly would be needed. Here are all the questions I have come up with that I need to answer before I can begin:

  1. In the power trasmission, how does the pulley connect to the shaft without sliding off? Shaft collar?
  2. How does the wheel connect to the shaft? Same as the pulley?
  3. In the VersaChassis picture it looks like half of a VersaBlock goes on the wheel side of the tubing across from the gearbox. If this is so, how does that VersaBlock attach?
  4. Where would you use the “WCP side bearing block”?
  5. I am right to assume that the “WCP Gearbox Bearing Block” is used to hold the bearing on the gearbox side of the tubing for the gearbox shaft?
  6. Lastly, I am currently trying to figure out how to use the “WCP How To: Belts” I was expecting to enter a tooth count for the pulley and the center-to-center distance and get back a belt length, but I guess there is more that I am missing.

Thanks in advance, any help at all is appreciated :smiley:

There’s a lot of useful information in this thread about using the Versachassis.

As for belt calculators, I prefer to use this one.

http://www.sdp-si.com/cd/default.htm

Awesome, one the longer replies on there answered one of my questions. Damp Robot says:
“assemble your drive gearboxes, and mount them to your side frame tubing by bolting them onto a half versablock located on the outside of the tubing, with their output shaft going through a bearing in the versablock.”
Though this doesn’t match the reference picture. Considering that I am using a ToughBox Mini instead, would you forsee any issues? Can I just go with long bolts straight through the mounting holes in the VersaBlock?

  1. On the Toughbox gearboxes, the output shaft is usually tapped to 1/4"-20 at the end so that you can put a washer and button head screw on to retain the pulley and any spacers you might add. However, most “west coast drives” have the drive gearbox directly driving one of the wheels, rather than via an additional belt/pulley stage.

  2. If you are running a West Coast drive, you’ll have to design this bit. The most common options are to either copy the toughbox output shaft, by tapping the wheel shaft and retaining the wheel with a washer, or to machine a retaining ring groove on the end of the shaft.

  3. The half VersaBlock gets bolted to the gearbox face rather than to another VersaBlock half. This is so you don’t need to machine a bearing hole in your frame, you can count on the VersaBlock to hold the bearing in place for you.

  4. The WCP side bearing block is another bearing block that takes up less space around the frame rail. It can be used in the same places, however, it requires a square slot machined in the side of the tube which it slides in. This requires some more sophisticated machining than the the VersaBlock.

  5. You are correct, the WCP Gearbox Bearing Block is a half bearing block that attaches to the drive gearbox around the tubing to support the bearing on the main drive shaft. This is just like the half VersaBlock you mentioned in #3, but using the WCP block instead.

  6. Yes. In the case of a WCP block, this large hole has to be a square slot for the block to ride in, but for a VersaBlock it just needs to leave room for the shaft to not hit anything, and can be pretty much any shape.

  7. The WCP Belt calculator is designed to show you the WCP/VexPro belt/pulley options that will work for your desired center to center distance, and unfortunately does not go the other way. The SDP/SI calculator Gregor linked is similarly limited to SDP/SI’s selection of belts and pulleys (which is larger), but it does the calculation with any set of inputs, filling in the missing numbers, so many of us find this one more useful.

Didn’t the KOP toughbox not include a plate for the output this year? I thought it just included the housing, and that housing mounted to the side rails. If that’s the case, you would need to machine a plate so the bearings have a plate to sit in. You could then put the versablock mounting holes into that plate, and have everything line up.

With the new products from VexPro and WCProducts, building a quality WCD can be done really quickly with little to no machining capabilities. Just to put it in some perspective, we used only a chop saw to cut the frame members down to length, and a drill press to drill holes for the bearing blocks. And none of these requires any form of accurate machining.

We have used both types of bearing blocks. Both the new sliding bearing blocks, and the older ones. I would highly suggest you go with the new ones because you just need to drill one oversized hole and clamp the bearing blocks on each side and you are done.

I think you are also a little confused about mounting a gearbox. You said that you would use the Toughbox Minis, but if you are to use those gearboxes you will be unable to build a true WCD. A true WCD has the center axle directly connecting the wheel to the gearbox without any intermediate chain/belts/gears, and I think the only way to build with the Toughbox Minis would be to chain the gearbox output to the middle wheel shaft. The part you linked is actually a part of the WCD versions of the gearboxes. Pic Here and link to gearbox.

If I were you, I would just go with using one of the WCProducts gearboxes as long as you can afford them. They are $90 each for a 3Cim single speed, but they are so much simpler to mount into a WCD and reliable. We used them and had nothing but good things to say about them.

In short, sorry if a come off as to pro WCProducts/VexPro, but their new WCD stuff is just so incredibly good that as long as you have the cash to spend, (we spent about $7000 for a 3 cim single speed including tubing/hex shaft/bearings) I would just go with what works really well.

We built a drive like this for our 2014 bot. The biggest difference from what you’re planning is that we used #25 chain instead of belts. I’ll upload our CAD (w/ a full set of drawings) when I get home tonight so you can see how we mounted the TB minis. We ran 4" x 1.5" Colsons on live axles with the TB minis geared 8.45:1. You will need the long hex output shaft (am-0801) for this design.

Here’s a pic to give you the general idea.

The ToughBox Minis used this year direct drove the center wheel. Are you saying that I won’t be able to mount it so that I can direct drive the center wheel?
The thing I need to check with that is if the output shaft is going to be long enough, or if that will have to be replaced as well. Unfortunately we can’t afford two new gearboxes right now, so I am going to try and find a way to make that work.

Thad House was right about the inner plate not being included in the KOP this year, though. In that case I may be able to use the 2013 version then, which did include the plates.

Awesome, thanks for pointing out the part I need. I’m eager to see how you used this year’s minis because I haven’t quite figured out how I would mount them.

Although the Toughbox Minis were direct drive, they were built to interface seamlessly with the new sheet metal frame on the KOP drive base. It looks like it would be a lot different to use them in a WCD application.

It looks like it will be a whole lot more difficult to both design and machine, and with you stating how you are trying to limit the amount of machining you have to do, Joel Glidden’s method looks like it requires a lot of precision machining to get working.

My team has a hard time accurately machining things, so we always look to use and buy as many cots parts as possible. I feel that if you even question your ability to connect the gearbox reliably, you should go and find the excess money to buy a gearbox which better interfaces with a WCD tubing.

Typical West Coast Drive gearboxes allow the chains and sprockets to go inside the gearbox. I suggest downloading a CAD model of the West Coast Product single speed West Coast Drive gearbox to study how it’s put together. That setup lets you avoid putting the chains between the wheels and the outside edge of the frame rails, which is best avoided since it makes your cantilevered axles longer/bendier and shrinks the space available in your frame.

I’m certain that a custom solution can be created to connect a Toughbox Mini to a VersaBlock WCD setup; one way would be to make two separate plates and house the sprockets between them. Another way would be to put two halves of a VersaBlock on the frame rail and offset the gearbox from the rail with standoffs to create space for the sprockets. Either way, one would at least need to machine some plates with mounting holes located reasonably accurately.

Why does your team want to build a non-KoP drive train? If funds are pretty limited, going with the kit drive is a great way to keep costs in check. And this year’s kit drive featured direct driven center wheels and belt drive - what’s not to like about it? I like VersaChassis a lot, but it’s not something I would recommend for a team if they lack the resources to buy or fabricate gearboxes to match it.

Here’s an excellent post of the parts one required to build a versachassis by Andrew Lawrence:

Our team will also be building a WCD as an off season activity:

For a close look at the versachassis in action, look no further than team Copioli’s reveal video:

We are using the same calculator that Brian posted to figure out what pulley and belt to get from WCP:
http://www.wcproducts.net/how-to-belts/
You decide the pulley size and the centre to centre distance to derermine the belt size.
From what I can see in videos and pictures, seems like team Copioli uses a 30 teeth pulley. Somebody correct me if I’m wrong.

I don’t have the CAD model of the plate that goes with the Mini’s, but is there a reason that that plate wouldn’t work?

Why does your team want to build a non-KoP drive train? If funds are pretty limited, going with the kit drive is a great way to keep costs in check. And this year’s kit drive featured direct driven center wheels and belt drive - what’s not to like about it? I like VersaChassis a lot, but it’s not something I would recommend for a team if they lack the resources to buy or fabricate gearboxes to match it.

The “why” has a couple reasons. First because it generally seems to be the superior tank-style drive. Also ease of maintenance hurt us badly this year and having something a bit simpler to access would help.
More than this, though, we want to focus on trying a variety of things in the offseason to better prepare for next season. A different shaped base (28" x 28"), a variety of wheels, and maybe different joysticks or controllers will help with that.
Third, we want to transition of programmer from Python to Java as well as get more than one student to work on programming. Programming a brand new drive base is something that could actually motivate a couple students to jump on programming.

Here’s the CAD.

Thanks, that’s awesome. One question though, what material / fasteners did you use the mount the gearbox to the frame? It looks kind of large piece of a large aluminum round stock with the ends tapped. Or it could even be a round shaft from Vex/AndyMark with the ends tapped as well.

The blue part is just a bent aluminum sheet metal bracket (1/8 in thick). It bolts to the TB mini through the top two holes that secure the mounting plate to the plastic housing. Then it is secured to the top of the robot frame via four 10-32 screws and rivet nuts (McMaster 93483A661). The green cylindrical parts are just some stand-offs we made from half inch round stock that we drilled through with a .196" clearance hole. We secure the gearbox to the side of the frame by just running a long 10-32 screw through the TB, the standoffs, and the frame.

Refer to drawings 4293_2014-005 and 4293-2014-018 for the standoff and the bracket.

Edit:
Also, we cut the bottom off of the TB mounting plate for ground clearance. You can just trace the profile of the housing on the plate and then use a band saw to cut it down. Drawing 4293_2014-019 shows all the mods we made to the mounting plate.

Thanks for all the replies everyone, the project is really coming along. A couple new questions that I came up with:

  1. I have never tapped anything harder than aluminum before, but we have a fairly decent set of taps that isn’t showing too much wear. How possible is it to tap the ends of this shaft in order to secure pulleys/wheels?
  2. I can save some money by going with round shafts in stead of hex. Will this long shaft (meant for the ToughBox Nano) work in the ToughBox Mini?
  3. Here is my total list of items to purchase, is this a reasonable price to pay? I was expecting a little lower as it would end up being a good deal greater than the voucher amount you get if you go without the KOP drivetrain.

The taps you’ve been using for aluminum should work fine for that shaft.

  1. See below for a screenshot of the TBNano round shaft installed in a TBMini. It fits, but you will need a hex bearing. Also, there are two things to note. First, the hexagonal portion of the shaft protrudes about .150" beyond the bearing. Make sure it’s not going to interfere with anything in your design. Second, the TBNano shaft is .335" shorter than the TBMini long hex shaft that is used in the 4293 design.
  2. Will take a look at your shopping list as soon as you share the gDoc with me =)

[/li]Ha, duh. Fixed, should be open to everyone now.

Seems like chain and sprocket would be cheaper than belts and pulleys. Also, I’m not sure why you need the WCP side bearing blocks. Do you have CAD you can share?