pic: Tiki Techs 2-Speed VexPro Driven WCD

The Tiki Techs VexPro Driven Two Speed West Coast Drive.

This frame is within last years perimeter rules.
Designed with the offset at the bushing blocks to center the transmission output on the frame rails.

Looking forward to the new competition this year!

If West Coast Drive originated in California, this must be WAY West Coast Drive! Looks awesome! Any particular reason you’re using the large wheels and large sprockets? Moving down to a 4" wheel size wouldn’t hurt and would save some weight.

The origins of WCD lead back to Arizona initially. Team 60 was the first (that I’m aware of) to do a cantilevered live axle drive.

Learn something new every day.

Neat Render,

If your wanting to do the sprockets on wheel, why not use the smallest VEXpro sprocket that fits?

Also did you guys do the math on the gearing? A 2 CIM Ball Lock @ 6" wheel without a 3rd stage shouldn’t work/too fast for FRC.


Thanks for all the comments. I am still a CAD rookie…

We have many sprocket sizes ordered. My understanding is that the larger the sprocket is, the less working load for a given amount of transmitted power, allowing the use of a smaller pitch chain. We are planning to use #25 chain this year since it is readily available locally at the bike shops. I voted for the three speed transmission personally, but was overruled.
There is still time for a change though…I hope…

This is our first attempt at a non KOP drive train.
Any input on gear ratios, wheels, etc., is highly appreciated…


Where is your Center of Gravity (CG) located? It appears that the CG is relatively centered. You may want to bias the CG to one end of the robot.

Yes, running a larger sprocket reduces the load on the chain; however teams are running down to 16 tooth sprockets for 25 series chain (on 4" wheels I believe). Even running 6" wheels, the sprockets don’t need to be nearly the size you have currently selected.

If weight becomes a concern, you can switch out those heavy metal pneumatic cylinders for some lighter plastic ones.

Keep up the good work.

Mr. H,

Awesome! Everyone has to start somewhere. That is true, the larger the sprocket the less working load on the chain. For reference, many teams that do WCD use a 16T-18T sprocket in the 3" to 6" wheel size. Looking at the sprockets available. It would be cheaper and light to use the 32T..

Three speed might be a bit much for your first time around, but either DOGor BALLshifting works well. There is a table on the DOG shifter page that shows output speeds based on wheel size.

With a larger wheel your going to need MORE reduction. You want to be somwewhere 4-9 FPS in low gear and 12-18 in high gear.

Hope some of this helps!

As everyone else has said this is a great first start into the world of custom drivetrains. Just two bits of advice. As everyone else said you could go down to a much smaller sprocket size for your outside chain runs. The other is that you need a little more reduction. Judging based on the picture your current speed would be 40 and 17 feet/second. In real life the robot would barely move. However vex does sell a third stage reduction kit for the 2 cim ball shifter. This moves it down to a more reasonable 13 and 6 feet/second at your current setup. IMHO a fairly good speed range for FRC. Just my thoughts, Hope it helps. And for future reference and doing these calcs yourself I would recommend downloading this. http://www.chiefdelphi.com/media/papers/2755
It’s the starting point for a lot of FRC drive trains and mechanisms.

Be sure your bike shops actually have #25 chain, most bike shops only carry bicycle chain which is a different pitch. #25 is used on some electric bikes and scooters though so they may have it. If they don’t, there is always amazon http://www.amazon.com/gp/aw/d/B004HKITHA

Moving on from the sprockets*, I like the belly layout. It’s obvious you’ve put a lot of thought into it, which is always good! A few little things:

  • It’s hard to tell from the iso how much room you have in between the Talons and the DS, but think about wire runs. I’d advocate for routing each controller’s power wires paired along the belly pan, but space might get tight. Running to the compressor switch will also be a bit of a haul. (Not suggesting any design change there; just think about your desired route. You might consider moving the spike.)

  • Can anyone report good competition success with mounting the D-Link so close to/inset within metal? We try to keep it as far away as possible with clear line-of-sight. If something like this works, it’s a really nice design constraint to avoid! Seems like a secure location otherwise.

  • In addition to chain clearance (OD sprocket+chain vs. OD wheel), keep an eye on your wheel-bumper clearance. You don’t need too much, and of course increasing it shrinks the usable drive base, but I’ve seen people design way too small a gap. I can’t tell what yours is from the iso, but remember that bumpers can flex a bit, and they make really bad brake pads for running wheels.:ahh:

  • Vertical batteries are definitely convenient, and from here the box looks pretty stable, but don’t underestimate the moment arm of a vertical battery. At the least, I’d keep in mind having continued access to tighten those flaps’ bolts. Around the ~40 match mark of being routinely T-boned, the box may start getting a little upset.

  • An even more minor nit pick: I can’t tell the distance between the air tanks and the frame rail, but you might want to use elbow connectors on the outside plugs so you don’t have to worry about where the tubing loop is while it’s so close to the DT chain.

BUMPERS must be supported by the structure/frame of the ROBOT (see Figure 4-6). To be considered supported:
A. a minimum of 1 in. at each end of the BUMPER must be backed by the FRAME PERIMETER,
B. the gap between the backing material and the frame must not be greater than ¼ in., and
C. no section of BUMPER greater than 8 in. may be unsupported.

It looks like you may run into trouble here. If you have one bumper on each side, then there is no frame material to support the bumpers along the wheels at their ends for at least 1 inch (part A).

If you have bumpers that are contiguous around the corners of the robot, then with 6 inches of wheel and what looks to be at least 2 inches between the corner of the frame perimeter and the next backing along the front/back rails, then you’re at the very least cutting it very close on the 8 in. unsupported (part C).

Your placement of the chain sprockets on the outside of the frame should allow you to simplify your axle set up in ways that most WCDs can’t do. By bolting the sprocket directly to the wheel there is no longer any need for the axle to be live. This means that you can have the bearings only in the wheels and eliminate the bearings in the frame. It also means that you can replace the hex shaft with a round shaft possibly simplifying machining and allowing you to use cheaper bearings. You should still have the blocks to move the axles, allowing the chain to be tensioned.

These simplifications would only apply to the outside wheels, the center wheels should still be driven by the hex shaft from the gearbox.

Charts like these are about the only thing I look at when deciding what ratios we use. Someone else did the math…we trust the info shown.

Second this.
We’ve used bicycle chain every year since 2007. Our old mentor used to custom make our sprockets even after he left and joined another team. We now have our main machinist do them with our students.

Looks great! Nice work.

How are you holding the frame rails together?

Hello everyone and thanks for the continued responses!

I will try to answer some of the questions mention.

This drive base is an off season design project more for my continued learning experience in CAD.

I am aware of many of the issues presented in the design and do really appreciate the comments.

Not knowing the game, much of the design is mute until then. What if we need to pick up off the ground? Much will need to be moved…

That being said I will address some of the previous comments.

The pneumatic cylinders will be the lighter plastic ones, the aluminum ones were the ones I had in my CAD library at the time. Though I do remember hearing of some of the plastic ones rupturing… Yikes!
I haven’t had the time to make the tubing, though I doubt the tanks will be there when we get to actually building.

I really wanted to go with the WCP transmissions but since they were not shipping until the middle of January that is far too late for us. We have enough delays and extra costs getting anything to Hawaii. :frowning:

Wheel size has yet to be determined. One of the coaches felt that 6” was the way to go.
Putting the cart in from of the horse if you ask me.

I do know that we did order the 2 speed ball shift transmission with the 3 stage option, as well as many of the various gears and sprockets. We should be able to use the math/charts and select the best gear and wheels for the robot accordingly. Thanks for letting me know a general target speed to shoot for, that helps.

There are a lot of motorcycles, mopeds and bicycles on the island, a great way to get around here in the sunny Kona days. Which means lots of the #25 chain available.

The Talons are laid out such that the input wires are all facing back towards the PD board and routed by the sidecar. This faces the output terminals towards the motors with no obstructions.

The router will not be in the pan. It was there just so the design could drive, if built, which it hasn’t been.
Our stock metal order is still on the boat. :ahh:
We normally mount the router as high and unobstructed as possible. The last few years it has been up on the tool support structure.

We have not developed the bumper system yet. Research is being done by the students on a better way of mounting. The last few we have used C channel and bolts. Not the fastest to swap but very rugged. We want to address that this year and hope the new frame design will help. I saw a lot of great bumper mount ideas at Worlds this year that I would like to try.
Some additional room will be added between the bumper and wheels just in case, per the suggestion.

The frame uses end caps with chain tensioners. These caps are able to bolt to each other at right angles for the outer frame. Once the cap is installed on the drive rails the side caps are bolted to them and the cross rails are slid on and then bolted to them. We will more than likely weld the center cross beams.

I would like to move the battery, perhaps have it lay down. The students built a real neat battery box that has been cut out with Hawaiian designs (turtles and sea grasses) and looks really great. I was trying to reuse it. :slight_smile: Perhaps when I get back to the school I will post a photo of it. They are very proud of it and rightly should be, it’s awesome!

I really do appreciate all the comments, please keep them coming…
Good luck this year to everyone… It is going to be an exciting new season!