pic: Tiki Techs 2-Speed VexPro Driven WCD
 

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

Learn something new every day.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

Aloha,

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..

Mahalo!

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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 DOG or BALL shifting 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!

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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).

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.

Re: pic: Tiki Techs 2-Speed VexPro Driven WCD
 

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.