pic: Practice DT



Practice Drivetrain I designed. 90% of the drive is COTS. Total dimensions are 28" long x 27" wide. Only 33% of bumper mount shown (note: Bumpers are not legal per 2013 rulings as they are below 2" from the floor. It is designed this way.) According to Solidworks it currently weighs ~50 lbs with everything shown, including the battery and electronics. Upper 1x1 tubes are solely for super structure mounting options, if applicable to design.

As always, feedback is greatly appreciated.

After a brief once-over, I notice the cylinders in the back, that hold the battery.

a) What are the made out of?
b) How do they mount?
c) They seem to mount with the edges right on top of the gusset plate that holds the upper 1x1 tubing, which, in my experience, is a problem.

Looking good!

How did you space out the pulleys in the gearbox? When I opened the CAD it looked like two 9mm VexPro HTD timing pulleys couldn’t fit without rubbing against the bearing and shifter plate. It looks great, really like the paint scheme.

The golden spacers are 3D printed. It’s a resource my team has readily available to us, so we like to use it every once in a while. They’re a bit large in this photo. In the latest iteration they’ve been slimmed down to 1/2" OD (I think they’re like 3/4" OD here). There are bolts (not put into the model until a later iteration done this morning) that go through the spacers and hold the plate steady to the frame. The new smaller iteration doesn’t interfere with the gusset plates.

Two 9mm VEXpro HTD timing belt pulleys fit perfectly into the WCP WCD single and dual speed transmissions - they were designed to fit them perfectly, and my earlier design used two next to each other no problem with 0 interference. However what I like to do is put a single 15mm pulley in place of the two 9mm pulleys. The actual 15mm pulley is toleranced a bit larger than 15mm to be able to hold two 9mm belts if needed.

To expand on this, the 15mm pulley has 17mm of space for a belt. This may not seem like enough, but RC from WCP has told me that the VexPro belts are actually 8.5mm instead of 9mm, allowing a perfect fit for two of the “9mm” belts. Useful information for anyone trying to save space and use belts in series with each other.

Additionally, I’d like to say that this model looks really nice!
And to think, just a year ago, you were here:
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They grow up so fast!

So over the span of a year, I replaced the cross braces with a bellypan and added superstructure mounting. :stuck_out_tongue: Such learn. Many improvement. So CAD.

Now that it is not midnight, and I have had a bit more time to look at it:

a) That battery holder look really snug, which is a good thing, BUT, I would give it at least a little wiggle room, then strap it down or something. Last season, our manufacturer made our battery container too small, and, as a result, we had to cut of one side, and strap the whole thing down really tightly.

b) What is the ground clearance on this? It seems to be 1/8" or less?

c) The spikes next to the CRio. Have you considered how difficult it would actually be to put the electronics on those? Unless you put the wiring on first, then put them in place.

There is 1/16" of clearance on all sides of the battery. It’s snug, but the battery can slide in easily enough and it’s strapped down with velcro. We ran this setup in the offseason and loved it.

A little more than 5/8" ground clearance.

Since our electronics are to be velcroed down, we can wire first then place. Though there is is plenty of room to wire up regardless of spike position (the angle of the picture makes it look strange).

Have you put any thought into sizing the drive belts and pulleys for this application?

It seems like you’re using 9mm HTD belts with pulleys that can’t be more than 24T. We have definitely had ratcheting and strength problems using 9mm wide belt with pulleys about that small. I would check the Gates spec sheet or run a test chassis before you bet your season on what fits most conveniently. I really think for a west coast setup you’re going to want 15mm wide belt.

Also, relying on a 17mm wide pulley to fit two belts that are “about 8.5mm wide” seems like it’s asking for trouble. Absolutely zero extra space for belts on a pulley isn’t a great idea.

I’d second this. On the prototype of last years gearbox we had two belts on the same pulley with no flange between them. Even with space between the belts, they would drift together and started to eat each other. Not enough for he belts to be anywhere near failing but there was plenty of rubber dust. I don’t think it’s a good idea to force the belts together.

Were you running exact center-to-center distance on your belts? While we don’t cram belts onto tiny pulleys we do run two belts without a flange in the middle and it’s worked fine for us. I suspect running exact centers helps prevent the belts from walking.

We ran this exact same setup in the offseason and it worked like a charm. 9mm HTD belts on 24T pulleys 9 1/2" C-C spacing with tensioners in a WCD setup.

How do you plan to mount encoders on this drive?

What are the wingnuts for?