sprockets added, 18t on the Versa-Planetary and 22t on the wheel shaft, this gives the ~18:1 ratio I wanted.
2.brackets made and added to attach side plates to belly pan.
material set the 6061, total weight right now is ~23lbs, this does not include chain and shaft collars.
the dimensions are currently 27"x36" but it can be any size really.
Sick Paint job like all the cool kids.
there is space to add another motor and gearbox on each side if 6 won’t cut it.
Right now, there is going to be 3 25 chains from each vp to the axle shafts between the two plates on each side, and then 2 25 chains on the axles outside the plates behind the wheels to chain everything together.
Decided to mount the side plates to the belly pan with some 2x2 angle because my team has a lot of this stuff laying around in our shop.
Should be pretty sturdy as everything is 1/8th plate. Ignore the triangle pockets for now as I just put them there to look cool and the real one will probably have some different pattern/our team logo or something.
didn’t add the wheels to the assembly because I couldn’t get them to constrain correctly
The whole issue is supporting both ends of the versaplanterary shafts and the two plates accomplish that pretty easy.
We made our drivetrain this year and last year out if 2x1 and it worked ok. It just takes a long time to mill everything.
Plus we have a plasma machine that can cut these plates in a few minutes.
The standard is usually just long 2x1s in the front and back. With a drivetrain like this, a good way to connect those to plates is to run a threaded rod all the way through the chassis with 4 10-32 screw heads inside the tube to align and square it. Other teams like to use down or spring pins as well.
Also, take a look at 3360’s 2016 robot they ran 775pro in their drive in versa with unsupported shaft all season and I think had less issue than 1296. might be better to have people from those teams chime in though before I speak for them.
I want to keep the front and back of the frame open as much as possible,
so I think I’m gonna go with 2x1 crossbeam next to the center-ish 775 and angle bracket it to the inside plate. I’ll add another photo when I get done later tonight.
Bumpers are going to be the hardest part to figure out.
If you want to do cutouts, place a crossbeam at the back of the cutout that spans the width of the chassis. You want closed shapes to make up your chassis to maximize strength.
I am a VersaPlanetary fanboy but using them for an FRC drivetrain? I’m thinking that is not going to end well for you.
There is a lot to like in your choice of 775Pros, I’m on record predicting that all the cool kids will be using them rather than CIMs on their drivetrains next year.
I hope you prototype this in the fall and test it in real match conditions because I don’t have a good feeling about this…
Thanks,
We are going to start working on putting this together in a few weeks and we will see what happens.
Using vp’s in a drivetrain has been done before in 2016 so if they managed to survive strong hold I have good vibes about them.
This year we used versaplanetary gearboxes for our drive train without a problem in 60+ matches. The main issue we encountered with them was with mounting them, as the few screws that secured them in place could get shook off. That being said, we used CIMs, so 775 gearboxes would have to handle a larger reduction and faster speeds.
Seconding Joe’s concerns, and raising: I can see 775pros used more and more in coming years, but my back-of-the-envelope calculations seem to indicate that 6 775’s is rarely better than 4 CIMs once you take motor controllers and gearing into account (a replay of Lunacy being the exception). 8 775’s seem to be a standout solution for a number of reasonable strategies, but not if you add the weight of a separate. gearbox. for each. motor. Rather than going to 8 gearboxes, I expect that soon we’ll be seeing some robots with two custom gearboxes each driven by four or more 775pros located on BOTH sides to put all of their torque onto a single output shaft. The bull gear of that gearbox will likely be 1/2" hex broached, if not larger!
Plus, do you really want all the weight and problems of six 2-stage VPs and ten chains/belts to drive what would qualify as a WC drive if some of the wheels were direct driven, and fill up half a dozen chunks of real estate in your bellypan?
Yes, it is starting to look like using a tube on each side will be faster in the long run. You can mill both bearing holes for one shaft with one setup and they will always line up. You would not need to make and install all those spacers. You would want to roughly mill out some access holes in the top and/or bottom for installing the chains between the VP’s and your axles an your axle bearings.
I don’t think the plasma cutter will be any good for cutting any of the holes so you will still have to take the pieces to the mill.
Are you putting in the access holes for the T-handle Allen wrenches to reach the screws that attach the VP’s?
Chop some sections of 2 x 1 tubing and attach them to the outside as outriggers for your bumpers. Easy.
Unless you end up really narrow, the space in the middle looks really well suited for installing your PDP, motor controllers and roboRio. Flip it all upside down, add a protective cover and you have a nice, wide surface for mounting your scoring mechanisms.
