Hello everyone! I’ve recently finished CADing a drivetrain, and I would love some feedback. I made this in preparation for the CADathon this week, and anybody is free to use it if they’d like. Thank you!
Drivetrain.step (20.8 MB)
Full assembly:
I would look at adding some standoffs in between the tube and outer plate just because you need to make sure that you are not dealing with any flex in the plate if you are hit. That could easily bind your wheels or thrown off your center to center if you bend that outer plate
If you are looking into adding standoffs to your drivebase and making that outer plate more rigid, I recommend looking into 254’s design as shown here. The 2x1s give the drive base more rigid structural support while also being relatively lightweight at the same time. You would have to move the chain inside near the electronics however, and would probably need to attach your gearbox to the 2x1 similar to how 1678 does it in their CAD here.
The most blaringly obvious problem is the massive over constraint on this shaft.
First off, I that rail pocketing looks super nice. As far as changes go, You have a little extra material around the edge of the gearbox (the outer square isn’t giving you a ton of extra rigidity) and I might add either standoffs between the rail and outer plate as @NustinJewton said, or adding a flange to that outer plate would help prevent it from flexing in on impact.
Great start! Always good to see people jumping into CAD before build. My three main critiques:
The lightening of the tubing is not helpful. If it is 1/8" wall tubing, it will be weaker and heavier lightened than 1/16" unlightened tubing will be. If it is 1/16" wall tubing, you probably can’t get away with that much lightening in the crossmembers, particularly without a structural belly pan - the tubing could buckle in extreme collision.
The outer flat plate isn’t really accomplishing much. The bearing support it provides isn’t really doing a lot for you (and in some cases causes an overconstraint). If you must keep the outer plate (which is a lot of weight for little function), just cantilever the wheels behind it rather than running the shafts through.
Others have touched on the overconstraint issue in the gearbox. Now it is not necessarily as dire as everyone says - you can get away with three per shaft if you design it right, but this use of five bearings absolutely is. For a design without bearing blocks like this one, I would suggest counterboring the outer bearing of the gearbox so it can “clock” into the bearing hole of the drive tube - this eliminates a bearing and helps alignment, allowing you to get away with three bearings assuming your gearbox assembly is bang on. Counterboring the gearbox standoffs should also help with the alignment, though both of these operations may not be desirable if you were just planning on jetting the plates.
Thanks for all your suggestions! I’ve made some updates based on what you all said. Mainly, removing the side plates to reduce weight and prevent overconstraint of shafts. I do plan on adding standoffs between the wheels, likely using tubing as Katthecat suggested, but the exact layout will depend on bumper rules so I’m holding off on those for now
Updated Drivetrain.step (20.6 MB)
I would actually leave the drive tubes un-pocketed. I’ve found that the little bit of rigidity gain goes a long way in the end. Everything else looks really good though, excellent work!
Have you ever really had a problem with it. We have pocketed it for forever and never had a problem.
We got hit pretty hard in an offseason event and dented one of our drive rails. If it had been pocketed like our elevator I’m not at all confident it would have survived. I personally advise against it, but your mileage may vary and it’s really up to whether you need the weight somewhere else or not. We try to go to competitions where the local acceleration due to gravity is the lowest so we don’t really care 
How much are you saving. For our pocketing it saved us 2lb over the entire chassis (we did not do it). If you get hit hard it will bend. Also pocketing takes a lot of machining time.
Well we were running on about 122 lbs at competitions and we had a very extensive amount of metal as we had 2 lifts so I don’t know exactly how much we saved but without it we would have been over. We also have the machining ability for it to not cause a problem for us.
This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.
