Latest iteration of our drivetrain design. We’ve flipped-flopped between tube, plate, and sheet for the past 3 iterations. We plan to get a new router over the summer so we can finally start integrating tube into our design process.
We like single speeds a lot but I did work on a flat two-speed as well.
Specs:
The entire drivebase is only 3 pieces which can be cut in just a few hours on a decent router. The sheet metal reduces part count and allows the wheels to be pushed farther forwards and backwards for slightly more stability.
I love the route you guys went with your frame this year despite the issues you encountered. I would consider a way to maintain your belts/chain in an emergency and install a tension system when the belts inevitably stretch. Seeing as how you have some lightening holes in there already, you have the room and ability to add them pretty easily.
Still amazed you made that chassis with a hand brake!
I like the design overall. Simple yet rugged. Fully capping the ends of the drive base in sheet metal is great.
I would worry, a lot, about bending those bumper brackets in. I think they need some intermediate support. I would also worry about the front flange of sheet metal being bent into what I assume is the front wheel.
Would you consider a different lightening pattern to avoid removing large portions of your lateral strength members? I would consider lightening features on the top/bottom of the tube to keep material where it will resist lateral impacts the most.
Wat… Isn’t the whole point of using belts that they don’t stretch?
They had a belt failure this season but I am not sure why. When you use the belts on a drive train usually you get some wear if the centers are not perfect so you will get some additional wear and tear on the belts from either being overstretched or too loose. When they are running on a drive train or any high speed application they can heat up then they start doing some interesting things. For most FRC drive trains you are not heating up that much but you will eventually push into another robot and have one slack side of a belt and one tight side from the extra force involved.
The tensioner/idler would help alleviate that in a pushing match and keep the belt from going slack on one side and skipping teeth. For a lot of games you may not even need it but it would be really nice for installation and emergency repair to be able to slack the belt and remove it quickly since it is buried in a tube.
Maybe a tension mechanism would be nice for assembly and/or service. That depends on implementation. However, it would not be required to address belt stretching because belts do not stretch when used properly. See: all the teams who have used the KoP drivetrain since at least 2013 with drive belts and no tension mechanisms. Heck, we disassembled our 2013 kit-drive robot this year and the drive belts were still tight.
Nice design! Have you ever made a similar design, but with only using one belt? Obviously some idler pulleys would need to be added to the left and right of the center pulley. What would be the drawbacks?
