pic: Light Weight Swerve Module

[Bryce2471]

Originally Posted by Kevin Ainsworth

Great design!!!
The more designs someone does the more they learn and the better they get.
Your designs get more compact and innovative every time, keep them coming.

What is shifting the gears? I don't see an air cylinder or servo in there.

I prefer the Vex Versa gearboxes also, due to the fact the output shaft has a flange. The Banebots gearbox doesn't have a flange on the output shaft and that can cause problems if not used correctly. We tried using a round sleeve and a screw/washer to pull the gear up against the Banebots gearbox bearing with bad results last year. We switched to clamp collars and everything ran smooth after that. I agree they're lighter and that's a benefit.

I am a little nervous about retaining the steering balls with a single clip at the top. We went through a discussion about using a clip on our 8WD setup and found they can take about 600lbs of force for a 1/2" shaft so the clip isn't the issue. I am more concerned with the strength of the upper plate that will be seeing that load. I think there are more forces there than you are considering. In normal operations the weight of the robot will bear down on the balls and this will be a non-issue. When the robot is pushed to the side and the balls try to climb out of their grooves you will see vertical load that might cause issues. Again you might be fine.

The other consideration is contamination getting into the steering ball tracks. We had issues with aluminum chips from drilling on the robot, debris from the field and the carpet fibers getting kicked up from the tires getting in the steering grooves. This is the reason that we are switching to sealed ball bearing on our 2nd generation swerves. We disassembled our units and replaced the balls multiple times last year. I would guess Bomb Squad doesn't have this issue because they leave the steering bearing setup above the wheel and not right next to the carpet. I would be interested to hear from them if they have seen this issue also. Maybe consider a labyrinth seal (a winding path to the balls instead of a straight slot between the plates). I was considering using two opposing L-shaped walls instead of two round grooves.

This is a single speed design. sorry if the description doesn't make that clear.

As far as the retaining clip, in order to cause the balls to try to crawl out their grooves and push up on the robot, the robot would have to pull several Gs of horizontal acceleration.

Thanks for warning about grit getting in the bearing. There is only 0.04" of clearance between the turning gear and the bottom plate, but I'll start thinking about ways to seal that gap.

What bearing did you use on your most recent module?

[AdamHeard]

Originally Posted by asid61

That tensioning method could be unreliable. Testing would be paramount, and easier would be to have discrete mounting holes for each tensoning distance.
By "top plate" I mean an upper support. Right now, the only thing keeping the module in place is the weight of the robot. You need to have some kind of way to secure the module from above as well, either by means of a plate on top of the module or by using some kind of loose clamp on the bottom plate.
As for gearboxes, I see what you mean. I'm cadding one like this but shifting right now, and the banebots is considerably lighter than the versaplanetary. However, I hear that they can be unreliable.

I've seen you rule out the slot tensioning method in a few places. Have you guys had a bad experience with it?

We've done it numerous times, on 550s all the way up to CIMs, without any issue. It's plenty reliable if the fasteners are tight.

You shouldn't use a socket head by itself as it's small head diameter doesn't grab a lot of meat, so we use buttons or a washer in addition.

[asid61]

Originally Posted by AdamHeard

I've seen you rule out the slot tensioning method in a few places. Have you guys had a bad experience with it?

We've done it numerous times, on 550s all the way up to CIMs, without any issue. It's plenty reliable if the fasteners are tight.

You shouldn't use a socket head by itself as it's small head diameter doesn't grab a lot of meat, so we use buttons or a washer in addition.

The primary reason reason for out drivetrain failing this year was tension-held bearing blocks on the corners of our WCD. There were two screws going through the bearing blocks on either side of the 2x1 with nuts on the other end. No matter how much we tightened the screws, the bearing blocks would always slip and cause drivetrain failure.After adding some sandpaper-like gripping tape in between the bearing blocks and the 2x1 post-season, we no longer had problems with the drivetrain failing. This is why I always recommend against any kind of friction fits.
Now, the forces are less extreme on the first stage of a transmission, but I still wouldn't do it in the middle of the season.

[AdamHeard]

Originally Posted by asid61

The primary reason reason for out drivetrain failing this year was tension-held bearing blocks on the corners of our WCD. There were two screws going through the bearing blocks on either side of the 2x1 with nuts on the other end. No matter how much we tightened the screws, the bearing blocks would always slip and cause drivetrain failure.After adding some sandpaper-like gripping tape in between the bearing blocks and the 2x1 post-season, we no longer had problems with the drivetrain failing. This is why I always recommend against any kind of friction fits.
Now, the forces are less extreme on the first stage of a transmission, but I still wouldn't do it in the middle of the season.

Ah.

The loads here aren't even comparable.

No slot obviously is more secure, but slots can be used for motor c-c adjustment without issue in FRC.

A nice trick is to angle the slot away from the direction of force (for belts/chain) as much as you can fit. This not only increases your tensioning resolution, but decreases the friction required to hold position.

For gears you actually want to aim at the other shaft, as the forces pushing the gears apart are the lowest of the forces generated in that interaction.

[Bryce2471]

I adjusted the weights of some components, and added all of the hardware accept snap rings. The new estimated weight is 5.4lbs each. Slightly heavier that the original estimate, but still pretty light. I'll start working on a shifting version soon.

[Tyler2517]

We ran a almost identical way of tensioning our cim in our swerve last year. We had no problem with it what so ever. Was really easy to keep in perfect tension as it was about 30 second to change the tension on it .