pic: REV 2 of GBX-116, Drill press swerve drive

[asid61]

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[Arpan]

I again can't express my happiness with this. Finally, swerve for the masses!

[mrnoble]

Is there some kind of Chief Delphi award? There should be, and this should win it for 2014. Thank you so much.

[Arpan]

Originally Posted by mrnoble

Is there some kind of Chief Delphi award? There should be, and this should win it for 2014. Thank you so much.

Seconded! Still not sure that you could get good enough tolerances to mesh miter gears with a drill press, though...
Maybe you could 3d print a guide that clamps over the part?

[Oblarg]

Originally Posted by Arpan

Seconded! Still not sure that you could get good enough tolerances to mesh miter gears with a drill press, though...

We did it for our roller intake last year, though it was sloppy and inefficient and I wouldn't recommend it for a drive.

[Joe G.]

I would agree that you are unlikely to achieve adequate tolerances for your bevel gears with a drill press. I would say that a non-coaxial swerve is a much better choice for a team aiming to minimize machining resources.

[Tyler2517]

You might have some problems on the yoke(the part holding the wheel) taking large amounts of side loads might cause damage. (ie. you getting rammed) -1640 has a little triangle piece that goes in their side plates that help.

The better the mitter gears's bores are machined the better your efficiency will be this will become noticeable on the field if it is out of a decent tolerance. If you machine gears the placement funky you will see problems. If the shafts for the mitter/gears in the yoke are not straight from the machining processes you will have some problems as well mainly a clean mesh on the mitter gears.

I do not see how you are handling thrust loads from the mitter gears. I also don't see how you handle the thrust loads from the yoke to the main tube.

We ran a single main tube like yours last year it was a 2X3 1/4" thick peace machined down to 1/8" on 3 side the bottom still being 1/4" We did do a lot of weight reduction on the box but we still saw deformation in the box at the end of the season. We think this was due to minor drops when placing it on the field on the cart and such. Remember that sometimes the largest loads you will see will not be in the field but in the pits or shop when something goes wrong and it falls 4 inches on the the shop floor off of its blocks.

Using thinner material will be a death wish to the module remember you are supporting the whole weight of the robot on those 4 tubes plus any shock loads.

I like the idea that its a drill press swerve but making it work on a drill press is not the easyist thing to do. My teams rookies could not make that fresh into the shop you may at the very least be having to use your most experienced team members to do this.

The tolerances needed for a good mitter gear mesh are much higher then most of your frc tolerances. Yes the bearing will help some of it but not all a very well located bore and very straight bore is needed i would recommend when machining the mitter gear bore in the yoke to lock the movement of the x/y and use parallels. Do a large number of tool changes to bore the first side and then the second if you can so that the shaft is straight.

Also the weight seams a bit light ours was 7lbs-5 ounces with heavy weight loss and no gears and only a small thing of #25 chain.

[asid61]

Thank you for all the advice!

On bevel gear meshing, I'm using the 12 pitch 15 tooth miter gears from Vex, so I thought that they might be okay with 0.01" tolerances. Your experiences tell otherwise, so I'll design a non-coaxial version as well.

Thank you Tyler for the advice. That's exactly what Iw as looking for here.
Thrust loads from the miter gears are acting on the bearings, but the bearings face outwards such that the flange side of the miter gear is taking the loads.

Box deformation was something I though would be minimized by the use of 1/8" tubing over 1/16", but I want to test the deformation first before upgrading to 3/16" wall or 1/4" wall tubing. Perhaps the lightening on yours affected it in unforseen ways.

The bottom module can be made into 1/4" wall tubing with hardly any effects, so I'll do that.

The weight is low because I'm used to optimizing weight in my designs; as a result I have thinner wall tubing here. If this was more than 9lbs, I would have scrapped it. That's just too much, even for something made on a drill press.

[magnets]

I have some serious concerns about the strength of this swerve. To begin with, the 3/16th wall rotating module looks really weak, especially at the top corners. I'd be very concerned with this part "parallelogramming".

Secondly, your spring wave washer isn't going to be able to hold the bevel gear in the correct place axially, and you don't have a way to deal with bevel gear thrust loads.

Finally, you have a very weak bearing setup for axial loads on the rotating module. The lower of the three hex bearings will take all of the load, and will most certainly be destroyed.

Also, have you ever tried running a chain on a 16 tooth sprocket that spins at 5300 rpm? It's terrifying. There's a reason teams use gear reductions!

[asid61]

Originally Posted by magnets

I have some serious concerns about the strength of this swerve. To begin with, the 3/16th wall rotating module looks really weak, especially at the top corners. I'd be very concerned with this part "parallelogramming".

Secondly, your spring wave washer isn't going to be able to hold the bevel gear in the correct place axially, and you don't have a way to deal with bevel gear thrust loads.

Finally, you have a very weak bearing setup for axial loads on the rotating module. The lower of the three hex bearings will take all of the load, and will most certainly be destroyed.

Also, have you ever tried running a chain on a 16 tooth sprocket that spins at 5300 rpm? It's terrifying. There's a reason teams use gear reductions!

I know about the 3/16" thickness. I'm changing it to 1/4", and I'm adding a couple spacers from McMaster for strength.

The wave washer diesn't actually take much load at all. Bevel gears are inclined to turn away from the axis of the mating bevel gear, so the wave washer just spaces it away when not driving. When driving, the bevel gear is forced against the inner race of the hex bearing.
Vex bevel gears have a small diameter boss on the back end which sit inside the diameter of the inner bearing race on the 3/8" hex bearings. If that actually becomes a conern, then it's easy to just add a thrust washer there. Can somebody explain why having the bevel gear boss on the bearing inner race won't work?

What do you suggest for the lower bearing? Keeping in mind that these are 3/8" hex bearings with a relatively large inner race, I'm not sure it will be a problem.

I did not consider chain speed. Thank you for pointing that out. Belts could actually be used in this application, so I'll switch to those. Alternatively, a cimple box or a vex 1-stage gearbox could do it too.

Most of these issues can be solved just by switching to non-coaxial.

[Jared]

This is a really cool idea and a neat design. I have a few comments/suggestions to make it stronger.

Originally Posted by asid61

I know about the 3/16" thickness. I'm changing it to 1/4", and I'm adding a couple spacers from McMaster for strength.

If you put some type of brace like 1640 does so that the module has 4 sides, it would likely get a lot stronger. I can't see if you've done this already, but if you have a lower dead axle that is a 3/8" bolt and you put spacers on it, you'll add a ton of stiffness to the rotating piece.

The wave washer diesn't actually take much load at all. Bevel gears are inclined to turn away from the axis of the mating bevel gear, so the wave washer just spaces it away when not driving.

I think you'll probably be okay here, especially if the distance the gear can move too close is small.

When driving, the bevel gear is forced against the inner race of the hex bearing.
Vex bevel gears have a small diameter boss on the back end which sit inside the diameter of the inner bearing race on the 3/8" hex bearings. If that actually becomes a conern, then it's easy to just add a thrust washer there. Can somebody explain why having the bevel gear boss on the bearing inner race won't work?

We've run a setup with a worm gear driven by three CIMs which had no thrust washer and saw no wear on the bearing or the worm. However, some teams here who have run a swerve (IIRC it was 2517?) have commented that they saw issue due to thrust loading a bearing. I would ask other teams and see if they got away with this.

What do you suggest for the lower bearing? Keeping in mind that these are 3/8" hex bearings with a relatively large inner race, I'm not sure it will be a problem.

The two bearings in the what looks like a 1 x 2 aluminum box will hold the 3/8" drive shaft pretty rigidly. The first concern is that there are only three total bearings. Whenever you push on the side of the rotating piece, you're loading the lowest hex bearing in the module. Bearings are really bad at these torques. It's like doing a West Coast drive style bearing block, but with only one bearing. Adding that second bearing changes it from trying to bend the shaft to the side, to an axial load, that the bearing can handle much better.

All that said, I would look into using a different type of bearing/bushing. All swerves that I've ever seen that are set up like this have two bearings/bushings that go on some round stock that sits on top of the rotating piece. Usually, these bearings are either huge (1" ID or so) ball bearings, IGUS bushings (see 1640's swerve), Silverthin bearings (>1" ID, see 118's old swerve), or some custom bushing (see revolution swerve from 221 robot systems).

The strength of this bearing should also be determined by what the field looks like. If there's a bump/step like in 2012, 2010, or 2004, or if there's something you can bump the wheel into, like the corner of the pyramid, you may want something very strong. If it's an open field, this may be less of a concern.

Also, I'd recommend going to a larger OD thrust washer, or just using a thrust bearing.

I did not consider chain speed. Thank you for pointing that out. Belts could actually be used in this application, so I'll switch to those. Alternatively, a cimple box or a vex 1-stage gearbox could do it too.

Most of these issues can be solved just by switching to non-coaxial.

We've run chain this fast in a shooter prototype. It's scary, but not impossible.

This is an awesome design, and it's surprisingly light compared to some more complicated swerves.