Our First Swerve

[matthewdenny]

2 Versions: One has A Cim and one has A Cim and MiniCIM. #35 chain from 15T to 42T sprockets on the 1/2 Hex Shaft. This goes strait into the 16T gear of a 2:1 reducing bevel box. The output is a strait 1/2" hex shaft from both sides of the bevel box to 2 Colson wheels. The bevel box has 36T sprocket axial mounted on it which is driven by A PG71 with a 16T sprocket by#25 chain.

There are 2 3/8" bolt holes on the side for attachment to the frame (Aluminum 2"x1" tube)

The structure is a 9.25" length of 2"x6" 1/8" wall Aluminum tube (the 2 motor version is an inch longer)

The 1 motor version is about 10 lbs, which I know is a lot for these, but weight isn't a major concern (were are more concerned about reliability and keeping it as something we can manufacture)

This is our first go round, and I was hoping you could point out things we need to change, or things we forgot.

Also sorry for the ugly CAD. We did it in Sketchup for speed and flexibility.

[asid61]

Interesting. The weight is quite high,, but the simplicity of this design is really good. Excellent, even, espcially considering that it's made in SketchUp. Look into getting some SolidWorks licenses for the team.
That being said, there are a few changes I would highly recommend:
1. Change the wheel to a single wheel in the center. Having such widely seperated wheels will contribute greatly to wheel "scrubbing" while turning.
2. Make those pulleys the correct diameter and width. Those look like 5mm wide belts right now or something, which is way too thin. Go with 9mm wide or 15mm wide belts.

What size box tubing is that? Can you source it? Do you have thrust bearings or thrust washers on there?

[matthewdenny]

Thanks for the kind words. We will probably make this in inventor soon.

We had considered a single wheel. But can't center it because the gearbox is the center of rotation. If we build this we will experiment with removing one of them for sure.

The pulleys are actually 35 chain on the top and 25 chain on the PG motor. We are more familiar working with chain so we decided to stick with that.

The box tube is from http://www.metalsdepot.com

We don't have thrust bearings or washers. We were hoping for some insight from CD on where they should go and what type of thing to get.

[page2067]

I give great credit for it not being derivative of other designs. Signaling independent thought. I also really like that this is a minimum required machining capability design - we look for that as a team that enjoys swerving but does not have much machining resources. This does tend to add weight.

I presumed what looks like belts is a crude rendition of chain and sprockets.

I do think having the two wheels, spread apart will cause a reduced response time for steering which I believe to be necessary for smooth transitions and driving experience

What size - diameter - colsons? 3.25"? probably fine with 1 CIM.

Nice addition to the swerve design discussions.

[asid61]

Originally Posted by matthewdenny

Thanks for the kind words. We will probably make this in inventor soon.

We had considered a single wheel. But can't center it because the gearbox is the center of rotation. If we build this we will experiment with removing one of them for sure.

The pulleys are actually 35 chain on the top and 25 chain on the PG motor. We are more familiar working with chain so we decided to stick with that.

The box tube is from http://www.metalsdepot.com

We don't have thrust bearings or washers. We were hoping for some insight from CD on where they should go and what type of thing to get.

For the center box, you have miter gears in there, no? Look up some of the other coaxial swerve designs to see how you can get the miter gear above the wheels and have two shafts there. That way, you have only one wheel, and it's right below the center of rotation.

Good thing on the chain. Chain is easier for me too because of the loosish tolerances. You can use #25 in both areas if you want.

Thrust bearings, washers, screws, (expensive) metals, springs, etc. etc. can all be has at mcmaster.com. It's one of the biggest suppliers for mechanical parts that I know of.

For plate stock and stuff, you could try onlinemetals.com. They offer sales very often, so sign up for their mailing list. You get 5% off any order or 10% any order over $100 each month and they send out coupon codes pretty often. However, they don't have as much variety as mcmaster.

[matthewdenny]

Where and what type of thrust bearings would you suggest? Where would you think we need them?

[matthewdenny]

Here's my calculations of turning the wheels..,

Cof Friction 1.0
Distance from point of rotation to edge of wheel .25 ft
Weight of robot 160 lbs

Weight on each of the 8 wheels = 20 lbs

Cof F*w*d= 1.0*20*.25=5 ftlbs
Since there are 2 wheels on each axle 10 ft lbs to rotate.

Does this seem right?

Also since the wheels can't rotate as they pivot there would be some torque to back drive the CIM also.

[asid61]

Originally Posted by matthewdenny

Where and what type of thrust bearings would you suggest? Where would you think we need them?

Tapered needle bearings I think. Like these : http://www.mcmaster.com/#5709k22/=v0eehh
Or just thrust washers from McMaster, the bronze ones.