Swerve module feedback


#1

Been working on this for a day or two on the side, haven’t seen a ton of motor in module designs over the last few years. Inspired by the revolution pro modules from 221 I created this as a rough concept.

I have access to a very large Laser and CNC breaks so the module pod is a laser cut and bent piece of 11ga. The top pivot and pivot block are 3d printed or machined from delrin/uhmw, and the pivot block clamps around the pivot in a similar way to how the revolution modules could be mounted. It’s designed to be mounted onto a 2*1 frame. 3" colsons 7.875" tall and 4.75" at widest point

Rotation could be powered several different ways.

What do you think about all this so far?

Edit: it can be made slightly more compact I just went with rounded numbers on spacing for most things.

https://grabcad.com/library/simple-swerve-1


#2

I don’t see any gears in the CAD. How were you planning on driving the wheels?
The idea for clamping is interesting, but from the looks of it you’d need a half-tight screw to remove play from the pivot assembly, unless I’m misunderstanding what I’m seeing.
Why a hex shaft to rotate the module over a 1.875" hole pattern like Versahubs have?
And finally are you planning on adding support down low? Thin sheet metal isn’t great for taking side loads.
Looks like a good start to a module, although it’s not clear to me why you don’t go full 221 and make it coaxial.


#3

To power the wheels its either going to be a a 10-36 tooth sprocket and chain, or a 12-48 gt2 pulley. I just haven’t decided

The side of the blue clamping block that has four holes gets mounted to the robot frame, and the side with two holes is where you tighten against the pivot, the holes in the robot frame need to actually be short slots and not just holes in order to tighten it all properly.

It has both a hex and the 1.875 bolt.circle in the pivot and base, I made it a hex just because the laser can cut it, so why not.

There’s four 1/4" holes for standoffs, two above and two below where the cim mounts.

I didn’t make it coaxial because I wanted to not use bevel gears and I also wanted the motor in the module to save space inside the robot frame


#4

The four standoffs, in their current location, won’t do much to stiffen up the material surrounding the wheel bearing. That is where I expect those plates to bend. The top two standoffs don’t really do anything tbh.

Also, how is the CIM installed? Is the orange sheet metal one piece? It seems nearly impossible to swap that CIM after the module is fully assembled.

-Mike


#5

I’d leave some room to get even more reduction for your speed. You’re looking at a free speed of 17.5 ft/s so you’re going to have to do some fun limiting on the controls side. We were at 15.5 ft/s initially this year on our swerve and killed our batteries way too quickly for our liking. Ended up stepping down to 11.5 ft/s - it was still plenty fast and didn’t drain our battery in 3 minutes.


#6

yes the orange sheet metal is a single piece, there is a slightly oversized hole on the one side to slip the CIM in and out.
I’ll see where I can add a standoff as close to the bottom as possible.

There’s room to make it a 12t-60t GT2 setup as well but under 12fps seemed kind of slow to me.
But I never really thought about it draining the battery that much, we did have a problem in 2017 with that.


#7

Has anyone used the GT2 belts on a drivetrain before? VEX says that its for low load applications


#8

Use this guide to check your loading:

Since you’re checking if 3mm pitch & 9mm width works rather than selecting a pitch size, maybe calculate a factor of safety instead of using a service factor.

(FWIW, GT2 has multiple pitches; I assume you’re referring to the Vexpro/WCP GT2/3mm size belts.)


#9

In the meantime of working on the larger mod I made this short coaxial guy. https://grabcad.com/library/small-swerve-4

Total height from floor to top is 5.924"
width of 3.25"
11ga thickness
laser cut.
this model is just missing shaft collars and spacers/standoffs.
How do you keep the vertical bevel gear from coming off the coax shaft? the vex 15 tooth gear doesn’t have any type of set screw?


#10

A 48t 5mm HTD pulley is 3" pitch diameter, and more than that with a flange. A 36 tooth sprocket is 3.01" outer diameter. A 34 tooth sprocket just barely fits, but more safe would be a 32 tooth.
32:12 is ~26fps free speed- far too fast for most robots and drivers.


#11

Yeah I’ll have to make the motor in module one slightly taller and 4" wheels minimum to get the gearing it needs.

One of the advantages of the coaxial design is it’s height is limited by just the bevel gear and wheels. With slightly less than an 1/8" between the bevel gear and the surface of the wheel it’s almost as small as you can go


#12

For the coaxial, if you’re using the 2.5" Colson wheels, be wary of wheel wear and ease of repair.

Swerves rely on having all wheels contacting the ground, otherwise some pretty heavy drift starts happening. When we used the 2.5" colsons, we found they wore in a fairly heavy way, and our swerve drifted quite a bit. We didn’t design the bottom axle for easy removal, so changing wheels was a pain. In the offseason we reworked the bottom axle to be easier, and it made changing wheels WAY easier.


#13

This one is actually using the 1.625" colsons, removing the axles should actually be pretty easy, the shaft would either be tapped or just have shaft collars.


#14

The wear on a smaller wheel will be worse, for sure. As long as they’re easy to remove, that’ll mitigate that potential problem.


#15

One clear downside of motor-in-module is getting sensor feedback out.

Anyone with more electrical experience than I have a recommendation for whether CANbus or encoder output will survive passing through a swivel ring better? I don’t really know where to start ::rtm::

Alternatively, anyone do swerve without a wheel speed encoder? How’d that go for you?


#16

You’re going to be burning through wheels like candy with 1.625" colsons, fair warning. We used 2.5" colsons and saw some wear after one event, enough where the wheels didn’t have their center ridge anymore.

If you’re looking at bevel gears / co-axial, consider a larger bevel that would be on the same shaft as the wheel. You can get some additional reduction here - we used a 20 tooth bevel to a 30 tooth bevel that was on a hex shaft with our wheels this year.

We were influenced heavily by 2767’s design which I’d recommend checking out. You can see our CAD from this past season here as well.


#17

hey that’s pretty neat, i remember seeing madtowns’ swerve in 2017 at houchamps and i believe they had similar large bevel gear attached to the wheels like that.

I just finished putting this one together a few minutes ago
https://grabcad.com/library/very-small-swerve-1

This one has 2.5" colsons, the hex shaft needs to be slightly longer but think this is about as small as its possible to make a coax module, the only place to take height from is my top pivot piece. the module itself is 2.75" from the floor and with the top pivot is just under 5"


#18

Ryan,

Who is your bevel gear source? Our current bevels are AndyMark. We’re looking at KHK.

Also our 2.5" Colsons quickly loose their crown shape and end up trapezoidal.


#19

We purchased ours from QTC gears. We used our lathe to take some of the larger bevel gear’s hub off and 1/2" hex broached both gears.

Specifically these:

http://shop.sdp-si.com/catalog/product/?id=KSB1.5-2030
http://shop.sdp-si.com/catalog/product/?id=KSB1.5-3020

They were the longest lead item and took almost half of build season to arrive.


#20

We used KHK gears this year. We highly recommend them.