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Unread 05-15-2018, 01:57 PM
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Swerve module feedback

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
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Last edited by gorrilla : 05-15-2018 at 02:46 PM.
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Unread 05-15-2018, 11:28 PM
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Re: Swerve module feedback

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.
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Unread 05-16-2018, 06:52 AM
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Re: Swerve module feedback

Quote:
Originally Posted by asid61 View Post
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.
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
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Unread 05-16-2018, 10:17 AM
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Re: Swerve module feedback

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Originally Posted by gorrilla View Post
There's four 1/4" holes for standoffs, two above and two below where the cim mounts.
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
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Unread 05-16-2018, 10:23 AM
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Re: Swerve module feedback

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Originally Posted by gorrilla View Post
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
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.
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Unread 05-16-2018, 11:34 AM
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Re: Swerve module feedback

Quote:
Originally Posted by Michael Corsetto View Post
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
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.


Quote:
Originally Posted by Ryan Dognaux View Post
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.
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.
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Unread 05-16-2018, 11:37 AM
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Re: Swerve module feedback

Has anyone used the GT2 belts on a drivetrain before? VEX says that its for low load applications
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Unread 05-16-2018, 12:30 PM
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Re: Swerve module feedback

Quote:
Originally Posted by gorrilla View Post
Has anyone used the GT2 belts on a drivetrain before? VEX says that its for low load applications
Use this guide to check your loading:
http://www.sdp-si.com/D265/PDF/D265T146.pdf

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.)
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Unread 05-16-2018, 03:07 PM
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Re: Swerve module feedback

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?
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Last edited by gorrilla : 05-16-2018 at 03:11 PM.
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Unread 05-16-2018, 06:09 PM
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Re: Swerve module feedback

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Originally Posted by gorrilla View Post
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
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.
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Unread 05-16-2018, 06:31 PM
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Re: Swerve module feedback

Quote:
Originally Posted by asid61 View Post
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.
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
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Unread 05-16-2018, 06:59 PM
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Re: Swerve module feedback

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.
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Re: Swerve module feedback

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Originally Posted by Mechvet View Post
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.
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.
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Unread 05-16-2018, 07:09 PM
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Re: Swerve module feedback

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Originally Posted by gorrilla View Post
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.
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.
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Re: Swerve module feedback

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

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