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Unread 10-12-2018, 08:43 PM
LoboCNC LoboCNC is offline
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Team 2605 Simplified Swerve Drive

Here's a vastly simplified swerve drive design we've been working on this summer:




First drive video: https://youtu.be/gDoVclosOZI

Like many teams, we've spent quite a bit of time trying to create a swerve drive that is easier to fabricate. Most of the complication comes from trying to keep the point where the wheel contacts the ground directly in-line with the steering axis to simplify the kinematics. With this design, we've punted on that and just used a bevel gear set to transmit the drive power from the concentric CIM motor shaft directly to the wheel which is offset to the side by about 1". It's not very hard to compensate for this small offset in the code, but the correction required is actually so small that for for the most part you can just ignore it. Have any other teams used this type of design? I've looked around a bit but haven't seen any so far.

Our school shop is moving to a new building right in the middle of this year's build season (!) so we wanted to design something very easy to make. There's no real machining to speak of - we had the flat plates water jet cut, and most of the other parts are 3D printed. We'll be posting the design details shortly for anyone who is interested.
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Unread 10-13-2018, 09:07 AM
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Re: Team 2605 Simplified Swerve Drive

Looks interesting, I'd love to see a CAD file. Where are your turning/drive encoders?

I am a big fan of putting the bevel gear right on the motor shaft, 2067 is working on a similar design in that regard.

Last edited by OwenD : 10-13-2018 at 09:09 AM. Reason: Added info
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Unread 10-13-2018, 10:44 AM
LoboCNC LoboCNC is offline
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Re: Team 2605 Simplified Swerve Drive

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Originally Posted by OwenD View Post
Looks interesting, I'd love to see a CAD file. Where are your turning/drive encoders?

I am a big fan of putting the bevel gear right on the motor shaft, 2067 is working on a similar design in that regard.
The steering encoder is on the Neverest steering motor that drives the belt. The drive encoder is an AMT103 encoder that you can just barely see in the second photo. It is mounted on the CIM shaft just above the bevel pinion gear.

The CAD files will be posted shortly once we clean up a couple of details.
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Unread 10-13-2018, 11:28 AM
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Re: Team 2605 Simplified Swerve Drive

Very interesting. It doesn’t look like the wheel offset causes too much wiggle as the module reorients. I look forward to seeing CAD and more testing results.

What kind of bearing set up are you using? That seems to be one of the last most-complicated parts of designing a swerve drive. Also what kind of wheel is that? It looks...strange.
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Last edited by AriMB : 10-13-2018 at 02:58 PM.
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Unread 10-13-2018, 12:31 PM
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Re: Team 2605 Simplified Swerve Drive

Where are the bearings that the module rotates on? It looks like it's just pivoting on the CIM shaft, which can't be correct.
Looks really slick on driving great work! Make sure you load it up heavy though to make sure those printed parts hold up.
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Unread 10-13-2018, 02:33 PM
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Re: Team 2605 Simplified Swerve Drive

Very nice swerve module. I like how simple the drive line is. What is the bevel gear reduction? 5:1? and what is either your wheel diameter or calculated free speed?
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Unread 10-13-2018, 02:54 PM
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Re: Team 2605 Simplified Swerve Drive

Knowing your previous work I'm a bit surprised you didn't integrate a 3D printed bevel gear into the wheel. Did you ever do any testing with one?
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Unread 10-13-2018, 03:02 PM
LoboCNC LoboCNC is offline
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Re: Team 2605 Simplified Swerve Drive

Quote:
Originally Posted by PatrickW View Post
Very nice swerve module. I like how simple the drive line is. What is the bevel gear reduction? 5:1? and what is either your wheel diameter or calculated free speed?
Thanks! The bevel gear reduction is 4:1 (1.5 module, or about 17 pitch), and the wheel diameter is 4". Assuming a top CIM motor speed of about 4000 RPM under a fairly minimal load, that gives a top speed of about 17.5 ft/sec. We probably would have preferred a 5:1 reduction, but it gets tricky finding the right gear set because the shaft of the CIM motor doesn't reach much past the rim of the wheel. That is, the big gear needs to be almost the diameter of the wheel.
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Unread 10-13-2018, 03:07 PM
LoboCNC LoboCNC is offline
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Re: Team 2605 Simplified Swerve Drive

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Originally Posted by mman1506 View Post
Knowing your previous work I'm a bit surprised you didn't integrate a 3D printed bevel gear into the wheel. Did you ever do any testing with one?
Actually, we just finished construction on just that - a 3D printed integrated bevel gear/wheel. Turns out PLA wears surprisingly well, but we'd need *a lot* of testing to be confident the teeth won't wear prematurely in during a competition or break during a match. If the design looks promising after some testing, we'll post that as well.
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Unread 10-13-2018, 03:12 PM
LoboCNC LoboCNC is offline
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Re: Team 2605 Simplified Swerve Drive

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Originally Posted by asid61 View Post
Where are the bearings that the module rotates on? It looks like it's just pivoting on the CIM shaft, which can't be correct.
Looks really slick on driving great work! Make sure you load it up heavy though to make sure those printed parts hold up.
I just tried posting a cross section image, but I'm a new member and still under moderator supervision so I don't know when that post will appear. Until then, the slew bearing buried in the center is a 6811 bearing ($9.00 on ebay) that is sandwiched in-between the printed steering pulley on the outside and another printed centering ring on the inside that screws to the base plate..
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Unread 10-13-2018, 04:49 PM
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Re: Team 2605 Simplified Swerve Drive

I don't have any experience working with swerve but I have see a lot of them and this one look to be one of if not the simplest that I have see.
Nice job!
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Unread 10-14-2018, 04:49 PM
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Re: Team 2605 Simplified Swerve Drive

Here's a cross section of the guts of the swerve module. The 6811 slew bearing is shown as a grey square in cross section. The outer race of the bearing is clamped with screws between the steering pulley (green) and the round aluminum plate. The inner race of the bearing is clamped between an inner ring (also in green) and the base plate. You can also see the cross section of the encoder. (Note all green parts are 3D printed.)

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