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Unread 11-08-2018, 01:07 AM
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33 The Killer Bees - 2018 Swerve Module

Below is a link to the CAD files for the swerve module design that 33 utilized during the 2018 season. There is a SolidWorks and STEP file available. The SolidWorks model has correct material, weight, and appearances applied to all parts.

The CAD file is of the back-left module from the 2018 robot. All of the modules on the robot were the same, with the only difference being the mounting plates being mirrored to each corner (back-left is the same as front-right), and that the front two modules had only one 775 motor driving each wheel.

We should follow up on this shortly with a whitepaper going over some of the mechanical details of the design and implementation this season. For now, feel free to ask any questions here and we would be more then happy to answer.

CAD Link Here



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Unread 11-08-2018, 01:38 AM
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Re: 33 The Killer Bees - 2018 Swerve Module

I love the modules, especially the use of 3d printing!

What is the benefit of using pairs of thrust bearings on the wheel shaft?
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Unread 11-08-2018, 08:04 AM
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Re: 33 The Killer Bees - 2018 Swerve Module

What went into the decision to put a speed controller on the module itself, instead of, say, using connectors to extend it's wires from a central board?
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Unread 11-08-2018, 09:04 AM
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Re: 33 The Killer Bees - 2018 Swerve Module

Quote:
Originally Posted by SaltisVonWaltis View Post
What went into the decision to put a speed controller on the module itself, instead of, say, using connectors to extend it's wires from a central board?
Not speaking on their behalf but my guess would be to keep the encoder cables shorter, along with if they designed these to swap out easily, then that's one less wire that needs disconnected.
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Unread 11-08-2018, 11:30 AM
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Re: 33 The Killer Bees - 2018 Swerve Module

Looks great! Just wondering though, how fast does it gear for?
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Unread 11-08-2018, 11:47 AM
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Re: 33 The Killer Bees - 2018 Swerve Module

I might've read past it but what is the reduction on the versa-planetary?
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Unread 11-08-2018, 12:34 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Was there a particular reason you chose to go with the MA3 absolute encoder for steering as opposed to another SRX Magnetic encoder?
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Unread 11-08-2018, 01:04 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Quote:
Originally Posted by Nuttyman54 View Post
Was there a particular reason you chose to go with the MA3 absolute encoder for steering as opposed to another SRX Magnetic encoder?
I'm also interested in this question. The reason we used the MA3 on our modules was because it has a supported shaft built in which in our case made the design a little simpler. Perhaps it's the same for them?
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Unread 11-08-2018, 01:22 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Very cool module design! It's really interesting to poke through the CAD and see all the little details. How did the needle roller bearings work out for you on the wheel shaft? The wheel shaft was made out of some kind of steel I presume?
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Unread 11-08-2018, 01:29 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Quote:
Originally Posted by Big-b View Post
I love the modules, especially the use of 3d printing!

What is the benefit of using pairs of thrust bearings on the wheel shaft?
The needle bearings they're using (for packaging reasons I assume) don't react thrust load so they need a separate bearing for this to react the load of the bevel gears . Makes for a rather expensive module hardware wise.
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Unread 11-08-2018, 02:32 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Quote:
Originally Posted by Type View Post
Quote:
Originally Posted by SaltisVonWaltis
What went into the decision to put a speed controller on the module itself, instead of, say, using connectors to extend it's wires from a central board?
Not speaking on their behalf but my guess would be to keep the encoder cables shorter, along with if they designed these to swap out easily, then that's one less wire that needs disconnected.
AJ is correct here.

Quote:
Originally Posted by Someperson17
Looks great! Just wondering though, how fast does it gear for?
The 3" wheels are driven by a 775Pro motor(s) and go through 3 gear stages: the first is a 100:12 32DP stage. The second is a 26:16 20DP stage. The final gear stage is a 15:15 bevel gear stage using the bevel gears sold by VEX.

The result free speed of the drive is about 18.1 fps.

Of course it depends on the game, but we would likely run a little slower in the future. It is difficult to get more reduction out of either of the first two gear stages in this design, so more reduction would be needed out of the bevel gear stage, by either using the AndyMark bevel gears, or some customized ones from another vendor (KHK, etc.). There may be other bevel gears becoming available so this design change is very much still a work in progress.

Quote:
Originally Posted by Connor McBride
I might've read past it but what is the reduction on the versa-planetary?
The steering of each module was powered by a 550 motor going through a 2-stage VP and a final gear reduction after. We used a 9:1 and a 5:1 stage inside the VP, and the final gear reduction after the VP was a 64:44 20DP stage. The final ratio of the system was 65.45:1.

One change we would make in the future would be to change this ratio to something closer to 100:1 with a 550, or something around 84:1 with a BAG. The modules steered plenty fast, and while we never burnt up a steering motor from regular performance, they were the limiting factor on how long we could practice before the drive needed a break (about every 20-30min of driving).

Quote:
Originally Posted by PatrickW
Quote:
Originally Posted by Nuttyman54
Was there a particular reason you chose to go with the MA3 absolute encoder for steering as opposed to another SRX Magnetic encoder?
I'm also interested in this question. The reason we used the MA3 on our modules was because it has a supported shaft built in which in our case made the design a little simpler. Perhaps it's the same for them?
I'm not sure I would say the shaft itself was the reason, but at the time it was definitely the simplest option for the current design available. The steering encoder was the last thing added to the design, so adding it the way we did was an easy way to do it.

We had an MA3 fail during finals at our 2nd district event in Milford, and it caused our drive to perform poorly and crash our lift into the scale, ultimately causing our alliance (sorry 67 and 1701!) to lose in the finals.

We still have not definitely found what caused the failure, but seeing as the wires looked completely fine and the sensor physically did not appear damaged in any way, our suspicion is ESD. The MA3 is definitely more susceptible to ESD then other options, and this would be a big reason we would switch to another option in the future.

We would definitely use a Mag encoder here in the future, and if not the CTR Mag Encoder, then we would make the output of the VP for the steering a 1:1 to the module so we could put the encoder stage into the VP.

Quote:
Originally Posted by Mike Schreiber
Quote:
Originally Posted by Big-b
I love the modules, especially the use of 3d printing!

What is the benefit of using pairs of thrust bearings on the wheel shaft?
The needle bearings they're using (for packaging reasons I assume) don't react thrust load so they need a separate bearing for this to react the load of the bevel gears . Makes for a rather expensive module hardware wise.
Quote:
Originally Posted by PatrickW
Very cool module design! It's really interesting to poke through the CAD and see all the little details. How did the needle roller bearings work out for you on the wheel shaft? The wheel shaft was made out of some kind of steel I presume?
Mike is right on all of this. The needle bearings were used due to packaging, as normal ball bearings had too large of an OD to fit with the bevel gear above.

With needle bearings, you need something to deal with the thrust load; ball bearings take care of this but needle bearings do not. The thrust bearings on the inside of the wheel forks deal with the thrust load. The thrust bearings on the outside of the forks are only there to allow us to bolt into either end of the shaft. Because it is a live shaft, we couldn't just bolt into the shaft up against the needle bearings, as the housing for the needle bearing does not rotate; if it was a ball bearing you can do this since there is an inner race of the bearing spinning with the shaft.

The wheel shaft was made from steel, more as a precaution then anything else. It was worth the weight to know the shaft wouldn't fail, as it is a drive shaft and is a smaller diameter then your average shaft. We also wanted to make sure the shaft did not wear too much in the needle bearings.

Overall the setup worked out well, but as Mike mentioned, the cost of the bearing setup for this is more then would be ideal. In future iterations we will be looking to find a way to just use 2 ball bearings for the wheel shaft to cut down complexity and cost; ideally making the shaft a dead axle would greatly simplify the design, using ball bearings on the wheel/bevel gear and the shaft being directly bolted to the wheel forks which would make the module even stronger.
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Unread 11-08-2018, 03:13 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Quote:
Originally Posted by Nick_Coussens View Post
The 3" wheels are driven by a 775Pro motor(s) and go through 3 gear stages: the first is a 100:12 32DP stage. The second is a 26:16 20DP stage. The final gear stage is a 15:15 bevel gear stage using the bevel gears sold by VEX.
How did the wear on the 32dp gears look at the end of the season - especially the ones with 2 motors on them?
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Unread 11-08-2018, 04:20 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

What advice do you guys have for using 3D printed nylon in FRC?

My team is currently experimenting with using our MakerGear M3s to print Taulman Nylon 645.
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Unread 11-08-2018, 04:33 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

What is the weight (as pictured)? I noticed that the picture shows 1 775 driving but the CAD shows 2. Can you drive it fine with just 1?
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Unread 11-08-2018, 07:53 PM
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Re: 33 The Killer Bees - 2018 Swerve Module

Quote:
Originally Posted by Nick_Coussens View Post
The thrust bearings on the outside of the forks are only there to allow us to bolt into either end of the shaft.
Why was that a requirement?
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