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Unread 08-11-2017, 11:13 AM
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Encoder Mounting

Hello,

So I'm designing swerve module mounts for my team this summer using the Revolution 2 Pro Swerve's from Team 221 LLC. I am currently having some trouble with encoders and am looking for some advice with those along with any other critiques on my design.

Currently I am using a CIMcoder to measure the quadrature of my drive wheels and it is mounted directly to the CIM underneath the mounting plate. I would, however, like to add an encoder to the 1/2 inch round shaft coming out of the GEM Gearbox. I read somewhere that the AMT103-V Encoders fit on a variety of shafts but I'm not sure how. An encoder placement above the gearbox should give more accurate wheel position and will also allow me to move the cim up 1/2 an inch so that it is farther from the ground.



http://imgur.com/a/g42Kd - link to the pictures

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Adam

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Unread 08-11-2017, 11:46 AM
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Re: Encoder Mounting

You're going to be hard pressed to find an encoder with a 1/2" shaft bore within any reasonable price range. A better option is to either turn down the end of the shaft to 1/4" and you can use something like this or use the surgical tubing and zip tie method to connect the 1/2" shaft to a shaft encoder like a Grayhill.
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Unread 08-11-2017, 02:11 PM
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Re: Encoder Mounting

Another option to consider would be a 1/4"-20 shank bolt. Cut off the head, thread the threaded end into that 1/4"-20 hole in the end of the shaft, and mount the encoder to the shank. Use threadlocker!
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Unread 08-11-2017, 04:57 PM
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Re: Encoder Mounting

Quote:
Originally Posted by Ari423 View Post
You're going to be hard pressed to find an encoder with a 1/2" shaft bore within any reasonable price range. A better option is to either turn down the end of the shaft to 1/4" and you can use something like this or use the surgical tubing and zip tie method to connect the 1/2" shaft to a shaft encoder like a Grayhill.
Thank you. I've seen the surgical tubing and zip tie method on the forums a couple times before, but I'm not really sure what it is. Can you explain how it works and if possible a picture of it in action?
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Unread 08-11-2017, 05:26 PM
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Re: Encoder Mounting

Quote:
Originally Posted by Adam_P View Post
Thank you. I've seen the surgical tubing and zip tie method on the forums a couple times before, but I'm not really sure what it is. Can you explain how it works and if possible a picture of it in action?
Here's an example of just surgical tubing.
https://drive.google.com/file/d/0BxN...ew?usp=sharing
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Unread 08-11-2017, 06:09 PM
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Re: Encoder Mounting

Quote:
Originally Posted by Adam_P View Post
Thank you. I've seen the surgical tubing and zip tie method on the forums a couple times before, but I'm not really sure what it is. Can you explain how it works and if possible a picture of it in action?
Quote:
Originally Posted by Jjmase123 View Post
Here's an example of just surgical tubing.
https://drive.google.com/file/d/0BxN...ew?usp=sharing
The surgical tubing and zip tie method is exactly as pictured there except with zip ties around the surgical tubing at each end to hold the surgical tubing tight. You'll definitely want the zip ties if the shafts are very different sizes to make sure the tubing doesn't slip on the smaller shaft.
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Unread 08-11-2017, 06:18 PM
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Re: Encoder Mounting

I've used the gem a couple times for different applications, and it's horribly inefficient. I know you weren't asking for input on it - but I'd never use a gem in a drivetrain.
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Unread 08-11-2017, 07:31 PM
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Re: Encoder Mounting

+1 on not using GEMs, they have poor efficiency. A belted first stage might work better, and it will eliminate the large gears.
Consider the Muchskull CIMcoder instead of the COTS version: https://www.chiefdelphi.com/forums/s...d.php?t=138750 Many people (myself included) have had gripes about the COTS CIMcoder.
The AMT-103 and AMT-102 series is magical. Very robust encoders. They have little sleeves they come with that are each able to fit over a different shaft size. They cover all metric and imperial sizes from 1-8mm, 1/16"-5/16".
I like your VP encoder but the way you have mounted the VP is somewhat sketchy. Consider using the front holes to mount it instead.

I've used the surgical tubing/zip tie method before and never had good results. I know other have gotten 0 slip, but I personally have never been able to do that. Using an AMT encoder or a helical coupler instead is a much safer option. WCP now sells helical couplers too.
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Unread 08-13-2017, 05:49 PM
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Re: Encoder Mounting

Quote:
Originally Posted by asid61 View Post
+1 on not using GEMs, they have poor efficiency. A belted first stage might work better, and it will eliminate the large gears.
Consider the Muchskull CIMcoder instead of the COTS version: https://www.chiefdelphi.com/forums/s...d.php?t=138750 Many people (myself included) have had gripes about the COTS CIMcoder.
The AMT-103 and AMT-102 series is magical. Very robust encoders. They have little sleeves they come with that are each able to fit over a different shaft size. They cover all metric and imperial sizes from 1-8mm, 1/16"-5/16".
I like your VP encoder but the way you have mounted the VP is somewhat sketchy. Consider using the front holes to mount it instead.

I've used the surgical tubing/zip tie method before and never had good results. I know other have gotten 0 slip, but I personally have never been able to do that. Using an AMT encoder or a helical coupler instead is a much safer option. WCP now sells helical couplers too.
Thanks for the advice about the CIMcoder and the 3D model. I think we'll go with the AMT encoder.

Also, what exactly is a belted first stage? Sorry, don't have much mechanical experience, I programmed last year ... Any example/picture would be great.

Also regarding the mounting of the VP + 775 pro: the reason I couldn't use the front holes was because it would've been touching the ground. Last year we used a method similar to the current design and it seemed to work, although not ideal. Should I consider adding another plate above for the front holes or are their any more reliable ways to mount it?
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Unread 08-13-2017, 05:51 PM
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Re: Encoder Mounting

Quote:
Originally Posted by Tom Line View Post
I've used the gem a couple times for different applications, and it's horribly inefficient. I know you weren't asking for input on it - but I'd never use a gem in a drivetrain.
Thank you. Definitely helpful, I've never used one before so I had no idea. Are their any other gearboxes that you would recommend. I'm looking for something with about a 4:1 gear ratio and possibly a little bit smaller that can mount to/work with a cim motor.
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Unread 08-13-2017, 07:22 PM
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Re: Encoder Mounting

Quote:
Originally Posted by Adam_P View Post
Thanks for the advice about the CIMcoder and the 3D model. I think we'll go with the AMT encoder.

Also, what exactly is a belted first stage? Sorry, don't have much mechanical experience, I programmed last year ... Any example/picture would be great.

Also regarding the mounting of the VP + 775 pro: the reason I couldn't use the front holes was because it would've been touching the ground. Last year we used a method similar to the current design and it seemed to work, although not ideal. Should I consider adding another plate above for the front holes or are their any more reliable ways to mount it?
By belted first stage, I mean using timing belts off the CIM. West Coast Products sells a timing belt pulley that fits right over the CIM shaft and has 12 teeth. Couple that with a larger Vexpro timing belt pulley like a 36 tooth, and there's a 3:1 reduction ratio right there. You could also use #25 chain for the first stage of reduction using the CIM-size Andymark sprockets, but chain can get pretty scary at 5000 rpm.

Adding another plate would be prudent. The way you have it mounted right now looks fairly prone to flexing, but if you machine things right you can still make it work. What tools do you have? CNC mills, manual mills, or just a drill press?
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Unread 08-14-2017, 11:54 AM
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Re: Encoder Mounting

Quote:
Originally Posted by asid61 View Post
By belted first stage, I mean using timing belts off the CIM. West Coast Products sells a timing belt pulley that fits right over the CIM shaft and has 12 teeth. Couple that with a larger Vexpro timing belt pulley like a 36 tooth, and there's a 3:1 reduction ratio right there. You could also use #25 chain for the first stage of reduction using the CIM-size Andymark sprockets, but chain can get pretty scary at 5000 rpm.

Adding another plate would be prudent. The way you have it mounted right now looks fairly prone to flexing, but if you machine things right you can still make it work. What tools do you have? CNC mills, manual mills, or just a drill press?
Is this more of what you were thinking (rough design) ?http://imgur.com/a/xkfnK

We do have access to a CNC mill, however we have had some problems with it so I don't want to rely on it too much.

For the cim, I needed at least a 4:1 ratio, so I incorporated the gears on top of the pulley. Is there a better way to do this?

Also, how should I keep the hex shaft in the plate? I was thinking a shaft collar or clip but there's probably a more reliable method.

Thanks
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Unread 08-14-2017, 12:59 PM
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Re: Encoder Mounting

Now, I could be wrong in this, but, I think this is more what Anand was referring to: https://www.chiefdelphi.com/media/im...3d8c8fb0_l.jpg

That's 1717's Swerve Module, from when they were still a team, which was a coaxial two-speed swerve module. The dog on their module, which allowed them to shift, was embedded on the axle which meshed with the CIM output. I know you're not building a shifting transmission but I'd still look to 1717's swerve. The belt across the top of the module allowed for them to transfer the CIM's power to the wheel module, quite far away, without a long chain of gearing.

By using a belt to transfer the power to the wheel module, you can physically linearize the module (which I prefer). While this can be good in certain cases, I like a linear design as it allows for bigger intakes, gear mechs, etc. on the front of the robot. I know 114 and 16 use this type of design for, I assume, this and many other reasons. Additionally, when using a VP or other planetary gearbox, you can easily shrink the size of the module. Here's a picture of 114's Swerve

http://i.imgur.com/PogljdA.png

Additionally, 1640 uses a modified version of a first-stage belt drive. I won't get into the details of their CVT Swerve, but they too use a first stage belt.

https://i.ytimg.com/vi/cXh4-96YXbY/maxresdefault.jpg

Here's yet another example of a belt for the CIM, except this version uses it as the second stage. I think it's really cool how they wrapped it around the BAG Motor with the VP to save space.

http://i59.photobucket.com/albums/g3...0/IMG_2026.jpg

If you have any questions, I'm always here to talk. I'm no engineer, just a college student who's researched way too much into Swerve.
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Unread 08-14-2017, 02:29 PM
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Re: Encoder Mounting

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Originally Posted by Jjmase123 View Post
... I know 114 and 16 use this type of design for, I assume, this and many other reasons. Additionally, when using a VP or other planetary gearbox, you can easily shrink the size of the module. Here's a picture of 114's Swerve

http://i.imgur.com/PogljdA.png
Thanks for the shoutout! Our swerve was pretty compact, but we did some post-season discussion on ideas to make it smaller.

As far as our sensors go, they're all mounted via 3D printed adapters. In the link above, the drive wheel encoders sit on a little "table" above the drive gears. Under that "table" is a printed hex adapter that mates the encoder to an unfinished Hex shaft.

Our steering encoders were mated to the large steering gear also via printed parts. We printed a modified version of the same gear, and had a printed encoder mount anchoring the absolute encoder to the robot frame.

EDIT:

Here's an image of the base of the robot.

You can see the large white gears (with 114 printed into them) mating against the swerve modules. These gears were printed out of ABS on a Stratasys UPrintSE with Solid infill. The shaft the gears ride is the input shaft of an absolute encoder. We chose to use a 1:1 steering sensing setup with absolute encoders to dodge the need for any homing, outside of minimal calibration when installing a module.

Overall, we learned a TON about swerve, and the students loved it (even if it was expensive and kind of a pain at times). Will we do it again? Who knows, depends on the game.

Last edited by Mechvet : 08-14-2017 at 02:34 PM.
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Unread 08-14-2017, 07:39 PM
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Re: Encoder Mounting

Quote:
Originally Posted by Adam_P View Post
Is this more of what you were thinking (rough design) ?http://imgur.com/a/xkfnK

We do have access to a CNC mill, however we have had some problems with it so I don't want to rely on it too much.

For the cim, I needed at least a 4:1 ratio, so I incorporated the gears on top of the pulley. Is there a better way to do this?

Also, how should I keep the hex shaft in the plate? I was thinking a shaft collar or clip but there's probably a more reliable method.

Thanks
If you really want a 4:1 ratio on the first stage (which I believe is a little overkill), then just use a small gear and large gear. A 8mm-to-0.5hex adapter on the CIM will let you use and 18t gear or larger for the first stage, and then just throw whatever size gear you need above the swerve pod (maybe an 84t Vex gear). Something like 20t on the CIM and 84t on the swerve can work. Andymark also sells a 17 tooth CIM pinion gear.

Your mounting strategy for the CIM and the VP are much improved with that latest CAD you made.
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