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Unread 08-19-2018, 09:59 PM
nickbrickmaster nickbrickmaster is offline
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pic: Pseudo-Differential Swerve

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Unread 08-19-2018, 10:03 PM
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Re: pic: Pseudo-Differential Swerve

The detail design looks good, but the concept has prior art: https://www.chiefdelphi.com/media/photos/44055. The biggest "con" with this style is that a difference in traction between the wheels (such as when climbing an obstacle) would prevent the module from controlling its speed and heading.
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Unread 08-19-2018, 10:59 PM
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Re: pic: Pseudo-Differential Swerve

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Originally Posted by nuclearnerd View Post
The detail design looks good, but the concept has prior art: https://www.chiefdelphi.com/media/photos/44055. The biggest "con" with this style is that a difference in traction between the wheels (such as when climbing an obstacle) would prevent the module from controlling its speed and heading.
The OP had cited that other diff swerve as the other one they're aware of. I do believe that 323 had a similar motor power setup for a non-differential swerve, but can't find screenshots at the moment.

Regardless, excellent modeling. It still doesn't solve the incredibly complicated problem of controlling them though
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Unread 08-19-2018, 11:02 PM
nickbrickmaster nickbrickmaster is offline
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Re: pic: Pseudo-Differential Swerve

Quote:
Originally Posted by nuclearnerd View Post
The detail design looks good, but the concept has prior art: https://www.chiefdelphi.com/media/photos/44055. The biggest "con" with this style is that a difference in traction between the wheels (such as when climbing an obstacle) would prevent the module from controlling its speed and heading.
Which is why I linked that thread in the OP.

That is a good point about the difference in traction that I didn't think of. That's certainly a point to consider when picking the right design for the job. This year I probably wouldn't have chosen this design due to the scale platform and the cable protectors, but with a flat field like Steamworks I think it would certainly be fine.

Edit: If anyone is looking for the original CAD link, I accidentally did some modifying on the linked version. Here's a static link to the version discussed in this thread.
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Unread 08-19-2018, 11:03 PM
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Re: pic: Pseudo-Differential Swerve

Quote:
Originally Posted by nuclearnerd View Post
The detail design looks good, but the concept has prior art: https://www.chiefdelphi.com/media/photos/44055. The biggest "con" with this style is that a difference in traction between the wheels (such as when climbing an obstacle) would prevent the module from controlling its speed and heading.
I'm sure that almost all designs in FRC have "prior art". That being said, I like this implementation much more than previous ones.
What I like about this style of module is that it's easy to understand and fairly simple to make. What I don't like is the intrisically large packaging and the extra cost in gears. This design appears to only have 2 stages of reduction, so it's actually probably saving money over a Versaplanetary-based design.
The slip ring will likely not be powerful to support both Talons + CAN, however, unless you put 30A breakers on the drive motors. Not terrible for 775s, but something to think about.
Another thing to take note of is the seemingly ~1200rpm turning speed. That's also very hard to change without just making the wheels super far apart. One of those things that needs to be tested to be sure.
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Unread 08-19-2018, 11:12 PM
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Re: pic: Pseudo-Differential Swerve

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Originally Posted by asid61 View Post
Another thing to take note of is the seemingly ~1200rpm turning speed. That's also very hard to change without just making the wheels super far apart. One of those things that needs to be tested to be sure.
Turning speed seems to be the biggest challenge to differential swerve, and will need considerable testing (in addition to the current calculations) to find the max and ideal numbers for.
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Unread 08-20-2018, 12:19 AM
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Re: pic: Pseudo-Differential Swerve

I think team 4143's done that:
https://www.youtube.com/watch?v=FqgvDJq3Jtc
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Unread 08-20-2018, 12:47 AM
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Re: pic: Pseudo-Differential Swerve

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Originally Posted by heatblast016 View Post
I think team 4143's done that:
https://www.youtube.com/watch?v=FqgvDJq3Jtc
Wait, I just saw that the OP linked that, never mind
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Unread 08-20-2018, 06:13 AM
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Re: pic: Pseudo-Differential Swerve

Made one of these in meat space once...

https://www.dropbox.com/s/hz6w9yll50...43.10.jpg?dl=0
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Unread 08-20-2018, 07:19 AM
Andrew Schreiber Andrew Schreiber is offline
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Re: pic: Pseudo-Differential Swerve

Quote:
Originally Posted by tjf View Post
The OP had cited that other diff swerve as the other one they're aware of. I do believe that 323 had a similar motor power setup for a non-differential swerve, but can't find screenshots at the moment.

Regardless, excellent modeling. It still doesn't solve the incredibly complicated problem of controlling them though
Two stage reduction off the pair of 775pros for main drive. 3d printed pulleys as the second stage. CAN ran through one of the sets of wires in the slip ring. Power for the two 775s through the other two. They were on 30A breakers.
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Unread 08-20-2018, 10:49 AM
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Re: pic: Pseudo-Differential Swerve

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Originally Posted by Andrew Schreiber View Post
Two stage reduction off the pair of 775pros for main drive. 3d printed pulleys as the second stage. CAN ran through one of the sets of wires in the slip ring. Power for the two 775s through the other two. They were on 30A breakers.
I moreso meant limiting the rotation in software to avoid spinning faster than the slipring is rated for.
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Unread 08-20-2018, 10:52 AM
Andrew Schreiber Andrew Schreiber is offline
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Re: pic: Pseudo-Differential Swerve

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Originally Posted by tjf View Post
I moreso meant limiting the rotation in software to avoid spinning faster than the slipring is rated for.
Nothing special. The steering motors used MotionMagic, the max V was probably set below the max rate of the slip ring... I say probably because I certainly didn't make any conscious efforts to limit it.

Not something you could do on this system easily though unless you were to cap the difference in velocity between the wheels?
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Unread 08-20-2018, 11:14 AM
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Re: pic: Pseudo-Differential Swerve

This isn't a "psuedo differential" - this is 100% a differential swerve, it just uses the ground / friction to transmit that differential force.

I've toyed with this concept a little bit as well, as it avoids the bevel gears altogether which is nice. The 4143 module that you linked to is the other one I've seen. So far it's been really challenging to package it better than bevel gear differential swerves - and you can sorta see that here.
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Unread 08-20-2018, 11:23 AM
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Re: pic: Pseudo-Differential Swerve

Quote:
Originally Posted by Andrew Schreiber View Post
Two stage reduction off the pair of 775pros for main drive. 3d printed pulleys as the second stage. CAN ran through one of the sets of wires in the slip ring. Power for the two 775s through the other two. They were on 30A breakers.
Did you guys have any issues sending the CAN through the slip ring? We have discussed it in the past but felt this would be a risk point. What slip ring did you use?
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Unread 08-20-2018, 11:24 AM
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Re: pic: Pseudo-Differential Swerve

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Originally Posted by Chris is me View Post
This isn't a "psuedo differential" - this is 100% a differential swerve, it just uses the ground / friction to transmit that differential force.

I've toyed with this concept a little bit as well, as it avoids the bevel gears altogether which is nice. The 4143 module that you linked to is the other one I've seen. So far it's been really challenging to package it better than bevel gear differential swerves - and you can sorta see that here.
Might be more appropriate to call it a skid steer differential swerve?

(In b4 motor-in-wheel-skidsteer-differential-swerve)
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