Different Swerve Drives

[MichaelBick]

Originally Posted by CalTran

I'm back with another question/update on our process. During the mechanical design write up of this project, a mentor and I conversed about the decision to chain sides together - and he suggested we attempt full independence. His reasoning is that the long chain runs that would be necessary would be invitations to the chain hitting something then skipping. Another thing he brought up not previously thought about was the investment of space necessary to chain sides together. I also believe we will be doing Co axially driven pods, as the infinite rotations and gearing would be somewhat advantageous.

As long as you have enough motors in the kit I would recommend going with the independent steering. It is mechanically simpler, and allows faster change of modules.

[Gdeaver]

After doing swerve for 3 years, I strongly agree with MICHAEL that independent steering modules are the way to go. Swerve has many more failure modes. Having chain runs all over the robot is a night mare to work on at a competition in the pits. Our swerve modules require the removal of 4 bolts and disconnection of 3 pairs of wires to remove a module. We can remove and replace a problem module and get on to the next match. Repair it later. Doing swerve is going to increase the complexity of the robot. Try to minimize the added complexity.

[Jeffy]

Cal,

I am excited to hear the team is interested in taking on a challenge like this.

Knowing the resources that 2410 has and an idea of the teams other
constraints like, money, time and talent. I would say look closely at how 973 does their swerve. What I think is really nice is that each swerve section is it's own module that is then bolted to the frame. I believe this method is something that is easily visualized, delegated and tweaked. Build 4 identical modules and a box frame with a plywood electronics board. Very solid testing module.

If you need any help, you know how to find me. Good luck!

-Jeff

P.S. send me CAD

Edit to add:
Cimple gears paired with 4 inch wheels seem to make a really nice combo.

[CalTran]

Update 11.8.12

After evaluation, the team has decided to do coaxial rather than distributed. With deliberation between our programmers and me, it was decided that working with an extended travel potentiometer is much simpler for them to do rather than working with an encoder. (Coding will most likely be done in C++, for those wondering.) Our decision is thus because we believe it will be easier in the future to switch to an encoder from potentiometer once we decided we would like more than one rotation. However, some more deliberation will be had once we can get in touch with some of our mentors from Rockwell Automation.

Also, at Jeffy's advice, I went over to FRC Designs and have dissected the Emperor Swerve corner module.
One of the things I am wondering about after looking at this design is how to design for the rotation. From what I can see in the CAD file, the wheel module is set inside a steering bearing and this is what allows for the wheel to rotate. Correct?

As well, we believe that the frame of our testing bed will be 80/20 extrusion, with the modules designed to slide on and off of the frame. As well as testing Swerve Drive on the platform, we will also look into a well-designed 6/8 wheel drive that could be slid on to the platform, so as to consolidate pricing of off season prototyping.

As a last point of note, when teams do fabricate the modules, how many are created? Four would be the minimum* (No spares), and I suppose the cap would be where you want to stop spending money on creating modules. Are two extra modules a happy medium to stop at? That would mean that we would need to fabricate six total modules.
*Note, Bomb Squad’s three wheel swerve is excluded from this analysis.

*Edit: http://www.chiefdelphi.com/forums/sh...Emperor+Swerve has shed some light on the various mountings and bearings necessary for rotation.

[Ether]

Originally Posted by CalTran

working with an extended travel potentiometer is much simpler for them to do rather than working with an encoder

NAND, but can you please explain why?

[CalTran]

The main reason the programming team came back with is that it is simpler to do one analog in from the potentiometer than multiple digital or a serial input(s) from an encoder. Also, from the preliminary research they did, pricing was a little higher than we'd like to do for an encoder. Both will work for our needs, but in terms of complexity we'd like to keep it simple, and the programmers said a pot would be the better of the two in that aspect.

[AdamHeard]

Originally Posted by CalTran

Update 11.8.12

After evaluation, the team has decided to do coaxial rather than distributed. With deliberation between our programmers and me, it was decided that working with an extended travel potentiometer is much simpler for them to do rather than working with an encoder. (Coding will most likely be done in C++, for those wondering.) Our decision is thus because we believe it will be easier in the future to switch to an encoder from potentiometer once we decided we would like more than one rotation. However, some more deliberation will be had once we can get in touch with some of our mentors from Rockwell Automation.

Also, at Jeffy's advice, I went over to FRC Designs and have dissected the Emperor Swerve corner module.
One of the things I am wondering about after looking at this design is how to design for the rotation. From what I can see in the CAD file, the wheel module is set inside a steering bearing and this is what allows for the wheel to rotate. Correct?

As well, we believe that the frame of our testing bed will be 80/20 extrusion, with the modules designed to slide on and off of the frame. As well as testing Swerve Drive on the platform, we will also look into a well-designed 6/8 wheel drive that could be slid on to the platform, so as to consolidate pricing of off season prototyping.

As a last point of note, when teams do fabricate the modules, how many are created? Four would be the minimum* (No spares), and I suppose the cap would be where you want to stop spending money on creating modules. Are two extra modules a happy medium to stop at? That would mean that we would need to fabricate six total modules.
*Note, Bomb Squad’s three wheel swerve is excluded from this analysis.

*Edit: http://www.chiefdelphi.com/forums/sh...Emperor+Swerve has shed some light on the various mountings and bearings necessary for rotation.

Keep in mind that the link you posted is a thoroughly different design in regards to bearing setups.

I like to think that our steering bearing setup, and what 1717 did, are about as simple as you can get. It's just two radial bearings spaced apart to react torque and radial loads, and then a large thrust bearing to react the robot weight.

[MichaelBick]

Originally Posted by AdamHeard

Keep in mind that the link you posted is a thoroughly different design in regards to bearing setups.

I like to think that our steering bearing setup, and what 1717 did, are about as simple as you can get. It's just two radial bearings spaced apart to react torque and radial loads, and then a large thrust bearing to react the robot weight.

To clarify on adam's post, the bearings that 973 ran is discussed by adam lower down in that thread.

[CalTran]

Originally Posted by MICHAELABICK

To clarify on adam's post, the bearings that 973 run is discussed by adam lower down in that thread.

Yeah I was referring to the discussion, not the bot in the title. Sorry for giving a scare ::

[Nate Laverdure]

Resurrecting this thread to mention that I just uploaded a whitepaper on this subject.

[Foster]

Thanks for the update of the info.

As an FYI, team 1640 is in their 4th season of "Unicorn" drive, 2010,2011,2012 and this year, 2013. Their fabrication info is on their website.

I've only seen them in practice driving it. This years incantation is quick and agile. There also seems to be some mind-meld of the driver and control system from the demos of Dewbot IX swirling around the base of the tower.

Check them out at the MAR districts.

Slip rings are reasonable for this application. Consider that the current that is commutated (sp?) in DC brushed motors goes through an interrupted slip ring.

You could make your own with copper tube, some insulators, and carbon brush blocks. To cut losses, use more blocks.

What's difficult is getting a clean signal across a slip ring.

[Grim Tuesday]

Originally Posted by three_d_dave

You could make your own with copper tube, some insulators, and carbon brush blocks. To cut losses, use more blocks.

Not on a competition robot you couldn't, unless the rules changed. R49 says any slip rings must be COTS.