18-08-2014 15:47

evanperryg

Re: pic: New swerve CAD from 2471

Seems like a pretty daring design, having the modules on the outside. Have you made sure that the modules won't be affected by a hard hit?

18-08-2014 15:55

Adrian Clark

Re: pic: New swerve CAD from 2471

I'd be worried about the strength of using pocketed 1/8" wall tubing to support the weight of the robot and the forces from the wheels. Most swerves I've seen with a similar coaxial setup use 1/4" plate.

I like the originality of you module packaging, why did you choose to do it this way?

Why have the modules on the outside? It would seem like your frame would be stronger and you'd have more electronic placement space with the framerails on the outside.

-Adrian

18-08-2014 16:15

Bryce2471

Re: pic: New swerve CAD from 2471

It is a somewhat daring design. Although there will be structural bumpers outside of the modules, that will distribute impact forces evenly across two modules and the surrounding welded frame.

18-08-2014 16:32

Bryce2471

Re: pic: New swerve CAD from 2471

Last year, in the off-season, we ran a coaxial swerve drive made from 0.1875" wall aluminum extrusion. It didn't have any problems with structural integrity, and it had a much harder job to do. The reason I believe this design will also not have any issue is that the modules are cut from a single piece of extruded aluminum, and they are closely supported by the 0.125" welded frame on both top and bottom.

The packaging was chosen to minimize the distance that the modules will have to carry the weight of the robot, before distributing that force to the frame. As well as to minimize weight and maximize space in the center of the robot.

If the frame were on the outside, there would have to be an extra inch of space left empty in the belly pan around the modules in each direction. This space would be necessary to remove the swerves, because the frame is C channel that raps around the top and bottom of the module.

Thanks for your questions and feedback!

18-08-2014 17:41

Dale

Re: pic: New swerve CAD from 2471

Very cool! Will this make it on a BunnyBot this year?

Also, what is your reduction off of the CIMs? It looks like it will be on the fast side but maybe that's what you intended.

18-08-2014 18:17

Bryce2471

Re: pic: New swerve CAD from 2471

Thanks! Yes, the plan is to test this out on a BunnyBot this fall.

The reduction is quite fast, although it's a bit slower than what we ran last year. The final reduction is 3.6:1, or approximately 2.4 inches per revolution of the CIM shaft.

18-08-2014 19:22

kk052

Re: pic: New swerve CAD from 2471

Hmmm... looks somewhat similar to one I've seen before...
just make sure the C brace the swerve's attach to are not shaved completly flat, or you might lose strength in the frame. also are you not worried that the belt might slip off the larger gear because its not flanged?
also most years bumpers must be supported every 8 inches do they mount on the swerves, or is there an additional bracket that is hidden?

18-08-2014 20:32

Dale

Re: pic: New swerve CAD from 2471

Well you certainly won't be winning any pushing battles going that fast but on the up side, if it works as well as last year, maybe you won't need to!

18-08-2014 22:26

Tyler2517

Re: pic: New swerve CAD from 2471

We proved this year that you don't need to push back to win a pushing battle just not get pushed.

I still think its geared a bit high.

18-08-2014 23:21

asid61

Re: pic: New swerve CAD from 2471

It's geared for around 14fps adjusted it looks like. That's not too fast.
Even so, I would be worried about collisions at that speed on the modules. A hard hit on a corner could render you immobile, as well as costing a few hundred dollars. Even if nothing breaks mechanically, encoders are pretty fragile.
With frame perimeter rules, are you really gaining extra room this way?

18-08-2014 23:28

Dale

Re: pic: New swerve CAD from 2471

It's also going to impact acceleration. I suspect being geared that high the robot will seldom actually get to top speed during a match before having to change direction. Usually robots geared that fast will have six CIM drive trains just for that reason.

19-08-2014 13:37

Bryce2471

Re: pic: New swerve CAD from 2471

I think you'll find that a robot geared for 14 fps on 4 cims will have plenty of power to accelerate quickly. Our comp bot did fine this year, and it was geared for about 18 fps. Our bunny bot was geared even faster that that, and it won. so obviously, it will depend on the game, but in my opinion, 14 fps isn't "too fast".

19-08-2014 13:42

Bryce2471

Re: pic: New swerve CAD from 2471

Last years modules only costed about $220 each. I expect this years to be a little higher, but still not too bad. the encoders we are using are non contacting magnetic absolute encoders, so I doubt the would break. Although, if they did, they only cost about $10.
I'm not really sure what you mean by "With frame perimeter rules, are you really gaining extra room this way?"

19-08-2014 13:48

Dale

Re: pic: New swerve CAD from 2471

Your robots were certainly zippy! I'd love to know how long it took the robot to get to its terminal velocity (and what that velocity is.) Maybe that would be a good fall project for your software folks graphing speed vs time as measured by an encoder on your 2014 robot.

Going that fast will also impact power consumption during acceleration. I wonder what the peak current is.

19-08-2014 14:01

Bryce2471

Re: pic: New swerve CAD from 2471

Yeah, that would be an interesting experiment. It would be hard to do either, maybe I'll get back to you with those numbers after our next shop meeting on Wednesday. You're right about power consumption. Our bunny bot pulled way too many amps when accelerating, and would often have a dead battery by the end of the match. Our comp bot wasn't so bad, but a battery would die after about 7-8 min of heavy practice. I'm just glad that we did't have to deal with our main breaker tripping!

19-08-2014 14:16

Andrew Schreiber

Re: pic: New swerve CAD from 2471

Source on these absolute encoders @ $10 a pop?

20-08-2014 14:16

Bryce2471

Re: pic: New swerve CAD from 2471

I forgot to post the estimated weight. According to inventor, these modules will be over a pound lighter that last year's model: Weighing in at 6 lbs each.
Including all that is pictured except the bumper, the drive base should weigh about 30.5 lbs.

20-08-2014 16:46

Gdeaver

Re: pic: New swerve CAD from 2471

Absolute encoder. TT electronics 6127 series. .25 to 4.75 volt output. more like 11$ a piece. Used on our swerve for 3 years now. Like them.

20-08-2014 17:00

Bryce2471

Re: pic: New swerve CAD from 2471

Oops. I PMed Andrew about this, but I forgot it still looks like I left him hanging.

Yeah, we've used those encoders sense champs this year.

20-08-2014 17:03

Andrew Schreiber

Re: pic: New swerve CAD from 2471

Thanks, what's the rotate over point look like? Just a transition from high voltage to low? Can I simply map 0-360 to .25-4.75 and call it a day?

20-08-2014 17:07

Bryce2471

Re: pic: New swerve CAD from 2471

Yes, you can then call it a day. It's really simple to code, and we've found that the end behavior is surprisingly linear.

You can also get the flattened shaft version, so that set screws won't slip.

20-08-2014 17:08

Andrew Schreiber

Re: pic: New swerve CAD from 2471

Thank you, just saved me a a fair bit of money in encoders.

21-08-2014 13:01

seanthompson

Re: pic: New swerve CAD from 2471

Can you post the link to the encoders please?

21-08-2014 21:43

otherguy

Re: pic: New swerve CAD from 2471

my guess is they are talking about this part:
http://octopart.com/6127v1a360l.5fs-...ogies-19910150

There are a number of different options it can be ordered in, see data sheet

Note these are rated at 500 RPM in the datasheet. So they likely more than sufficient for monitoring the position of a part - like the wheel's heading in this case. Without proper gearing they are likely not a good choice for use on things like a shooter wheel. If you're looking to monitor wheel rate of travel over ground, these aren't appropriate unless you've got wheels bigger than 6" or have geared the encoder down (assuming you're targeting a top speed or around 14fps).

21-08-2014 21:47

Dale

Re: pic: New swerve CAD from 2471

Plus it's an analog output so in a high RPM application you'd be monitoring a saw tooth signal on the analog port.

03-11-2014 20:15

aaron_

Re: pic: New swerve CAD from 2471

Looks very cool! And yes, I assume they are using this part http://componentsearch.com/search/se...127V1A360L.5FS