04-19-2010 01:42 PM

Re: pic: 1671 Swerve Module

Slick! Care to answer some questions about your design? More specifically, why cantilever the belts, rather than put them inside the module? Also, I love the use of belts. When routed correctly, they outperform chain in both lifetime and torque transmission.

Also, a tip on top support crab modules: For FRC level contact, you might find yourself wanting more support on that top pivot. Even a single degree of deflection of the module makes you lose 90% of your contact patch on the ground...

04-19-2010 03:12 PM

steelerborn

Re: pic: 1671 Swerve Module

Thanks
I was actually thinking about putting the belt sprockets on the inside of the module. But I then thought that having them on the outside will allow easier access to the belts. We have never used belts before does it matter how easy they are to access?

04-19-2010 03:16 PM

martin417

Re: pic: 1671 Swerve Module

We used belts exclusively this year, and even though we had some slippage during shoving matches and bump crossings, we never had to replace a belt, and no visible wear occurred. So no, I don't think you need access.

04-19-2010 03:24 PM

steelerborn

Re: pic: 1671 Swerve Module

Okay, thank you guys.
I will modify the cad today it is a pretty quick fix.

04-19-2010 04:10 PM

Re: pic: 1671 Swerve Module

As long as it's properly tensioned, the system should be fine. However, properly tensioning and aligning belts can a bit of a dynamic situation when in FIRST. Constantly flexing frames can lead to sudden losses or gains in tension, unless you can design a quite rigid chassis.

I really dig the direction you're heading in, so keep it up! A Belt drive crab isn't common, and if you can pull it off it ought to yield some nice weight advantages.

04-19-2010 05:27 PM

steelerborn

Re: pic: 1671 Swerve Module

Yeah I have wanted to use belts for quite some time now. But we were nervous about starting it without testing so we waited for the offseason to come around.

Yeah a weight advantage is always good to have.

04-19-2010 06:39 PM

Jamie Kalb

Re: pic: 1671 Swerve Module

Looks nice! Is it based on the 118 swerve modules (or 221's "Revolution Modules")?

If you're going to run a swerve with belts, you should look into 1717's 2010 machine:



They might be able to give you some advice on it.

You said this is for an off-season project? Can't wait to see the final version(s)! Remember to post pictures, and good luck with it.

Edit: One more thing. For an off-season project, this probably won't matter, but for a competition robot, if you have the machining capabilities, time, and budget, you should probably replace those shaft collars with snaprings. Those setscrews have a nasty habit of coming loose at the worst possible times, and snaprings take up a heck of a lot less space and weight, too.

04-19-2010 06:56 PM

steelerborn

Re: pic: 1671 Swerve Module

Yeah I looked at the revolution first but wanted to change some things, mainly the use of chain.

1717 does have an awesome swerve I was talking to them about it at the la regional. Our overall base however is using 3 wd in place of the usual 4. So this cuts the weight of a whole module.

I will definitely look into that thanks for the tip.

And yes we will post more pics as time goes on.

04-19-2010 07:07 PM

Jamie Kalb

Re: pic: 1671 Swerve Module

Nice. Keep up the good work.

One more thing I just remembered. I can't tell from the picture, but do you have thrust bearings/bushings in place to distribute the thrust loads from those miter gears? Since the gears are working at an angle, there will be a significant thrust load along their axes. If you don't have a bearing/bushing in place to handle this, you can end up damaging parts very quickly. We found this out the hard way in our worm drive kicker gearbox this year. If you go to the 221 website and take a look at the close-ups of the Revolution (or download the CAD file), I believe you can see the thrust bushings implemented correctly.

04-19-2010 07:12 PM

steelerborn

Re: pic: 1671 Swerve Module

Yeah it is hard to tell from the picture, but yes there is bearings in place for that purpose. The angle makes it difficult to tell.

04-19-2010 07:15 PM

Chris is me

Re: pic: 1671 Swerve Module

Any thoughts on replacing the timing belt on the outside with gears, perhaps even with a slight reduction? I imagine that would be a little easier to maintain.

04-19-2010 07:23 PM

steelerborn

Re: pic: 1671 Swerve Module

Yeah I had looked into that too. I went and looked at 148's swerve system from 2008 (tumbleweed) they used gears on the outside too. But in the end I realized that it really wasn't the direction I wanted to head (light weight module). So I talked with my mentors and they brought up timing belts and showed me a great site for belt parts. But the module frame remained the same.

04-20-2010 02:21 AM

steelerborn

Re: pic: 1671 Swerve Module

Okay
I finished the changes on the module tonight and uploaded the new picture. It should be up soon. Thank you guys for all your help.

04-20-2010 08:49 AM

JesseK

Re: pic: 1671 Swerve Module

During 118's Crab Module Lecture in 2009, they suggested making the reduction after the miter gears as large as possible in order to reduce the amount of torque transferred through the miter gears. This prevented them from slipping under heavy load due to the slightest misalignment. It may also make the gearbox lighter since you might only need a single reduction coming out of it.