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Unread 03-08-2010, 13:12
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Re: pic: Crab Module

I've just posted as a picture drawings of our 2010 pivot design. As Foster points out, these pivots have been through 6 competitions, 4 extended demonstrations and a lot of practice driving. The design has held up to abuse extremely well. Our 2010 robot was our team's first pivot bot. Being pushed or rammed sideways is no problem.

We began this design process last summer, so if you are looking to be able to use this next year, your timing is right. We started with a VEX-scale prototype (mounting a cRIO) on which we did motion-control and software development. Then went on to documenting the driving math. Finally we started designing pivots using Inventor. We went though 6 major and more minor revisions before we were ready to build.

I'd recommend that the transfer axle (flanged ball) bearings press in from the inside of the assembly, not the outside. As shown, they are likely to come out (in fact be pushed out on the gear side).

We used thrust bearings to take the axial loadings developed by the miter gears. Each of our miter gears is backed by a thrust bearing.

This allowed the use of roller bearings for the coaxial drive shaft. Since the roller bearings have a smaller OD than ball bearing races, we were able to keep the pivot tube 1" OD.

We also used a thrust bearing to bear the load of the robot on the pivot's top.

Hope this helps.
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Unread 03-08-2010, 20:00
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Re: pic: Crab Module

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Originally Posted by Chris is me View Post
why not just buy modules from them?
Cost, for one. Our labor is free (that makes us robot slaves, right? )

No sin in copying an excellent design. Different for the sake of different isn't necessarily better.
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Unread 03-08-2010, 21:05
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Re: pic: Crab Module

Quote:
this looks exactly like the 221 module
One of the primary reasons for the similarity is because I do not fully understand how many coaxial swerve modules are mounted. I recently figured out how to mount a module to a chassis because of their drawings.

JesseK, thank you very much for linking that presentation. I found it quite helpful. I expect that I shall be looking at other presentations from that website in the future.

Unfortunately, my team would probably be unable to produce such a module next season due to our lack of manufacturing resources (we currently have 2 drill presses and a band saw). However, we should be able to in later years once we update our shop with money from a grant.
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Unread 04-08-2010, 08:27
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Re: pic: Crab Module

Quote:
Originally Posted by Team2374 View Post
Unfortunately, my team would probably be unable to produce such a module next season due to our lack of manufacturing resources (we currently have 2 drill presses and a band saw). However, we should be able to in later years once we update our shop with money from a grant.
There is plenty of time between now and next season. Look around your area and see if you can establish a relationship with a machine shop nearby. Even if you don't use them to build a crab module, at least you will be adding a resource.

-Brando
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