254 Gearbox Analysis

[craigboez]

Always great innovators, the Cheesy Poofs did not disappoint last year. Their 2010 effort was an outstanding one, and I've decided to put togther a case study and present it to my team in preparation for the upcoming season. In doing I realized just how great their gearbox was and thought I'd share and also try to collaboratively reverse engineer it.

Basic Overview
http://www.team254.com/media/photos/...e=orig&id=4247

They advertise this as a two speed transmission, running at 5 and 15 fps, which strangely has two shifting cylinders. It was part of an 8-wheel drive robot, with one wheel per side direct drive and three more driven by the pictured sprockets. The truly unique feature is the Power Take Off (PTO) that they used to power their lift mechanism. Under normal operation the gearboxes would power the drivetrain. Under PTO mode those motors were repurposed for lifting the robot. Very successfully I might add. Check out the end of this clip:
http://www.thebluealliance.net/tbatv/match/2010sj_f1m1

I wasn't able to uncover any great pics of the PTO mechanism, but this side view clearly shows a pneumatic cylinder that would appear to be the toggle mechanism.
http://www.team254.com/media/photos/...e=orig&id=3139
EDIT: This appears to be a false assumption

You can see an upper sprocket in this pic, a top view. This is presumably used to drive a chain that powered their lifter. There does not appear to be a dog gear so I'm unsure how they so reliably transferred power from one output shaft to another. Anybody know?
http://www.team254.com/media/photos/...e=orig&id=4249

Also, what is this clutch for? It looks like a small slip clutch, maybe used to limit torque?
EDIT: This is a different gearbox from the pictures above. This was used to power the roller/ball collector mechanism.
http://www.team254.com/media/photos/...e=orig&id=4251

[Dillon Carey]

I believe the last picture is the setup for their ball accumulator. A lot of teams last year that had pinch roller setups used some sort of clutch to keep constant pressure on an acquired ball and not burn out a motor.

[Vikesrock]

Originally Posted by craigboez

In doing I realized just how great their gearbox was and thought I'd share and also try to collaboratively reverse engineer it.

This may be a stupid question, but did you try going straight to the source with any specific questions you had? One of the great things about FIRST is most teams are willing to share if you're willing to ask.

[Chris is me]

I was able to learn anything I wanted about the gearbox by just asking them in Atlanta. Reverse engineering is fun, but it's easier to learn about the decisions that went into these robots from the source, really.

[Cyberphil]

Having asked 254 direct questions myself, I am sure they would more than glad to explain this mechanism to you! They are an amazing team, and always create a dominating robot because of designs like this.

[ajlapp]

I think the last photo is a release for a ratchet system......this would stop the lift mechanism from back driving.

The first photo shows the two separate dog shifters. I believe those are three position air cylinders.

[craigboez]

I'm sure all the members of 254 are very helpful, I just don't happen to know any of them. This public forum that they most likely check frequently seemed like a good place to start a discussion. Plus then everyone gets to benefit from this, not just me.

After looking at this further, I think a few of my initial assumptions were incorrect. It would appear that the "lower" dog plays the role of speed changer and the "upper" dog serves to engage or disengage the PTO. At first I thought both of those were part of the speed changing equipment. That accounts for two of the three pneumatic cylinders. I am still unsure of what the third, larger pneumatic cylinder is used for.

The first photo shows the two separate dog shifters. I believe those are three position air cylinders.

I'd agree. It looks to be a Bimba FOP style cylinder. Reference page 2.35 of this PDF: http://bimba.com/pdf/catalogs/FL_FlatCylinders.pdf

I believe the last picture is the setup for their ball accumulator. A lot of teams last year that had pinch roller setups used some sort of clutch to keep constant pressure on an acquired ball and not burn out a motor.

I'd agree. This bot has several gearboxes and they all look alike, so I confused the ball collector gearbox with the drivetrain/PTO gearbox.

[NickE]

Craigboez,

I'm Nick and I'm the design/build captain from Team 254. Thanks for the kind words about our design and we'd be thrilled to talk to you more about it. Everything you've posted about our robot seems accurate but if you have any questions, feel free to contact us and we'll try our best to answer them. My email is on our team website or you can contact me via PM or in this thread.

Nick

[Brandon Holley]

Originally Posted by craigboez

That accounts for two of the three pneumatic cylinders. I am still unsure of what the third, larger pneumatic cylinder is used for.

I'm pretty sure the 3rd cylinder you are referring to is the release for the pawl on their ratchet system used in the PTO.

-Brando