pic: Unique drive concept
 

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That looks interesting......Can I assume the vertical 'big' CIM is used to turn the table for steering?

duh.....of course it is. I got to read your caption first. Please post any refinements. I'm going to bring this to my team's resident VEX expert for a prototype.

Shawn???? Are you reading this.

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I think that is how it works...

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thats really cool

I'm going to try that with VEX

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I'm not sure, but ball casters might have less friction than omniwheels

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we had a bad history with casters this year. i wouldn't recommend it. that design is sort of present in our 05 bot. its not multi directional http://www.chiefdelphi.com/media/photos/20299
it shows it with
ball casters but. later we switched them out with omnis and personally its my favorite bot to drive. its a great idea i might want to try that out.

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The Champion Lightning Bots of Team 2010 built a somewhat similar drive system this year, but instead of both drive modules on a single turntable, they were on separate pivot points driven by a Globe motor chained to them via a 2:1 sprocket reduction. When pointed straight ahead, the system was laid out the same as in your concept drawing. The four corners of the frame had ball casters instead of omniwheels. Each drive module had 180 degrees of rotation limited by potentiometer feedback.

2010 used 2 A-M traction wheels for their driven wheels, each of which was powered by a custom 2-CIM motor single speed transmission. The wheels were mounted 16" apart, center to center. It proved to be a very maneuverable and reliable design, although the casters did make it next to impossible for them to climb ramps.

The drive modules were inspired by those used on Team 48's 2002 robot. This style of module requires plenty of clearance for the motors to freely rotate.

2010's 2007 Drive Module

Steering Linkage Overhead View

Globe Motor Mounting

Drivetrain Side View

Your solution is definitely unique - If you decide to attempt to build it, best of luck attempting to solve its particular design challenges!

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Thats a really cool idea... I would also have to agree that ball casters would be a better idea then omni wheels.
My main concern with this idea is the torque required to move the center 'module', because most of your contact with the ground will come from those two middle wheels... and if they provide too much friction you may just end up turning the whole body of the robot. So instead of having a crab drive you have your robots body turreted.... with your center two wheels staying put...

To solve this you would have to either program the wheels to turn the direction your are trying to move the middle module, basically running the wheels in opposite directions helping the big CIM turn your center module. Or you may want to use omni wheels over the kit wheels...

This is defiantly something you would want to do some calculations and small prototyping to see if it would actually work, cool idea thou!

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Very interesting concept, a nice simplified swerve concept. I think I may also try and find the parts/money to try and test it with Vex (although the bushing around the base of the drive will probably be hard to reproduce, I might have to prototype it without it).
Some thoughts to consider:
As it stands, this drive will have difficulty climbing ramps/inclines/large(r) steps. When the leading set of wheels starts to go up the incline, the drive wheels will be lifted off the ground, and the bot will roll back down. If you added some form of suspension to the omnis, this could possibly fix the situation, but that increases the weight/complexity. It's really a game/strategy dependent decision.
You're going to have to consider your wire runs carefully (but that is true for pretty much any swerve).
It might not be possible, but it would save a considerable amount of chain (and space that cannot be used to mount because chain is there) if the steering motor is moved to the central support.

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What makes it so that the wheel bogey in the middle turns across the carpet rather than the frame rotating around the wheels?

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Yeah, I was thinking that omniwheels might be needed in the middle, but normal wheels are obviously preferable for traction reasons if it dosen't push backwards like you suggested. A prototype is really the only way to find out for sure. It'd probably have some programming compensation like you said too.

I agree with Lil' Lavery that ramp climbing is a problem, omniwheels or casters, but I have a few concepts to play around with for some kind of suspension.

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Last year when we were throwing around ideas for drivetrains and such, we came up with a concept similar to one drawn. We tossed it for the very reason that lavery posted, and also for the reason that if we ever got into a pushing match, the slightest bit of lift would lose it for us.

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almost as maneuverable as my off season idea; spherebot:)

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I think everyone else have covered most of the things about that base. The first thing that caught my eye was the 1x1 that is holding the powered module up. What is the thickness on that? Also... what is the thickness of the shaft that is coming out (going into that 1x1) to connect to the sprocket (in order to turn)? I am assuming its 1/2". Are you worried about that 1x1 bending/sheering? How much does it weigh as is in the picture?

Very interesting concept. I hope after some modifications on the drawing you will be able to manufacture this and share the outcomes. Good luck.

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http://www.firstroboticscanada.org/site/node/372

http://www.firstroboticscanada.org/site/node/323

Im guessing you already knew about these when comming up with the design, but my advice is to try to contact whoever did these and discuss the pro's and con's with them.

There used to be more pictures of similar drive methods but they seem to have been lost when waterloo moved all its info to FIRSTroboticsCanada

-Simon

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those are 111 and 236, respectively.

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I designed a concept system similar to this a few years ago. I addressed this problems with the inclusion of traction plates, operated by pneumatics. This plates would drop down and restrict the movement of the outer frame when you rotated the turntable.

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Wow! you just designed what 172 imagined and prototyped earlier this season (but got nowhere with...)
Early in the design stage, we were experimenting with drive train ideas. What we ended up with were independent drive sections that could pivot to climb ramps, but we thought, what if we went further than that: what if the independent drive sections could turn independently as well, much like the front yoke on a toy wagon.

We coined this type of swerve drive as "Little Red Wagon Drive" and basically mulled it over in the background while this year's robot was built. We even got as far as building a Vex prototype (although it isn't documented as far as I know of, and it has probably been disassembled by now)

The main difference between Little Red Wagon drive and your design is the placement of the pivot. Instead of having the turntable on the middle, it would be located in the front of the robot, with casters (or omnis) supporting the back. The pivoting drive section in front would simply pull the rest of the robot along, much like, well, a wagon (or almost like a front wheel drive automobile)

If I can find any pictures of our vex prototype, I will be sure to post them. I'm sure everyone at 172 would be happy to see our pet design project actually get somewhere, even if it is designed and built by a team elsewhere!

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If you were to power your omniwheels then that would give you the ability to fully control the rotation of the robot.

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Thanks for all the feedback!

I'll probably be building a full scale prototype early this summer once all our offseason events are done. Right now I'm working on an improved CAD verison.

Some improvements:

-Better turret support
-lighter
-Central platform can move vertically downward 2.5 inches via spring if it is lifted off the ground, solving the pushing problem and allowing it to climb ramps to some degree.

You already can, just drive the left and right middle wheels in opposite directions and hold the turret control motor still.

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I had been thinking up a very similar plan earlier this season.. Its cool I'm not the only one with these kind of ideas

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We built a similar design for ZONE ZEAL (2002?). The biggest difference was that a pivot was not powered by a separate motor. There was a stop and the turn table would only turn 180 degrees and a potentiometer to read the rotation angle. The drive wheels were used to turn the pivot. We used 1 joystick tank drive and if you wanted to turn left, you would move the joystik to the left. the software would drive the right motor forward and the left motor backward until the potentiometer indicated that the turntable was pointing left. Of course forward would drive it forward and back would drive it backward. We used ball casters on the corners. I will see if I can find some pictures, but it was probably our worst design as a whole so it may take me awhile to dig them up.

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I remember that robot and was going to mention something about it, yet I didn't know what team's robot it was. You're right, it wasn't very effective that year as powerful drives were needed and that design doesn't offer much in the way of power.

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So far, this is pretty interesting...

I'm still wondering what advantages and disadvantages exists in comparison to a traditional (if you can call them that) crab/swerve drives.

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My partner and I built a drive system extremely close to this for an AGV to transport materials throughout our factory. The only difference is, ours used a central turntable with driven 'casters' on all four sides linked by a timing belt.

Eventually we scrapped the idea since the robot drifted slightly off of square with the building and could not correct its body angle... the only thing it could do is move in different directions.

Have you prototyped this? Can it turn by some method i'm not seeing? If it works like I think it does, I have a suggestion that might let you turn...

-q

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You should be able to turn the chassis by tanking the two drive motors on the turntable... but that's in theory of course.

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ditch the turntable motor...add somesort of 'brake' or 'lock' to "lock" the turntable in 1 direction.

now just turn the right wheel forward and the left backward or vice versa and the turntable spins itself.


save yourself the weight and complexity of another motor.

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DING DING DING! *game show music* thats what we came up with too. ;)

-q

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Something about this design puzzled me until the aforementioned post appeared. The middle wheel module would have to be fairly free of friction relative to the frame in order to turn within the frame. This would allow the center drive module to turn in nearly any direction and provide movement in that direction. Great concept! However, what if you want the whole robot to turn? You would need to create friction between the the center drive module and the rest of the frame. I'm assuming that comes from holding the drive module in place relative to the frame and running the drive wheels in opposite directions. Is my assumption correct?

To echo what Sean said about high-siding the drive wheels - make sure the challenge does not require ramp-climbing of ANY kind. Even the shallowest of inclines will render your robot immobile. We experienced this challenge during this year's competition. I beg all teams to consider how to be most accomodating and complementary when designing a robot that interacts with another robot on your alliance - i.e. climbing ramps to score 15 or 30 points.

Another factor to consider with this design is when your robot gets into pushing matches - if your robot is lifted up even slightly on one end you will be at the mercy of your opponent.

I really like the idea - with some tweaking I think it could be a great design!

Sean

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Great idea, i'll experiment with this when I make a prototype.

That was the plan for turning.

The redesign has a feature that should compensate for this. The turret looks something like this now.

The spring (if gravity isn't enough) will push the center platform down up to 3 inches when lifted off the ground by ramp or defensive robot The result will look like this:

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This may also require that the turreting mechanism be able to pivot relative to the frame, as well -- and the diameter of your turntable will still considerably limit the maximum angle you can climb.

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how about adding the suspension to the omniwheels at the corner.....saves some complexity dont you think?...

just give yourself enough ground clearance with the frame

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I know that a lot of robots that have crab drives or omni wheels can be moved rather easily, but how easily do you think this could be pushed around?

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Crab drives are much harder to push than omni wheeled drives. (Just ask 118 and 469.) It's a crab, so I don't see much of a problem with it holding its ground. Then again, it might decide to run away and go around the defense.

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This is between a crab and omni drive. It's only got one crab "module" so it would be easy to push for the most part, especially if any of the robot were lifted slightly.

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This has no less traction than a regular 2 wheel skid steer

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Bad news buddy: Team 240 did something almost exactly like that in Aim High, Triple Play, and according to alumni, almost every year since the team was founded. The only difference is the pivot point was the drivetrain end (front or back, didn't matter) and to do a 180 would swing the entire robot around.
What you're suggesting, if you think about it, will just make the robot do drifts. All. Day. Long.