pic: Unique drive concept

[RogerR]

Originally Posted by Simon Strauss

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

those are 111 and 236, respectively.

[Scott Morgan]

Originally Posted by M. Krass

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

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.

[K.Porter]

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!

[Cuog]

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

[Joe G.]

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.

Originally Posted by Cuog

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

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

[zander_108]

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

[gburlison]

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.

[Jeremiah Johnson]

Originally Posted by gburlison

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.

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.

[AdamHeard]

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.

[Qbranch]

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

[Jeremiah Johnson]

Originally Posted by Qbranch

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

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

[Brandon Holley]

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.

[Qbranch]

Originally Posted by Brandon Holley

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.

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

-q

[Sean Schuff]

Originally Posted by Jonathan Norris

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...

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

[Joe G.]

Originally Posted by Brandon Holley

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.

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

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

That was the plan for turning.

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.

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: