pic: Drivetrain Concept

[crazyStone]

Yes you are correct, it is based off of 148 modules from this year. The original design had the switching transmissions within the wheel modules but due to difficulties with mantaince and access the design was changed to allow the switching transmission to be completely independent of the modules. The drive is a 4 wheel traction on the outside and then 4 trick omni's on the insides of the modules. Then a chain is linked from the inner transmission to the shaft that the traction wheel is attached to. The switching transmissions drop right out of the bottom for easy exchange. Besides that the gear ratios are rather extreme, the low gear to traction is 1:40 and then omnis are 1:20 and the high gear for traction is 1:8 and the high for omni is 1:4. These should faciaity major pushing power. Any comments would be appreciated. Perhaps someone has already created such a drivetrain in which case I apoligize for that but I did not see any other similiar drivetrains besides 148 as the base.

[JesseK]

I do believe that the 4 pneumatic cylinder towers will act more like a shock absorption system when the robot is fully loaded with all of the weight, since air compresses. ~26lbs (60psi) of force per cylinder * 8 cylinders is ~208lbs of to lift the whole thing -- slowing down from high speed may cause an inertial moment that can overcome the 104lbs on the front/rear. This most likely wouldn't be a problem until both wheels of a single module touch the ground. At that point, something's going to rip itself apart (most likely the belt connecting the two wheels).

I believe that's why 148 uses leverage to articulate their modules. It puts the weight of the robot on a pivot rather than directly on the pneumatic cylinder. This reduces the shocks, inertial moments, etc that the cylinder experiences. It also reduces the number of cylinders required to articulate the drive train, thus reducing its weight.

You could also combine each gearbox on each side -- there's no reason to have 4 independent gearboxes since its controlled exactly like a skid steer with high/low gears.

[crazyStone]

Yes, Thank you for that advice, the interia is something that definitly will play a key factor. The choice for the smaller pistons was the fact they use less air then a single large piston. Also the individiual transmissions are used because of the slight boost in efficency and the ease of replacement and custom gearing ratios. However if we encounter difficulties with manufacturing custom gearboxes each side will recieve one AndyMark SuperShifter and that will slide in from the bottom.

[lemiant]

Why would you switch from traction wheels to omni's? All other versions of this I have seen switched to mecanums. Also I recommend taking Jesse's advice; this drive is already hard enough, unless you're wildstang I'd try to add as much simplicity as possibly. (Wildstang would also go for simplicity, not because they have to, but because they understand it's importance, hence their awesomeness)

[crazyStone]

Originally Posted by lemiant

Why would you switch from traction wheels to omni's? All other versions of this I have seen switched to mecanums.

148's drivetrain "nonadrive" is the base for this design, and they were pretty successful with using the traction and omni. Yes it can be simplified and it will be simplified but its more fun on cad to design it from scratch when you have the time, and gives good practice instead of just dropping in a STEP. file. Your advice on simplicity is appreciated, the design has been improved to allow much easier access to the modules. Since before the transmissions were IN the switching modules and that would have put a lot of stress on the metal frame of the modules.

http://www.youtube.com/watch?v=RkR3GezFP14

[lemiant]

Originally Posted by crazyStone

148's drivetrain "nonadrive" is the base for this design, and they were pretty successful with using the traction and omni. Yes it can be simplified and it will be simplified but its more fun on cad to design it from scratch when you have the time, and gives good practice instead of just dropping in a STEP. file. Your advice on simplicity is appreciated, the design has been improved to allow much easier access to the modules. Since before the transmissions were IN the switching modules and that would have put a lot of stress on the metal frame of the modules.

http://www.youtube.com/watch?v=RkR3GezFP14

With Nona drive though, there was a 9th omni wheel perpendicular to the other 8 (hence nona). This allowed 148 to strafe. Seeing as it's just for fun, then go right ahead, I just wanted to check that you knew what you were getting into.

Also, nice video

[Aren Siekmeier]

Doing this all from scratch will definitely give you lots of great CAD practice. While people are mostly critiquing the design itself here, the model looks good.

As for the design, yes 148 had their "nonadrive" again this year, but it wasn't really. They removed the sideways omni wheel in the center that gave them omnidirectional capabilities because (I think) of the way their driver liked to do things. So this drive train will not be able to strafe unless you swap in mecanums or add a sideways omni wheel (or do something else).

If you're going to have the gearboxes offboard, you really should combine each side. You will have half the gears and half the pneumatics, and you can use standard Super Shifters which make it waaaaaaaay easier to change ratios. Unless you go with mechanums. Then you need to drive each wheel separately.

[Hawiian Cadder]

Originally Posted by compwiztobe

Doing this all from scratch will definitely give you lots of great CAD practice. While people are mostly critiquing the design itself here, the model looks good.

As for the design, yes 148 had their "nonadrive" again this year, but it wasn't really. They removed the sideways omni wheel in the center that gave them omnidirectional capabilities because (I think) of the way their driver liked to do things. So this drive train will not be able to strafe unless you swap in mecanums or add a sideways omni wheel (or do something else).

If you're going to have the gearboxes offboard, you really should combine each side. You will have half the gears and half the pneumatics, and you can use standard Super Shifters which make it waaaaaaaay easier to change ratios. Unless you go with mechanums. Then you need to drive each wheel separately.

right, but their driver was able to sort of drift, which made it one of the fastest robots in turning around to place tubes.

[Aren Siekmeier]

Originally Posted by Hawiian Cadder

right, but their driver was able to sort of drift, which made it one of the fastest robots in turning around to place tubes.

Yeah, like a power slide.

[Andrew Remmers]

If I'm not mistaken couldn't this also be a 4 speed shifter?

With the two ratios on the gearbox than then the two different ratios given on the wheel sizes and reductions (don't know if they are synced)....

Thats. Insane. I like it!

- Andrew

[crazyStone]

Just realized there was a mistake in the design concerning which Supershifter drove which side. A redesign is nessecary and taking place and should clear up some of the issues of the 2 transmissions. We are now attempting to link both front modules to one supershifter and both back modules to the other. Instead of the linking front and back on each side like it is now.

[lemiant]

Originally Posted by crazyStone

Just realized there was a mistake in the design concerning which Supershifter drove which side. A redesign is nessecary and taking place and should clear up some of the issues of the 2 transmissions. We are now attempting to link both front modules to one supershifter and both back modules to the other. Instead of the linking front and back on each side like it is now.

If I understand this right you're switching from this linkage:

<front>
o o
| |
o o

to this:

<front>
o-o

o-o

If that is the case you won't be able to turn.

[crazyStone]

good point which represents the reasoning behind having 4 gearboxes. You limit mobility if you restrict the ways you can turn if you link front and back together.