Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I'm more comparing the xbox design which only utilize two motors and doesn't shift or have a reverse gear. It weighed 90 lbs. Yes I know the robot they show was a prototype and a lot of weight can be reduces out of the other materials. I thought there drivetrain in general was very nice in design. Four more motors and the gearing to join them, a multi-speed option, and a reverse gear would add weight on top of being centralized and being a swerve drive. I think a good design would be about equal to or maybe even a little less than using multiple gearboxes. I just don't see a large enough benefit for the complexities added in having both a centralized drive and centralized steering.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I would look at this question from an overall robot design standpoint... If you have one huge (relatively) gearbox in the center of your robot, thats going to limit you on your ability to integrate your mechanisms into the robot, espescially an arm with a wide degree of freedom. If you do the two seperate transmissions route, you leave the entire center of your robot free for whatever you see fit. If you look around, there are a lot of evolving 'drive module' designs that have the entire drive sections of the robot all compact in thier own self supporting 5" wide (sometimes even smaller) sections on the outside of the robot. Also something to care about, having that big gearbox in the middle of the robot could require you to raise anything else that would typically go down the center of your bot and drastically raise your CoG.


If you are using steel shafts, the weight adds up extremely quickly. A full robot lenght shaft would also need to be very supported into your robot, and to have one for each set of wheels, that is a whole lot of weight. Check into the bending moment on shafts that long, and then to have it be a powered drive shaft.... you get the idea. Having just 4x 5 inch non-powered wheel supporting shafts is a big advantage in the weight saving department.


Adding a shifter into a gearbox should probably not require many extra shafts than you would normally have. Just the one shifter shaft which you will need in a unified gearbox anyway. If you are adding a lot of extra, you may want to check your gearing layout. Having 2 individual shifting pistons doesn't mean you will use a lot of air. This year on our fall drive base and competition robot we used 2 individual 1/2" throw 3/4" bore pnuematics and were about to shift about 35 times conservatively. No onbaord compressor was ever required. Even if you had 2 1" throw pistons, are you really going to be shifting that much in a single match?


On top of just added weight, thats 7 motors minimum you are looking at into just your drive. You need to remember the wonderful rules of power distribution, and make sure you have acceptable motors for the rest of your mechanisms. The turning motor will need its own gearbox also and shafts/chain to make it to all 4 wheels. A reversing gear would require another extra shaft and ultimately, more weight. Wheel support is not something you should go lightly on. I know in 2002 some teams who lifted goals ended up paying for it in the long run when thier wheels bowed outward after a few competitions.
In all, do you think the added complexity and weight are worth it? Not to mention the array of extra parts that will need to be designed and fabricated.