pic: New Drive System for 703

[Cowmankoza]

Upon looking at the design again (I still love it), my only concern is the side panels, are they lexan? I'm just worried abotu a side hard impact shattering them and leaving gears all over the field. But good luck to you guys!

[Guy Davidson]

That's a problem easily negated by bumpers.

-Guy

[Alex Cormier]

Originally Posted by Cowmankoza

Upon looking at the design again (I still love it), my only concern is the side panels, are they lexan? I'm just worried abotu a side hard impact shattering them and leaving gears all over the field. But good luck to you guys!

1126 has in the past few years used around 1/4" lexan for the sides. It saves weight and is very nice. You just need to use it proper like chain, there must be support in the proper places.

[Eric Scheuing]

Do you guys have a CAD team? I feel bad for whoever has to make that. Design Accelerator FTW.

[Lil' Lavery]

So many people have asked why, and I'll try and elaborate on what Billfred and the members of 703 have said.
This design effectively emulates many positive features of a treaded drive system, as well as eliminates some of the negatives of chain and belt driven drives. The close proximity of the wheels allows for the robot to have a very, very, low ground clearance and still have the ability to climb ramps, steps, and platforms without bottoming out or high centering. The greater quantity of wheels creates more contact area with the ground, which in turn allows for a more even distribution of weight (although, still not nearly as well as a tread in this respect). The fact that all 14 wheels are driven allows for any wheels to lose contact with the ground (such as when traveling up an incline) and for the robot to still have the ability to drive. The use of intermediate idler gears instead of chain or belting eliminates the risk of the chain/belting popping off or slipping. It also may have actually saved weight depending on the size of the sprocket/pulleys and the chain run (if they would have chosen a "staggered" chain run, so that a single chain failure doesn't result in the failure of the whole side of the drive, it probably would have weighed much more than the gears).
There are some cons to this drive system as well. Spur gears are slightly less efficient than chain (not by much though), but so many gears magnifies that slightly. Additionally, while failures should be far less often, if/when they do occur, it is likely to be far more spectacular and require probably a more complex fix than if they had used chain or belting (although, once again, this design was chosen to try and make sure failures wouldn't occur). Additionally, the 14 wheels themselves are far heavier than the 4 or 6 pulleys they would have likely used in a tread drive.

[cbale2000]

Originally Posted by Cowmankoza

Upon looking at the design again (I still love it), my only concern is the side panels, are they lexan? I'm just worried abotu a side hard impact shattering them and leaving gears all over the field. But good luck to you guys!

We do plan on using Bumpers this year (much to my dismay) I just hope they don't interfere with robot operations like I saw some did in last years game.

Originally Posted by Eric Scheuing

Do you guys have a CAD team? I feel bad for whoever has to make that. Design Accelerator FTW.

We don't really use CAD that much (We help design it but our mentors tend to handle making the blueprints of the parts). We've modeled our robots in Inventor before but it's usually just for the sake of doing it (though we have found it useful when trying to make an animation).

Originally Posted by Lil' Lavery

So many people have asked why, and I'll try and elaborate on what Billfred and the members of 703 have said.
This design effectively emulates many positive features of a treaded drive system, as well as eliminates some of the negatives of chain and belt driven drives. The close proximity of the wheels allows for the robot to have a very, very, low ground clearance and still have the ability to climb ramps, steps, and platforms without bottoming out or high centering. The greater quantity of wheels creates more contact area with the ground, which in turn allows for a more even distribution of weight (although, still not nearly as well as a tread in this respect). The fact that all 14 wheels are driven allows for any wheels to lose contact with the ground (such as when traveling up an incline) and for the robot to still have the ability to drive. The use of intermediate idler gears instead of chain or belting eliminates the risk of the chain/belting popping off or slipping. It also may have actually saved weight depending on the size of the sprocket/pulleys and the chain run (if you they would have chosen a "staggered" chain run, so that a single chain failure doesn't result in the failure of the whole side of the drive, it probably would have weighed much more than the gears).
There are some cons to this drive system as well. Spur gears are slightly less efficient than chain (not by much though), but so many gears magnifies that slightly. Additionally, while failures should be far less often, if/when they do occur, it is likely to be far more spectacular and require probably a more complex fix than if they had used chain or belting (although, once again, this design was chosen to try and make sure failures wouldn't occur). Additionally, the 14 wheels themselves are far heavier than the 4 or 6 pulleys they would have likely used in a tread drive.

You're right on there, couldn't have put it better myself.


I will just add though, we figure if a single wheel came off, we have each wheel independently connected to the chassis using easy to remove pins, so if something happened to one wheel, all we have to do is pop another one in. Now if something major did happen and we lost a whole side it probably wouldn't be any harder than replacing a tread as it would require nearly the same actions to do.
Every year we get progressively better at making the robot fast to repair, this year will probably see fastest repairs we've made yet.

[LWS]

A good bit of the discussion seems centered on how effective the design is in getting all of those wheels to work (e.g. no chains, etc). The real question it seems is, why have all of those wheels? The only effective answer I have seen so far is to avoid "high centering" when going up ramps.

The common response to all of those wheels is "they would give lots of traction". But will this approach be more effective in doing so than one with fewer wheels? The simple model of friction (which is what traction really is) states that maximum friction force is the coefficient of friction multiplied by the normal force (i.e. the weight pushing down on the wheels). The coefficient is a function of the material of the wheel and the carpet. Assuming that there is a given weight for the robot, this weight would be distributed over the wheels, and if there were more wheels, there is less weight per wheel.

The short story is that adding more wheels in this case does not add more traction. The fallacy that it would comes from the "outdoor scenario", where terrain may have low coefficients of friction (e.g. snow). The idea here is that more drive wheels can avoid the situation where wheels slip, and the friction coefficient lessens (going from static to kinetic friction).

Wikipedia has more info for those interested.
http://en.wikipedia.org/wiki/Friction

[EricH]

Originally Posted by LWS

A good bit of the discussion seems centered on how effective the design is in getting all of those wheels to work (e.g. no chains, etc). The real question it seems is, why have all of those wheels? The only effective answer I have seen so far is to avoid "high centering" when going up ramps.

The common response to all of those wheels is "they would give lots of traction". But will this approach be more effective in doing so than one with fewer wheels? The simple model of friction (which is what traction really is) states that maximum friction force is the coefficient of friction multiplied by the normal force (i.e. the weight pushing down on the wheels). The coefficient is a function of the material of the wheel and the carpet. Assuming that there is a given weight for the robot, this weight would be distributed over the wheels, and if there were more wheels, there is less weight per wheel.

The real reason is that the team wanted a treaded robot without the treads. (As in, the best points of both wheel and tread systems.) We shall see whether they succeeded or not when they compete.

[Lil' Lavery]

Originally Posted by LWS

A good bit of the discussion seems centered on how effective the design is in getting all of those wheels to work (e.g. no chains, etc). The real question it seems is, why have all of those wheels? The only effective answer I have seen so far is to avoid "high centering" when going up ramps.
[/url]

Don't forget lesser weight (and a more even distribution of weight) on each wheel. This means that less force passes through each wheel, meaning a lesser chance of failure (especially of items such as treads...or the carpet they touch).