pic: drivetrain idea (comments please)



A simple design for a drivetrain. The frame is 1x2 aluminum stock. I’m also thinking of using ifi traction wheels for the center wheels. I’ve lowered the center wheels 1/16 of an inch, is that a good amount?
Any other comments welcomed and appreciated.

looks very similar to what 1712 did last year …
http://www.chiefdelphi.com/media/photos/29579
1/8" was the center wheel drop we settled on and we were very happy about the performance of our drive train. Some say 1/16" may not be enough drop, but I’ve never actually seen it to verify.

I’m assuming you mean 1x2 aluminum extrusion. 1/16" or 1/8" wall thickness? Is it all rectangular extrusion, or is some of that C channel (I can’t tell from the picture). How is it fastened together?

As for the driveline, what do the chain runs look like, how are they tensioned?

What’s your final gear reduction off the tranny?

It’s 1/8 in wall thickness, all rectangular extrusion, and it’s welded together. (is C channel stong enough to replace some of it with.) My idea for the chain run was to have one chain around the rear and middle wheels and the gearbox sprocket on the inside of the wheels. With another chain going up to the front from the middle wheel on the outside. Not sure how its tensioned jet.

For us 1/8in drop has worked very well though 1/16in was never attempted.

Questions: will you be supporting your toughbox further or is that it. second why use such a big sprocket when you can use a much smaller one

side note: this will only be the second time that we have used wheels (we have used tracks) and are still new to wheels.

It will use the same mount that came in last years kit, a diagonal support. the sprockets are mostly for looks and the gear ratio will depend on our strategy in the next game.

We used c-channel last year and it was plenty strong. we also only used angle stock on the ends and plywood as a base to provide lateral strength.

We had no problems except a pent angle stock in the front from the collisions but it was no big deal with the plywood behind it.

If you have the machining capabilities and if you are going to use 1/8 inch tubes, look at loosing weight by drilling holes or pocketing by cncing. Weight matters and the drivetrain looks pretty nice. I’ll get back to you on the tensioners, I have some in the making right now.

What!? No more treads!? Blasphemy! :ahh:

I’ll admit the ol’ 753 design didn’t seem to help teams 997 or 668 this year, but they’ve won lots of regionals over the years…

As for the drop, I’ve found that 0" with two omnis works best… But that’s just me :wink:

Yeah, the tracks didn’t help 997, we bearly lost at Davis. The two omni’s in the front works really well and the 1024, the Kilabytes, had a lot of success this season with it. The only thing is with omni’s is that you lose a tad bit of pushing power. If you want to do the drop with 6 traction wheels, every drivetrain is different. So different drops are needed. But the general idea is that only 4 wheels touch the ground at one point in time. If you want the drop to be adjustable, try this:
http://inlinethumb16.webshots.com/43791/2885144470103728295S500x500Q85.jpg](http://good-times.webshots.com/photo/2885144470103728295YvhZiF)
It worked really well on our offseason robot. The top is CNC’ed into the frame and the second part bolts on.

If you use center traction wheels. Definitly make sure that your outer wheels will slide. Like omni…

As long as your frame is stiff, you will be perfectly fine with 1/8" drop. You can use 6 traction wheels with this and you will be able to turn well and have great pushing power. If you want to use omni wheels then you do not want any drop at all. I am a fan of all traction wheels for more power and so that all of the wheels are the same for replacing them if something goes wrong. Either way you go just remember it is either a drop of the center wheel with all traction wheels or omnis with no drop, never both.

1/8" is a pretty standard drop, and should drive just fine. I also echo the recommendation to us C channel where you can to save weight. The front and the back rails are especially good candidates for that, and you could also use them on the inner driveline rails if you do it right.

If you have the capability, direct drive to one of the wheel pairs (typically the center pair) is a great option. I don’t know if you can do that with the KOP gearboxes, but one less chain means less weight, and also ensures that you can still drive, even if you throw all your chains.

Are you planning on running the chain between the middle and rear wheel then up and over the tranny? If so, I would be concerned about the chain wrap on the transmission gear and how much tension you’ll need to keep it from skipping. That looks like maybe 60 degrees of wrap.

I would also agree that directly driving the center wheel if at all possible is the best solution. As has been said even in some extreme case that you throw every chain, you will still be mobile and able to play the game. Also with this extra safety, you can run#25 chain or even timing belt without worrying that if one breaks you will be immobile. As far as using the kitbox in direct drive it can be as simple as having a new output shaft fabricated and making a hub for the center wheel or you could fab up completely new plates and only retain the gears form the kit transmission. Either way it is relatively easy to do and I would be willing to show you some designs I have done using kit stuff. Also I’m sure you could find a machine shop to fab up a new output shaft to keep cost down.

IMO if you’re expecting to break #25 chain you are doing something wrong :ahh:

Aside from the fact that even with 3 chains at least one wheel will always be powered if one chain breaks (I can attest to this having happened ;)).

Most of the off-the-shelf gearboxes (with the exception of the AM SS) require a second reduction after the gearbox, especially with 6" wheels. A second reduction will also allow you to “tune” your speed.

Just my 100 sense.

I would recommend running your chain like so:


] = wheel
s = sprocket
c = chain

]s
  c
  ss  (GEARBOX HERE)
   c
]ss
  c
  c
  c
]s

Like so:

http://andyburchardt.com/robotics_renders/KTK%20Drive%201.jpg

I never expect to break a #25 chain in the drivetrain and in fact we ran the entire season without ever having to replace the drive chains. However, for some people who seem to still be shy about using #25 chain and reaping the great weight savings, using it in a drivetrain where the center wheels are directly driven gives an even greater incentive to use the lighter chain.

#25 chain is more sensitive to proper tensioning. #35 allows teams to be really sloppy and still quite effective.

As to the original question: I like the idea, very similar to our 2007 robot. We used a kitbot frame with a second level of frame at the height of the top of the wheels, primarily to get a flat platform.

Your implementation seems somewhat heavier than necessary. The inner rail doesn’t add much strength, it can be 1/16" wall, while the outer rail will take a beating, count on bumpers to stiffen it and lend impact resistance.

You also need to consider cross-rails from outer to inner rail, and again from one inner rail to the other - that way, an impact’s force is transmitted to all four elements, not just the one impacted.

If you can mount the gearboxes lower - gotta think about the sprocket wrap - you can end up with a flat (or nearly so) platform over which your manipulator can be built.

Don