pic: Spectrum Fall 2013 Drivetrain

[AllenGregoryIV]

Originally Posted by DampRobot

I'm a skeptic. Why should I like geared drivetrains?

At least in my mind, a timing belt drivetrain is both lighter and more efficient, and a chain drive is much easier to build and quicker to fix. I do see that chains and belts becoming de-tensioned is a disadvantage, but the solution to this is a cam or exact c-c system. Is there some specific advantage that gears offer over belts or chain that can't be attained in either system?

I can't tell you why you should like it but I can tell you what's attractive to us.

Off The Shelf Parts
Outside of the sheet metal which we get produced by our sponsor, every piece in this is off the shelf and can be assembled with little to no modification. Nothing requires a lathe or a mill. Seeing as we don't have access to either (yet), this is an important feature. It's currently near impossible to meet this requirement with belts.

Narrow
The new robot dimensions (assuming they stick around) make the standard kit bot way of doing chains seem really large, the kit bot or VEXpro drive in a day are good examples. For reference those are the types of drives we have used before. A WCD might be a bit thinner but we don't have milling and welding resources but we have a great laser cutter/sheet metal sponsor.

No tensioning or ever throwing belts/chains
A good drivetrain has a great tensioning system and never throws belts or chains. I am not confident enough that we can build a drivetrain that will meet those requirements. The gear drive solves that problem.

No need for access from the top of the box
We now have the entire width of the robot for our game playing elements. We can cover the entire top of the drive train and not worry about having to ever reach in a fix a chain or belt. We can replace wheels extremely quickly with just one bolt each. This also might be marginally safer as it is harder to get a finger or drop something in the drive.

Can change wheel configurations easily
10, 8, or 6 wheel configurations are all available with this robot without changing much of anything except removing a wheel or two. You could build the same thing into a chain/belt system but that would be a lot of tensioning.

It's a prototype
And the last reason is it's a prototype and it's different. In 3 months I might be completely on the other side of this issue and telling people to never build gear drivetrains ever. If that does end up being the case, we'll have with a nice stock of gears to use for future gearboxes and a story to tell.

[Ryan Dognaux]

Originally Posted by AllenGregoryIV

The "long" output shaft is used in the 2 stage transmission to allow for a sprocket(s) or another gear to drive another one that actually powers the wheel.

Thanks for pointing that out, I didn't even realize there was a 3rd stage available. That makes things a lot easier.

Also thanks to you and Madison for posting your prototype drive trains in the off-season. It's been fun to read the discussion and mull over some ideas for sheet metal fab drive trains.

[Paul Copioli]

Originally Posted by Chris is me

I really don't understand the functional difference between direct driving a wheel using a 3 stage ball shifter and using a two stage ball shifter + gear reduction to drive the wheel. I'm pretty sure there isn't one, really. You're already filling the drive line with gears, might as well put a reduction in that drive line too.

Yep, that's what we do. In fact, the Verskey pattern in the gears was meant to help with gear alignment for this purpose.

[Chris is me]

I'm not trying to bash your drive nor am I against the concept of a gear drive. If we had the time and the drive to do something different I'm sure my team would prototype one as well. Just thought I would share some info about belts.

Originally Posted by AllenGregoryIV

I can't tell you why you should like it but I can tell you what's attractive to us.
No tensioning or ever throwing belts/chains
A good drivetrain has a great tensioning system and never throws belts or chains. I am not confident enough that we can build a drivetrain that will meet those requirements. The gear drive solves that problem.

If you can manufacture a drivetrain with enough precision for a functional gear drive, you have more than enough precision to make a dead spaced belt drive, which does not need tensioners.

No need for access from the top of the box
We now have the entire width of the robot for our game playing elements. We can cover the entire top of the drive train and not worry about having to ever reach in a fix a chain or belt. We can replace wheels extremely quickly with just one bolt each. This also might be marginally safer as it is harder to get a finger or drop something in the drive.

A properly designed belt drivetrain should never need any maintenance. For the past three seasons we have not touched a drive belt since week 4-5 of build season (unless we had to remove an axle for another reason, but that doesn't really count). So this same advantage can apply to belts as well.

[AllenGregoryIV]

Originally Posted by Chris is me

I'm not trying to bash your drive nor am I against the concept of a gear drive. If we had the time and the drive to do something different I'm sure my team would prototype one as well. Just thought I would share some info about belts.



If you can manufacture a drivetrain with enough precision for a functional gear drive, you have more than enough precision to make a dead spaced belt drive, which does not need tensioners.



A properly designed belt drivetrain should never need any maintenance. For the past three seasons we have not touched a drive belt since week 4-5 of build season (unless we had to remove an axle for another reason, but that doesn't really count). So this same advantage can apply to belts as well.

Yes but where do I get pulleys with the 6 hole pattern already machined (and preferably with versakeys)? Aren or Paul want to chime in here?

Also I did a quick cost break down of the Gear Drive vs. an 8 wheel #25 chain drive.
The gear system is about $170 more.

Here are the spreadsheets.

[donkehote]

Originally Posted by AllenGregoryIV

Yes but where do I get pulleys with the 6 hole pattern already machined (and preferably with versakeys)? Aren or Paul want to chime in here?

andymark?

http://www.andymark.com/product-p/am-2234.htm

we used these in our shooter this year. worked great! I would love to see more sizes available in plastic. Buying from gates in canada takes a long time, and is far too expensive. Still did it this year though, and it was worth it.

[AllenGregoryIV]

Originally Posted by donkehote

andymark?

http://www.andymark.com/product-p/am-2234.htm

we used these in our shooter this year. worked great! I would love to see more sizes available in plastic. Buying from gates in canada takes a long time, and is far too expensive. Still did it this year though, and it was worth it.

Thanks Kevin, I should have clarified, that I was looking for more sizes that just the 42t AM pulleys.

[AdamHeard]

OH yeah! GT2 or HTD pulleys with a versakey pattern! Aren make it happen!

[DampRobot]

Originally Posted by AdamHeard

OH yeah! GT2 or HTD pulleys with a versakey pattern! Aren make it happen!

I'd be surprised if this wasn't already in the works at IFI or at other suppliers.

[Ajennings8896]

Looks like a really good drivetrain, I'll have to have my team look at this and maybe try something new this year. We usually just use the standard drivetrain but this looks like something we could do this year.

[donkehote]

Originally Posted by AllenGregoryIV

Thanks Kevin, I should have clarified, that I was looking for more sizes that just the 42t AM pulleys.

I wish there were more sizes too. Ive been thinking of cadding up a drivetrain using only gears, but I could never justify the weight when compared to the same thing with the plastic 42 tooth pulleys and 15mm belts. Always liked the idea though.
How are you planning on adjusting the backlash on all those gears, or are you not worried. I cant see it being a major issue, but i thought id ask.

[cadandcookies]

Originally Posted by AdamHeard

OH yeah! GT2 or HTD pulleys with a versakey pattern! Aren make it happen!

This. Please. Please. Please. (If we keep asking does the chances of it actually happening go up).

The only current problem with belts (at lease in my opinion) is that pulleys require decent amount of post machining to be utilized the most effectively. COTS FIRST-standard pulleys would fix that (as I understand it there's something about licensing the tooth profile that stands in the way, but mon dieu if this could happen it would make my 2014 build season).

[AllenGregoryIV]

Originally Posted by donkehote

I wish there were more sizes too. Ive been thinking of cadding up a drivetrain using only gears, but I could never justify the weight when compared to the same thing with the plastic 42 tooth pulleys and 15mm belts. Always liked the idea though.
How are you planning on adjusting the backlash on all those gears, or are you not worried. I cant see it being a major issue, but i thought id ask.

I agree that belts would be lighter, though we really haven't had a weight problem the last two years. We actually have been struggling to get up to 120lbs, to get more traction. Right now I would take the smaller footprint over the lesser weight option.

I haven't thought about the backlash, several teams have done gear drives and haven't mentioned it being a problem.

[IndySam]

Originally Posted by AllenGregoryIV

I agree that belts would be lighter, though we really haven't had a weight problem the last two years. We actually have been struggling to get up to 120lbs, to get more traction. Right now I would take the smaller footprint over the lesser weight option.

I haven't thought about the backlash, several teams have done gear drives and haven't mentioned it being a problem.

Backlash, what backlash? Not a problem. Also we were under 80lbs this year so weight wasn't a problem for us.

The new small drive size was one of the factors that made a gear drive practical this past year in both weight and cost.

[Seth Mallory]

Originally Posted by AllenGregoryIV

I agree that belts would be lighter, though we really haven't had a weight problem the last two years. We actually have been struggling to get up to 120lbs, to get more traction. Right now I would take the smaller footprint over the lesser weight option.

I haven't thought about the backlash, several teams have done gear drives and haven't mentioned it being a problem.

I like your effort for making a smaller footprint. For the last couple of years 192 has been working to reduce the footprint in a different way. For those that know 192 you will be shocked to hear that the students have a new gear box that should be more space saving then the last 2 years.