The best multi-speed transmission

[Alpha 997]

Originally Posted by squirrel

I agree! but having that weight already committed to the drive base forces the rest of the robot to be as light as possible.

Good point. But the extra weight somewhere else would still be nice.

[Travis Covington]

Originally Posted by squirrel

I agree! but having that weight already committed to the drive base forces the rest of the robot to be as light as possible.

And then when you are 4lbs overweight, you drill two thousand holes in everything to remove the weight...

I can see where your argument is valid had we sacrificed strength for weight savings, or something similar... But in our case, we sacrificed nothing, and saved nearly 10 pounds total from our previous years chassis and drivetrain with the same if not better robustness and strength.

[Alpha 997]

Originally Posted by Travis Covington

And then when you are 4lbs overweight, you drill two thousand holes in everything to remove the weight...

I can see where your argument is valid had we sacrificed strength for weight savings, or something similar... But in our case, we sacrificed nothing, and saved nearly 10 pounds total from our previous years chassis and drivetrain with the same if not better robustness and strength.

Where did you guys get the transmission?

[Travis Covington]

Originally Posted by squirrel

I can understand making a manipulator transmission as light as possible. The problem I see with a light drive transmission, is that the saved weight might be put higher up on the robot...resulting in a tippy bot.

Wheels, frame, and drivetrain is where you want the weight to be.

Agreed... however, I would much rather cut a chunk of my 10 lb lead block off than have to drill a bunch of holes in the rest of the robot because we forgot to put on the LED, the team numbers, or the PVC flagpole mount... you get my point.

[MrForbes]

In your case, you apparently did not have to sacrifice anything for the weight savings. In our case, bulding our own lightweight transmissions would mean not building the rest of the robot! due to limited resources.

I think if you set the weight budget about 10 lbs under the max weight allowed, and you keep track of it during build, you can probably get the robot done within wieght. Also if you start with a heavy drive base, it's easier to shave weight off it at the end if needed, than if you start with it as light as possible.

[Alpha 997]

Can we please stop arguing about the pros and cons of light-weight gear box or how to save weight? That is not what this thread is for.

[Doug G]

Originally Posted by Alpha 997

Where did you guys get the transmission?

They designed it and built it!! They have been redesigning / refining their shifting transmissions each year since '02 I think.

Here's their '02 shifting transmission...

oops.. a better pic in CD-Media

Sure have come along way since then! I'm not sure how much more improvement can be done.. 6 motor CVT's?

[Alpha 997]

Originally Posted by Doug G

They designed it and built it!! They have been redesigning / refining their shifting transmissions each year since '02 I think.

Here's their '02 shifting transmission...

oops.. a better pic in CD-Media

Sure have come along way since then! I'm not sure how much more improvement can be done.. 6 motor CVT's?

Ohh... Did 254 build theirs too?

[AdamHeard]

Originally Posted by Alpha 997

Ohh... Did 254 build theirs too?

254 and 968 collaborate and work together.

Every part (except the bolts and bearings of course) of the transmissions were custom machined. You can not buy them at all.

Currently the two best (for overall FIRST use), off the shelf (which seems to be what you are looking for), shifting transmissions are the AndyMark two speeds and the Dewalt drill 3 speeds.

The dewalts take more work, but are 3 speed and cheaper.

The AndyMarks are easier to work with, are already done and can take two motors without modifications.

Personally, I would take the andymarks.

[MrForbes]

I agree, 1726 used DeWalts last year, and had some troubles with them. We used the AM air shift transmissions this year and they worked just fine, runout, weight, and all.

There is not much available to buy as far as shifting robot transmissions. You need to be able to make parts yourself, adapt parts yourself (such as the modified AM transmissions you have on this year's robot), or get help from someone who has the ability to make this stuff. It's not easy!

I'm gonna rank transmissions in a little list here. Keep in mind these are all my opinions and observances, so yeah.

1. Best! Your own custom tranny. You can build it to the weight, size, and everything that you want. It also gives you great control over your bot, as you can change everything to be what you want.

2. The upcoming (soon to be sold) transmissions from Trossen Robotics partnered with OutBack manufacturing. These are still in the design phase, but they'll be quite the system. Very robust and light, as well as decently cost effective.

3. AM shifters. I've never used these because my team keeps making me design and build my own, but I love these things! They're incredibly cost effective and robust for their weight. They're also proven, reliable, and an all around good system. They get the Craig Seal Of Approval.

4. Dewalts. These are a great budget tranny, but I'm not a fan of their robustness. People may brag about them being sturdy, but I've seen too many of them shatter. There's just a certain amount of structure you gain out of going with larger and non planetary systems. I'm not dissing these, I still think they're great. Personally, I would limit them to budget bots and Crab systems looking for multi speeds.

[Joe Ross]

Don't forget this one: http://www.chiefdelphi.com/forums/sh...ad.php?t=26490

Originally Posted by Joe Ross

Don't forget this one: http://www.chiefdelphi.com/forums/sh...ad.php?t=26490

That's a custom tranny. It falls under the first one, because you can change it to fit your own bot. However, it is really nice... except for the cluster shifting. Make it dog and I'd love it.

[Doug G]

Originally Posted by Alpha 997

Ohh... Did 254 build theirs too?

I believe it was a collaboration between 254 and 968.

Acually in '03 they didn't have a shifting transmission design until the Cal Games comp seen here...

That design went into their '04 bot seen here.

'05 was further refined when they added FP's with AndyMark Planetaries...

'06 seemed similar to '05... pic here

There are some transmission designs in the white papers section - check them out. I remember looking at Andy Baker's design back in '03 and inspired us to make our own and it looked like this... It was so heavy and bulky we never actually used it in a competition bot. With the motors on it, it weighed in at 22 lbs.

Then we got inspired by Paul Copioli, Thunderchickens, and tried to make our own version of CVT (kinda) that looked like this.... That never worked as well as we hoped, but nonetheless the students learned A LOT by trying.

So do some research and start designing a transmission of your own. Even if you don't use it, you'll be ready to adapt to any new changes FIRST makes for the upcoming seasons.

[Gabe]

One advantage that nobody has mentioned for a lightweight transmission is rotational inertia. Force must be applied over a longer period of time when the wheel (in this case the gear) has greater mass. On startup this means that batteries will experience a current surge for a shorter period of time. Less weight also means faster acceleration.

This year was the first year we built a custom two-speed transmission. It is a ball-shift with a 1:9 and 1:3 ratio gearing with a single Minibike motor. See here: http://www.chiefdelphi.com/forums/sh...ad.php?t=55786
We learned from our stupid mistakes, like you never calculate from unloaded speed (oops), and look at power ratings before choosing motor (oops again). Although an impressive achievement, it has weight issues that could have been addressed by using smaller diametral pitch gears (I'm thinking 32 DP). We learned alot from our experience, and expect to see big improvements next year.