You are correct sir, I love the design.

Ratio Change
 

A few months ago I was doing some numbers on this drivetrain and found that a 60:40 ratio would be much more effective in place of the 50:50 ratio. The 60 being on the final drive stage. Your center to center distance remains the same. The ratio difference in the original design I think is too big and you could have a more practical sprocket reduction (or a greater choice in wheel size) after the gearbox with the new ratio. What do you think?

A Few Questions
 

I've spent countless hours looking into my own personal development of this gearbox. Looking through catalogs, doing calculations, drawings, etc.

Given the game is accomodating, my team is seriously looking into building a drivetrain very similar to that of team 226 next year. To make our life a little easier, I was wondering if you can provide any dimensions on the side plates and bearing hole locations. Do all the shafts' axes of rotation lie in the same plane? Also, I was wondering the length of the side plate spacers. That would be very much appreciated.


A couple more questions:
Is the Chiaphua shaft and the central shaft 3/8 or 1/2 diameter? And how is the Chiaphua shaft attatched to the Chia's armature output shaft: is it pressed, welded or keyed?

Re: A Few Questions
 

In reference to the TechnoKat tranmission shown in the CAD pic above, I wish that we did have some further reduction in this gearbox. Our main drivetrain mechanical problem this year was AFTER this gearbox, where we had a 11:40 ratio to reduce the speed before driving the tracks. The torque that the 11 tooth gear saw was high and we stripped gears. (however, we had no problems with this gearbox)


Finally, (Kyle is right) I have freed up some time at work and I will be able to do the white paper on this gearbox, which is a dramatic improvement from 2002 gearbox. My goal is to be done with it by IRI (July 18) and have hard copies to hand out at IRI.

Sand... to answer some of your questions:

Yes, all of the axii line in the same plane, with the exception of the drill motor.

The length of the side plate spacers... I need to look at the prints for that one. I think that they are around 1.2".

The CIM motor was keyed to the inside of the 12 tooth gear shaft. This 12 tooth gear was on a 3/8" shaft, a 32 pitch gear was pressed and welded onto the same shaft (mated with a 14 tooth pinion on the drill motor)... and this shaft/gear assembly was broached for an 8mm shaft with a 2mm keyway, mating with the CIM motor.

Andy B.

Re: Re: A Few Questions
 

That's a 12T? On Matt's transmission it appears to be a 16 from this post. Did you both just go little bit different ways there?

Re: Re: Re: A Few Questions
 

We definitely went different ways. We both started with our design from 2002 (which we put on the internet one year ago)... I made alot of improvements for 2003 for our robot and Matt must've done alot of improvements also.

On that note... if you look at the teams who used our 2002 gearbox, all of them took the published design and improved upon it. Travis Covington of 968 made improvements on it for his team and Paul Copioli of 217 improved it for the Thunderchickens.

Then, there is Paul and Travis of team 48, who put the shifting mechanism as a separate box with just input and output shafts, improving it in a different way.

It was really neat to see what everyone did with this design... how they improved it and made it work for their 'bot. The funny thing about all of this was that none of us talked to each other about it. Travis and I probably compared notes the most, but that was only after he made his design improvements. Paul's job as a designer is to make gearboxes for robot arms, so it's not like he needs advice anyway. Heck, he gave me advice back in 2002 when I was making the first version of this thing.

Andy B.

Re: Re: Re: A Few Questions
 

Sanddrag,

What we did in the first stage was make it so that you didn't need any special tools (Such as a broach for the keyway), here is the order we made the first stage (That mounts on the CIM motor) While we could have made things custom, time & money as well as available tools kept us using off the shelf parts.

Step 1:Bought a stock 16 tooth Martin gear.

Problem 1: the bore was larger than the output shaft of the CIM motor.
Solution 1: took a piece of drill rod of the proper size to fit the bore, put a slight knurl on it in the lathe, put a light coat of Green thread lock (essentially high strength epoxy) and pressed it into the gear. When Dry, we bored out the piece of drill rod to slightly under the output shaft of the CIM motor.

Step 2: Made another piece of Drill rod to fit into the new bore on the 16 tooth gear and turned the end down so that it fit the bore of the PIC design 48 tooth gear. We attached them together on this temporary shaft so they were welded together perfectly in line with each other.

Step 3: Take this new assembly of two standard gears welded to each other and turn the hub down on the PIC design gear so that it becomes the end of the shaft and fits in the bearing opposite of the CIM motor.

Step 4: Press the whole assembly onto the CIM motor with more Green LockTite. Advantage: No Setscrews, keyways or anything. Disadvantage: It isn't ever coming off for any reason.

This was how we accomplished the first stage and you can make it easily with only a lathe, welder, and small press.

Next stage of 20 tooth and 50 tooth was simply welding to shaft.

We diverged somewhat from the #45 2002 design but then we left off the Lovejoy coupling and used #25 chain drive to the tank treads (20 tooth/60 tooth) only because lack of planning dictated that we didn't know how the gearbox was going to fit in the chassis and connect up. I would have rather used all gear drive but the chain guides solved our problems. Keep in mind with all the power this had, it never broke a #25 chain. We did however go through 8 Breckoflex belts this year including 4 of the solid center ribbed belts.

I really have to hand it to Team 45 for posting the design so that others could use it either fully or as a great starting point. It is one of those things that advances the community as a whole.

With this much steel, it is imperative that you lighten each and every gear, however having this much weight down low in our chassis is what kept our stacker from falling over like many of the others even though it was over 40" tall.

Just interested, how many teams have seen or have costom pressed gears on thier drill motors? By pressed I mean they have taken off the pinion and pressed on another. Because, wouldn't it be really useful if you could press on a 20 pitch gear, and make everything easy?

It would be somewhat useful, except that even the smallest 20 pitch gear (something like 10 or 12 tooth) is still pretty large and has a standard bore much bigger than the drill output shaft. You would need to press in a drill rod or something into the gear then re-bore it out. Having a larger gear like that would almost certainly also require supporting the output shaft also on the side opposite the motor (Team 45 already does this, we didn't)

The smallest 20P I've ever found is a 12T which is still pretty big like Matt said. Having three things pressed together sounds kind of iffy to me. A 32P steel gear works just fine for the relatively small loads being applied right there.

Martin has and 11 tooth 20dp gear and a 10 tooth 20dp spline shaft. We used them both this year.

This was one of our "lessons learned" from 2003: leave yourself enough center distance to vary a wide range of gear ratios after the output shaft of the shifting gearbox.

From the output shaft of our gearbox, we had a coupler, a gear reduction, and then our drive wheel. This gear reduction started out as 2.5:1, but it ended up being 4:1, using a 41 tooth gear (custom) and a 10 tooth gear. I wish we knew we needed a 4:1 when we set the center distances of the gears... they would've been farther apart. This mistake was the cause of many mechanical breakdowns (3 in Pittsburgh and 1 in Chicago).

Andy B.