NED HELP ON BUILDING 1 OR 2 SPEED GEARBOX

[team2061]

Originally Posted by EricH

That particular gearbox seems to be a means of connecting two CIMs to the same planetary gear. Not sure which team built it, but they could probably give you an estimate of cost.

P.S. Could you turn caps lock off? Having it on makes it sound like we're being shouted at.

im soory i guess i got used to typing in caps lock, but i no longer will.=)

[team2061]

Originally Posted by lukevanoort

The orange things are some sort of shaft coupling, and the black thing is probably an optical encoder

im sorry you guys but im very new to this. what is a shaft coupling and an optical encoder??

[lukevanoort]

Originally Posted by EricH

That particular gearbox seems to be a means of connecting two CIMs to the same planetary gear. Not sure which team built it, but they could probably give you an estimate of cost.

I don't think that that is a planetary, it looks just like a very large one-stage spur gear reduction.

Originally Posted by team2061

im sorry you guys but im very new to this. what is a shaft coupling and an optical encoder??

A shaft coupling is something that attaches to two shafts and locks them together so that torque can be transferred from one to the other.

At its most literal meaning, an optical encoder is something that uses light to 'encode' something into a form readable by a computer. In this case, it takes rotation on its shaft and outputs a pulse of electricity every time the encoder shaft moves a certain number of degrees. To find out more about encoders, read this.

[EricH]

Originally Posted by lukevanoort

I don't think that that is a planetary, it looks just like a very large one-stage spur gear reduction.

I'd say planetary because it'd be pretty hard to get the reduction from a CIM in ONE stage by means of a spur gear.

One thing that could make life easier is a link to the picture in CD-Media, not just the picture alone. (Couldn't find it by searching; trying again now.)

[Cory]

Those orange pieces are Lovejoy shaft couplings. They can be found here

I used these pretty extensively when I was on 100. They are very nice as far as shaft couplings go. They have a flexible rubber "spider" that sits between the two coupling pieces that allows slight misalignment of the two shafts. They worked extremely well in my experience. The only downside is that they are HEAVY. If you use anymore than a few, the weight will add up very quickly.

[sanddrag]

Originally Posted by Cory

Those orange pieces are Lovejoy shaft couplings. They can be found here

I used these pretty extensively when I was on 100. They are very nice as far as shaft couplings go.

I've used these a few times as well. Some things I've learned about them from my experience: Use a larger outside diameter if possible. It will be able to take more severe loading and misalignment. Use Hytrel spiders/inserts as opposed to the Buna-N rubber. The rubber ones cannot take as much torque and can wear out. Rigidly mount whatever is on each side of the lfex coupling. Flexing of the mount can cause flex coupling failure.

[team2061]

Thank You guys very much i really appreciate it.

[Andy Baker]

Here are some basic recommendations for designing and building your own gearbox for FIRST Robotics Applications:

1. Fabrication accuracy is key. No matter how good your design is, if your fabrication is not good, then headaches will persist for the entire season. Learn from experienced people (skilled trades folks, instructors, etc.) with regard to making precise features like bearing press fits, concentric keyed holes, and accurately placed bearing holes on a plate.

2. Use 20 dp (diametric pitch) gears. These are fairly abundant. Industry standard gears of this pitch can be purchased from McMaster-Carr, MSC, Martin, Berg, Boston Gear, Stock Drive Products, Rino Mechanical, and other vendors. They can be found with a pressure angle of 20 and 14.5 degrees. These don't mesh well together (they do, but things get really noisy). I think that the 14.5 degree version is a bit more abundant. Also, Misumi is probably be best resource for metric gears. I recommend module 1 for most FRC applications.

3. In gearbox design, add 0.003" to your center-to-center distance. This allows for a bit of eccentricity of your gears, and only adds a negligible bit of backlash.

4. Find a resource for 1/2" or 3/8" hex broaching, and then use 1/2" or 3/8" hex shafting instead of keyed shafts. However... I'll admit that keyed shaft gearboxes are getting easier these days since McMaster-Carr and other places will sell stock of pre-keyed steel and aluminum shafts.

5. I recommend steel gears to start out with. However, if you can justify using plastic, aluminum or brass gears, then those work also. These, of course, can withstand less force and gears will shear if the force on the gear is higher than the gear tooth's cross sectional area x the yield strength of the gear's material. I would also multiply in a safety factor of 2x.

6. When in doubt, increase your face width. Usually, 3/8" is a good face width, but for higher torque situations you may want to go to 1/2" or 5/8" wide gears.

7. Don't forget to lube. Lithium grease is always a good lubricant on a simple gearbox. If you want things to move back and forth on a shaft, like in a dog shifting gearbox, use a lighter lubricant such as an oil.

8. Buy the parts that are difficult to fabricate, and then make your own parts. Many people ask me "why do you sell spare parts for your shifters and gearboxes... do these parts wear down?" My answer to this is "no... they don't wear down, but we sell individual parts so teams can design and build their own gearboxes by using a few of our parts."

9. Get your design made and take pride in your gearbox.

Andy B.

[Richard Wallace]

Originally Posted by Andy Baker

9. Get your design made and take pride in your gearbox.

Or you could design and build an awesome scoring mechanism and take pride in THAT, while you drive your robot with Andy's gearboxes.

[IndySam]

Originally Posted by Richard

Or you could design and build an awesome scoring mechanism and take pride in THAT, while you drive your robot with Andy's gearboxes.

Bingo!

Building your own is a great idea but teams that do it successfully usually do a lot of development in the off-season. If you want to shift, buy a AM or use the dewalt and then develop your own this summer.

[gburlison]

Originally Posted by EricH

I'd say planetary because it'd be pretty hard to get the reduction from a CIM in ONE stage by means of a spur gear.

This gearbox has a 16 to 1 ratio using 5 tooth stem pinion gears on the CIMs and a 80 tooth spur gear on the output shaft. The use of a stem pinion gear requires a coupler since it is too small to fit on a CIM shaft.

[EricH]

Originally Posted by gburlison

This gearbox has a 16 to 1 ratio using 5 tooth stem pinion gears on the CIMs and a 80 tooth spur gear on the output shaft. The use of a stem pinion gear requires a coupler since it is too small to fit on a CIM shaft.

Makes more sense. Is that one of yours, or did you just analyze it to death?

Edit: Yes, it is 662's 2007 robot. The discussion and original picture are here.
Edit2: Did you guys run into any issues? How much did it cost? What other info would help this team?

[gburlison]

Originally Posted by EricH

Makes more sense. Is that one of yours, or did you just analyze it to death?

Edit: Yes, it is 662's 2007 robot. The discussion and original picture are here.
Edit2: Did you guys run into any issues? How much did it cost? What other info would help this team?

Team2061 sent me a PM and I provided him more details, but the short answer is that it cost about $100. It is a simple one stage gearbox using the smallest stem pinions we could find (5 tooth) and the biggest spur gear practical (80 tooth). There is one main issue with this gearbox and that is alignment. The output shaft is supported in three bearings, so misalignment can cause binding. The first year we built this design, we used solid couplers on the CIMs and this also suffered from misalignment and binding. The Lovejoy Couplers took care of any possible binding of the stem pinion gears. Just for reference, this is our first Gen of this Gearbox. http://www.chiefdelphi.com/media/photos/19829

[Tom Bottiglieri]

My recommendation would be to purchase one of the previously stated boxes. Take it apart, study it, and learn how everything works. Take what you've learned, let it ferment for a few months, then put that knowledge to good use next season designing your own.