pic: Bane Bots Gearbox CAD

[roboticWanderor]

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[R.C.]

Hey dude,

Any specs on it, reductions? Output Torque and fps would be nice. If you want, send me the animation and I could upload it for you.

-RC

[Tom Line]

I'm curious - why use the delrin on the sides rather than aluminum? Sure, it's half as dense, but it's also not as stiff and requires a thicker piece and is (in my experience) more expensive.

[AdamHeard]

I'm curious why the sprocket is on the motor side.

Also, what are the specs of the initial reduction; with the commonality between the various Banebots motors and the FP motors, it seems it would be ideal to make this accept any motor (standardized pinion) and possibly multiple. What are you using as the motor pinion? The 15T 32DP from AndyMark seems to be the best choice on the market.

Originally Posted by Tom Line

I'm curious - why use the delrin on the sides rather than aluminum? Sure, it's half as dense, but it's also not as stiff and requires a thicker piece and is (in my experience) more expensive.

I've found delrin to be uniformly less expensive than aluminum plate of equal thickness.

Delrin actually works out rather well, you can leave it nice and thick (1/4" for example), not pocket it out, and still be rather lightweight (equivalent to a about the weight of a 3/32" aluminum plate). If the gearbox is designed correctly for the material, it is plenty stiff. A nicely pocketed 1/4" Aluminum plate is usually in the ballpark of a solid delrin counterpart, and the delrin will take less time to produce (you can cut it faster, and by leaving it solid, have less to cut as well).

[AndyB]

Originally Posted by AdamHeard

I'm curious why the sprocket is on the motor side.

Assuming this is for some sort of manipulator/arm/elevator, I would assume that the gearbox would be mounted on the inside for added protection to the motor. Obviously, the chain run would be in a more convenient location as well.

[ducttapedude]

IMO Delrin a solid delrin plate ends up being about the same weight as a heavily machined plate of aluminum but not nearly as rigid. I've seen a few delrin gearboxes and you can seem them flex pretty easily, not anything horrible or dangerous, but noticeable. Also, the threading the in the delrin does not last as well, you can use a nut of course, but, just another con in my opinion.

Originally Posted by AdamHeard

I've found delrin to be uniformly less expensive than aluminum plate of equal thickness.

Delrin actually works out rather well, you can leave it nice and thick (1/4" for example), not pocket it out, and still be rather lightweight (equivalent to a about the weight of a 3/32" aluminum plate). If the gearbox is designed correctly for the material, it is plenty stiff. A nicely pocketed 1/4" Aluminum plate is usually in the ballpark of a solid delrin counterpart, and the delrin will take less time to produce (you can cut it faster, and by leaving it solid, have less to cut as well).

[Travis Covington]

Originally Posted by ducttapedude

IMO Delrin a solid delrin plate ends up being about the same weight as a heavily machined plate of aluminum but not nearly as rigid. I've seen a few delrin gearboxes and you can seem them flex pretty easily, not anything horrible or dangerous, but noticeable. Also, the threading the in the delrin does not last as well, you can use a nut of course, but, just another con in my opinion.

^^Agreed. Delrin isn't as great as many people think. We utilized it the last few years strictly for its ease of machining and the reduced weight. I would much prefer a waterjet plate with a quick pass on the CNC to clean up the bores. Access to a waterjet has always been the issue though, but this is something we are looking at for future use.

The strength to weight ratio of delrin is still significantly less than aluminum, and for heavy reduction gearboxes, you need to be very careful with how you use it. For example, we have made some 250:1 arm gearboxes in the past that I would never consider using delrin sideplates with. Just make sure you are using it for the right reasons. Aluminum sideplates also act as great heatsinks, and for games like overdrive, the CIMs could use as much heat dissapation as possible.

No material is a miracle material; especially not delrin. Each material choice has advantages in specific applications, and thus should be chosen appropriately. Delrin, like aluminum is on the lighter end of the material spectrum. Like Travis said, high torque and heavy reduction applications are best done with something with a little more torsional stiffness.

Delrin does carry certain advantages. Exhibit A: Weight. For most light duty applications in FIRST, such as drive gearbox plates, and lower torque systems, delrin is quite well suited. Its a fairly soft material, which makes machining the plates incredibly easy and fast. It can be less expensive than aluminum of equal size if you know where to look. Exhibit B: Style. Admit it, a lot of teams care about this. Far more than will openly say so. Delrin can be found in nice clean colors, which can add aesthetics to a robot when chosen wisely. Exhibit C: Machine time. Less units of work for more than satisfactory strength make Delrin a mighty tempting material.

However, if a team doesn't spend their time doing some math and stress calculations, the weight gains will be for naught when a major component shears.

Team 114 had great success in building our drive gearbox sideplates out of Delrin. A few tips from what we learned: Washers. If you don't put washers on your bolts, you'll dent the delrin and lose strength. Machining wise, it's a joy to work with. We were able to produce all of our gearbox plates in house on a tiny little desktop CNC. Weight wise, they turned out insanely light.

[roboticWanderor]

This is not that heavy of a reduction, just 24:1. the only thing i am really worried about is the mount of the actual motor, I had to bore into the delrin a bit to get the motor pinion far enough out the other side, making the material that holds in the motor is 1/8 thick instead of 1/4 like the rest of the gearbox. However, it's a pretty high rpm, low torque motor, so I wouldn't expect it to be taking much force, plus it has thicker material surrounding it...


Oh, and i cant show the video because solidworks does not like to encode it correctly... =(

Originally Posted by roboticWanderor

This is not that heavy of a reduction, just 24:1. the only thing i am really worried about is the mount of the actual motor, I had to bore into the delrin a bit to get the motor pinion far enough out the other side, making the material that holds in the motor is 1/8 thick instead of 1/4 like the rest of the gearbox. However, it's a pretty high rpm, low torque motor, so I wouldn't expect it to be taking much force, plus it has thicker material surrounding it...

The banebots motor should be fine with this. If you were mounting a CIM on that, it would be an entirely different story....

[=Martin=Taylor=]

We saw the 254 gearboxes in 2007 and were like: "ABS! Of course! Why didn't we think of that!?"

We bought some .25" ABS scraps at Tap for 50 cents each and used them in the trannies.

Had we thought to ask 254 about their robot we may have discovered that they were actually using delrin which is about .4 g/cm^3 denser.

[R.C.]

Originally Posted by Hachiban VIII

We saw the 254 gearboxes in 2007 and were like: "ABS! Of course! Why didn't we think of that!?"

We bought some .25" ABS scraps at Tap for 50 cents each and used them in the trannies.

Had we thought to ask 254 about their robot we may have discovered that they were actually using delrin which is about .4 g/cm^3 denser.

How did the plates hold up.

[=Martin=Taylor=]

Originally Posted by rc_cola1323

How did the plates hold up.

They held up fine.

The elevator gearbox was just 3/16" ABS and it survived 100+ hurdles as the elevator slammed up and down.