Dual CIMs gear box adapter
 

On the Bane Bots website they sell an adapter to put 2 CIMs on 1 12:1 gear box. Does anyone know how effiecient this setup is? Can the gear box handle it?
~Olav Oksnevad

Re: Dual CIMs gear box adapter
 

The set up adds one extra gear pair to the gearbox so the efficiency is going to drop some but they are simple spur gears so I would estimate 95% as efficient as using the single motor set up.

As to how efficient the entire gearbox is, that is a bit trickier.

I typically use 85% per stage for planetary gear boxes* That would mean that the banebot 56mm gearbox would be about 72% efficient. The dual motor gearbox would be about 69% efficient, a difference not even worth worrying about (IMHO).

Joe J.


*assuming the ratio is low enough -- at ratios much higher than 6:1 per stage, the efficiency drops like a rock, at 10 to 1 the efficiency is often in the 30-40% range -- for just one stage. YIKES! That is why if you want 100:1 ratio in a planetary gearbox it is better to do 4:1 + 5:1 + 5:1 rather than 10:1 + 10:1 One has an efficiency of over 60% while the other has an efficiency below 15%

Re: Dual CIMs gear box adapter
 

Dr. Joe I recently heard that planetary gearboxes were much more efficient than that(on the order of 98%) but I'd hate to argue with you and what I heard could very well have just been hearsay. Do you have a good website or other source you could direct me to that explains the efficiencies of planetary gearboxes?

Re: Dual CIMs gear box adapter
 

Think about it logically. A spur gear is typically about 95% efficient. A planetary gearbox contains multiple spur gears, therefore, it should be less efficient than a spur gear.

Re: Dual CIMs gear box adapter
 

Efficiency of planetary gearboxes are notoriously difficult to understand.

I worked for one of the guys who first put permanent magnet motors in production on a Cadillac door lock system (he has over 100 patents and 4 "Boss Kettering" Awards for valuable intellectual property). Anyway, just to be clear, he was not an idiot. One of his favorite war stories was the time he once put tried to put a printed circuit board motor with a very high ratio planetary gearbox in production for a power window lift system. He used 95% efficiency per stage, thinking, "hey, they are just like spur gears, right?" WRONG! They are not. The are much less efficient and it is not due to the friction at the pivots either because in desperation he put ball bearings on every pivot -- with no noticeable improvement in efficiency.

With low gear ratios you can get quite high efficiencies. After 6 you are asking for trouble.

As to the 85%, I have gotten into trouble over estimating efficiencies. I can think of no cases where underestimating them did so.

I think 85% is a good number to use when you are designing your robot. If you get 90% per stage, life is good, your motor is not working as hard as you had planned for, but if you plan on 95% and get only 85% your motor is a smoking heap of slag...

Joe J.

Re: Dual CIMs gear box adapter
 

Thanks for the explanation Joe.

I guess my team is safe from the inefficiency monster, they're using the dewalt gearbox which doesn't do more than 4:1 per stage(or some other reasonable number). I have over the years lowered my efficiency expectations from 95% four years ago to just 75% now, but my team has a history of funky methods for power transfer.

Re: Dual CIMs gear box adapter
 

I would imagine that if BaneBots is selling the kit for the Two CIM's into one 56mm Transmission kit, that the Transmission should be able to handle it.

That being said, there are more parts that can fail, and that's never a good thing.

If one of the CIMs fails, you have to disassemble the gearbox, take the new gear off of the broken CIM, put it on a new CIM, then re-assemble the thing. Given the amount of time it takes to change the motor on the single 56mm transmission (This is with the gears already matching), which is about 5-10 minutes depending on the person or whatnot, having to dismantle the converter would take longer. I say it's best to think about what would take the most time to fix if it fails/gets damaged badly and try to minimize about that, even if it means it weighs more.

The weight advantage, however, would be better. Two 2-to-1 converters on 56mm transmissions weighs less than four CIMs with four 56mm transmissions.

The effeciency shouldn't be too bad, either. If you really need the torque, too, you can acquire one of the 16:1 kits that BaneBots sells on their website.

Re: Dual CIMs gear box adapter
 

Has anyone received one of these yet? I badly need a CAD model. Or at least some prints from BB.

Re: Dual CIMs gear box adapter
 

Keep searching, I think it is out there somewhere already. I saw a model of it used in a preliminary design that our CAD team is kicking around now, so either one of those guys got impatient and made it himself or they found it somewhere. When I get a response from one of them I'll post again, unless someone else finds the model first.

Re: Dual CIMs gear box adapter
 

Sorry about the double post -- just bumping this back up to correct my earlier comment.

Sanddrag, it turns out my CAD guys are in the same boat as you. They just took their best guess and made a preliminary model of the adapter, intending to correct it either (1) when BaneBots publishes some dimensions, (2) when someone with skills, an actual part, and some calipers makes and posts a CAD model, or (3) when the two adapters I have ordered arrive.

Re: Dual CIMs gear box adapter
 

Thankfully, more than one team has already purchased these gearboxes. You can find the overall dimensions Here.

BEN