shaft couplers
 

Just wondering what teams have used this method for quick transmission swaps at comp. The team that I mentor had a huge transmission failure going into the elimination rounds, and I thought that this would have saved the day for them. I brought this up to the CAD team and they loved the idea and will be implementing it hopefully in an offseason project. I would really love any thoughts from teams that have used the set-up.

Thanks

Here is a link for the part:
http://www.mcmaster.com/#shaft-couplers/=cg27rd

Re: shaft couplers
 

I know 973 used them as a coupling method to the metric output shaft of the KOP gearbox in 2005.

I'm not sure this quick change ability is that much of a benefit, what was the cause of their failure? If it's something likely to happen again I'd focus my efforts there instead.

Re: shaft couplers
 

I can speak for my team that coupling a shaft could really help.

The couplers in your link we actually use to link our potentiometers to our shafts. We have both the rigid and semi flexible and they worked well.

I would be a bit worried about torque transmission if I was going to couple the output of a driving shaft so sizing the coupler would be essential.

In that respect, at championships we got hit with the infamous Banebot775 short in our lift gearbox. It wasn't pretty since this gearbox was tied to our lifter drum. Luckily we had a coupling device to connect the drum and gearbox instead of making it one big assembly. If it was a single assembly, it would have been major surgery to take the entire assembly out.

What we had was a home-made shaft coupler. The output shaft of the gearbox and the input side of the drum were both 0.5" hex. So we simply broached a hex into cylindrical stock and added a couple set screws. This allowed us to take the gearbox out, swap the motor and get back underway in minimal time. On top of that, we did a quick look at the torque and loads into the coupler and found it would be sufficient for what we needed to do.

Re: shaft couplers
 

It was with the Banebots motor, our encoder malfunctioned and caused the arm to continually raise till it hit the mechanical stop and just continued to drive since it did not know when to stop. The CAD team this year did a marvelous job and we had a plan in place. Obviously you cannot predict every negative scenario and this only happened once in all of our matches. So we want to have the ability that if the need arises, a quick swap would be beneficial. I am glad to see that it served its purpose kaliken. And if you are designing the bot in CAD it is not that difficult to add this system in. I am so proud of these kids they did all of the CAD and I only helped with fixing some mistakes that were made before they were sent to be manufactured. It never hurts to just have the option on the bot.

Re: shaft couplers
 

Just remember that the setscrew type don't transmit torque all that well, particularly rapidly changing torque. The split type are more reliable in that application.

Re: shaft couplers
 

In 2007, shaft couplers were the cause of failure for 696 in two matches at the Los Angeles regional. They sat motionless on the field for two matches due to shaft coupler spiders getting torn up. I don't like them for FRC robots. They take up too much space.

Re: shaft couplers
 

Consider replacing set screws with cotter pins or spring pins.

Re: shaft couplers
 

Cotter pins are the best. I made 694 use them so many times when set screws and keys failed.

On one of our old robots, there were some old gearboxes with threaded output shaft. They used tapped couplers to connect to smooth shaft. I thought that was really bizarre, but the tap + set screws made a really solid connection that was a total pain to remove.

Re: shaft couplers
 

We have used shaft couplers in the past, and they work fine, but can be very bulky. I would recommend having the last stage of gear or chain reduction outside the transmission, so it is not directly coupled with whatever you are driving. This makes transmission swaps much easier.

On our arm, when one of the 775 motor started self destructing by spitting out fan blades (surprise!) we simply took off the chain, pulled the gearbox, and dropped in a replacement.

In our drive system, the gearbox has a gear on the output shaft that engages with a gear on one of the middle wheel shafts, which stays mounted in the frame permanently. So when the shifter pin broke, we were able to pull out the gearbox and swap it very quickly.

A lot of designs use an extra long shaft on the gearbox to direct drive a wheel, but this makes it a real pain to take the gearbox out.

Obviously designing for quick replacement is a nice thing to have, but as Adam said, it might be more beneficial to find out what caused the problem in the first place. In our case, I think the shifter pin broke because we didn't limit the stroke of the air cylinder properly.