Using a Bag Motor Without Gearbox

[legogeek24]

Hello everyone! I'm spending a couple weeks in the United Arab Emirates helping out rookie team 4928, the Arabian Knights. I think they're making great progress and it's definitely been a lot of fun!

My question is about bag motors. We want to use a bag motor to run our intake roller, but we don't know how to mount it to a shaft. The obvious choice is a gearbox, but since we're in the UAE, shipping takes a significant amount of time and costs an exorbitant amount of money. Does anyone have ideas for a different way to mount a bag motor to a shaft, like the kit igus bar?

Our idea was to drill a hole through both the igus bar and the bag motor shaft, but its so small I'm not sure how well that would work. Any thoughts?

Also, we're not set on the bag motor, we'd be willing to use any of the other kit motors of comparable size (we don't want to use a mini-cim because of weight - it's being mounted at the end of a long arm).

[MrForbes]

We did some crude testing using a four inch diameter intake roller, and discovered that it wants to turn at several hundred RPM. There really aren't any motors in the kit that will do the job without some gear reduction.

One that is promising is the PG71 gearmotor...but it appears to need one stage of reduction removed from the gearbox, to essentially turn it into a PG27 gearmotor. I haven't looked at the rules enough to see if this is something you could do?

[Nemo]

The BAG motor runs up to 14000 RPM, which is probably way too fast for your intake roller. I suggest using the AndyMark PG-71 gear motor if you haven't already used that for another mechanism. That already has a gearbox on it and might be in a speed range that would work for your intake roller.

[Nemo]

Originally Posted by MrForbes

We did some crude testing using a four inch diameter intake roller, and discovered that it wants to turn at several hundred RPM. There really aren't any motors in the kit that will do the job without some gear reduction.

One that is promising is the PG71 gearmotor...but it appears to need one stage of reduction removed from the gearbox, to essentially turn it into a PG27 gearmotor. I haven't looked at the rules enough to see if this is something you could do?

You beat me to it.

It would be legal to modify the PG71 gearbox. The gearbox and motor are separate parts, unlike the situation with window motors and their integral gearboxes. The rules list the AM-2161 motor as the allowable motor, not the entire PG71 assembly that includes the planetary gearbox.

That's not to say it would be easy to take a stage out of the PG71 gearbox, though. I've never had one of those apart, but at a minimum the external housing would be too long after you took a stage out.

[MrForbes]

Originally Posted by Nemo

That's not to say it would be easy to take a stage out of the PG71 gearbox, though. I've never had one of those apart, but at a minimum the external housing would be too long after you took a stage out.

Cutting the housing shorter is probably the one modification that a rookie team could make to a multi stage planetary gearbox...although if they only have one, the odds of the results being successful first try may not be so good.

[Coach Norm]

Originally Posted by legogeek24

My question is about bag motors. We want to use a bag motor to run our intake roller, but we don't know how to mount it to a shaft. The obvious choice is a gearbox, but since we're in the UAE, shipping takes a significant amount of time and costs an exorbitant amount of money. Does anyone have ideas for a different way to mount a bag motor to a shaft, like the kit igus bar?

Also, we're not set on the bag motor, we'd be willing to use any of the other kit motors of comparable size (we don't want to use a mini-cim because of weight - it's being mounted at the end of a long arm).

We have never used them before, but I know teams have used drill motors transmissions and electric screw drivers with past KOP motors. Might be something to look into.

I know the Killer Bees, Bomb Squad and Spectrum's John Allen Gregory have had posts and experience with these techniques in the past.

[Richard Wallace]

3620 used a drill transmission for intake in 2012.

Our choice was the classic DeWalt model 940 XRP, mainly because I had some experience with that drill in earlier years. Several teams used it back in the day before such a nice variety of easier COTS gearboxes became available (thank you, AndyMark and VexPro!)

Please look at the classic CD whitepaper "Nothing But DeWalts".

One tip: it will be easier to use a drill transmission if the drill motor you are replacing with a BAG motor has the same shaft diameter (4mm). I have had good results drilling a 9/64" diameter hole in the end of the drill motor shaft to about the depth of the pinion, thereby weakening the shaft just enough so it will deform to let the pinion off.

[legogeek24]

Thanks for the ideas! Due to the unfortunate fact that none of the products mentioned are available locally (and our unwillingness to damage our PG71 gearbox), we decided to just use the mini-CIM or unmodified PG71. It's not perfect, but the best we can do with the resources. Thanks!

[nathannfm]

If you are going to a competition in the states (or anywhere with better shipping rates) you could order the gearbox/motor you want, have it sent to the hotel or a friend in the area a few days early and receive it at the competition. You could look up the mounting pattern and have an interface ready to go, swap out the Mini Cim and you are on your way.