Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

Over the course of the build season, we went through three iterations of our climbing mechanism, the first two being pneumatic, and the third powered by a CIM. Rev. 2 was implemented in time for our Week 0 Scrimmage, but it had a fundamental flaw that required a quick redesign. We decided to start over on 3:00 Sunday afternoon. Our frantic "three days to go" design session was centered around using parts we had lying around in the shop. This led to us using a slightly scary solution for our gearbox: a CIM attached to a three stage Versaplanetary with a 75:1 reduction (Motor-->Output: 3:1, 5:1, 5:1). We were scared because we knew that this gearbox was never designed to take this kind of a load, but it was our only option.

54 hours later, we finally tested our new system an hour before bag and tag. Due to a few easily remedied binding issues (our linear bearings were actually 8 year old drawer slides with no ball bearings) we stalled the CIM multiple times, and the gearbox remained perfectly intact.

Since Tuesday, I have been doing some research on other options for planetary gearboxes for CIMs, as well as looking into the actual load ratings for versaplanetaries.

What I've found so far:

The Versaplanetary has two failure modes, the output shaft and the "10:1 Carrier Plate" Source
The 1/2" hex shaft (what we're using, supported on both sides) is rated for 116 ft-lbs
We don't have a 10:1 ratio, so I believe we can ignore the carrier plate rating (74 ft-lbs)

What I'm confused about:
Does this mean that the Versaplanetary will never fail in a 3:1 or 5:1 gear stage?
Are we in major red, considering that a stalled CIM would give 134 ft-lbs of torque at the output shaft?

Our first other consideration was to switch to a Banebots P80. However, I was surprised to read that it is rated for only 85 ft-lbs, about half of what we want for safety. Why is this gearbox so weak if it's designed for CIM? Here on chief, I found a bunch of horror stories of P80's self destructing.

Our final option is to use a versaplanetary or P80 as a first stage (something comfortable, 20:1?) leading into a spur gear or chain reduction.

Anybody have any thoughts or comments? Please let me know If I have made any errors in my reasoning, I'm still a bit new at this.

Thanks!

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

For what it's worth, our climber is using a mini-toughbox, with an additional 15:25 chain reduction. It's nice and fast, and plenty powerful enough - I mini-CIM could get us all the way to the top, but we added a second for a little more speed (we wanted the bar to hit the bumpers when we climb, not one of our vertical frame members) and to help keep the motors cool while running.

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

We are using a Versa 5:1 with a 775 motor. It drives a ball-screw with a .2" lead. Robot weighs 93lb nekid.

It looks like you are in danger of failing your shaft if you stall the gear box under full power for any length of time.

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

Lowering the amount of reduction on the VP and adding an additional stage of chain or spur gear reduction is going to be a safe bet.

IMHO, stay clear of the P80, it has a storied history of failure you do not want to encounter 30+ inches off the floor.

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

This is the way I would do it. Perhaps as simple as a VP (20:1 or 15:1) and a 1:5.33 VEXpro Single Speed Gearbox.

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

All,

First off, the load rating for the VP is very comservative so I think using the VP in this instance is fine.

Also, since the rating is based on the ultimate stress failure of the aluminum hex, going to a single stage gearbox with a 7075 aluminum shaft (or unhardened steel shaft) won't be any better.

In any case, you should be fine with the VP direct to your output for the climber.

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

Wow!

That perspective is actually a little game changing. How would you feel about versas on a drivetrain?

Re: Climbing with CIM's: Versaplanetary Vs. P80 Vs. Multistage Planrtary/Spur Combo
 

Thanks Paul, I wasn't sure if the failure was caused by the spline or some other part of the shaft specific to the VP.