Strength of Versaplanetary & PG-188
 

Can anyone speak about the strength difference between the VersaPlanetary gearboxes and the PG gearboxes?

Our team had issues with PG gearboxes shredding last year. We had one driving an arm that sometimes was hit and therefore put shock on the gearbox. We are looking for a more robust solution. We are wondering if the Versaplanetary gearboxes can withstand higher shock loading. I have also heard of teams "protecting" all brands of planetary gearboxes from damage through one or two external reductions of gears or chain. Another option I am considering is ditching planetary gearboxes entirely and moving towards custom gearboxes with full size gears.

What experience do others have with this? And what method mentioned above do you think would be the best to solve our problem? Thanks to all in advance!

Re: Strength of Versaplanetary & PG-188
 

Versaplanetaries can take a lot more torque (around triple to quadruple). Look at the load ratings guide if you want more in-depth information on what the VP can handle.
A method that I've seen many teams use for large arms is a VP for a 100:1 or 300:1 reduction, followed by a sprocket reduction to the arm to gear down even further.
Custom gearboxes are fun, but can be very time-consuming to design and make. At the very least if you go that route, consider a 10:1 VP first stage reduction just to make your gearbox smaller.

Re: Strength of Versaplanetary & PG-188
 

IMO, this is the best solution to your problem. Custom spur gearboxes are nice, but when you need a 100:1 or higher reduction it gets prohibitively big.

Re: Strength of Versaplanetary & PG-188
 

It's very easy to fall into a trap of sorts with custom gearboxes, where things feel safer and stronger than they are. If you aren't experienced in high reduction custom gearboxes, I would avoid replacing a VP with a custom gearbox to solve a strength issue. Figure out why the VP is breaking first, and what the custom gearbox solves.

The VPs are pretty durable, but it's good practice for any high reduction gearbox to use a chain reduction afterwards to isolate the gearbox. This helps reduce shock load in addition to total load (the gearbox only sees the pre-reduction load). Feeding a VP into a spur reduction isn't necessarily a bad idea, but for something like a long arm you can still have problems if you don't design carefully. (There's probably going to be some sarcastic comment replying to my post referencing early attempts at gear driven arms that my old team has attempted...)

I think for most long robot arms you can do VP -> spur reduction -> chain reduction if you are careful, keep the chain tensioned, and keep everything within safe specs.

Re: Strength of Versaplanetary & PG-188
 

The only issue we ever ran into with a Versaplanetary was when we sheared the sun gear on a 10:1 stage of a 300:1 gearbox. In retrospect it was our fault for assembling it the way we did (we should have had the 3:1 at the output shaft and not the 10:1), and after making the necessary corrections we never had any issues with it again.

Even in the rare instances of failures though VP gearboxes are extremely easy to replace stages on. The exception being in our case due to the way we mounted ours making it difficult to take apart (which, incidentally, would not have been an issue at all with the new v2 VP gearboxes).

Re: Strength of Versaplanetary & PG-188
 

If you pay attention to the recommendations listed on the Vex website you shouldn't have too many problems For mechanisms that are going to experience a bunch of shock loading, our team tries to use a final chain and sprocket stage to minimize this.

Some of the many possibilities for gear reductions are not recommended by VEX.... please take a look at this pdf from their website:

https://content.vexrobotics.com/vexp...4-20161121.pdf

Depending on the motor.... you will see that some reductions are not advised. Primarily those that use the 9:1 and 10:1 gear sets....these have very tiny sun gears that cannot take the load. the only issues we have ever had have been with these 9:1 and 10:1 gears sets under loading.