Team 449 Climber

[Oblarg]

Originally Posted by jojoguy10

I'd be very interested to know how it performs at about 150lbs (maximum robot weight is 154lbs)

The gearing was selected very conservatively to ensure that we're on the rising side of the power output curve.

The current gearbox is 50:1. Mini-CIM output torque is listed at 1.4 N*m. Our winch drum is 1.25'' diameter, so .625'' radius.

Neglecting friction, we have:

(150 lbs * .625'')/(1.4 N*m * 50) = ~15% of stall torque.

Now, I have really no idea how big the frictional losses actually are in this system, but I don't think there's any way they'll take us from 15% motor loading to over 50% (which is peak power, i.e. the loading for which this gearing provides optimal climb rate).

Fully-loaded climb rate (using the frictionless numbers) is somewhere around 6'' per second.

Upon reflection, we could probably gear it a bit faster (we had done the math for the gearbox when we were considering a larger-diameter winch).

[T^2]

Your gearbox will fail you after a regional's worth of matches, maybe sooner. The aluminum ring gear will flex enough to allow the planet gears to ratchet, and you will lose the climb.

[Oblarg]

Originally Posted by T^2

Your gearbox will fail you after a regional's worth of matches, maybe sooner. The aluminum ring gear will flex enough to allow the planet gears to ratchet, and you will lose the climb.

Are you sure? The 50:1/mini-CIM combo is labeled as acceptable by VexPro's documentation, and as noted above we're not actually anywhere near the peak loading on it.

[T^2]

Originally Posted by Oblarg

Are you sure? The 50:1/mini-CIM combo is labeled as acceptable by VexPro's documentation, and as noted above we're not actually anywhere near the peak loading on it.

Catapult failure in first 2014 regional, canburglar failure in second 2015 regional. Similar physical setups.

[Oblarg]

Originally Posted by T^2

Catapult failure in first 2014 regional, canburglar failure in second 2015 regional. Similar physical setups.

Any gearbox suggestions, then?

[T^2]

Maybe custom if you have resources. Vexpro CIM gearboxes would work, but bulky because you'd need two reductions.

[Oblarg]

Originally Posted by T^2

Maybe custom if you have resources. Vexpro CIM gearboxes would work, but bulky because you'd need two reductions.

We don't have much in the way of machining resources at all (miter saw, drill press, and a little hobby lathe), and the drive gearboxes would be an absolute nightmare in terms of space/weight.

I think I'd rather try to add a 2:1 reduction or similar via. chain to reduce torque on the gearbox if this proves to be problematic.

[Ari423]

Originally Posted by T^2

Catapult failure in first 2014 regional, canburglar failure in second 2015 regional. Similar physical setups.

Are you sure you were using the VersaPlanetaries correctly? I've used them a number of times without problems and I've pretty much only heard good things about them. Were you properly greasing them? Did you check the max loading guide before choosing a reduction? Did you assemble them in highest to lowest reduction order? Did you support the end of the shaft?

[SuperBK]

Wait - there is a knot in the at the bottom end of the rope? Or, Are you planning to bring your own rope and its legal to have a knot at the bottom to grab onto?

[Oblarg]

Originally Posted by SuperBK

Wait - there is a knot in the at the bottom end of the rope? Or, Are you planning to bring your own rope and its legal to have a knot at the bottom to grab onto?

https://firstfrc.blob.core.windows.n...ligibility.pdf

[Kevin Thorp]

Thanks for posting your design.

If there is any concern about Versaplanetarys taking the load, you could go with half the gear reduction and a 1:2 chain sprocket ratio.

[Oblarg]

Originally Posted by Kevin Thorp

Thanks for posting your design.

If there is any concern about Versaplanetarys taking the load, you could go with half the gear reduction and a 1:2 chain sprocket ratio.

Yeah, I considered that earlier in the thread. We're really not that worried about it, though, given the loading and VexPro's documentation.

[Bluejackets]

Without a ratchet how does it not come back down?

[Oblarg]

Originally Posted by Bluejackets

Without a ratchet how does it not come back down?

There's a half-inch ratcheting wrench on the hex shaft.

[Paul Copioli]

Originally Posted by T^2

Your gearbox will fail you after a regional's worth of matches, maybe sooner. The aluminum ring gear will flex enough to allow the planet gears to ratchet, and you will lose the climb.

Bold words are mine for emphasis.

This is completely false. This is not how the ring gear works in a planetary system. The only load that goes in the direction to cause the gear to flex is the separation forces of the planets, which is quite low even when the gearbox is overloaded. Please do not make claims that look like statements of fact when you have no idea what is actually going on.

Now, I am sorry that you had failures, but I can tell you that a steady climb is NOTHING like catapult and can burglar loading scenarios as those have extremely high shock loads. I an willing to bet that you either had planet carrier failure or a failure of the spline. I would like to hear about the details of your setup and I can pinpoint exactly what failed and why.

We did excessive failure testing on the VersaPlanetary and failed it in ways you can't even imagine. That is how we developed the load rating table and that is why the 10:1 has lower load rating due to the nature of the failures.

Again, I would love to help pinpoint what happened on your can burglar and catapult, but my team used VPs for both applications with exactly 0 failures.

Paul