Torque limit of 10:1 VP gears

Technical
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We have been unable to find the torque limit of 10:1 VP gears. We would like to lift our robot with 2 775s connected on one shaft with 16t sprockets, using 2 10:1 VP gears (100:1 total). Previous posts have cautioned against high torque loads on 10:1 VP gears but not specifics. If data is not available, would appreciate anecdotal evidence of climbing elevators or suggestions.

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There is a load rating guide on the vexpro page for the versplanetary. It looks at static load, not shock load, though so you might want to de-rate their recommend ratios by 2-3x if your system will see a lot of shock.

100:1 is up there, and a bit risky. The less reduction in the stage the stronger it is as there will be more meat between the center spline and carrier pin holes.

I’d recommend using a 3:1, 4:1 or 5:1 as the output when using such high reductions.

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We tried that setup in 2017 for our climber and it was a disaster. The gearboxes would literally explode on the field, and we only had like a 100lb robot. The most reliable we found was 40-50:1 and if we needed more reduction than that then we either used gear or sprocket reduction

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Thanks. Are the 10;1s always safe as the first stage? Would a 70:1 be significantly safer? It tolerates less torque but I am having trouble estimating shock load tolerance. Our elevator should not normally experience shock loads.

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Was your first stage 10;1? Did you try 70:1?

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Is the elevator chain powered with the 16T as the output?

Another option I like is to add a spur reduction like 18:40 up to 18:84 (whatever fits) to reduce the ratio required in the versplanetary.

Fwiw 973’s climb last year lifted the entire robot on two 25:1 775s with a 16T #25 sprocket output for a robot about 30 lbs underweight.

We didn’t need the climb to hold position via break mode so a low ratio worked.

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Yes
We will look into that

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We used 2x 775s each mated to 49:1 (two 7:1 stages) for our 2017 rope climber. It worked well (i.e. climbed fast and didn’t explode). We avoided 10:1 due to all the stories we heard of them seizing under load.

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https://docs.google.com/gview?url=http://link.vex.com/vexpro/pdf/VersaPlanetary-LoadRatings&embedded=true

2 stage 10:1 is “Green” for 1/2 inch hex output and 775Pro. A 3 stage to get you in the same range may give you more reliablility.

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It is better to make a 3 stake versa planetary for 100:1 maybe 5:5:4 alway with the biggest reduction closest to the motor

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You actually want the smallest reduction (strongest stage) at the output.

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Sorry your are right typo on that

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I asked this question in another post but never got an answer. What ratio would you have used to hold the robot up for 5 seconds last year, without a brake?

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Do not use 10:1 VP Gears for climbing with a 775. We tried using only 1 775 10:1, 10:1 in 2017 and kept stripping teeth. We ultimately switched to two 775s, through 2 different VPs, with 5:4:4, and a slight chain reduction to ensure we didn’t break the stages. 5:5:4 most likely would have been fine.

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Personally I’ve had terrible experience with the 10:1 gear rations… Honestly the only ones that ever end up breaking due to that tiny sungear

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This is with a dual-input VP, correct?
If so, 1 100:1 VP per 775 might be a safer bet if you can accommodate it.

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Actually they are connected to the same shaft, not same gear box. Running opposite directions.

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Aaah, thought you meant they were feeding into the same VP input shaft.
A climber should be relatively low shock load, compared to an arm or certain style shooters. I’d run with the 2x 10:1 for now, but leave room to shoehorn in a 3 stage VP or alternate solution.

We’ve done some ugly things with 300:1 VPs ard the first problem is usually the carrier pins backing out, but the 10:1s absolutely have a record of exploding.

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Just out of curiosity, when 10:1 gearboxes fail, what is it that is actually broken? I keep hearing that the problem is the small 8t sun gear, but when I started looking at the geometry, the thing that bothers me most is the large planet gears separated from each other by so-slightly more than their outer diameter. Does the sun gear fall apart, and if so how (loses teeth, breaks off of spline, other), or do the planet gear teeth hit each other (likely broken or missing teeth on at least two planet gears)?

Geometry Issue

Here’s the geometry issue I see: VPs have module 0.5 gears (that is, the pitch diameter is 0.5mm times the number of teeth). The 72t ring gear has a pitch diameter of 36mm. Looking at the 10:1, the sun gear has 8 teeth, meaning it has a pitch diameter of 4mm and pitch radius of 2mm, and the planet gears have 32 teeth, for a pitch diameter of 16mm and pitch radius of 8mm. The axes of rotation of the planet gears are therefore 2mm+8mm=10mm from the axis of the gearbox. Most gears have an outside diameter about 2 teeth larger than their pitch diameter, so the outside diameter of those 32t planet gears is 17mm. The distance between the axes of two planet gears is 10mm * sqrt(3) = 17.32…mm That is, there is less than one-third of a millimeter between the planet gears’ teeth as the flash past each other.

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