Broken Krakens using single stage Max Planetary Gearbox

Technical
1

Hi all,
Just wanted to make people aware of this. It seems like when you use a single stage max planetary with a kraken, the kraken’s output shaft is long enough that you cant assemble the gearbox without compressing the kraken shaft. We were being careless and forced the max planetary together and it killed the kraken.
Rev has updated the docs on the kraken max coupler page since this happened.

Sequence of events:

  • We installed brand new kraken into a single stage 3:1 maxplanetary
  • Robot was powered on and the motor was spun with phoenix tuner. The motor stuttered and then stopped spinning
  • intake was taken apart to look for something causing friction which would stall the motor. during that process we tried spinning the motor off the gearbox and saw that it wouldn’t spin.
  • At this point we assumed the kraken was bad and grabbed another one. Just to be sure this wasn’t a code issue, we spun the new motor with phoenix tuner before it was installed.
  • Motor was installed into max plan. This time installed by a mentor, felt a little resistance when tightening it down, but didn’t think too much of it.
  • once motor was installed, tried to run it in phoenix tuner and motor did the same thing as before: stuttered and then stopped spinning.
  • Took motor off and started inspecting the gearbox. This is when we realized the kraken shaft was touching the button head that holds in the output shaft

We measured the kraken shafts of the two motors that had been in the gearbox and a brand new one and realized that they were ~60 thou shorter. It seem like when you apply that much force to the kraken it kills something inside it.

When you look at the kraken/max planetary assembly in cad you can see that when stacked up as intended there is some extra space between the motor and the gearbox

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What we had done is over tighten the screws that hold the base plate to the rest of the stages. This compressed the kraken shafts. You can see the conflict in the image below between the shaft and the screw.

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Solution:
We made a 1/8" plate that spaced out the motor from the gearbox. Something thinner like .090" would probably be better as the difference in spacing is 0.0773" but 1/8" was what we had.

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Here is a link to the onshape where I checked the spacing and made the spacer plate:

19 Likes
2

I see they added the disclaimer “A single cartridge reduction setup will still require modifying the Kraken X60 shaft to prevent damage to your motor” but don’t give any guidance on what modifications need to be made. Anyone know exactly what needs to change?

3

I think they are telling us to cut the shaft down. It is not clear to me how that can work. Even if you cut the shaft down, the length of the coupler prevents the motor from getting any closer.
I don’t see how cutting the shaft alone solves the problem even if you are doing a 1:1 (no stage). Maybe I am missing something, I hope/assume REV tested a single stage MP with a kraken.

This, plus a desire to not modify our kraken shafts, is why we did the spacer instead.

edit: I had the wrong coupler in cad - if you cut the shaft down by ~65 thou it should clear the bolt

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4

Check out ultra low profile bolts. You might find one that will give you the clearance.

1 Like
5

We haven’t encountered this issue, but WCP does sell a nice motor spacer in both 1/4" and 1/2" flavors, could be another option for teams looking to space the kraken out for a single stage MaxPlanetary GB.

-Mike

5 Likes
6

Unfortunately, we have tried this and found that the kraken coupler that goes inside the gearbox is no longer nicely sandwiched and slides out over time. it’s a tight press fit when installing, but has loosened over time.

has anyone cut the shaft down or use kraken shaft spacers to fill this gap?

7

So far we have just used a .090" shim between the kraken and the planetary input stage without any issues.

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