are all ISIS cranks compatible?

For instance Grin Technologies right now has QX ISIS cranks and NV ISIS cranks (https://www.ebikes.ca/shop/uni-shop/cranks.html), will they all fit a nimbus unicycle? Or is there something specific about the different brands?
Thanks in advance!

I have tried the Nimbus, Quax, KH and Impact ISIS cranks. They all work! There are differences in length, flair, cross-section shape, etc. But they all should work with any ISIS hub. There can be variations in how far the cranks slide onto the spindle. If you are buying new cranks, I suggest you get a set of ISIS compatible spacers in different sizes. Otherwise, you could cause your cranks and hub to wear prematurely because of a poor installation. More info than you probably wanted…

elpuebloUNido, thank you, that is a perfect amount of information, I will definitely grab some spacers as well, I appreciate you taking the time to write this out.

In theory it’s a standard, but in reality manufacturers don’t have the same tech tolerances. Result is, some cranks come out with no tools, or no effort, whilst some make you sweat just tightening them onto the hub.

I believe that all ISIS hubs and cranks produced now are close enough in their tolerances that they are interchangeable with some fiddling with spacers (I use stacks of snap-rings for fine adjustment). Very early ISIS hubs and cranks from KOXX were on the very edge of the spec and had didn’t play well with other brands. It’s the same standard for bike bottom brackets and cranks as well.

How do you decide how many spacers to use? What are you looking at for this adjustment?

For spacer sizing:
This is from an old thread, there shall be a press fit connection between the male and the female tapered spline of about 3 to 6 mm, normally around 5 mm. In practice this means, when you attach your crank arms by hand, there shall be around 3 to 6 mm space between crank shoulder and spacer (if not: take a thinner spacer!). Then you tighten it till there is no gap between spacer and crank left to reach the proper amount of press fit and then up to about 40 Nm which will tense up the screw enough so that it can not loosen itself.

You can buy an assortment of spacers for not much, https://www.unicycle.com/nimbus-isis-hub-spacer-kit/

I found that different size spacers are needed on some and to find out what thickness is needed I put the arm on without a spacer and tighten crank bolt just enough that the arm is on securely then measure the gap behind the arm using the shank of a drill bit ie 4,5,6mm etc

I push them on by hand and see how much space there is between the bearing and the crank then use a spacer that’s 3 or 4mm skinnier.

If the spacer is too thin the cranks won’t tighten up to them like a stop and allow the crank to creep a bit eventually loosening.
If the spacer is too thick the tapered spline won’t be a good tight fit and again you might see some movement. This is where you are most likely to hear a creak from the interface.

I don’t recall ever closing more than a 3mm gap while tightening a crank bolt. 6mm seems excessive, though the people who wrote the spec must’ve known what they were talking about. Since the ISIS spec was written, however, cranks have been produced with higher-temperature forged aluminum. I wonder if a harder material might require a smaller gap to fill. I also wonder if filling a larger gap will cause the cranks to fit further up the spindle on successive installations.