Hi Andy and
to the forum.
Unfortunately there are many factors that affect the required spoke length, including the hub diameter
(this varies with motor type), Rim diameter and type
(conventional or deep "V" section rim), spoke pattern
(crossed, radial or paired holes etc.) which makes it very difficult to predict which spoke length you will require.
Even Magic Pies with the same diameter
(and fitted with identical GM rims) require spokes of different lengths to allow for the different spoke patterns:
Not sure which version it is. It's the one with the wiring coming out through the axle.
If the wire is coming out of the end of the hollow axle, it is unlikely to be a Magic Pie. Take a look at the picture in the previous posts to see if you can identify the motor type.
If you can't recognise the motor type, perhaps you can
post a picture of your motor to help us to identify it.
Alan