Motor update time!
Firstly, I appreciate all the feedback and discussion that we had around the first batch of these motors. It is our first time working in conjunction with a manufacturer (Reacher Tech) to develop custom motors so we are pretty excited to have a platform that we can continuously make better for eskate.
Just for some background, the motors started out like this which are the V4 version designed by Reacher:
We then completely redesigned the motor working with the engineer at Reacher Tech to come up with a new version that is more compact, robust, has more torque and made the cooling system able to actually work with the addition of air intake vents, as well as Radium-ified the appearance 
The result was pretty awesome in our opinion. Perhaps one of the most underrated features is that we are now running 4 of the same decent sized ball bearing (most other motors have 3 bearings often different in size and very thin which is bad for longevity). And the bearings aren’t installed with a huge press or anything so it is possible to replace them at the end of their lifespan without being a massive pain. This means the motors can last a very long time if not beaten to death climbing rocky mountains.
Unfortunately though there were some key issues that took us by surprise. I have condensed them below in case you don’t wish to read about everything:
Over battle hardening
Firstly, there was a misunderstanding of what is “battle hardening” and how far to go with it. Instead of just reinforcing the magnets with epoxy we were surprised to see the entire core of the motor had been potted in resin, which negates the cooling system.
Sensor issues
Unfortunately this was the least of our worries, as we had more importantly discovered the hall sensors didn’t seem to work properly. Sometimes they would detect and work, but often they would not detect in vesc or fail after a short while, despite the sensors showing ok readings when measuring with a custom made test device. So we ran the motor under load on our dyno and checked the sensor readings with an oscilloscope to find that there was quite a lot of electrical noise, with voltage spikes that can trigger false readings. The same would go for the temperature sensor, and I know all about what kind of injury temperature sensor noise can cause after riding a board with Maytech 6396 motors. Quite dangerous when vesc prefers to protect the motors instead of the rider.
Thanks to the help of this forum it became quite obvious that running delicate sensor wires through the stator slots of a motor where they are sandwiched between spinning rare earth magnets and an electromagnet running at high frequency is probably the cause of the electrical noise. That and some other issues to do with these particular hall effect sensors themselves.
Other problems
There were some other small things like shim washers being too big and rubbing the bearing cage so we replaced those with smaller ones for our beta testers, as well as the sensor cable being too short and stiff, the wrong loctite used on retaining screws, and visual appearance things like white residue in the vents that couldn’t be cleaned off.
So on the latest revision of the Radium/Reacher motors we changed just about everything to do with the sensor system, so much so that the sensor pcb is on the opposite side of the motor (thanks @Trampa for the great suggestion!). We changed the hall effect sensors to a different brand and type, added decoupling capacitors to the sensor pcb, and moved the sensors to front of the motor where the wires can run straight out without going near the stator or magnets. We also changed the sensor wires themselves from 80C rated PVC to 150C rated teflon in a multicore flexible cable and added glue to stop the pins moving on the sensor plug. We ditched the resin coating on the stator to allow air to flow between the coils, and upped the strength of the magnets for more torque. There is also now sufficient Loctite of the right kinds in the right places, and we are currently testing the latest batch to assess if they are ready to be made available for purchase 
So far the sensors are working great, and you can now feel hot air coming out of the exhaust vents when you spin the motors up after some riding.
Here are some fancy photos of how they look:
https://radium-performance.com/collections/frontpage/products/radium-6485-motor