Inmotion V11 Electric Unicycle Repair

  Rider crash and poor initial quality result in a complex repair.

Event Report 20221027

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The Experience

Back in May 2022 I got a "wild hare" and decided to purchase a couple of electric unicycles (EUC).  While, to the casual observer, this  might seem to be a rather random decision, the truth is that it was a bit more well-considered that purely random.  I like new experiences, particularly those that involve motion.  An old buddy referred to them as "kinetic sports".  Over the years I have owned a series of 3-wheelers, 4-wheelers, jet skis, snow skis, water skis and similar toys.  We recently purchased a pair of e-bikes to allow us to explore our town without the burden of driving and parking a car.  We have used the bikes more than I expected and at last check were at about 750 miles on the meter for both bikes.  But, the bikes have several unavoidable limitations - size footprint and weight.  The fantasy was that a couple of e-bikes would allow us the ability to explore terrain near our camps when we are rolling in Thor (our 4x4 camper).  We spent several weeks considering the circumstances and concluded that the size and weight of 2 e-bikes were incompatible with mounting them on Thor.  While way below the specified GVW for the truck, the mounting geometry was problematic.  Particularly when you consider that we actually 4-wheel with Thor and any mount supporting 150 lbs would be under great stress when rolling.

After considering a number of alternatives for mounting the e-bikes, both off-the-shelf and custom, we concluded that given our current setup, an external mount was impractical and an internal mount was impossible due to size.  Since the objective is to provide campground mobility, it seemed as if the cart was leading the horse.  After some additional research, I decided that an electric unicycle would meet the requirements (albeit with some constraints) and the EUCs we were considering would fit in a existing tool box on Thor without additional fabrication.  Plus, the tool box would provide moderate weather protection and would have a low loading height (unlike the e-bikes that would have to be way, way above ground level to avoid approach/departure angle conflicts when off-roading).  True, there would be a steep learning curve for operation of the EUC, but hey, I like new experiences.

I purchased an Inmotion V11 EUC with a pneumatic suspension.  Experiencing the "steep learning curve", it took about 5 hours of practice over a week to be able to achieve an "unassisted roll" with limited control (direction and speed).  During practice in my driveway, I ran into the tires on Thor and the rubber EUC wheel locked against Thor's tire.  In response to no possible tire rotation, the servo board in the EUC applied max current to the motors, thus frying the output power transistors.  I was heartbroken.  Since COVID and the supply chain disruption was still in full swing, I expected that shipping times for a replacement board would be measured in months.  Not sure what to do, I queried Kathleen as to whether she was "committed" to the EUC and she said "yes".  So I ordered both the replacement board and another complete EUC.  The new EUC arrived in 3 days (same as the first one), but as expected, the board took months.  In the meantime, our skills and interest level increased so I ordered a third EUC (also delivered in 3 days).

Both Kathleen and I have become reasonably proficient on the 'wheels.  In my case, I have logged over 1200 miles since I took delivery of the 3rd 'wheel.  When the replacement board arrived, there was no driving force to repair the first wheel.  In fact, there was a negative reason because the disassembly was quite complex.  So, the board, in its shipping container when on the shelf in the garage where it sat until I was politely prodded to action and compelled to attack the problem.  The short photo sequence below shows that repair action as well as an unexpected discovery.

All the photos below were taken with my Sony A7R4 camera with 35mm and 90mm macro lenses.  All images were shot in uncompressed RAW format (at about 120mb per image).  Digital images were developed with Capture One and reduced to 1200x800 pixels for inclusion in this page.

The photos below are what we saw.

A photo of our "in-service" EUCs.  The left 'wheel is mine, the right one is Kathleen's.  Note that my 'wheel has "power pads" which both provide some mechanical padding between the shins and the 'wheel and some additional ability to stop faster by mechanically coupling the shins to the wheel via the ledge.  Also note that Kathleen's 'wheel has the trolley handle deployed.  The handle allows you to easily roll the 60 lb wheel up slopes and stairs by using the motor assist feature.  Light upward or downward pressure on the handle cause the 2200W motor to roll in the forward/reverse direction.  Both 'wheels were dusty as they were used at Calico MogFest on the dirt roads.

A zoom on my tire shows substantial wear due to my 1220+ miles of rolling.  I corner reasonably hard because I enjoy the "carving" of the wheel on the asphalt.  This sensation is similar to that experienced when snow skiing down gentle slopes.  This tire will be replaced soon and I already have the replacement tire and tube in the garage.

Now moving on to the original damaged 'wheel, the side saddles were removed exposing the suspension rails and 4 socket head cap screws that attach the rails to the frame handle.  The handle is made of cast aluminum while the balance of the 'wheel is constructed of machined and anodized aluminum, plastic or carbon fiber.  The objective is to remove the handle allowing access to the electronics that are located under the stamped aluminum dome behind the red shock valves.  Pressure in both sided of the shock was released and the nuts that hold the handle to the shock ram were removed.  The socket head cap screws were removed with a 4mm hex key and the handle disconnected and removed.

  Using a flat head screwdriver, the dome was loosened and removed exposing the control electronics.  Note that there are 2 boards - upper and lower.  The upper board is the CPU board and the lower board (the one that is damaged) is below.  The large yellow connectors are for power coming from the 84 volt battery.  These are high-current connectors and must be handled with care.  Positions of connectors were noted and zip ties were cut.

The inside of the dome was inspected and revealed arcing from a short had occurred.  The arcing melted the cover.

Inspection of the other side of the assembly revealed chafing of ALL THREE of the motor supply wires.  This wheel uses a 3-phase brushless DC motor and the blue, green and yellow wires supply current for the three phases respectively.  It should be noted that the plastic pass-through connector was deformed/damaged, likely due to careless assembly of the 'wheel's electronics during manufacture.  Several other wires were pinched by the cover.  Also note that the shrink wrap used to cover the motor supply wires did not extend to where the actual damage occurred.  The left-side shock strut (with Schrader valve) is visible to the center right of the photo above.

Power and control plugs were disconnected and secured.  Top board was removed revealing the bottom board.

The new power board was supplied not as a repair part, but rather as a sub-assembly extracted from the production line.  The board was attached to a brand new cast aluminum heat sink and the first action was to remove this board from the heat sink.  Very odd and costly for the company.  Each of the black screws along the bottom of the casting attach one of the metal oxide semiconductor field effect transistors (MOSFET) to the heat sink.  These MOSFETS are the power control for the 'wheel and they can reach high temperature if they are not correctly connected to the heat sink.  Underneath the MOSFETS is a pad of silicone coated with thermal grease (to improve heat conduction) to allow lower temperature operation of the devices.

After the bottom board was removed, a closer inspection of the motor supply cables was possible.  There are several items of note in the photo above.  First, each of the 3 phases were compromised.  It is highly unlikely this was due to mechanic vibration as the 'wheel only had 3 miles on the odometer.  Second, the shrink wrap insulation did not extend to the area where the chafing occurred.  Finally, the plastic connector appears to have been damaged by incorrect installation of the cover.  A conclusive repair solution was needed.

The new power controller (bottom) board was installed and heat shrink insulation was added to the motor supply cables.  Another layer of heat shrink tubing would be required to provide a safe installation.

Additional heat shrink tubing was installed over the motor supply cables.  The space under the dome of the cover was restricted, so several combinations of cable routing were required to prevent mechanical interference between the cables, the dome and other electronic components.  Special care was expended to insure that no cable pinching resulted from installation of the dome.

Once the insulation issues were addressed and the final wire routing determined, reassembly was reasonably easy.  If you are performing a similar repair, insure that all pressure is removed from both sides of each shock.  Failure to do so will impair your ability to reattach the handle to the shock sliders.

Both shocks were re-inflated to factory specs and power was applied to the system.  Happily, the 'wheel booted on the first try.  The battery array was very low, but it had been sitting for nearly 7 months.  Once the batteries were fully charged, a firmware update was performed.

The board "exchange" was much more complicated and more time consuming than expected.  It was clear that the design of the 'wheel was not done with ease of maintenance as an objective.  With Kathleen's assistance to hold the 'wheel during actions, this repair took about 4 hours.  Discovering the insulation abrasion was a surprise, particularly since this is essentially a new 'wheel (3 miles).

Hopefully, with the repairs to the cabling, this 'wheel will be better than new (or at least better than when it was delivered to me).

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