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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