BILL OF MATERIALS (FOR THIS PART OF THE BUILD)
In this episode, we convert the mechanical aspects of the trike to electric. We are not tackling the "Smart" electronics at this stage. We first need to understand the challenges ahead once we test ride it still dumb and dangerous.
The motor controller and throttle weren't worth a build as they are very inexpensive to purchase. Since our build spanned multiple disciplines, not everything we needed was on Newark, so I included the raw specs with this BOM:
650W, 36V, 450RPM Output Geared Motor
34 Tooth Sprocket
15mm bore freewheel
36V Thumb Throttle and Motor Controller
(2) Inline Fuse Holders
(2) 25 A Fuses
3" x 3/16" Carbon Steal plate
1/4"x 20 Grade 8 bolting
Dual Piston Brake caliper and hydraulic actuator (as found on ATVs)
MOUNTING THE MOTOR
After assessing the Trike and mocking up its rear carriage in Autodesk Fusion 360, we elected to mount the motor to a 3/16" plate that was then bolted to the top bracing of the carriage. It allowed for a direct shot for the new chain after cutting the trike basket. It also would allow for installing the batteries low to keep the center of gravity of the trike low.
We found there was not enough clearance to install the new sprocket. So, we elected to eliminate the original band brake at that center location and install a disk brake at the drive wheel. We plan to make this actuate from the MKR1000 versus by cable.
We wired the 3 batteries in series to create a 36V power source.
Here is the overview of the system. Note: At this point we don't have the MKR1000 Brain Box Shown in the diagram - so it's still dumb and dangerous!
Basically, the MKR1000 brain box we will make puts 3.3V to a transistor that, in turn, pulls in a relay. The relay switches from its normally closed state to the open state. Wired to the relay is the independent motor controllers brake interlock. This, in turn, allows the motor controller to drive the motor. Basically, we will hack one brake interlock to get interlocks on pedaling, speed, tilting, proximity, and alarm. But first, we need to test it mechanically.
It assembled nicely and Connor took the motorized for a test drive in its l dumb and dangerous state.
The test drive identified the following hazards:
- You could easily run over your legs with the back wheels if you accidently hit the throttle when stopped with your feet down.
- In a panic, its hard not to remember to take your thumb off the throttle while braking.
- The original brakes do not stop the trike quickly enough.
- The trike has to take wide turns. Tight turns that you would do on a bike will actually cause it to go up on one wheel in the back. This is not a problem for the paved rail trails we ride, but would be bad for a crowded beach.
We are very happy with the batteries. We have ridden nearly 3 hours on the out-of-the-box charge!
Stay tuned for our next video where we code and breadboard the "Smarts" of the design using the MKR1000 and various sensors of the maker kit.