Electric-trike build

USING TECHNOLOGY TO REGAIN EXERCISE AND FUN

A US sheddie family uses technology to regain exercise and fun

Why would anyone ever want to build a motorized, threewheeled, adult’s tricycle with the intent to use for exercise? Well, there’s a bit of a backstory.

When our son was just around two years old, we took a family hiking trip in the mountains of West Virginia in the US. On the final night of our adventures, we found a nice lodge on the way back where we elected to enjoy dinner and stay the night.

My wife seemed overly tired and, oddly, developed a sense of vertigo. I thought the uneven plank flooring of the old lodge was just messing with her balance. We decided to turn in early and get a good night’s sleep. The next

morning, on top of the vertigo, her left arm was numb.

Being just about an hour away from home, we headed to our doctor. Things moved quickly and within 12 hours, we were faced with the diagnosis of relapsing– remitting multiple sclerosis (MS).

Necessary changes

The new physical limits put an immediate halt to our outdoor recreation. Now, several years later, her physical condition is such that she can walk, though sometimes assisted with a cane, but her balance and left side are weak.

We ultimately moved from that side of the US to the Midwest. At our new location, we have over 128km of rail-grade, paved trails that allow electric bikes limited to 15mph (24kph). The trails are absolutely beautiful and that is what gave us the idea of making the motorized Ultimate Smart Trike. Using today’s technology and some maker know-how, we set out to design a trike to assist exercising by overcoming my wife’s specific physical challenges.

I thought the uneven plank flooring of the old lodge was just messing with her balance

Design parameters

To get back on the trails, we needed to establish a means of cycling that addressed:

• poor balance, so difficulty in keeping the bike in one’s own lane

• weak grip with the left hand when squeezing the bike brake

• inability to stand so as to ‘torque’ up hills

• inability to step high over the centre bar to mount the bike

• fatigue due to left-leg pain

• inability to open the garage door without dismounting.

Trike features

The smart aspect of our trike design is focused primarily on safety but also has a few other convenience features while still encouraging exercise. With a motor that is strong enough to assist up hills, we could not risk it introducing energy that could bring harm.

So my son and I came up with the following smart features:

• motor interlock due to over-tilt

• motor interlock when the brake is applied

• motor interlock when objects are too close

• motor interlock if pedalling is stopped or the rider has not yet started pedalling

• motor interlock if the rider has not yet travelled at minimum speed

• datalogging of speed, distance, travel time, tilt, calories burned, and interlock hits with identifying reason onto SD card

• LCD display of speed, distance, travel time, calories burned, and interlockstatus information

• garage-door opener/closer

• bike security alarm.

While we were at it, we thought of a couple of additional mechanical improvements as well:

• the ability to pedal unassisted, shift gears, and freewheel while coasting

• improvement of the stopping ability using a hydraulically actuated brake.

Hardware

To address all of these design parameters and features, we determined the following major components:

• inexpensive, six-speed, three-wheeled trike with a low centre bar to address balance

• 36V, 500rpm motor geared for 11mph (18kph)

• 36V motor controller and thumb throttle

• 34-tooth sprocket

• 15mm bore freewheel for the sprocket

• (three) 12V, 18AH batteries

• hydraulically actuated disc brake to reduce strength needed to squeeze the brake

• Arduino MKR1000 IoT (internet of things) kit for the brain box

• ESP8266 microchip to actuate the garage door

• ultrasonic proximity sensor

• tilt sensor to interlock the motor on hills or if tilting

• Hall effect sensors to allow calculation of pedalling and speed

• Adafruit Trinket microcontroller to open the garage door

• 3D printer filament for the brain-box enclosure

• 3∕4- by 1∕8-inch bar stock for the battery rack

All in, it cost about $US900 to build. However, to buy a trike from a manufacturer without nearly as many smart technology features is $US2995. To get us back on the trails, this build was a definite go for us!

We could not risk it introducing energy that could bring harm

Engineering design

This project took many aspects of engineering design: mechanical for the drivetrain, electrical for the motor power, IoT for the garage-door opener, and programming for its safety and convenience features such as the calorie tracker.

Let’s look at the electromechanical aspects. Although we designed the system to still require pedalling, my wife is assisted by a 36V motor. We first mocked up the trike’s rear carriage in Autodesk Fusion 360 to get an idea of how we would retrofit a motor.

In all, this was an amazing build for my family. My son Connor got great practice with all kinds of tools, software, and maker techniques. With the DIY targeted-assistive technology, my wife was able to overcome her physical challenges from MS to enjoy exercising and exploring our new region from the trails.

You can find the 3D files, schematics, bill of materials, and MKR1000 code on our GitHub repository at: github.com/RaisingAwesome/UltimateTrike.

All in, it cost about $US900 to build. However, to buy a trike from a manufacturer without nearly as many smart technology features is $US2995

Photographs: Sean Miller

Below: For the electrical design, we were able to purchase an online motor controller to link to our MKR1000 custom brain box. To interlock the motor, we simply simulated electronically the brake being pulled. This makes use of the off-the-shelf controller’s brake interlock. Here you can see the full wiring diagram

Right: We bolted a three- by 3 ∕16-inch plate to the top bars of the carriage to serve as a motor base. The ideal location for the batteries worked out to be low and centred. However, we were so eager to get it on the road that we simply secured them in the basket

BIKE ALARM CALORIES-BURNED COUNTER GARAGE-DOOR OPENER TRIP DATA LOGGER 36V MOTOR FRONT COLLISION DETECTOR BRAKE INTERLOCK SPEEDOMETER ODOMETER TILT INTERLOCK

Once we added the mass of the batteries and motor, the factory band brake on the trike was insufficient and too difficult to squeeze for my wife. So we modified the band brake to serve as a hub for a hydraulically actuated disc brake

Left: This much improved stopping power and allowed us to place a limit switch at the actuator to interlock the motor. The limit switch pulls a pin on the MKR1000 to ground. In our MKR1000 code, this signals to interlock the motor

Right: We then fitted the No. 40 chain to the sprocket. We used a nail punch and a small rotary cutting tool to size the chain

Left: To install the disc brake and 34-tooth sprocket, we simply removed one wheel, loosened the original cartridge set screws, and drove out the rear axle with a wooden dowel. We then sleeved on our new gear assembly and disc brake

Below: With a 3 ∕16-inch plate and a portable bandsaw, we were able to cut a plate to serve as a bracket to mount the brake caliper precisely on the installed disc

Below: We first breadboarded the overall circuit using momentary switches in place of Hall effect sensors. This allowed us to use our fingers to simulate pedalling, wheels rotating, and pulling the brake. With the breadboarded brain box, we were able to perfect the code for all our desired features, including triggering the garage door without having to dismount the trike, through the click of a button on the throttle

Above: Connor twisted cables to route to all the sensors mounted on the bike. To do so, we repurposed an old telephone landline cable we scavenged from the basement. Placing three individual conductors in a vice, he used a drill to twist all three neatly together

Above: To pull that off, the code in the MKR1000 monitors a dedicated pin. When the throttle switch is hit, the pin goes to ground. The code then sends a web client command to IFTTT.com. In turn it sends a command to our ESP8266, which is located at our door. It simply electrically switches one of our repurposed garage-door keychain buttons

The trail system allows us to get about anywhere in town, including to the grocery store, so we wanted to keep the basket. We used an air-driven cut-off wheel to make short work of a new opening

Left: An ultrasonic proximity sensor was mounted at the front of the trike. This feeds back to the MKR1000 to shut off the motor if anything is in front of the trike

Above: We designed a 3D-printed enclosure using Autodesk Fusion 360. On a side note, this software is great for designing just about anything, including furniture

At the heart of the brain box is an Arduino MKR1000. This allowed us to apply various sensors to capture trip data and interlock the motor should there be an unsafe condition

Left: Here we have the pedal sensor. It has a rare earth magnet that travels past a Hall effect sensor. This takes a pin to ground on the MKR1000, letting it know that the pedal is travelling. The MKR1000 code translates this to rpm. Once a minimum rpm is reached, it will allow the motor to receive power. This prevents accidentally hitting the throttle and causing injury when sitting idle and flat-footed. The Hall effect sensor bracket was 3D printed but actually could have been neatly duct taped in place

Left: On a rear wheel, we installed another Hall effect sensor to calculate speed. Our MKR1000 code also requires a minimum speed to be met before allowing power to the motor. This prevents a kick when the motor is first engaged

Right and below: With the board soldered together and in its enclosure, we then jacked the trike up and garage tested it

Right: On its maiden voyage, my wife took the trike on the steepest hills in our neighbourhood

Above: Our MKR1000 brain box has an SD card that logs data for us throughout the trip. It allowed us to dial in the tilt sensor so it doesn’t interlock the motors too conservatively

Above: For the bike alarm, we simply coded the MKR1000 to have a menu feature to enable the alarm. If the bike tilts, the pedals move, or a wheel spins, a piezo alarm will sound. Of course, we made it also interlock the motor in this state as well

Right: With batteries removed, the weight of the trike comes in at 32.5kg, just under the maximum for a standard ceilingstorage system. So we didn’t have to give up any space in our workshop!