Electric Propeller-Driven Tricycle Conversion

A while ago, I picked up a high power brushless DC motor and carbon fiber propeller from a lab at my university. They were being thrown out. I thought "wow! These are some great parts, I am definitely going to build a spectacular project with them". Then, the propeller and motor sat on my desk doing nothing for a few months... Sometime later, I was at a used bike auction and picked up a bicycle for 10 dollars! This was not as good of a deal as you may think it was(the bike was missing wheels, a chain, and various other important things), but it did give me an idea.

You know those fan boats that they drive down in the swamps of Florida? What if I applied that idea to a bike....

And so began my project: The Propeller Tricycle.

(Keep in mind, this is a dangerous vehicle and my version is very much still a prototype. Do not attempt to build unless you know what you are doing.)

Stuff you need:

• The Bike: I was able to get a cheap bike frame from an auction, but most any frame will work. Many people have an old bike sitting in their garage. All you need is a frame that is capable of holding a front wheel and has rear suspension.
• Motor: I found out that my scrap motor was from a harbor freight chainsaw after reading this quite entertaining article. If you are actually trying to build this thing, you have a few options. Number one, cannibalize a harbor freight chainsaw. I think this is the one my motor came from. They are actually pretty good motors for the price, the only thing that would make them better is a hall effect sensor array. Number two, buy a hobby brushless dc motor. They will probably be a significantly higher quality.
• VESC: This is the part that actually controls the motor. They are a bit pricy, but are very nice. Here is where you can buy a similar one to what I used. You may also want to just take the controller out of the chainsaw itself. Then you don't have to spend anymore money. I have not tried this but if you do, let me know!
• The Propeller: I happened to get lucky enough to find this part, so I cannot vouch for the best website to buy one. Amazon has similar propellers for a hefty price, but I am sure that they could be found cheaper on aliexpress or some similar website. My 34in propeller worked great with the chainsaw motor.
• Propeller mounting supplies: I mounted my propeller using a McMaster shaft collar that I drilled and tapped mounting screw holes in. This one works great for the harbor freight motor.
• Control electronics: I used an Arduino Nano, button, slide potentiometer, spring, and servo-wires to build my control system. I pulled all of these from my makerspace's electronics drawers, but you can purchase them from amazon or digikey.
• Battery: I started by using my home made 42v Ebike battery to drive this fanbike, but it was not able to put out enough current. I eventually switched to a 32v 14ah nimh battery in series with a 12v 13ah lead acid battery(the 2 chemistries are fine together as long as you do not charge them in series). This gave it plenty of power. Just make sure the battery voltage is lower than the max VESC voltage.
• Back wheels: I personally used castor wheels that I found in the trash for this, but most small wheels should work. You just need a wheel that is preferably smaller than a bicycle tire.
• Mechanical Hardware: The rest of the parts needed for this project are somewhat open ended. I gathered a bunch of scrap wood and metal to build the frame/motor mount, but you might do differently. If you really plan on building this thing, then I would recommend reading the rest of this instructable, then making a visit you your local hardware store(or scrap yard) to get the rest of the parts.

I started by making a mount for the motor out some 90 degree aluminum L bars. A round space was cut out of the side using a band saw to accommodate space for the motor. I then marked and drilled out 4 holes that were lined up with the holes on the motor bracket. This mount had an additional piece of aluminum attached to the bottom to give it structural support. The resulting mounting structure was then bolted to a piece of plywood weighed down with various pieces of shop equipment.

To mount the propeller, I first obtained a shaft collar from McMaster. The motor shaft is completely smooth, so this is the most reliable method for attaching something. I then lined up and centered the propeller using a 3D printed jig and used a mill to drill out 2 screw holes. These holes were the right diameter to be tapped to the size of the screws I was using. The result was a reliable and strong propeller mount.

The VESC now needed to be attached to the motor and programmed. The 3 output wires of the VESC were connected to the 3 input wires of the motor. I used a lot of solder and heat shrink tubing for this step. It does not matter how you connect these wires, as switching any two connections will just make the motor reverse. If the motor is spinning the wrong way, the direction can be changed in the VESC programming.

To program the VESC, connect it first to the battery, then to your computer. You will want to remove the propeller before calibrating and programming it (just in case the motor decides to go berserk). Then, downloaded an open source program called VESC tool. This program is awesome. It has all sorts of settings that you can use to make the VESC bend to your will. After this, run the setup wizard "setup motors FOC" found at the top of the screen. This runs a series of tests to determine your motor's internal resistance, inductance, and other parameters that will optimize power output. I then set the current limits under the 'motor' section to 40 amps, as this is the maximum value that I wanted my battery to output. This is also lower than the VESC's max output of 50 amps. You can choose a different value if you have a different VESC and battery pack. After you are done programming the settings, upload them to the board using the 'Write Motor Configuration' button on the right taskbar.

To test the motor, click on the icon with the arrow keys, located on the left side of the VESC tool program. Once this is selected, the motor can be tested by pressing and holding one of your arrow keys while simultaneously pressing and holding the other. Luckily, my motor worked!

I highly recommend looking into all the various functionalities of VESC tool. While there are way to many settings to explain in this instructable, what I have described thus far will be sufficient for this project.

I then needed to build some kind of structure to mount the propeller to the bike. This structure would need to be wide enough to prevent the bike from tipping over. It also needed to be strong enough to support a person, batteries, and motor. There would also need to be places for wheels to go and a way to mount it to the bike frame that I had.

To help brainstorm this design, I laid out the various parts on the floor and did a bit of thinking.

It was now time to build the propeller bike. I started with a 1x6 inch pinewood board. I realized that this fit perfectly on the bottom of the back diamond part of the frame. To secure it, I used 4 conduit clamps with a secondary pinewood board bolted to the top, effectively sandwiching the tubes of the frame between to pieces of wood.

To mount the wheels and fan, I took a 2x4 and bolted it to the bottom of the 1x6. The 3 bolts used here were also used to secure the propeller structure in place as well. I then drilled on both sides of said 2x4 and used them to securely mount the wheels. While these are castor wheels, they are mounted in such a way that they are fixed.

This version is shown in the first image attached to this step. It was not very stable. Riding it felt like I was always on the verge of splintering the wood. Luckily that never happened, but more support was needed.

I began adding more wood and more metal to it. I bolted a 2x2 running parallel to the bottom of the 1x6 plank to give the midsection more support. I also bolted a particle board sheet to the intersection of the 2x4, 2x2, and 1x6 to give that joint more stability. I finally added 4 cross braces to distribute the force from the propeller and diminish swaying of the vehicle. 2 of the supports were aluminum L bar, and 2 of them were scrap steel used for shelving.

After all of these modification, the bike was very stable and ready for electronics.

The power electronics in this bike are quite simple. The main power on/off switch is an e-stop button located conveniently in a place where I can press it with the back of my foot should a problematic situation arise. This was placed in series between an XT-90 connector(battery side) and the VESC. The wire that I used to connect the VESC to the motor and the battery was 6 gauge. This was to prevent any power loss from the large electric currents flowing through.

The VESC was originally bolted to the pinewood board on bike, but I decided to move it up onto one of the support beams to make room for more batteries.

The final part of this project was building an ergonomic system that I could use to control the speed of the propeller. This system would also need to include safety interlocks. I decided build a box that would mount on the handlebars of my bike. This box would contain an arduino and have a slide potentiometer and a pushbutton. It would be powered by the VESC and also send data back to it in the form of a PWM signal.

To build this, I first connected a button to pin 3 of my arduino, the PWM input of the VESC to pin 10, and the middle of a sliding potentiometer to pin A0. The other ends of the sliding potentiometer can be connected to 5v and ground. The 5 volt and ground wires from the VESC(looks like a servo wire) need to be connected to the 5v and ground pins of the arduino as well.

After you have completed the wiring, it will be time to test the circuit. First, upload the included code to the arduino(keeping in mind the pin connections that I mentioned). You will then need to connect the propeller bike to power, connect your computer to the VESC, and open VESC tool. Under App settings>general, select APP to Use: PPM. Then under PPM>general, select Control Type: Duty Cycle, No Reverse. Finally, adjust the mapping setting so when you adjust the sliding potentiometer on the arduino, the duty cycle bar will go between 1 and 100. You will need to select the real-time data stream option in the right menu to see these results. The arduino will be sending out a PWM signal that contains pulses of a certain width(time). The VESC needs to know what the minimum and maximum pulse width is so it can map that to the propeller output power. After this is complete, click the 'Write App Configuration' button.

To mount these control electronics to the bike, I used a 3D printed part and a laser-cut box. The 3D printed part was designed in SOLIDWORKS and creates a flat surface on the drop handlebars to attach a box to. It also has a hole to attach a hose clamp for the purpose of securing it to the bars.

The box was made on this really cool website that generates fingered boxes for laser cutting. I made sure to add holes for the button and slide potentiometer as well. After mounting all the electronics, I super-glued the box to the 3D printed part and attached a spring to pull the potentiometer up. That way when you let go, the throttle turns off.

The functionality of the controller is as follows. When it is first powered on, nothing happens. When the button is pressed and held down, the propeller ramps up speed into idle mode. Here, it is spinning quite slowly. Then, the throttle potentiometer can be moved. This will start ramping up the motor speed proportional to the potentiometer position. At any point if the button is released, the fan will rapidly decelerate.

Relevant files are attached below.

Deep in the the parking garage at my university, a small clicking sound reverberates off the concrete walls. This was the click of an e-stop button switching to the 'Run' state. Then... A second click. The click of a smaller button. Following this click is the sound of something spinning in the distance. The sound somewhat resembles desk fan on it's last leg. The sound is getting louder now. What seemed to be a broken desk fan at first now sounds like an airplane coming down the runway at full speed! You look to see what could be the cause of this commotion, and your eyes behold a quite odd sight. A college student with a motorcycle helmet is barreling toward you at a high speed! His vehicle? Some odd contraption that looks like the local bike repair shop decided to fix a swamp boat. It was...

The Propeller Trike.

Thanks for reading! I had a good bit of fun working on this project. There are a lot of things to work on though. My first order of business is to weld a stronger and more sturdy frame, then bend/weld a cage for the fan(things need to be at least somewhat safe here). Any ideas or improvements are welcomed in the comments.