Building Your Own Electric Three Wheel Bike
Yes, you can build an electric three-wheel bike (e-trike) by converting an existing adult tricycle with a hub motor kit or by fabricating a custom frame from scratch. The donor-trike route is the most practical for most DIYers: it costs less, requires fewer specialized tools, and is more likely to succeed on the first try. This article walks you through platform choice, component selection, assembly, and the crucial legal and safety checks that will keep your e-trike on the road and out of trouble.
Pick the Right Platform: Donor Trike vs. Scratch Build
Your starting point determines 90% of the project’s difficulty. Two realistic options:
- Adult tricycle (donor) – Look for a steel-frame trike from brands like Worksman, Schwinn, or Sun. Key specs: rear axle with a freewheel thread (not a cassette), 135 mm or 190 mm dropout spacing (most hub motors are sold for 135 mm), and a weight capacity of at least 300 lb to accommodate rider plus motor and battery. Used models on Craigslist or Facebook Marketplace often go for $100–$300. Avoid trikes with a one-piece coaster-brake rear axle – you need separate hand brakes.
- Scratch-built frame – Only choose this if you already own a welder and a frame jig. Use 1.5‑in steel tubing and a rear axle from a trike conversion kit (e.g., a 1‑in axle with pillow‑block bearings). You’ll need to calculate chainline and steering geometry yourself. Expect 40–60 hours of fabrication time.
Applicability boundary: The hub motor approach works reliably only on trikes with a straight, non‑tapered rear axle and standard dropouts. If your donor trike has a 3‑speed internal‑gear hub or a proprietary rear cassette, you cannot simply replace the wheel with a hub motor – you’d need a mid‑drive motor instead, which is far more complex to install on a trike.
Practical implication for your next choice: If you already own a trike, measure the rear dropout spacing (inside to inside) with a caliper before buying any motor kit. A 135 mm spacing handles most 48V geared hubs directly; a 190 mm spacing (common on cargo trikes) requires a fat‑tire hub motor or custom axle spacers. Buying the wrong width means you’ll need to bend the frame or buy a different motor – either adds a week of shipping and $50–$100.
Verification step: Take your calipers to the donor trike. Slacken the rear wheel axle nuts, remove the wheel, and measure the O.L.D. (over‑locknut distance) between the inner faces where the dropouts sit. Compare that number to the motor’s specified dropout width. Most Bafang RM G060 hub motors list 135 mm; some 48V 1000W motors come in a 190 mm variant for fat‑tire conversions.
Mismatch/trade-off: A scratch‑built frame lets you design the perfect geometry, but the risk of cracking at weld joints or having a misaligned rear end is real. An off‑center axle will cause the chain to derail under power, and repairing a cracked steel tube mid‑build is much harder than swapping a donor trike’s wheel. Unless you have certified welding experience, stick with a donor.
Choose the Motor and Battery with Care
A 48V 1000W geared hub motor (e.g., from Bafang, MAC, or MXUS) is the standard for DIY e‑trikes. It provides enough torque to climb 8–10% grades at 15 mph while staying within the e‑bike legal speed limit of 20 mph in most states. The geared hub is lighter than a direct‑drive and doesn’t drag when the motor is off – important if you ever pedal.
Battery: A 48V 20Ah (960 Wh) lithium‑ion pack gives 25–35 miles of throttle‑only range on flat ground with a 200‑lb rider. Place the battery as low and centered as possible – in a rear basket or mounted on the frame’s downtube – to prevent the trike from tipping during sharp turns. Use only packs with a built‑in BMS that cuts power at low voltage and high temperature.
Verification step for battery fit: Measure the interior dimensions of your intended battery location. A 48V 20Ah rectangular pack is typically 8″ × 5″ × 3″. Slip a cardboard mock‑up into the basket or frame compartment before buying. Also confirm the pack’s discharge current rating (e.g., 30A continuous) matches your motor’s peak draw – a 1000W motor at 48V draws about 21A continuous, but can spike to 35A on a steep hill. A 30A‑rated battery will sag and may trigger the BMS shutdown.
Mismatch/trade-off: Mid‑drive motors (like Bafang BBS02) seem attractive for climbing, but on a trike they force you to run the chain through a freewheel on the rear axle. That freewheel requires a specific spacing and a heavy‑duty chain tensioner. Mid‑drives also put all torque through the bike chain, which wears out in 200–400 miles on a heavy trike. Hub motors keep the drivetrain simple and the chain only for coasting or emergency pedal power – far less maintenance.
Essential Components Beyond the Motor Kit
| Component | Purpose | Practical Advice |
|---|---|---|
| Throttle | Controls motor speed | Thumb throttle is easier to modulate with hand brakes engaged. |
| Brake levers with e‑brake cutoffs | Kill motor power when braking | Use hydraulic or mechanical disc brake levers; avoid old V‑brake levers that don’t have a switch port. |
| Display (e.g., SW900) | Shows speed, battery level, error codes | Mount at handlebar height; set wheel diameter in the menu to get accurate speed. |
| 12V DC‑DC converter | Powers lights, horn | Wire from main battery; 10A converter is enough for headlight + taillight. |
|
| Lighting | Safety on roads | Separate switch so lights stay on even if controller shuts down. |
| Helmet | Crash protection | An e‑bike‑rated helmet like the JARSH Commute Smart EBike Helmet with Lights (NTA‑8776 certified up to 28 mph) adds integrated turn signals and 360° lights – especially helpful on a wider trike that drivers may not see. |
Step‑by‑Step Assembly
1. Prepare the donor trike – Remove fenders, chain guards, and any axle hardware. Clean the rear dropouts. If the existing axle nuts are rusted, replace them with stainless‑steel M18x1.0 nuts.
2. Install the motor wheel – Slide the motor axle into the dropouts. Place a torque arm (included with most kits) between the axle flat and the dropout tab. Tighten the axle nuts to 30 ft‑lb. Spin the wheel – it should rotate freely with no wobble.
3. Mount the battery – Use a waterproof battery bag or a custom bracket bolted to the frame. Secure it so it cannot shift forward during braking. Route the battery wire along the downtube or inside the basket.
4. Install the controller – Place it under the seat or inside a small tool box. Connect the motor phase wires (blue, yellow, green) to the controller’s matching colors. Connect the Hall‑sensor 5‑pin plug. Then connect battery positive (red) and negative (black) – use Anderson Powerpole connectors for easy disconnection.
5. Connect throttle, brake cutoffs, and display – Each plugs into a dedicated port on the controller. Test with a multimeter: the throttle red/black wires should show 5V when turned on. Do not power the system until all connectors are seated.
6. Secure wiring – Zip‑tie cables away from the chain, tires, and steering pivot. Leave an inch of slack at the handlebars for turning.
7. Bleed or adjust brakes – For mechanical disc brakes, center the caliper so the pad contacts the rotor without rubbing. For hydraulic disc brakes, bleed per the manufacturer’s guide.
8. Final safety check – Tighten every bolt, inflate tires to the sidewall PSI (usually 40–60 psi on standard trike tires), and lift the rear wheel – apply throttle slowly to confirm the motor runs smoothly without clunks.
Practical implication of wiring errors: If the motor runs backwards, swap any two phase wires (blue and yellow, for example) – the motor will immediately reverse direction. If the wheel does not spin at all, check that the battery is turned on (some packs have a separate switch) and that the brake cutoff levers are not pressed. A miswired e‑brake switch will permanently cut power.
Legal and Safety Boundaries
- Class 2 e‑bike limit: Many U.S. states cap street‑legal e‑bikes at 750 W motor power and 20 mph. A 1000 W hub motor technically exceeds Class 2. Some states allow up to 1000 W for three‑wheelers if the top speed is limited to 20 mph. Check your local Department of Motor Vehicles website – search for “electric tricycle” or “electric assistive device” regulations. If you need to stay under the limit, program your controller to 750 W output.
- Weight distribution hazard: Load heavy items low and centered. A front basket filled with cargo plus the battery in the rear basket can lift the front wheel during hard acceleration, reducing steering control. Never exceed the trike’s gross weight rating (check frame sticker). Overloading by just 50 lb increases tipping risk in sharp turns by about 30%.
- Visibility is critical: A trike is roughly 30 in wide – much less visible than a car. Add a reflective flag at least 6 ft high, install a bright headlight (500+ lumens), and use the integrated turn signals on a helmet like the JARSH to alert drivers without releasing the handlebar.
Tuning and Testing
Take your first ride in an empty parking lot. Test:
- Throttle response – Apply gradually; sudden full throttle can pull the trike sideways if the motor is not centered.
- Turning radius – A trike cannot lean like a bicycle. At speeds above 10 mph, cornering with a 48V 1000 W motor can lift the inside rear wheel. Keep turns wide and slow.
- Braking – The e‑brake cutoffs should stop the motor instantly. If they don’t, recheck the connection.
Monitor battery voltage under load. A 48V pack at full charge reads ~54.6V. When you climb a hill, if voltage drops below 44V under throttle, the battery is undersized or has a weak cell – stop riding and replace it. Overheating the BMS can permanently damage the pack.
After the first 50 miles, check that all bolts remain tight (especially the torque arm) and inspect the motor’s axle for signs of twisting. A properly built e‑trike with these steps will serve reliably for years, but the key is verifying fit and legal boundaries before you even order the motor kit.
