8KW Enduro E-Bike build

Building an E-bike for long distance commute has been on my mind for sometime. But the rising gas prices was the last push I needed to jump into this project. After months of planning and waiting for components from China, I finally started building.

Requirements

I wanted an E-bike with at least 100 miles of range at 25mph and a top speed of 35-40mph. My dreams for a backpacking rig necessitated an E-bike with good torque to carry load. Now I had to choose between mid drive and hub drive motor for the build. While a simple BBSHD 1000w mid drive would have done the job, I desired the quietness and simplicity of a hub motor.

The system will be an 8kw peak system with plenty of torque and a decent top speed. You might see stealth bomber clone type bike builds with 60-65mph top speeds but they are usually inefficient at city speeds where you are legally limited to 28mph. So a high torque motor with high efficiency at low speeds is the ideal one for this project.

Motor

A long range build means a larger battery and hence a heavy ebike. To carry this weight, I needed a hub motor with high torque. Qs205 6T 3KW hub motor was a sensible choice since it is not that heavy compared to QS273 and also available at 3T, 5T, 6T turn count variants unlike generic 1000w hub motors online. I chose 6T model(high torque) since I don’t care about high speed and I needed high torque at low RPM without putting too much stress on battery.

The motor is filled with 10ml statorade from Grin and hub-sinks for good thermal dissipation.

QS205 6T motor with statorade and hubsink installed

Note: All variants(3T, 5T, 6T) produce similar power; it is just the current it takes at a given voltage to generate similar torque differs between them.

Battery

The system is going to be 8KW peak and the voltage will be 72V. So the peak battery current should at least be 110A. I opted Tesla model 3 21700 (4800mAh) cells since they were available at cheaper price online. I built a 20S8P configuration of 21700 cells which amounts to 72v 38.4Ah and approximately 2.8KWh capacity. This is built using copper-nickel sandwich for lowest possible IR drop. This battery can supply 38A(1C) to 114A(3C) continuously which is the upper limit(8KW) for my bike.

Controller

Most of the bike controllers are super bulky and slightly overkill for my requirement. So I went with VESC based makerX HV200 controller. It can supply 200A continuously based on the data sheet.

Frame

Usually folks go with generic stealth bomber clone type frames for such high powered bike builds but they are heavy. So I went with a slightly skinnier version of the frame I got from Alibaba for the project. The battery I built didn’t fit through side panels. So I had to cut the bottom of the frame, welded like a panel with bolts below and slide the battery in from below.