Introduction
My desire to design an electrically assisted bicycle is not new. It dates back over 50 years to my grandfather’s basement! But at the time, I didn’t have the necessary resources to make this project a reality, just a large low-voltage motor and a large car battery.
Today, things have changed a lot: for my first solar bike, I started with an electric bike I built in 2011. In 2020, I added a solar trailer equipped with a 140W panel to recharge the battery. With this kit, I covered about 1,500 km, an experience that excited me and made me want to go further.
It was during this time that I met Stéphane, who introduced me to the Sun Trip, an extraordinary adventure where you travel thousands of kilometers by bike using only solar energy to move forward. I thought it was a great idea. But to participate, I needed to design something more powerful and, above all, more comfortable. I wanted to participate inSun Trip 2023!
My equipment
The bike
In the fall of 2022, I purchased a used HP Velotechnik trike and immediately began transforming it to meet my needs. This choice was obvious: the trike offered stability, comfort, and an ideal base for integrating solar panels and powerful electric assistance.
The Motor
Like other Suntripers, I decided to opt for a dual motor: a mid-mounted motor combined with a Direct Drive hub motor. I started by assembling the motors and performing a few brief static tests, an exercise I had already done with my previous bike. The results were conclusive, so I could move on to the next step.
The battery
I opt for two 1000 Wh batteries.
The solar equipment or solar trailer
I choose to install three 130 W panels that will be adjustable manually or automatically thanks to a sensor I designed.
Technical design
I now need to make a model to visualize what the final project will look like. For this, I use 20 x 20 mm wooden profiles, which I assemble in the most practical and intuitive way possible. I also plan to reinforce the strength of the trike by adding structural reinforcements to optimize its robustness. Indeed, while some prefer to bring a certain flexibility to their creations, for my part, I prefer robustness. This choice, however, comes at a cost, but we’ll get to that later…
When sketching my future solar trike, I also need to plan for locations to accommodate:
• the two 1000 Wh batteries,
• the three solar regulators for each of the three panels,
• the rear motor controller
• and an Arduino microcontroller to automatically manage the solar panel orientation, lighting, and various light signals.
Since these components, especially the batteries, are quite heavy, I need to ensure they are positioned as low as possible to maintain a low center of gravity. This is essential to ensure good stability when cornering and to guarantee safe and efficient driving.
Ordering the Equipment
After developing the specifications and establishing a precise list of the necessary components, I move on to the next step: ordering the equipment from various specialized suppliers.
The largest order, after the motorization and the photovoltaic panels, involves the purchase of 20 x 20 mm aluminum tubes, which I find in a specialized online store.
Then comes a multitude of hardware: screws, nuts, pop rivets, etc. I prefer not to count the number of trips to the local hardware store to complete these purchases!
For electronics, the process is similar, but the majority of orders are placed online, as are specific bicycle accessories.
Mechanical Fabrication
It’s time to roll up our sleeves: measuring, sawing the aluminum tubes, drilling, and adding gussets with a generous dose of stainless steel pop rivets.
To secure the panel frame, I designed two brackets that distribute the load while protecting fragile components, particularly the suspension locking screws. before.
An important detail: I designed the two battery cases to allow for quick ejection in the event of a fire. This system relies on a latch lock, releasing each battery by simply pulling a dedicated ejection handle. The electrical disconnection is performed simultaneously.
I also make four plywood boxes to house the two batteries, the chargers, and the rear motor and panel motor controllers. Each box incorporates a ventilation system, two of which are automatically controlled. These cases provide effective protection against rain and mud.
At the rear of the trike, I reattached the new frame to the luggage rack, increasing its strength to accommodate the four cases.
I added a set of two interlocking square aluminum profiles to support the weight of the batteries, thus ensuring optimal strength.
The luggage will be placed on these cases and held in place with a net on the outside.
The three 240 cm x 80 cm photovoltaic panels are mounted on an aluminum frame, which can be tilted right and left by approximately 75° using an electric jack.
All corners are reinforced with aluminum gussets. The screws and rivets are mostly made of stainless steel.
Electrical and Electronic Design
Since electronics is my profession, I must admit I’ve indulged myself a bit in this area. However, I’ll try to remain concise. Furthermore, I wanted to avoid turning this aspect of my bike into a “gas factory,” as everyone knows that complexity increases the risk of breakdown. However, the 16,000 km already covered have demonstrated the reliability of this aspect.
Some of the terms or techniques I’ll use may not be clear to everyone. I therefore remain available to provide additional explanations if necessary.
Batteries
Two 48V 21Ah lithium batteries, connected in parallel, power the trike. I designed two solid-state relays based on high-power MOSFETs, allowing the motor controllers to be easily disconnected with a simple switch. This particularly powerful MOSFET can handle up to 200 amps at 100 volts. This is the IXFK200N10P model from IXYS, available for around €20 each at mouser.fr
The 48 V power supply powers also a step-down converter to provide 12V at 20A. This converter is controlled by the same MOSFET model and a switch. The 12V voltage powers the panel actuator, lighting, a microcontroller, and includes a dedicated output for connecting external accessories. (Radio, telephone, GPS….)
Engines
My trike is equipped with two motors with distinct characteristics. The front motor is a BAFANG mid-drive motor. It is geared, allowing it to deliver high torque while remaining compact. Its temperature is constantly monitored. Easy to install, it offers great versatility and integrates seamlessly in place of the original crankset.
The rear motor, meanwhile, is a Nine Continent Direct Drive wheel motor – model RH212, sold by GRIN Technologie Europe. Unlike the front motor, it contains no gears, simplifying its design and reducing potential sources of failure. The only wear parts are two sealed, permanently lubricated ball bearings, ensuring exceptional longevity. However, to maintain its reliability, as with the front motor, it is crucial to monitor its temperature, especially during prolonged efforts or in demanding conditions. For this reason, choose a high-performance controller capable of monitoring all these parameters.
These two motors work together. The rear motor is primarily used on flat terrain or slight slopes, where it provides constant propulsion. When the slope becomes steeper and the speed drops below a certain threshold, the front motor takes over to support the effort. This ensures that the rear motor remains powered at all times, while the front motor intervenes to increase traction on steep slopes.
Furthermore, this configuration provides additional safety: if one motor fails, the other can take over, ensuring continuous travel.
Sensors
Speed and braking data must be transmitted to each of the two motor controllers to ensure optimal management. To achieve this, I designed optocoupled hubs to transmit the information to each controller, thus avoiding the need to install separate sensors for each motor. For the mid-drive motor, there is also a separately wired derailment sensor. This information is not necessary for the rear engine.
For automatic panel orientation, I designed a light sensor capable of automatically directing the panels toward the brightest area of the sky. Unable to find a sufficiently compact sensor commercially, I had to make it myself.
Solar Regulators
I use three regulators, one for each of the three solar panels. Again, a power MOSFET allows you to select whether or not to charge the batteries. The box housing the regulators is ventilated.
The microcontroller
It’s a mini-computer that communicates with peripherals such as lighting, an electric actuator, or ventilation via a control panel and sensors. I chose an “Arduino Nano” model. Although working copies are available for less than €5, I prefer the original ARDUINO.CC models, which are slightly more expensive, between €10 and €25.
To use this microcontroller, it must be programmed, which requires knowledge of the C language. Without programming, it’s completely inoperable… I won’t go into detail on this element, but it’s essential to provide great flexibility. Thanks to its scalable program, it allows for easy adjustment of command reception and command sending to peripherals. This program, specific to my trike, cannot be adapted to any other configuration. For this, it would be necessary to completely review the program.
The “Cycle Analyst”
These devices, designed by Grin Technologies, are essential for monitoring my trike’s power consumption. They’re practically a laboratory device. I use two:
– The one on the left manages the rear motor, its temperature, speed limitation, and energy recovery during descents and braking.
– The one on the right only controls the front motor’s power consumption and monitors solar charging.
Both can be configured via a PC, offering a multitude of possibilities. Although not essential, it’s invaluable for those who want to optimize their consumption and improve their bike’s performance. They also allow for rapid detection of anomalies, preventing them from becoming critical.
In the photo, you can also see, on the left, the Arduino control screen with its red and green buttons.
The wiring
I have extensively used ultra-flexible, silicone-insulated multi-strand cables for high currents. These cables are distinguished by their exceptional flexibility and offer remarkable thermal, electrical, and mechanical resistance.
All the connectors on these cables are XT90 or XT60 models, known for their reliability.
Protections
All circuits are protected by either fuses or circuit breakers. Specifically, each battery box has a 30A waterproof circuit breaker.
The fuses are similar to those found in cars.
Tires
Schwalbe Marathon Plus Tour tires, renowned for their excellent durability.
Braking and Suspension
I have three Avid disc and cable brakes on my trike. They’re easier to maintain when you’re out and about. The two front brakes, mounted on 160 mm discs and calipers, are stock. There was no brake on the rear wheel. I added one with a caliper of the same brand and a 180 mm disc.
The two front suspensions are elastomer. The rear wheel originally had a coil spring and shock absorber. I replaced it with a RockShox air suspension, which is much more comfortable and prevents bottoming out. I checked the suspension pressure approximately every 5,000 km.
Pad changes every 8,000 to 10,000 km. Accelerated wear on rear brakes. Thanks to regenerative braking, pad wear is reduced.
Drivetrain
44-tooth front chainring and a 9-speed cassette with 11/36 teeth at the rear. The chain consists of three KMC e9 chains. Original Shimano brand derailleur.
Feedback
Every project has its share of breakdowns, which aren’t meant to discourage you, but rather to help you progress and achieve an even more efficient machine. First and foremost, the transmission. This is the part that caused me the most problems, being a constantly moving part and therefore subject to the most stress.
Transmission
During a 12,000 km trip, all the problems encountered demonstrate that the transmission must be checked very regularly:
• A broken chain due to a protective tube that had come loose and jammed the chain, causing a derailment, then the breakage of a quick release. I still had to replace my chain after about 8,000 km because it had stretched beyond the recommended limit. It’s worth noting that mid-drive motors contribute in part to this stretching, as they put more strain on the chain. For this reason, I limited the mid-drive motor’s power to 300 W.
• Loosening the chain guide pulley retaining screw under the seat. This caused the pulley to become misaligned and the retaining screw to bend slightly. This point should be checked regularly.
• A loose chainring fixing screw.
• A lack of precision in the derailleur shifting.
Wheels
I encountered some issues with the spokes on my rear wheel. Fortunately, the expertise of Guillaume Devot (Grin Technologies Europe) allowed them to be resolved quickly. The spokes had become loose, and although I re-tensioned them myself, it wasn’t enough, as I mistakenly assumed they were sufficiently tight. The often-poor trails I traveled required regular spoke tension checks. Despite this, I “only” broke three spokes during the entire trip.
Tires
My Schwalbe tires proved to be excellently durable. My rear tire was 80% worn and my two front tires were 40% worn, without a single puncture throughout the trip.
Areas for Improvement
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Improvements
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