Electric Bicycles

re: electric bicycle conversions From David Sampanis

For the last two years I have been tinkering with electric bike conversions.

The biggest issue is the placement of the batteries. They need to be placed as low as possible to the ground, or else the high center of gravity creates instability, difficult manuevering and even parking.

The best solution I have seen is the Santa Barbara Bicycle model, which uses a removable battery pack with a handle and key locking mechanism, placed low on the center post. This allows the battery (which almost weighs as much as the bike) to be easily separated from the bike. It also alows for using multiple battery packs, where 1 can be charging at home or work, while the other is being used, so you have a freshly charged pack at your destination waiting for you to swap out.

A simple home garage solution could involve attaching gel cel sealed lead acid batteries to low parts of the frame. Electric tool batteries are smaller and lighter for the same output and are readily available, but more expensive.

Electrically, the most complex set up contains a controller box for the motor, with a speed control (which is just a potentiometer). An on/off switch activates the controller. The brake control has a wire which will turn off the motor automatically when the brake is pressed. The speed control tells the controller how many pulses of electricity to send to the motor per unit of time. Fewer pulses, lower speed, all the way up to non-pulsed full power.

For motors, there are hub motors and separate motors. The hub motors are available for either the front wheel, or the rear, or both. The hub motors have two wires coming out from the hollowed out axle, which does not spin, since it is tighly bolted to the frame. Hub based motors are a nice solution since they are simple and don't require much work to use. Sometimes a hub based motor is wider than a typical bike rim, so your fork or frame may not be compatible. Just measure it before you order your parts.

You can also order your own scooter motor and mount it with it's own chain or belt drive. This is probably not worthwhile due to all of the custom work required, but it is possible.

One would have to ask themselves what they are trying to accomplish. For most common applications, inexpensive ready made electric bikes are available, and our tinkering won't improve them or be a cost effective use of time. For most people, it makes more sense to just buy an off the shelf electric bike, rather than converting your own bike.

For me, I live on a mountain top, with my only access is by a very steep 2 mile long dirt road, each way. In fact it is so steep that only four wheel drive cars can drive it. Since I am on 100% solar and wind power, I have been working on creating electric bikes which could handle my road. Because my road is so steep, slippery and bumpy, off the shelf bikes were not cutting it.

My first attempt involved a factory made beach cruiser with a rear hub motor and the batteries mounted on the luggage rack. It came with a 350 watt hub motor and 3 12v sealed lead acid batteries. I bought it on eBay for about $400. For cruising around town it was fine, but for my needs it was geared way too high to climb my hill. At full motor power and full pedal power, I couldn't get 50' up the grade.

Next, I shopped around at the bike shops, and found the tiniest sprocket available and substituted it on the pedal gear, and shortened the chain. The results were better, but I was exausted after a few hundred feet of steep uphill pedaling with full motor assist. Next I added a front wheel hub motor in addition to the rear one. This requred switching forks to accomodate the larger rim width. With the different fork, I also had to switch out the front brake apparatus to fit the new fork. With both motors going full blast and me pedaling my max, I could now make it about 500' up the steep hill but it was still very, very hard work.

This may have been because I was driving both motors with the same controller and battery pack, splitting the available electrical power. This bike has been collecting dust for me since then, and I've been working on a different unit.

Another lesson that I learned with this experiment was that there was no need for a controller with that set up. I found I was only using full power, or no power, so a simple control switch was adaquate, and made the electrical system much simpler.

The next experiment involved a gas scooter that someone else had converted to an electric racing scooter. It had a large compartment that could fit two full size car batteries. I bought two new deep cycle marine batteries, bypassed the controller, and installed a solenoid to control the motor using the existing throttle switch to send the solenoid the trigger voltage.

The scooter was able to climb a 500' hill a few times, and logged a total of 2.0 miles, half of it steep uphill climbing, and the other half coasting back down to the point of beginning over and over again. After 2.0 miles of this, 1/2 uphill and half coasting, the brand new batteries were completely dead and the motor was hot. Still not quite the performance I needed for the 4 mile steep trip.

Next I ordered a smaller drive gear for the motor, and a new belt to fit the new set up. Another $150 and 45 days later, I tried the new configuration. I was able to log 5.0 miles on the same up/down loop before the batteries died.

After that run, I noticed that the front tire had been a bit low on air, and after re-charging the batteries from the solar panels, and refilling the front tire with air, I was able to log 8.1 miles on the same course. Today I will attempt driving my whole dirt road for the first time.

On tribe.net, I met a man on the east coast who is making his own electric bikes for traditional needs, and he has been doing some incredible things. He is getting 40 miles on a single charge, and can do 35mph uphill with no pedal assist if he chooses. His user name is Lazarus on tribe.net and is very knowlegable and helpfull.

Parts for tinkerers are available on eBay and from a number of industrial surplus companies, and are easily found using an internet search.

Another upcoming project for me will be a four wheel drive, all electric, off road surrey, powered by roof mounted solar panels, again for my specialized needs.

For those of you who live on the flatlands, or only need to contend with a few hills here and there, the existing off the shelf electric bike technology should be fully functional for your needs, and available at a reasonable price, certainly much cheaper and easier than making your own.

If you are interested in tinkering to create something that isn't available on the market, let's talk, or even set up an electric bike maker's user group.

David Sampanis