Tuesday, March 24, 2009

Hybrid Bicycle Experiment

We recently became a one-car household so I've been doing some experimenting with alternate forms of transportation. The bicycle was working fine, especially when combined with public transportation, but it was nowhere nearly as fast or convenient as a car. However, driving the one and only car we own to work just so it can sit in the parking structure all day and leaving my wife stranded at home without wheels--well, that wasn't an option.

Riding the bike was fun for the most part but mashing my way over the Cahuenga pass, in traffic, in the rain, late at night, not so much. What I needed was a little push to make it a little easier and the answer seemed to be to augment the energy from my legs with an electric motor.

I already had a couple of bicycles so I had a backup in case the experiment went awry. Good thing too.

The motor I settled on was a Bafang geared front hub. The reason I went with a front hub was because it seemed simpler to mount. A geared motor should have more torque than a direct drive which should make climbing the hill pretty much effortless. Another advantage of a geared motor is that it freewheels. Some may say freewheeling is a disadvantage because it cannot regenerate electricity and recharge the battery like a hybrid car--but this requires a special controller and I didn't want to over complicate things since this was my first e-bike build.

I got the motor as a kit that included building the hub into a 700c wheel along with an ecrazyman controller, twist throttle and brake levers with cutoff switches so you can't apply power and brakes at the same time.

What the kit didn't include was a battery and that's where I went all out and got the latest craze in e-bikes, a lithium iron phosphate, LiFePO4, 48 volt 20 amp hour Ping battery pack.

Granted, it doesn't look like much more than a bunch of metal strips wrapped up in black duct tape, but it should deliver quite a jolt of power for many years, more than enough to get me to and from work. Notice that it has three wires, a positive, a charging negative and a discharging negative. Also notice that it doesn't have a connector and the end of the wires. The charger came with a connector but the controller had a completely different connector. Neither of these connectors were standard of the shelf items so I soldered common XLR audio connectors that are available in any neighborhood Radio Shack store--though you might have to do some searching because the sales people probably won't know they have XLR connectors.

I was able to find a Topeak trunk bag that fit the battery perfectly. The bag, paired with a Topeak rack made it very easy to remove the pack from the bike and take it inside for charging. However, in order to make this practical the controller and all the other wires and connectors had to live somewhere other than the trunk bag so I got a frame bag which worked great for this purpose.

Except for the connector for the battery everything seemed pretty much straight forward even though absolutely no instructions were included with any of the items that I ordered. Some wire colors didn't match up but the connectors did, like this one for the brakes:

While on the brakes, the controller had only one brake connector but of course there's a front and rear brake. I ended up splicing the brake wires in parallel so that applying either brake would cut off power to the motor.

So, all the connectors fit and the wires matched up by color and it was time to go for a test ride.

It worked! It ran little rougher than I expected and there wasn't much pull, but it pulled--for about two blocks then it cut out. That wasn't very impressive, but whoa did the motor get hot! It turned out that I succeeded in burning out the motor on the very first test run.

With the help of John Robert Homes from Holmes Hobbies we were able to determine that the problem was that the proper way of hooking things up is connecting the green wire to the yellow and the yellow to green. What? That's right, the motor manufacturer and the controller maker obviously weren't talking to each other when they made their products. In any case, JRH replaced my burned out motor stator assembly at no charge and once I got the wires switched over it finally delivered as promised.

This time I made it a few blocks before encountering yet another problem. The hub motor attaches to the front fork with a sort of "key" in the axle:

The fit was nice and tight but after just a few accelerations--wow that was cool, it has so much torque that the front wheel spins when I take off. Oops:

The fork dropouts deformed and the axle spun around a few turns and nearly broke off the cable! It turns out that what I needed was a set of torque arms, another hard learned lesson. Gee, this would be so much easier if it came with instructions!

I didn't have the facility to fabricate anything beefy enough so I ended up Googling around and found some made specifically for e-bikes made by AmpedBikes. Just to be safe I bought a pair and put one on each side.

Finished, finally--or so I thought.

The spinning front wheel was annoying so I put on my extra large Wald front basket. I was planning on using the removable battery feature for bus rides but technically, you're not supposed to mount a bicycle with an "over sized" basket on a bus bike rack. However, as it turned out I got to work much faster without having to use the bus so it didn't make a difference. Besides, I now had a cargo bike capable of carrying three bags of groceries--and then some with the panniers on the trunk bag deployed.

I did take the bike on the metro rail system regularly for the ride home--no need to remove the battery for that.

The cruising speed on the flats was a rather quick 22 miles per hour. Yeah, I know, that doesn't sound like much but believe me, on a bicycle without any suspension it is plenty fast. Even the hill that had me huffing and puffing before the conversion was an easy 18 MPH on the uphill side and coasting downhill, geared motor so no drag, was the same scary 35 MPH. I burned out a few brake pads on that route!

One thing that was a problem was plugging in the battery, the connector would always arc. If the pins were not lined up properly it could make a rather loud pop. Of course this wasn't very good on the connector so I tried this trick:

I used XLR instead of Deans connectors and it seemed like it would work.

But it didn't stop the arcing so I removed it. I think a better solution would be to put a heavy duty switch on the power line but I got used to the spark when connecting the battery, though it did blacken the pins on the XLR connector it didn't seem to affect performance.

I rode the bike daily for a little over a month through wind, cold and even rain over the brutal Los Angeles winter--OK, it wasn't all that brutal but I rode the bike when my bike riding co-workers wimped out.

There were a few problems, like the time I got off work late and I was in a hurry to get home so I decided to ride over the hill instead of take the train. There's several miles of rough road without street lights and I hit a huge pot hole at full speed. I usually don't get flats but with the extra weight of the battery my rear tire didn't stand a chance. My wife came to the rescue so I wouldn't have to do a repair job on a dark road in the rain--glad we kept one car, and the bicycle carrier!

The only other problem that I had was when the brake levers got wet they would short out. It wasn't all that bad, just a quick brake and release would shake them dry enough to continue. That problem went away after one day without rain.

All stories have an ending and this one ended one morning going into work. After crossing the Cahuenga Pass the motor lost most of it's power and it was feeling very rough. Did I wear out the gears? Did the motor burn out? I'm not really sure. It might be repairable but the quick fix would be to replace the motor--or get a Vespa. Since it was my dream all along to get a Vespa and the e-bike was just an experiment I decided to end the experiment and put the bike up for sale.

The motor might be shot, the bike abused but the battery is in even better shape than when I bought it. Turns out that LiFePO4 batteries need a break in period of about a month before they can stand a deep discharge without damaging the cells. How far will the bike go on a charge? Only the next owner will be able to answer that question.