Archive for July, 2009

Mulch under the fence, berry patch

July 27, 2009

Alexis was on call this weekend so I headed down east.  After spending a good part of Saturday visiting with an old friend, Sunday was given over to orchard work.  I had wanted to mow the orchard and mulch around the trees with chips, but the wet summer and recent 3 inches of rain rendered regions of it downright soggy.  The rain had also had a stimulative effect on the grass growing under the electric fence, so I went around the inside and outside of the electric fence with a string trimmer, and concluded that the plastic netting that serves as backup to the electric  wasn’t going to survive very long with grass and weeds growing in and getting beaten back repeatedly.  So I got a big 2-wheeled wheelbarrow (ground way too soft for machinery after all the rain) and schlepped the wood chips we produced earlier in the summer, spreading them in a thick layer under the fence line.  Summer’s rank growth has demonstrated that the small amount of chips we put under the fence this spring were about 10% of the necessary quantity.  My folks showed up to lend a hand, and we got about half of the perimeter fence done.  By then it was lunch time, and I had had about enough of grunting the wheelbarrow over rough ground.  After lunch I spent a couple hours clearing in the new berry patch out behind the cabin, where the hazlenut bushes seem to be taking quite well to their new home.

As I prepared to head back to Boston, I noticed the front page of one section of the Portland Sunday paper, where the two stories were about the rise of electric bicycles in China and a new effort to produce locally-made wood pellets for Maine.  At least for a brief moment I had the sense that the world might actually be changing.

Pedal-Electric Hybrid Bike – Status and Photos

July 17, 2009

electric bike - left side

[More pics below, showing details of the throttle, drive chain tensioner, motor, and battery mounts.  I’ve also started a page on the sidebar with technical details, in case other folks want to build a similar rig.]

I rode the electric-assisted bike to work 3 days this week.  This evening I made it home in 34:40 rolling minutes; with stoplights etc the elapsed time was 36 minutes.  This is effectively the same amount of time that it takes to drive, unless there is bad traffic in which case it is at least 45 minutes to drive. There are still a handful of refinements to be made, but overall I think it is a success.

Comfortable cruising speed with little or no pedal effort is 25 mph on the flat; battery life with moderate pedal input seems to be around 20 miles; I have not run the batteries flat but there is a noticeable drop-off in power; this AM I completed a round trip I started the previous afternoon without recharge, and the voltage on arrival was around 23.5.  Top speed at full sprint (human+electric) is around 31mph on the flat.  Acceleration and top speed are sufficient to comfortably keep pace with cars in traffic.

At first I had some issues with the chain coming off the electric drive side; I’ve corrected this for now by adding a chain tensioner sprocket to the return side of the drive, but it’s a bit of a kludge so more refinements will probably be called for.  The chain drive makes a noticeable sound at moderate speeds; at cruising speed it’s not very noticeable over the sound of the wind rushing in your ears.  I haven’t had someone else zoom past me at cruising speed so I don’t know how annoying it is to be buzzed by the thing.  I think a toothed belt drive might be superior in terms of sound; if it could be made a bit quieter the aesthetics would be that much better.  Given the noise I’ve been letting off the throttle when passing other cyclists and sprinting past with muscle power; recreational cyclists don’t seem surprised (I guess they’re used to folks on road bikes whizzing past) but a couple of spandex-clad road warriors have sprinted up behind me to see what I’m about; of the two I’ve interacted with both were intrigued rather than offended to be waxed by a scruffy looking guy on an old steel electrictrified bike.

electric bike - handlebar

electric bike - drive side detail

electric bike - motor side detail

Electric hybrid bicycle prototype operational

July 12, 2009

For the last couple of weeks I’ve been working on an electric hybrid bike.  The motivation is that my place of employment is about 12 miles from home, and while I should be man enough to bike it both ways every day, the reality is that I usually drive.  It’s about 30 mins to drive, and 50 mins to bike, and I figured if I could reclaim some of the 40 min/day difference, I would be more likely to bike it more often.  I researched electric bike conversions, but they seem to be really heavy – one kit with a Crystalyte wheel motor tipped the scales at 50 pounds, not including the bike, for 360 Wh of lead acid storage.  I figured since I was willing to pedal, I didn’t need 700W of power, and I’d really like to end up with something I could still carry, so I designed and built my own.  Here’s an image from partway through assembly:


core drivetrain components of 300W power bicycle assist system

I found a 300W 24V brushless motor with an integrated controller online, along with a freewheel and a couple of sprockets.  I got two gel lead acid 10Ah 12V bricks from digikey, and hacked up a spring-loaded potentiometer to drive the input.  The bike is a nice simple Miyata road bike that I bought from Adam for $100.  The drive is entirely in parallel; the right side human power drivetrain is unchanged, and the trickiest part of the whole thing was to arrange the left side electric drive.  I bought a flip-flop hub at Wheelworks in Somerville, which has short 1.375″ right hand threads on both sides.  Though the thread is short it accepted a standard 7 speed freewheel no problem, but on the left hand side there was nothing to keep the freewheel (which also has a standard right hand thread) from spinning off under load.  There’s a smaller left hand thread on the right side of the flipflop hub, but it was too close in diameter to the larger freewheel thread to get a jam nut on there, since the freewheel was thicker than the two threads put together.  So I ended up threading another ring into the deep internal thread on the freewheel, and jamming it against the body of the hub.  With high strength loctite I am hopeful that it will continue to hold up.  The large sprocket on the wheel is driven by a 25 pitch chain from the motor, which I mounted to a plate fixed within the main triangle of the frame by brackets to the water bottle braze-ons.  With a few hours of hacking in the machine shop over the last few days I fitted all the pieces together and arrived at a working prototype.

This afternoon I put it to test, and I am happy to report that it performs quite satisfactorily.  I hooked up the batteries, kicked off, and engaged the electric drive, and was pleased to find that despite the high gear (only about 8:1 reduction) it accelerates reasonably smartly on pure electric, and fantastically with combined electric and pedal effort.  The top speed I achieved with moderate pedal assist was was about 30mph, but I was hampered somewhat by stoplights, traffic, and a sense of self-preservation.  If I had the throttle in a position that permitted more comfortable cycling stance I could have put more muscle into it and found the real top end, but 30mph is more than sufficient for everyday use.  I took a test ride over to Holly and Becky’s house in Somerville, and was pleased to find that I could rip up the Summer Street hill in top gear, again with only moderate effort on the pedals.  The entire rig weighs in at 47 pounds.

While the prototype works well enough to convince me of the validity of the concept, there are still some things that need attending to before making it a regular commuting setup.   The two main issues are the battery attachment system (consisting of aluminum angle, hot glue, and zip ties) which needs a complete rework, and the electric drive chain tends to slap against the chainstay and could use a spring-loaded tensioner.  I need to put the throttle in a better place, and I have a feeling I’m going to wish I had those fancy built-into-the-brake-levers type shifters for maximum efficiency in accelerating.  Also, it would be good to put a fuse in the battery circuit.