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Introduction
The concept of putting an electric motor on a recumbent bicycle is not new. So when I decided to write this article, I wanted to document some unique information aside from the obvious that others might benefit from. So where I think I had an original idea, I marked that section with an asterisk “*”.
If you are new to Electric Bikes, check out the introduction I wrote, or visit the electric bike web site. If you already know what e-bikes are all about, read on to see if there’s anything here you can use.
Steve Duncan
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Origins of the Hawkins Electric Lawn Chair
I purchased this project with the bike, motor, controller and accessories from Mr. Ed Hawkins. Those who frequent discussion groups related to electric bikes and scooters will recognize Ed as an early experimenter and one who was not afraid to try things others were satisfied to read about. When I contacted Ed about buying the project, he related it to “riding a lawn chair”, and the name just stuck.
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The Bike Itself
The recumbent bicycle is a blue Easy Racers EZ-1 SC (Super Cruiser), and is made for Easy Racers by Sun Bicycles. It is a Compact Long Wheel-Base (CLWB) which makes for a comfortable, sturdy bike with a short learning curve. It also makes a great platform for conversions. And at a list price of $549, it’s affordable too.
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Bicycle Modifications
Removing the Front Derailleur*
The bike has 21 speeds, but with the motor-assist, I no longer needed all those low gears. In addition, the Magura twist grip throttle was offset by the index shifter, making access to the brake lever awkward. So I completely removed the front derailleur, cable and shifter and moved the rear derailleur control to the left side.
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Using only the large 52 tooth chain ring, I can pedal up to speeds of 35 MPH. In the lowest gear I can still spin away at 5 MPH if the motor gives out. Chain slack is minimized and I am able to avoid using the mid-ship chain idler wheel for less drag and a quieter chain.
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Aftermarket Tires and Tubes
The EZ-1 comes stock with Kenda Kontact tires which are rated at 65 lbs. I replaced these with 110 lb rated Maxxis Hookworm tires; 20” in the rear and 16” in the front. The difference in rolling resistance is very noticeable but so is the jarring effect when you go over the slightest bump. For the incredible grip you get at any lean angle, I think it’s worth it. I run them at 100 lbs but they can be used at pressures as low as 85 lbs.
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I’ve always used Mr. Tuffy tire liners, but for this bike I use those and thorn-proof tubes. Despite those precautions, I still managed to get one flat in the rear so far. Luckily, I carry a pump which I was able to use every mile or so until I got home where I could perform the hour long job of removing the rear wheel to change it. Since it takes so long to remove and replace the rear wheel, I will always just buy a new $5 thorn-proof tube and not try to patch the old one.
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Brake Pads
I am using Ritchey Logic LP brake pads. I’ve put the black (all condition) on the rear, and red (severe conditions) on the front. They are inexpensive ($8-10/pair) and are wearing very evenly.
Accessories
Ed did not scrimp on the accessories for the project he sold to me. These include:
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This is one of those kidney-shaped over the shoulder back packs. What worked out really well is the way I was able to hang it from the top cross bar of my seat back. It adds a lot of carrying capacity to the bike and does not otherwise get in the way.
Piezo-electric Dual-note Horn*
I wanted an electrical horn that would be an attention-getter. Radio Shack has quite an assortment of piezo-electric buzzers rated by frequency and loudness in decibels. Many car horns are actually “dual note” and combine two horns of different frequencies, so I thought I’d try the same thing. I chose two different buzzers in the 1-3KHz range that were rated over 20 volts. I power them with two 9V batteries in series that should last for years. Since these little guys are very directional, I mounted them on the bottom of the fairing, facing forward. The result is not ear-shattering, but attention-getting nonetheless.
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The Motor, Controller and Gearing
Prior to conversion, the motor was a stock High-torque Kollmorgen 400 watt brushless DC (BLDC) unit, just like on my 2001 Flyer scooters. In the conversion process, in this case performed by ThunderStruck Motors, the Hall-effect sensor connections and motor windings are brought outside the motor, bypassing the internal “potted” controller.
If you take the original peak power rating of the motor (400 watts) and divide by the stock 24 volts (I = P/E) you get a peak current of 16.7 amps. At 36 volts, this setup should be conservatively rated at 600 watts, and since a peak output of 20 amps is not out of line for these “D” cells (Dynapower rates them at 70 amps?!?), a peak input power to the motor of 750 watts is quite realistic. 750 watts is approximately 1 HP, and has been cited as the “magic number” when it comes to sufficient power to obtain reasonable speeds on hills and flats.
Gearing and Drive Chain
In order to obtain decent top speed with a 20” rear tire, the special 22 tooth pinion gear from EVdeals was used. Top speed on level terrain with a 170 lb rider is between 21-22 MPH (35 KMH). Although I would like to see 25 MPH unassisted, this combination of power and gearing gives me very acceptable assist on even steep grades, where I can typically maintain 14-15 MPH. Using the 22 tooth gear and by adding a half-link, the stock drive chain can be used without a tensioner block. This creates a very smooth, quiet chain drive. Because chain stretch is more critical without a tensioner, I purchased a 10 foot roll of C-25 chain at a local bearing shop ($12, US Bearings, Portland, OR; ask for “KC”) and I’m making my own replacement chains inexpensively* which I can change more frequently.
A note regarding my speed measurements… I calibrated my Topeak Panoram speedometer/cyclometer using a GPS over a distance of at least 10 miles until the distance error was less than .05 (1/2 of 1/10th) mile. Attempting to match the speed on the computer to the GPS was fruitless since they are averaging at different rates and rarely match exactly at any point in time. The assumption is that the cyclometer is made correctly such that an accurate distance measurement insures an accurate speed readout. The maximum speed I’ve obtained down a steep grade is almost 40 MPH. With 110 lb tires, you don’t want to hit even a small rock at those speeds.
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External Controller
As with most Currie conversions, I inherited the Transmagnetics 3 phase 36V 50A controller board. Although robust and smooth in it’s delivery of power, I can find little or no documentation on it. According to Brian Hall at ThunderStruck Motors the controller has low voltage cut off and temperature protection, but no over-voltage or reverse polarity protection. So as others will attest, don’t hook it up backwards or you will be buying another one.
It was supplied to me in a Radio Shack project box that comes with both plastic and aluminum covers. In order to fit the controller in the box, the cylindrical supports for the cover screws needed to be milled (or otherwise mangled) away. For ventilation and wire routing, three ˝ inch holes were drilled on one side of the box.
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NiMH Battery Pack
One of the nicest parts of my EV is the 9Ah NiMH battery pack. It was originally obtained from Powerassist.com, who at the time of this writing is no longer on the web. It is composed of 30 180 gram 9Ah “D” cells in series, welded together with battery bar. They are arranged in 6 rows of 5 cells, stacked two cells high. I had one bad weld early on which I was able to get repaired and more recently had to replace a shorted cell. See my companion article, “Anatomy of a NiMH Pack”* for details. Before it went down, the Powerassist web site had a pointer to the Taiwan dynapower.com site, who offers 9Ah D cells, packs and matching chargers. From the look of the charger and specifications for the D cells, I strongly suspect they were the source for the components in my pack. My pack also employs a thermistor, a temperature-sensitive resistor which notifies the charger when the pack has begun to overheat during the charging process. It is 12.5K ohms at room temperature, and charging ceases below 5K ohms.
I can tell how hot my pack is by putting an ohm meter across the negative and center terminals of my charging port.* If it is under 4K ohms, I know it needs time to cool before charging. Just be careful not to probe the plus and minus terminals instead.
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Location of Battery*
I have suspended the battery under the seat on the (optional) panniers that extend below it. I added two sturdy cross members, elevating the front one to avoid chain interference. I placed the pack in a nylon camera bag, and nestled the bag in a old-style hard-drive bay. The bay is attached to the cross- members with commercial Velcro. This is a good location for weight distribution.
Charging the Battery
My 2.5A charger employs thermal cut-off, and my personal practice is to allow the battery to cool as completely as possible before charging. Otherwise, charging the pack when hot will result in premature shut-off.
Occasionally I employ “double-charging”, a practice of applying a second “topping” charge after the battery has cooled from the primary charge. I believe that if monitored closely, this technique can obtain the full potential of the pack without over-charging. With a single charge to a cold pack, I can ride 10-12 miles before significant power loss. After a second charge, my range extends to almost 20 miles (with plenty of pedaling). And as Ed told me, NiMH packs are “all about heat”. Indeed, a hot, freshly charged pack on a nice warm day seems optimal.
Wiring Harness and Power Switch*
The original power connection was a Currie power harness from a US ProDrive kit. During use, the wires got quite hot, so I made my own harness using #10 wire. For the power switch, I employed an automotive-type battery shut off switch, with a large, plastic removable key. It’s effective and looks cool too. I dressed all the external wires with corrugated, split black plastic conduit. It provides a very nice finished look.
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Summary
The EZ1-SC makes an excellent platform for the Currie system. No modification is needed to the wheel to accommodate the motor plate or spoke clamp system. The under-seat mounting location is perfect for a compact NiMH battery pack, where equivalent SLAs would not fit.
With the gearing described, it is possible to obtain speeds of 14-16 MPH on an average commute. The 20” rear wheel and 22 teeth gear in combination are just “tall” enough for the reasonable top speed of 21-22 MPH.
The CLWB recumbent itself is easy to ride, comfortable and inexpensive. It’s a winner!
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