Step Two–Adding a Chinese Electric Assist System

Look carefully at this picture:  at the top of the blue tub, is the 20 A circuit breaker; below that is the 20AH 48V lithium battery weighing about 15 lbs, supported by 5 springs; to the left is the controller; the 600 watt motor (about 3/4 HP) is in shadow below the battery, its sprocket covered by a plywood chain-guard.

To add electric assist, go to Wallmarts and buy a large plastic tub and screw it at each lower corner to the trike frame. Go to http://www.goldenmotor.ca/ and talk personally to Gary. He’s up near Toronto, and order 4 things: a 600 watt BLDC motor, a controller, a thumb acellerator, a battery charger, which comes with the battery, and a 20 ampere-hour 48 volt lithium battery.   This battery, by multiplying by the operating voltage is one KWH of energy.   With shipping, these items will knock a hole in $1000. Swallow hard. You’ve now spent almost all the money you will need to finish this project. I find the 600 Watt motor is just right. I cruise at 7 amps, which is 350 watts, acellerate from a stop at 10 amps which is 500 watts, and occasionally touch 15 amps on a steep hill which is 750 watts for a short time. That 20 AH battery gives me a range of 60 to 80 miles on a battery charge, depending on conditions and how hard you pedal.   I recently pedaled  the 36 miles from Newburyport, Mass to Boston and used .495 KWH of energy.   This is the equivalent energy of 1/4 cup (about one shot-glass) of gas, giving a range of 72 miles/charge,  and an efficiency of 2400MPGe.   This does not include, however,  the peanut-butter sandwich calories it took to keep me happy on the drive.  This  efficiency is 36 times greater  than the best automobile presently on the road, and demonstrates the efficiency gains from very  low weight (lower acceleration forces and rolling resistance), low speed (lower aerodynamic drag), and human-assist (the human body’s very efficient energy conversions).

But back to building the electric assist!     Since that battery cost you $600, you want to take special care never to short it out. So go to your local hardware store and buy a 20 amp circuit breaker and immediately wire it in series with one of the battery leads. That’s the black box you see on the far end of the blue tub. On the floor make a plywood piece and screw the motor to that.  You’ll need to have the sprocket on the motor made thinner at a machine shop to accept a 1/8″ bicycle chain, which you can buy from a local bike shop. Then buy a large 27 tooth sprocket from Staton-inc, order number 410, and have that bored out to slip over the shoulder of the unused sprocket on the double freewheel on Utah Trike’s rear axle.  Utah trikes uses a double freewheel to do the job of a differential.

Firmly centered on the shoulder, the new sprocket is bolted to the quad’s sprocket with small bolts. Alas, to do this you have to remove the double freewheel from the quad.   If I were doing this project over, I might keep the heavier sprocket which comes with the motor and then use a wider chain and heavier sprocket for the rear axle.   This drive is working three times harder than bicycle forces, so a little heavier would cause less stretching,  less tooth jumping under load.  This said,  the present system is working well after about 2000 miles

Since the sprocket which comes on the motor is 9 tooth, this 9/27 ratio drops the motor speed to one third, allowing hill climbing at 6-12 mph and max speed 22-24 on the level. Being a bicyclist, I am always pedalling, but you can ride without pedalling  whenever you’re tired.

Install the controller on the sidewall of the tub, the battery charger receptacle there too, and  cover over the chain with a cover, so you can put groceries in the extra space without having the chain grind them up. Then mount the thumb accellerator on the right handlebar, moving the Nuvinci variable speed controller to the left side. You’ll need a nice system to tighten the chain, which is working hard and stretches every two or three weeks.   I now have a great, easily adjustable system, which is shown below:

What you’re building here is called a parallel hybrid. Each system, the electric and the pedal, operates simultaneously and independently. The pedal system works through a “Schlumpf” two-speed sprocket and a Nuvinci variable speed mid-drive unit. See Utah trikes pictures. The electric system is direct chain-driven to the double-freewheel. In the best of all worlds it would have a freewheel so as not to have the drag of the chain and motor when coasting, or being in the pedal-only mode.

The battery is suspended by 5 hardware store springs, to cut down on ‘unsprung weight’ since the quadracycle has no suspension.   Likewise the mesh seat, which comes with the quad,  is removed from the seat frame, which then uses bike inner tubes for a soft ride and going easy on the quad’s axles when a big bump is encountered.

If you’ve never ridden an electric-assist machine, you’re in for a treat here.   Human power and electric power is a marriage made in heaven.   As hills approach you shift down the Nuvinci drive as the hill is encountered and back off on the thumb throttle.   The motor here is an AC motor.  The permanent magnet rotor  follows the speed of the three-phase rotating field created in the stator by the controller.   So the thumb throttle does not directly control the ampere load felt by the battery, but rather the ‘expected speed’ of that throttle position.   This means you can go up almost any hill without overloading the battery.

I wish I could tell you the exact range of Sunbeam.   So far,  using a ‘cycle analyst’ (also available from Golden Motors) to measure energy drain, I can be pretty sure that the range is 60-80 miles per  battery charge; BUT I’ve never driven that far!

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