There might be a few people left in the
world who think electric vehicles are passé. You know, suitable only for
commuting by those travelling just a few kilometres. And as for performance –
well, forget it. Trouble is no-one told
Bill owns the world’s quickest electric drag bike – and with a time of 8.168 seconds at 155.78 mph for the quarter mile. In anyone’s terms it’s not slow. Bill has been drag racing electric vehicles since 1997, starting with his electric daily driver, a 1985 VW cabriolet. But when he kept breaking things he decided to build a dedicated electric drag racer, the aptly named Killacycle. The bike first raced in 1999 and has since been constantly developed and uprated.
“The bike is very simple,” says Bill with classic understatement. “It is, as I love to say, just a giant cordless drill with wheels.”
The motorcycle is powered by 990 small lithium ion cells provided by A123 Systems. The cells weigh 73kg and supply up to 1575 amps at 374V. Or: 390hp is available. Including burn-outs, the KillaCycle could do seven runs on just one battery charge. Each a drag run uses just 10 cents of electricity!
Custom battery management controls, developed by Denver CNC, are used. Two 6.7 inch Model L-91 electric motors drive a chain drive to the rear wheel, and are controlled by a Café Electric Z2K Motor Controller. The motors are series-wound DC. As you’d expect, no off the shelf motors are suitable so Bill has the L-91 motors modified to suit. “Jim Husted of Hi-Torque Electric beefs these up for me and fixes them when we turn them into blobs of molten metal with plasma burns all over them,” says Bill.
“We launch the bike with both motors in series. We cram 2000 amps through them to get about 400 ft-lbs of torque out of each one.” This translates into almost 2000 ft-lbs of torque at the 10 inch wide rear tyre.
“The bike takes off from the line pulling about 2.9 g's, covering the first 60 ft in 1.169 seconds.” This means that the bike is doing 60 mph at about the 47 ft mark (and 1.04 seconds.) While in series, the motors each get all the controller output current of 2000 amps, but they only get a maximum of half the pack voltage of 375 volts. As the motors spin up, they need more voltage, so we switch them into parallel.
“We switch the motors into parallel about a third of the way down the track. When you are riding the bike, this feels like you are shifting an automatic transmission. “In parallel, we divide the available 2000 amps into each motor, but each can get the full pack voltage. This halves the maximum torque but lets the motors spin at about twice the speed.” It is very much like shifting gears, but in an electrical sense.
We heat the 990 A123Systems M1 cells (26650) up to 75 degrees C in the pits using heaters built into the pack. Ordinary Li-Ion laptop cells would have flames coming out of them at this temperature, by the way. “We do this heating to get maximum horsepower from the cells. We pull 175 amps out of each of the 70 gram cells. When the bike comes back from the run, the battery pack temperature is near (or just a touch over) 100 degrees Celsius. We then cool the pack down to 75 C by attaching a shop vacuum to it and blowing air through it.”
It takes about 10 minutes to recharge the pack and be ready for another run. Scotty Pollacheck rides the bike and also is responsible for tyres and suspension set-up. “Scotty can run the bike using the throttle or simply push the launch button and let the controller run its program,” continues Bill. “The throttle is a lot like the volume control on your stereo. It has a 5 k-ohm variable resistor built into it that sends a signal to the controller as you twist the grip.”
And if something goes wrong, how does Scotty find the ‘off’ switch? “There are two $900 "Bubba" EV500 KiloVAC contactors, one on the positive of the pack output and the other on the negative. These are used for safety disconnects should the controller get stuck ‘on’ and directly connect the battery to the motors. A flick of a switch with Scotty's left thumb, or a yank on the lanyard attached to his right arm, will open each of these contactors and will shut the bike down instantly.”
Apart from its drive system, mechanically the drag bike is conventional. The front end was made specifically for drag racing by Trac Dynamics. The wheels are made by PMFR. The frame was scratch built from 4130 aircraft tubing by Wes Messick while the body was made by AeroTech.
And are Bill and his team content to rest on their laurels? Nope! “We are trying to find a motor-control AC inverter company to partner up with that can help us build the 1000 horsepower drive package we will need when we go to the next level with A123 Systems Ultra-cells.”
“As spectacular as our present A123Systems nanophosphate M1 cells are, these new Ultra cells will have nearly twice the horsepower that we are getting now in the same weight battery pack. If we can build the inverter and motors we need, we have a very good chance at taking away some records from the top fuel drag bikes. The power-to-weight numbers are there, we just need help building this 1000 horsepower monster inverter...” More power to them!