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 Colorado’s Bill Dube and his team...
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 – and
the aptly named Killacycle is it. 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 no less than 990
small lithium ion cells provided by A123 Systems. The cells weigh just 73kg and
yet can supply up to 1575 amps at 374V. Another way of putting that is to say
that 390hp is available... Including burn-outs, the KillaCycle could make seven
runs on just one battery charge. Another interesting point: a drag run uses just
10 cents of electricity!
Custom battery management controls, developed by
Denver CNC, are used. The electric motors, two 6.7 inch Model L-91 motors that
drive a chain drive to the rear wheel, 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
for us 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!
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