First, check out the photos here:
https://picasaweb.google.com/100638303250559390013/Elektratow

Mitchell Shipley <<elektratow>>
has recently upgraded his hang glider and paraglider electric motor-based towing
system, which he first built last year and used here at Quest Air for many tows.
It is designed to have a wide range of pulling line tension from very light for
small passengers on Condor 330's to tandem hang glider and paragliders. He has
replaced the previous electric motor going from a brushed motor to a brushless
(less maintenance) and from 8 KW continuous power with 15 KW peak, to 12 KW
continuous and 30 KW peak power.

He has increased the voltage by adding two more batteries (which can easily be
disconnected to allow for a lower range of throttle operation) to operate at 72
volts (which increases the power). The motor and controller will handle up to 96
volts.

He has replaced the controller with a more versatile and powerful one from
Kelley Controls.
The electric motor, made in the US, was supplied with a complete electric car
vehicle (car, cart, motorcycle, etc.) package from Kelley. The controller is
computer programmable. You set the values and then leave them alone.

Braking is all provided by the controller and motor, regenerative braking. There
is no separate mechanical braking system.

Mitch likes the fact that with one small switch the system is instantly ready to
start pulling up pilots and students. He appreciates the fact that he has a very
wide range of tow force from a few foot pounds to over 200 foot pounds. The
system as configured (a function of motor and line drum pulley diameters
primarily) can generate good climbing tow forces (for climb rates in the 400-800
fpm range) at up to 45 mph for hang gliders. He can gently touch the throttle to
get light pilots in the air.

He also likes the almost constant automatic line tension that the controller
provides without any operator input. It is not completely constant as he was
hoping for, but close – maybe plus or minus 10% around constant. So if a sudden
gust hits a pilot on tow, the controller automatically reduces or increases
voltage to the motor (at 16 Khz using Pulse Width Modulation control) to hold
the line tension close to a constant value, determined by the throttle position,
as the motor speeds up or slows down appropriately. Pilots (both hang and
paraglider) universally say it is the smoothest tow they have ever had.

I had a chance to operate the system pulling Mitch on a ATV set to neutral.
Mitch also towed me and we could get that ATV really moving. The control was
easy and all I had to do it set the regenerative brake (with a loop of Kevlar)
before Mitch backed up with the ATV, pulling the end of the line back to the
winch. No worries about the
line tangling on the spool.