A Miniature High-rate Speed Controller                 by Keith Walker
======================================

I have finally found the time to document the high rate speed controller
that I promised to you all about a year ago. I hope the results will
make up for the long wait.

I have designed this one in two halves. The power MOS FETs are mounted
on a separate printed circuit board. This is so that you can use this
controller for anythhing from a Speed 400 to a twelve cell, 30 amp motor
just by plugging it onto the correct FET board. [see comment at the end
-- EJB]

The FET board can be wired directly to the motor brush-holders with heavy
wire. This will eliminate the resistance of a pair of connectors and long
power wires, and will keep the FETs in a ventillated area in the plane.

I have used the same controller for both an Astro 05 and an AP 29 motor.
I leave the FET boards on the motors, and move the rest of the controller
from plane to plane.

Construction is very straightforward. You can make a printed circuit
board from the pattern here using a photographic method. If you don't
have the equipment to do this, you can mark the hole centers on a piece
of copper clad board, and hand paint the circuit as I described in
previous construction articles.

If you prefer, you can wire one up on prototype P.C. board that has holes
all over it, on 0.1" centres, and a copper pad on each hole. Just use the
circuit board pattern as a wiring guide and wire the components together
using their own leads. Use a bit of insulation on the wires where they
are very close together.

Test the finished circuit using a 12 volt lamp bulb, or a motor with no
propeller on it. The two adjustments are interactive, but with a little
patience, they can be set to correct settings.

Start with both potentiometers set to the centre of their travel. Set the
transmitter throttle stick to the middle of its range. Adjust VR2 to give
about half throttle. If the range is too large or small for the throw of
the throttle stick, move VR1 a little one way, and re-set VR2 to half
throttle at mid stick setting. If the range changes in the wrong direction,
move VR1 in the opposite direction, and try again. After a few times, the
range will be where you prefer it. Just make sure that the motor will turn
completely off at the lowest throttle setting, and is fully on at the
highest setting.

I hope you have fun with this project, and that you enjoy flying with the
results of your labours.
                                        Good flying, Keith


[To make a higher current FET board, simply add duplicates of R15 and Q2,
wired in parallel with R15 and Q2; e.g. R16, R17, Q3, Q4, with free ends
of resistors all connected to R14, drains of Q3, Q4 connected to the drain
of Q2, and sources of Q3, Q4 connected to the source of Q2.          EJB]