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G'day All

First up: Maritime College project motor (I sponsored a student project of
the Australian Maritime College by re-building a motor with lots of sensors
and fields able to be reconfigured three ways).

We've had it on a pony brake dyno (a manually operated disc brake with a
newtons-scale meter on it to determine torque). The motor was able to drive
the scale to about 3.6kW out at about 75% efficiency (although the readings
were a bit quick so a better statement would be 70 to 80% efficiency). Far
too much for the poor disk brake, so only 30 seconds run at a time.

The motor has a pair of boat 'bilge blowers' as the cooling. Rotor heat is
a lot more than fields, going by the short runs we had. A clear window
where the brush timing lever sticks out really shows the effect of moving
the timing (like at 250A and neutral timing shows arcing from the edge of
the brush holder to the comm riser, due to a close clearance from part of
the modifications, goes away when the timing is advanced).

Their techs are out of time so they're paying me to wire up the control
system, but they've dumped other problems on me to sort out (like supplying
a wooden box with a flap lid to put it into, then saying "do what you need
to without spending too much.." Aaargh, they've just blown the budget by
needing to buy/build a real box!)

Second (re-starting of a previous thought path)

For their boat I've knocked up a 'pot-box' by taking the gearbox off a
little laboratory pump, in order to rotate a pot all the way from a limited
rotation arm.

This brings me back to an earlier thought of designing a kit of bits that
can be lazer cut to assemble a potbox from, with holes in all the right
places to assemble left or right handed, limit switches when/where needed,
etc.

As I see it the limitations of a Curtis-type potbox are as follows:
* There is a requirement for a special pot
* there is nowhere on the potbox to attach the sheath (outer) of the
control cable
* you have to decide ahead of time as to left or right handed, with or
without a limit switch
* the lever arm pick-up point is a "pick-a-hole" which may not get ideal
positioning, although I haven't heard anyone comment on this.

For my "kit" design I would look at:
* Since it would only rotate the pot a maximum of 90 degrees, for a Zilla
(which needs three wires) a suitable automotive throttle-body pot would be
needed. For a Curtis (which needs two wires) instead of a 5k pot rotating
270 degrees, a 20k pot rotated 67.5 degrees or a 25k pot rotated 54 degrees
will do instead. The kit parts would have holes to install whatever was
needed, although I haven't worked out the requirements for a throttle-body
pot yet.
* holes to insert end-of-travel stops to suit the various pot rotation
requirements
* the lever arm would have a series of slots rather than holes to attach
the cable to (or just a series of holes that are in two or three lines,
close enough together so that they overlap a little)
* The kit design would include a 'horn' either as part of the front plate,
or mountable to it, that gives a place to attach the cable outer to,
possibly slotted with a clamp to get a good alignment to the lever arm and
* a second 'horn' to connect the return spring to with a set of holes to
hook the springs into (so that the user can find easily-found extension
springs to use to set the throttle "weight" rather than an
around-in-a-circle spring to set the return 'weight'
* pre-positioned holes to mount standard miniature type micro switches in
various locations for zero throttle and full throttle mounting when required

As a one-off it'd be a bit expensive, but if I can sell/trade others it'd
be worth while.

Comments/opinions/4" x 2"?

Regards

[Technik] James
 
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