# AMC project motor, DIY potbox kit thoughts



## EVDL List (Jul 27, 2007)

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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