This page created on 03/12/01 last updated 03/25/01

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Kilian's Robot Shop of Horrors - 03/09/2001

Alan writes:

This night, we hooked up a car alternator to a gas engine, and drove a 24 Volt DC motor with the alternator output. Bob wants to drive two HUGE DC motors, and doesn't want to build two HUGE DC motor controllers, so he decided to drive two car alternators connected directly to the DC motors. By controlling the DC field current for each alternator which is the range 0 to 3 Amps at 12 Volts DC, he can control the current to the motors which is 0-40 Volts DC and up to 45 Amps. It's a thing of beauty.

So Bob and Jeff hooked up the whole thing on a chunk of 2x6 and we fired it up. It's strange to see a 12-volt alternator generating 40 Volts DC, but I guess that there is nothing stopping it. [It will probably go alot higher but we tried to keep it down to something reasonable. JWS]

As we increased the field current, the alternator put out more power.

Here is a table of field current, output voltage, output current and conditions:

Field currentShunt CurrentOutput voltageConditions
0.30 Amps1.0 Amp4.8 VoltsGas engine at idle
0.60 Amps1.5 Amp17 VoltsGas engine Faster
0.60 Amps14 Amp6 VoltsStalled motor ( 84 Watts in)
0.81 Amps 26 Voltsmotor no-load
0.81 Amps20 Amp8 Voltsmotor stalled (160 Watts in)
1.1 Amps13 Amp30 Voltscan not stall motor (390 Watts in)
1.1 Amps27 Amp8.8 Voltsmotor stalled (230 Watts in)
1.32 Amps34 Amp10 Voltsmotor stalled (340 Watts in)
1.85 Amps45 Amp12 Voltsmotor stalled (540 Watts in)

The gas engine just BARELY began to show signs of load at partial throttle.


Bob's "Strawberry Robot" project

Bob and his 5.5 Horsepower Honda engine
and three car alternators.

Just before we decided to close the garage door.

The engine and one 60 Amp alternator belted together.

Oh man, we got wires! Large grey 24 VDC motor.

Jeff hooking up the DC motor connections.

Meters for: Field current, output voltage and output current.

The belt tensioner keeps vibrating loose. Duct tape fixed it.

One of the boards we used to load down the motor output shaft.
Don't try this with your fingers. (See below)

Brynn's "Tryclops" project

Bob looking at the "Tryclops".

Jeff trapped inside the "Tryclops".
[Twilight Zone music plays in the background...]


$11.25 motor from AMETEK. Not much armature there.

Checking the current draw.

Hard to see, but one supply lead is connected to the
motor case. Things would get real exciting if you had two of
these on a metal frame without removing this wire.

Bob and his revolution-per-second O'Meter.

Half-white and half-black tape on the top of the pulley gives
us a reading of 76 revs per second on the meter.

What happens if you try to stop a motor shaft using your
fingers. (Jeff M.) We forgot to emphasize enough times
"Don't do anything TOO stupid"
which is our motto.

Update: The blister one week later.
So don't try this at home.

Other stuff

Alan and Jeff M looking at Alan's robot "Trippy"

Bob looking at Brynn's camera.

A scope trace of my bench power supply going into
current limit while driving a motor.

A CyberOptics 4-channel PID loop motion control board.

An HP7550 plotter test page. MAN this plotter is fast.
Brynn set it to warp-9 speed somehow.

Brynn taking a picture of a motor.

Alan's scooter motor/gearbox.

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