I'm not getting very far figuring out how my vintage chart recorder
paper-feed drive mechanism works.
If you know your 1Ph synchronous motors, including hysteresis
synchronous motors, or synchronous motors with capacitor permanently in
circuit, then you may have the edge.
Here is the paper-feed mechanism and the circuit that I copied:
I'm bamboozled by how it works myself.
All ideas taken into consideration.
Thanks if you solve it's operation.
The thing is what does M1 do?
Its moving too slow and in the wrong direction turn the SHAFT at the
correct SLOW speed.
And you would think M2 might not be able to go slow enough to turn the
SHAFT at the correct SLOW speed.
But let's look at HIGH speed.
If M2 is a 12 pole machine, it's regular RPM would be 500(according to
the formula: 120 x f
Maybe it will run at 1000RPM by a suitable choice of capacitor?
If that is the case, we can see how the required 1000RPM would come from.
But, if that ran at 1000RPM it would transmit torque through the clutch
to M1, the spindle of which could not be turned. You cannot try to turn
M1 spindle from it;s spindle end, only from the rotor end because it's a
I think you have to be quite inventive/clever to figure how this
contraption works. :c)
M2 is a very old 1940s design. I believe it it originally had a
permanent magnet rotor and was used as a 12 pole. 24v stepper
Your M2 looks like a rewound version probably with a 35% cobalt
hysteresis armature. This would give it an approximately constant
It's possible that it's not used as a motor but simply switched
in to provide a constant braking torque to reduce the speed of
According to your schematic, m1 doesn't have a starting cap. So, a
synchronous motor, which isn't self starting and will run fine in either
direction. Motors of this type were typically hand started by spinning
the shaft (some old electric mains clocks), or used a mechanical
spring/cam arrangement on the shaft to ensure auto staring in the
correct direction. Have a look at this to see if it's gummed up, needs a
clean and oil, whatever.
The second motor looks a like it is self starting via the 90 degree
phase shift second winding and cap and may also be designed to start m1.
You should be able to swap the wires on one or other of the two windings
on M2 to get for/rev rotation.
Some of the older electro mechanical stuff could be pretty wierd, just
to save a few parts :-)...
Chris has got it nearly right.
M1 looks like a typical synchronous motor as used in clocks and,
probably has a mechanical "trip" that makes it start in a set
direction. In older electric clocks, you often had a level out the
back which you manually used to effect this. Later and better clocks
had the "automatic" version. It will be a very low torque but geared
so that the speed is reduced and torgue increased (just like a
clock). I'd suggest from experienxce that this will provide a slow
chart speed. BTW, the "trip" is like a pawl. If the motor starts
correctly, then it simply "slips". If the motor, initilly, starts in
the wrong direction, the "pawl" bites - stops the motor and the
"hicough" makes it start again in the correct direction.
M2 is a typical synchronous (two phase) motor. Sorry Chris. The cap
is in parallel. All you need is a phase shift ! If you have ever
seen a Parvalux fractional HP motor as specified for the Quorn T&C
Grinder, you'd have come acros higher powered versions. Connecting
the capacitor across the other winding will reverse the motor
direction. The synchronous speed will be 3000/6 ie 500 RPM if it has
12 poles. The value of the capacitor will NOT change the speed, just
the torque to spme extent.
May I now guess that M2 has a through shaft ? If so, I suspect that
the operation is as follows. M1 is a geared motor providing drive to
the papaer (slow speed) by driving the set of gears visible on the RHS
via the shaft of M2 which free-wheels. The clutch being engaged.
When High-speed is selected by operation of the switch energsing M2,
it drives the same set of gears in the same direction, but the clutch,
now being "overdrived" slips. M1 continues to rotate. Just think
about the mechaniical connexion between M1 and M2 and you will see
what I mean.
Let me know if anything I've guessed was incorrect.
M1 *is* a typical synchronous motor (Crouzet type 392). It is self
starting and is marked as CL (clockwise). If I hold the clutch device at
one end, torque is passed through the clutch and doing that makes the
motor turn counter clockwise, however, it soon corrects itself and
returns to clockwise direction. It is a geared motor 240V, 50 Hz and
runs at 25 RPM.
M2 I believe is an hysterisis synchronous motor having a through-shaft.
It appears that it has two windings that are referenced as "1" and "2",
as well as "X" ad "Y".
Above link we see that we can connect a capacitor *permanently* in
series with one of the coils of an hysterisis synchronous motor - mains
directly to the other coil.
In my circuit, the capacitor is connected in parallel with one of the
coils which is different, but we must note that mains is now across both
coils, unlike the usual connection.
As to operation of this contraption:
SLOW SPEED (Minutes)
Say M2 is not energised.
In order for M1 to properly drive the SHAFT it would need to rotate the
SHAFT clockwise (looking into the SHAFT, i.e. looking to the RIGHT). M1
wants to rotate SHAFT counter clockwise because it's a clockwise motor.
The clutch will transmit torque to M2 as M1's rotation is the right way
to operate it. The gearing set to 1/2". I've measured the time it takes
M1 to move the chart paper 1/2", which is 40 seconds. This speed is too
fast, the SHAFT speed would need to be 16.67 RPM to move paper at 1/2"
So, these are the problems with M1 driving the SHAFT at SLOW speed.
HIGH SPEED (Seconds)
Multiplying 16.67 RPM by 60 would give the SHAFT speed for HIGH speed
operation. That is 1000 RPM.
The synchronous speed of M2 would be 500 RPM if it has 12 poles which it
has I'm sure. That is only half the required rotation of SHAFT in HIGH
Let's assume M1 is still running.
The clutch will transmit torque when the one side is moving COUNTER
CLOCKWISE" *relative to the other side*.
If M2 was to be rotating at 1000 RPM in a direction to make SHAFT rotate
the correct way, point Q (see above) is the say the input side and it is
moving 1025 RPM counter clockwise relative to point P.
Because torque is tranmitted from Q to P, (and also P to Q) M2 wants to
overcome M1 and change it's speed from 25 RPM clockwise, to 1000 RPM
counter clockise. In this situation M1 would win, making M2's spindle
rotate at some speed lower than 25 RPM, and in the wrong direction for
Really M1 should rotate at it's synchronous speed I think, not 16.67 RPM.
Yes indeed. If the SHAFT is meant to go the same way as M1 drives the
SHAFT, and M2 drives the SHAFT the same way as M1, the thing works.
But, I've connected M1 direct to the SHAFT and the sprockets in the
paper have the paper feeding the spool of paper, rather than drawing
from it. That's the big spanner in the works.
You are spot on!
It just came to me the error I was making. So simple.
The true picture is this:
Bolting on M2 does not put it's axis concentric with SHAFT. The pinion
on M2 spindle cogs with a pinion on SHAFT. And that will lead to a
reversal of whatever way the M1 and M2's spindle turns. So, M1 will make
sprokets move the correct way.
Also, this solves the speed problem. The pinion on the spindle is
smaller than the one on SHAFT. SHAFT needs to revolve at 16.67 RPM, but
the spindle needs to be running at a different speed, at 25 RPM, because
cogs/pinions will reduce the RPM from 25 to 16.67 RPM.
What doea this do for the HIGH speedsituation? The spindle should
rotate 60 times 25 RPM = 1500 RPM. SHAFT turns at 1000 RPM.
The only outstanding issue is how does M2 do 1500 RPM, if it's a 12 pole
motor running at 50 Hz?
Yes, the cap across the second winding would induce a phase shift in
relation to the first and if the cap were arranged to resonate the
winding, the phase shift would in fact be 90 degrees. Cap in series
would still be valid though, so why is it done this way ?. Less wire in
each winding as each then only has to handle half the line voltage ?...
Although M2 has 12 stator pole pieces it is wound as a 4pole 1500
Numbering the slots 1 - 12 one pole winding occupies slots
1,2 5,6. The remaining windings following the same pattern fill
all the slots