I think you're referring to the Bosch GPA 750 which is officially 1HP and
favoured by builders of combat robots, though they usually weld them up for
added durability!. A quick Google should find all the info, Ellis components
are I believe the only UK stockist and it's around £100, though that could
have changed as I've been out of the robot wars thing for a while now. Oh
and they are 24V, I would have thought 250V DC was a very odd voltage for a
motor of this size.
If it's really 24V you're after
I've got a couple of 24V traction motors spare, anonymous but I'd
guess at least 1 hp from their size, apparently unused.
Traditional & Modern canal craft repairs
Vintage diesel engine service
That model number rings a bell. It may not be exactly what Brian is
looking for, but it just came into my mind. When I was interested in one
(for building a model submarine which I never built) Bosch offered to
sell me one direct. It was definitely more than £100 though. I think
Leeson might make some DC motors which run at a higher voltage.
Ellis components are the UK distributor for Bosch electrical parts but trade
only, I think Parkside Railways stocks them at a mark-up of course:
Not a cheap motor and as others have said it's a pressed steel (relatively)
light weight frame, hence the robot wars people mig weld the frame together
to add strength, lightness is of course important to them as they have
strict weight limits so a more solid motor is not ideal.
Its probably an odd voltage now, but not so much in the past. The
standard mains AC supply is relatively new thing, and many locations in
the UK had DC supply into the late 1930s and some through the war. DC
was typically supplied at 400 to 500 volts on a three wire system,
where the central wire was earth and lay roughly between the two. A
motor/generator set called a balancer acted to trim the voltage either
side of earth.
I suspect the requirement for DC motors at this voltage died out when
the CEGB finally managed to get us all onto one system - this was
started in 1927, but took a long while to implement.
I have a 1940s/1950s lathe that uses an old GEC motor 1HP at 220VDC
with 170V field coils as part of a variable speed drive system. One of
the USA Monarch lathes had a similar system, but they probably worked
at lower DC voltages, as the AC over there is lower voltage.
I have not seen a modern motor that has a similar specification, and
would be interested to know if such a thing exists.
Shame they don't have motors within UPS systems (or do they ?).
I have wondered for some years how we ended up with the mains voltage
we did. I had assumed it was a balance between a high enough voltage to
reduce resistive losses and a low enough voltage that a shock would
wake you up and not be deadly. No doubt the CEGB decided, but I am not
sure how. Maybe the same criterion is used in UPS systems.
I am a little anxious about setting up the 220V DC within my lathe
enclosure as I don't want a shock from it, though I have had many mains
shocks without anything other than a BIG wake up call, but we had a 2kV
DC source in a lab I worked in and I was told it was deadly - so I
treated it like a cobra.
My grandfather (also a model engineer) couldn't feel mains. He had a
live workbench and didn't realise until my father visited and got two
shocks off it (the first one being blamed on static). He could also
test the HT leads on cars to tell you which was good and which bad by
sticking his finger in the spark plug socket.
And they call me thick-skinned !!
Well, in a fit of madness, I bought a variable frequency inverter. These
are easy to find and I rather thought that finding a motor would be as
Daft really but what can you do when the buying mist descends?
I have spent (wasted) the last couple of hours trying to find out
exactly what motor spec I will need. My lathe is a Myford Super7B.
All I seem to have discovered is that the output shaft is 5/8ths. No
doubt they can't be had anymore and I will not be able to fit the
current pulley to the new motor.
Can anyone tell me what the mounting dimensions are. I could go and
measure mine but it is a bugger to move until I actually come to swap
out the motor. I would rather not have to do it twice. In any case, I
seem to need the actual frame size and, probably, some more modern NEMA
Also, it turns out there are 2-pole and 4-pole motors. What on earth is
all that about? I was only just coming to terms with the idea of star
and delta winding. Nobody mentions what their motor is so I assume that
can be adjusted internally to either configuration.
Can anyone help me with the appropriate motor specs? Oh, and a supplier
or two would be nice.
It's either a 1/3 or a 1/2 HP 3 phase motor with a 5/8" shaft. Late
model lathes had 1/2HP 3 phase motors. It should be foot mounted. A 2
pole motor turns at 2850rpm with 50hz and a 4 pole turns at1450rpm on
50 hz. You want a 4 pole version.
Everything else doesn't really matter since the motor mount/ platform
is adjustable in just about every direction.
An original motor would fit easily but I have fitted a modern brand
new metric framed one on a Super 7 for a friend. I had to turn a
spacer up to fit a 5/8" pulley on a 14mm shaft.
I fitted an inverter and three-phase motor to my S7 Plus, both
supplied by a regular contributor to this group. The new 0.5hp
three-phase motor is considerably smaller than Myford's original
noisy, overheating, vibrating, heavy single-phase monster. It was
therefore necessary to make an adapter plate (I used 3/8" aluminium
alloy) for the motor mounting, which is probably easier than hunting
for a motor with the right holes.
It was also necessary to make a spindle extension and this was done
before the old motor was removed. The original pulley is mounted on
the extension. I also made a control box to make best use of the
features in the inverter.
The result is well worth every single penny and every single minute
spent on making the alteration. You really will wonder how you ever
managed without it.
From the motor plate:
M.G.C. Systems VDE 0530/IEC34-1
3 phase M Type MA-AL71-14-4A
(illegible character) Y 230/440V
cos phi 0.91
1400 (-1) min (presumably rpm)
I seem to be making bushes to fit pulleys to motors quite regularly.
The technique I use is to turn the OD of a BMS rod to fit the pulley and
bore the inside to fit the motor shaft. Part off to form a short length of
tube. Turn another piece of scrap to the OD of the motor shaft and fit into
the tubular spacer.
Mill a slot along the length to the tube using the inner scrap to stop the
tube collapsing. Make the slot the same width as the keyway in the motor
shaft or very slightly wider.
If the keyway in the pulley is the same width as the motor keyway then a
simple key but deeper than standard is all you need. If as usual the pulley
keyway is wider than that of the motor then a stepped key can be made.
Hope this makes sense.
Steve, that sounds a lot like a motor that I have. Probably weighs about
25 kg, is about the size of a large pumpkin, and has something like a
5/8" shaft. I'm saving it with the intention of using it to drive a very
large Van de Graaff generator, but as yet it's a project I haven't got
round to. Unfortunately my motor hasn't got a data plate. I'll take a
picture tonight or tomorrow and post it to see if they're the same.