Re: Re: Brushless Servo

Further to my message below re motors
One possible source also is old chart recorders.

The simplest of these are/were just a moving coil meter movemeht carrying a
pen, with the paper driven past it by either a clockwork arrangement or a
small synchronous motor geared to the paper roll - these later have often
got a stack of different change gears within them, which can be useful as
they offer different gear ratios between the same shaft centres - quite clever.

The more complex chart recorders may have a DC servo motor driving the pen
via a capstan and stainless wire arangement. These have a feedback
arrangement either a digital quadrature encoder, or an analogue feedback
arrangement.

NB. Some of the encoders are GRAY code absolute angle position indicators.
Some of these motors are quite hefty speciemins - due to the need for high
pen accelerations to raise the response frequency. Makers include Texas
Instruments and others.

Sanborn Recorders - usually big flatbeds had a wonderful paper drive system
with a heavy duty drive gearbox. The gears were about 3/8" face width
stainless steel, and these were electro-magnetically controled by solenoids,
to select a wide range of gear ratios depending on which combination of
solenoids were energised. From memory the selector solenoids were either
12v or 24 volt.

Another source is the range of ink jet and laser printers. Some H.P Inkjets
contain a stepper motor paper drive, and a 9 volt DC gearhead motor with
quadrature encoder fitted to position the print head. Lovely unit! Also the
lasers have an assortment of servo type motors. Dead ones of either, can
be picked up for very little and they almost never cook the motors! Usually
the fuser assembly or the electronics, and either are so expensive people
buy new machines.

Jim Gregg


At 08:49 10/10/99 +0800, you wrote:

>From: Jim GREGG <gregg@...>
>
>Hi List.
>Re Tape drive motors.
>The unhelpful answer is BOTH steppers and motors are used, and it VARIES.
>
>Reel drives are usually DC motors but not always, sometimes AC mtors are used.
>These (AC & DC) are usually fairly low power often 24/28 volt.
>
>The capstan motors which actually drive the tape when reading or writing,
>are either DC or stepper motors, and the DC ones at least will usually have
>some kind of encoder attached, but usually only giving a speed output, ie no
>quadrature output.
>
>To an old HiFi buff the concept of a stepper driving the tape was a total
>contradiction in the world of electronics - but this is digital not analogue.
>
>Jim Gregg
>
>At 06:48 10/10/99 +1300, you wrote:
>>From: "Raynor Johnston" <rhj-rbj@...>
>>
>>Yes Jon... absolutely right with closer inspection it's dca is 2.1 amps so I
>>guess not a lot of use for too much.
>>
>>On this list i think people have mentioned that the older large central
>>computer processors are a source of quality motors suitable for axis drives.
>>The suggestion was that the tape drives..the sort that drive those big tape
>>reels on the vertical face of the processor...so beloved in 'Hollywoods
>>James Bond mad prof control rooms ilk' are quality servos or steppers. Can
>>anyone expand on that are there any names that have those ie. IBM
>>models......etc. so I can take a look about here and are they steppers or
>>servos?
>>thanks all
>>Raynor Johnston (NZ)
>> -----Original Message-----
>>>From Jon
>>>Well, the info is confusing. Is that REALLY 21 Amps? Seems VERY excessive
>>>for a photocopier. Anyway, 30 V x 21 A = 630 Watts in, should be able to
>>>produce 600 Watts out, at least. So, either the 21 Amps has lost a decimal
>>>point or this motor has an enormous peak current rating, with a dismal
>>>continuous rating (39 W). I don't know what sort of XYZ robot you are
>>>planning, but this might be able to operate a gripper or something, but not
>>>too good a prospect for an axis drive. What is the DC resistance of one
>>>of the windings?
>>>
>>>Jon
>>
>>>Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
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>>
>>
>
>>Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the

discussion of shop built systems in the above catagories.

>To Unsubscribe, read archives, change to or from digest.
>Go to: http://www.onelist.com/isregistered.cgi
>Log on, and you will go to Member Center, and you can make changes there.
>For the FAQ, go to http://www.ktmarketing.com/faq.html
>bill,
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>
>