Windscreen Wiper Motors

I do voluntary work for a charity called Remap; we make custom aids for disabled people. I have a case that requires on a small, high torque,
low speed, 12V electric motor, and a car windscreen motor seemed to be ideal. Unfortunately, after a small amount of successful use, the motor lost power. Stripping the motor revealed the cause - the carbon brushes were tangential to the commutator rather than radial, and reversing the motor wore a slightly different contact area on the brushes, thus reducing the contact area and hence the power. Clearly they were never intended to be reversed. I'm told that the older type of windscreen motors had radial brushes and could be reversed, but nobody seems to know how to identify them. Can anyone help please?
--
Regards, Gary Wooding
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lemel_man wrote:

Even with radial brushes the motor construction may not be intended for bi-directional use due to the means of taking the motor shaft end load. I have a few with radial brushes and they definitely don't run as well in the direction not intended although one has seen bi-directional use for a while without failing. One thing you might want to do is get the Bosch motor catalogue or look it up online as that give motor characteristics, duty cycle, and directional use information.
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Gary
There are a umpteen arrangements of brushgear in these automotive motors. If you are selecting a motor, say by visiting a car breaker then many of the wiper motors I have seen have some external indication of where the brushes are situated just by looking at the features and shape of the motor casing.
As you say they are only designed to run in one direction and if you do find one with suitable brushgear you will still probably need to beef up the thrust arrangements so that too is bidirectional.
Why not look for an electric window motor? They have similar gearing and wattage (but might not be continuously rated at full load.

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Another automotive motor to consider is a 'seat motor'. These are designed to drag a car seat and a 20 stone occupant forwards and backwards. Should be powerful enough for most applications.
John H
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or these, Doga motors, http://www.oem.co.uk /
--
mick



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wrote:

Is there a way to tell the intended direction of rotation? I have a similar application. I only need rotation in one direction as long as I know the correct direction. Thanks.
Pete Keillor

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Pete Keillor wrote:

I have a couple of Magnetti Marelli wiper motors and they have a directional arrow on the gear casing on the output shaft side. I can't say if all do that. Having a quick look through my Bosch motor catalogue most, but not all, motors having the DIN taper spline output are unidirectional. I have a Bosch and some Doga motors with no markings but I know they are bidirectional.

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On Tue, 17 Apr 2012 12:22:26 +0100, David Billington

I should have looked more closely before posting. Turns out my unit has one lead grounded to the case. Runs well assuming that's neg. and other is pos.
Thanks.
Pete Keillor <snip>
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Thanks for all the input guys; windscreen motors are clearly not suitable for this application, which is a powered reclining back-rest for a wheelchair. And space is at a premium - as is cost. I'll try and find a suitable window winder motor.
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Perhaps I am being dense but why adapt a wiper motor or window motor, when a car seat motor is designed for the job and is just as readily available from scrap yards? That's like trying to re-invent the wheel.
Cliff Coggin.
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On 18/04/2012 08:15, Cliff Coggin wrote:

You could well be right, I don't know enough about the car seat mechanism to decide. The wheelchair is a special one that is designed a little like an office chair on steroids. The seat is on a pedestal that pivots on a special chassis. The backrest is attached to the seat with a single narrow bracket - again rather like an office chair. The bracket is hinged and reclines only 30 degrees; the user requires it to fully recline, ie 90 degrees, when they are in it. I'm having to make a replacement bracket hinge that does just that, but there is very little room. Here is a photo of the original hinge to give a general idea of the space limitations. http://tinyurl.com/7a2feaw What do you think?
--
Regards, Gary Wooding
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lemel_man wrote:

Have you looked at the Bosch catalogue as they do motors and jacking screw assemblies. Have a look here http://rb-aa.bosch.com/boaaemocs/?language=en-GB
I'd give you a closer link but it uses a java session ID so wouldn't work. Once you have a Bosch part number you can often look it up on the internet and find out what vehicle it is fitted to and then you can try and find one.
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You might also consider a satellite dish jack like this :
http://www.ebay.co.uk/sch/i.html?_nkw=satellite+actuator&_armrs=1&_from=&_ipg They seem to be mostly 36V but may run slowly at 12.
Electric screwdrivers are also a useful source of low-geared motors.
-adrian
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