Gerhard Fiedler wrote:

> we're currently using this gear motor in a servo-type application:
> http://www.casaferreira.com.br/pdf/CEP453042.pdf
> 
> 12VDC, 57W, nominal 9Nm/75rpm/18A, stall 36Nm/50A, idle speed 100rpm, gear
> 63:1
> 
> There are two problems I need to solve. One is that the stall torque is not
> enough. Ideally it would have 50 Nm. The idle speed is not critical and may
> be lower, so a similar power motor with a different gearing should be ok.
> 
> The other problem is that this particular motor has a plastic gear that is
> designed as a "mechanical fuse" to prevent burning out of the motor. The
> connection between that gear and the output shaft sometimes strips off,
> probably when there's a mechanical backlash on the output shaft.
> 
> So I'm looking for a gear motor (or a gear + motor combo) in that power
> range (should not be less power, but may be somewhat more) with a higher
> stall torque, a solid gearing (ideally some kind of metal) and an idle
> speed that's at least 80 rpm or so.
> 
> The final purpose is to move a push/pull cable back and forth. We generate
> this linear movement through a lever mounted to the motor shaft. So in
> theory a linear actuator could also do it. The problem with most actuators
> we have is twofold: one is the overall length; they tend to be much longer
> than we have space for. We need a total movement of ~70mm and have around
> 160mm space, lengthwise. Linear actuators tend to be longer. The other
> problem is that most of them are much slower. In the current application,
> the mounting point at the lever moves the distance in some 200 ms (at half
> load). But one that fits and that is fast enough could be even better.
> 
> And of course I don't have several hundred dollars to spend on that :)  The
> one we're using now costs around $50. Small production quantities (several
> hundred per year). Final destination is USA.
> 
> Does anybody know where I can find such a gear motor or gear+motor combo
> (or linear actuator)? I've looked a lot, but they either are made for
> different voltage (24+V or AC), are much slower (<10rpm) or faster (and
> therefore weaker), or much more expensive.

Thanks to all who responded. I got a lot of interesting ideas, some of
which I had tried earlier that got a new momentum. Unluckily, it also
confirmed that it's not as easy as selecting an opamp... There is not
really a "market" for this type of equipment in my quantities, and
datasheets for the mass-market products are difficult to find. Or the
market that exists is way out of my price range.

My current thought is to use a normal 12VDC ~60W motor and drive a threaded
bolt, making a custom linear actuator. The linear actuators I found that
work this way are usually too slow. I'll see whether there's a reason for
that... I need at least 10 cm/s, ideal would be 20 cm/s.

Another possibility would be to continue using my gear motor and drive a
belt. That would also get me more force on the cable than I have now.

Gerhard

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