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From: Paul Hovnanian
Subject: Re: Project (was: Help with relays please.)
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Organization: Software Conflagration Control
References: <firstname.lastname@example.org> <3D937DB8.B2320A30@boeing.com> <3D9461CE.331A960A@boeing.com>
Date: Mon, 30 Sep 2002 14:31:18 GMT
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"N. Thornton" wrote:
> Paul Hovnanian wrote in message news:
> > "N. Thornton" wrote:
> > > > This question leads me to dredge up an old idea for a project.
> > > >
> > > > A winch monitor, to read the motor winding temp., current,
> > > > voltage and (using some strain guages) the winch load.
> > > >
> > > > I never did find a source of strain guages that could be incorporated
> > > > into the mounting bolts of a winch. The stall rating on winches is
> > > > anything from 8000 lbs to 15000 lbs.
> > > >
> > > > Any ideas for parts sources?
> > >
> > > Anyone can make a strain gauge. Just make one direct on the mounting
> > > hardware. Its only wire and glue. A differential one would be best.
> > This is true. But a strain gauge actually measures deflection, so I'd
> > be depending on the vehicles frame/bumper/winch bracket to have a
> > linear and repeatable stress vs strain relationship.
> Well I assume it would be steel, not aluminium. And you'd zero it each
> time before reading - automatically without the user noticing. Would
> that do?
I'm not sure. My winch is mounted directly to my front bumper. This
acts as a part of the vehicle's frame and is subject to some amount of
strain as it flexes while traveling over uneven ground. The strain gauge
would see this flexing even if the winch wasn't in use.
> > To be technically correct, what I need is called a load cell, which
> > is (usually) a strain gauge incorporated into some structure with
> > a predictable spring constant.
> But the you'd have to modify the mountings.
That's probably a good idea. Mount the winch to a steel plate which is
turn mounted to the bumper only through the load cells.
> > > Wouldnt it be easier though to measure winch current? Either approach
> > > would need to be calibrated.
> > I'd like to do that as well. But there are times that the winch
> > is under load even when the motor is off (the brake is engaged)
> > and I'd like to get a reading then as well. In addition, the
> > dynamics of accelerating a mass with significant inertia might make
> > the motor current to winch load a messy relationship.
> Mmm. Your reading would soon settle though... maybe thats not good
> enough for your app.
And the line tension vs motor torque changes as it winds up on the drum
(sometimes not very evenly) and its effective diameter changes.
> There is another way: run the steel rope through a small box that
> picks up its resonant frequency, then you'd know the tension. You
> wouldn't need to ping it, real life'd do that.
> It'd be a little box with a roller at each side, you open the lid, put
> it on the rope, and close. Now you have a fixed length of rope between
> the 2 rollers, and a moving coil pickup will pickup the rope section's
> resonant f.
That might work, as long as getting clogged with mud doesn't affect it.
> I'm trying to think of something that would avoid the end customer
> having to make their own strain gauge and know where to put it... that
> would really kill sales! I dont think I've got it there... but you
> might be able to go somewhere from that perhaps.
This is what load cells are. Strain gauges integrated into some sort
of mounting. For a winch, the mounting kits are pretty standard, so
a few sizes would probably cover most situations.
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