Many years ago a superb indoor flyer, who was quite creative, designed a torque meter with a spiral spring, instead of the traditional straight wire spring. It was nicely compact. I built one and quickly discovered the problem with it. Since the bearing had to take the axial load of the rubber tension, the meter was "sticky". I added a ball bearing, but the problem persisted. I tried to think of a way to add a thin tension wire that could handle the load, but it didn't work out. So, I think the main issue of a digital scale torque meter will be the influence of the friction in the bearing. A wire meter with a "sloppy" bearing is better than a ball bearing under load.
Digital readouts probably will not improve the resolution of the meter. If a long wire is used, and the meter face has scales on it to handle more than one revolution, the resolution can be as fine as anyone needs. In addition, digital scales are nearly useless in a dynamic situation. It is far easier to read a needle moving against a lined scale than it is to interpret a bunch of numbers racing by.
Ray
--- In Indoor_Construction_at_yahoogroups.com, Tony MATHEWS <tmathews1@...> wrote:
>
>
> Tapio,
>
> Check out this interesting torque meter idea on this discussion:
> http://www.hippocketaeronautics.com/hpa_forum/index.php/topic,3650.25.html
>
>
>
> Should be right up your alley. A 1" long rotating wire arm set perpindicular to the main shaft (on bearings) contacts a digital gram scale so that torque in in/oz can be read off directly. Anyone have any experience with something similar?
>
>
>
> Tony
>
>
> To: Indoor_Construction_at_yahoogroups.com
> From: tapio.linkosalo_at_...
> Date: Mon, 19 Apr 2010 15:26:15 +0300
> Subject: [Indoor_Construction] Torque meter bearing?
>
>
>
>
>
>
>
> I have two torque meters, both constructed from different diameters of
> brass tubing to house a torque wire. The larger for F1M and similar is
> built by a friend and works very nicely, but my copy for F1D is not as
> sensitive as I would wish it to be. It is somewhat difficult to make
> sure that the zero level is as it should be, and also I have concerns
> about the accuracy vs. sensitivity. Looks like a brass tubing rotating
> in another one has too much friction for the small forces we are
> measuring here. I even tried to dremel the inner tubing so that it has
> the bearing surfaces at the very ends of the tubing, but it did not help
> much.
>
> So any suggestions for improving the bearing? Would teflon or nylon make
> a more sensitive bearing, or should I replace the sliding bearing with a
> ball bearing?
>
> The other end is no problem as I use O-rings and have that fixed; do not
> need to have the meter for unwinding rubber.
>
> -Tapio-
>
Received on Tue Apr 27 2010 - 06:24:47 CEST