Throw Gauge.
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Some while ago I was searching for ways to improve my flying by browsing various websites for tips on how to set up models for aerobatics etc and I came across references to a ‘Throw Gauge’ or “Throw Meter”. This device allows accurate measurement of the angle a control surface moves; and apparently is necessary to set these up precisely to fly aerobatics to a high standard. “Goody” I thought “I’ll get one of these and then I’ll be able to fly like the champs.
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Looking around I could only find one, made in the states and sold over here by Pro-Build for ~£25. On closer inspection of the pictures it looked very much like a clothes peg with a scale and bob-weight attached, so being a mean so-and-so, I thought “I can make that”. So I did, and it is shown in the various pictures.
At this point I should perhaps make it clear that it hasn’t, so far, improved my flying (who said we noticed…!), but it has been useful in the following ways.
The first model I applied it to was my 68” Glens Extra. This is lovely precise model to fly but at the time had a slight tendency to ‘screw’ out of loops and bunts. It has a split elevator driven by separate servo on each side. Application of the Throw Gauge to each half revealed that one side was moving further ‘up’ than the other, by a significant 10°. Using the gauge and adjusting the electronic trims for each servo quickly cured this problem, and definitely showed up in the flying.
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Now if it screws out of a loop its down to me…well actually it is generally a problem with the wind or phase of the moon, it’s rarely MY fault of course.!!
A very similar situation occurred on my Magic 3D. Again split elevators driven by two servos but in this case the servos are connected to a Y-lead so I could not electronically trim each side. In this case not only was one side moving much more than the other but it also suffered up/down differential, i.e. more up than down at maximum stick position. On the Magic 3D the elevators move ±45° but as initially set up one side was -30° to +48°, and the other was -45° to +40°.
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Now you might say “surely you can spot that by measuring the deflection with a ruler”. Well maybe, but I didn’t. I should also hasten to say that the linkages and servo arms were set up that same on both sides. Eventually by a combination of changing elevator horn length and the angle of the servo arms relative to zero I got the elevators move in sync.
I also found it very useful to set up the elevons on the flying wing I flew in a recent club competition. (shown in the header above in it's younger days - see also WIG) Didn’t stop the damn thing crashing but "by George" the elevons were precisely set when it did! |
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The photos above and to the right show the device fitted to the ailerons of the Magic 3D. If you are interested in making one the next picture shows all the parts. File out the jaws of a peg as shown and glue a wooden block on one side, drilled for the scale pivot and saddle pivot. The saddle is light ply and balsa blocks. The scale is again 3mm light ply with an M3 T-nut. Add a collar of light ply to accommodate the T-nut on the backside (not visible above). The pointer and bob weight are soldered either side of a brass 3.0mm dia collet. I used a terminal block from an electrical ‘chocolate block’ connector with a bit of lead for added weight.
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Assemble the saddle so it pivots freely. Attach the scale with an M3 screw and tighten so that it is just pinched on but can still be re-positioned. The pointed is held on with an M3 nyloc-nut (or two locked M3 plain nuts) so that it rotates freely.
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In use you attach the gauge to the control surface and then move the scale so that it read zero, them operate the control up and down and see what you get. Note that you may be able to work with out the saddle but it helps to accommodate different thicknesses and angles of control surface. Keep it as light as possible so that the servos are not doing too much work holding at zero.
If anybody wants to use same scale printing click here to down load a pdf of the scale. Scale pdf. |
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