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Jul 09, 2010, 09:15 AM
repeat foam bender
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Motor Mount Thrust Angles

UPDATE: Calculations were previously limited to down and right thrust. Now, down, up, right, and left thrust angles are possible.

Here's a simple and accurate way make a motor mount with thrust angles as spec'd in your airplane design.

Grab the following spreadsheet:


After entering your thrust angles, print the spreadsheet and cut out the pie chart you need (3-hole in the following example). I make the following sandwich and clamp it onto a hard flat surface until dry:

wax paper
square piece of 1/8" birch plywood
printed paper pie chart, face down
wax paper

This gives a super strong motor mount and the clamping squeezes out most of the epoxy, so it's lightweight. The wax paper protects your workbench and tools; remove when dry.

Next, center punch the pie chart lamination, tack down onto a scrap of wood, and cut out with a hole saw of the size you need, preferably on a drill press. Sand rough edges. Now place the motor on the mount and line up its flange holes to the lines on the pie chart. Drill holes for the screws.

Now it'll look like this:

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The picture shows it already mounted on the plane. The "top" line (left of the shaded area on the pie chart) was used to visually align the mount.

Now you're ready to mount the motor. Add washers to get the required shim thickness, like so:

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Done! This motor is angled 5 down and 3 right.

Note: This is just my preferred motor mount building method, but you can use the spreadsheet with other mounts. Just enter your numbers, print and align the pie chart to the mount, mark the hole locations, remove the chart, drill, shim, etc.
Last edited by ruddym; Nov 15, 2011 at 01:21 PM.
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Mar 30, 2011, 01:11 PM
David the Swarfer


Thanks man, this is awesome. I managed to figure out spacers for a 4 hole mount but didn't get the 'angle the bolt holes' thing at all. I mounted mine with the holes straight and then slipped in bits of .5mm plastic under 3 corners until the plane flies more or less straight.
It is an e-QSC and is a blast, despite being somewhat (10oz) over design weight.

Now working on a nutball.
Mar 30, 2011, 04:13 PM
repeat foam bender
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Revision 2

  • Calculations were previously limited to down and right thrust. Now, down, up, right, and left thrust angles are possible.
  • To enable all the possible thrust angles, the pie charts now must be refreshed using the rotate_charts macro (Ctrl+Shift+W).
Last edited by ruddym; Nov 15, 2011 at 01:24 PM.

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