How to build a low-cost thrust stand - continued

Previous: How to build a thrust stand

Push the rod through one arm, then place the other one over it temporarily in the position it will be glued. Using a pencil or pen, mark the area where the two pieces of wood meet. Remove one piece of wood, and smear aliphatic resin wood glue on the area you marked. Push the piece of wood back over the brass rod, mate the two pieces up, and lightly place the clamps on the joint. Using a square, ensure that the angle of the arms is exactly 90 degrees, then tighten the clamps. Check the angle again, and reset the angle if it moved while tightening the clamps. Let dry sufficiently before removing the clamps, according to the directions of the glue used.

While the glue is drying, drill the holes for the support arms. If you used 1x3's for your thrust arms, the width at the joint should be 1 and 1/2 inches wide. Add an additional 1/2" (12 mm) to this, and place the support arms this distance apart from each other on the base. They should be about 1/2" (12 mm) from one end of the board, and centered between the sides. Draw a rectangle around each one, then remove them and select appropriate points to drill pilot holes for the 3" screws. Drill these 4 holes, then mark where these pilot holes will meet the end of the support arms, and drill pilot holes in them, to avoid cracking the wood. Insert two screws and attach ONE support arm onto the base at this time, with the ball bearing facing in.

When the glue has dried sufficiently on the thrust arm, remove the C-clamps and set one side of the brass rod into the attached support piece. Block the arm in place with scrap wood so that it is level with the base. Now measure the distance between the bottom of the arm and the top of your scale. Remove the arm, and insert a 1" screw into the bottom of the arm at the point you previously marked so that it sets at this distance outside of the wood arm. Put the arm back onto the attached support, and then attach the second support. We're nearly done!

Attach the 3/8" square stock, assuming you will be using a motor mount that utilizes this kind of mount (GWS uses a plastic one for most of their motors, and many brushless motors use either a metal or plastic mount that is 3/8" square). If you do not use motors with this kind of mount, measure the point of the pilot hole around to the front of the arm, being careful to make the line square and true. This will be the centerline to which each and every motor shaft must be aligned. If desired, you can attach a small piece of plywood to the face of the arm to make a larger surface area to attach motor mounts. The distance forward from the arm is not relevant, but the distance from the motor shaft to the brass rod MUST remain the same as the one from the scale "screw" to the brass rod on the horizontal arm.

What next? Place your thrust stand in a CLEAR area (not near any walls or people!) and be sure to set it up so you are standing behind the spinning propeller. Now attach a motor and prop! Place your scale under the screw, and turn the scale on. You may need to "tare" the scale (or "zero" it) for the weight of the arm to be "zero." (Alternatively, you can simply subtract this amount from the scale reading when the motor is powered up.) Some people forgo using half of a radio system by utilizing a servo tester in place of an ESC, but if you don't have one, simply hook up a receiver, ESC and battery to your motor, and turn on your transmitter.

Remember all that business about knowing what amperage your motor pulls? This is a great way to find out what it is? Between your battery and speed controller, connect a "Wattmeter" or similar equipment (mine happens to be an E-Flight Power Meter). Select the "amps" setting. SLOWLY increase the throttle function of your transmitter up to full speed, ensuring that the thrust doesn't yank the entire assembly off your table or workbench (ideally, you could screw the stand to the bench). Look at the amps - write it down!! Look at the weight the arm transfers to the scale - write it down!! Turn the throttle off, then change propellors, and repeat the process. And importantly, if you're using LiPo batteries and the motor / prop combination is drawing more amps than the "C" rating of your battery, then only utilize full power for short bursts. Or better yet - to be really safe - use a different battery or motor / prop combination that draws fewer amps.

You've now added an invaluable tool to your radio control workshop, allowing you to better match propellors to motors, and motor/prop combinations to planes AND batteries. You can calculate the wattage produced by a given motor / prop / battery combination, and compare what is most efficient, what produces the most power in watts, or what produces the most thrust in ounces/grams. This is one of those items where the phrase "Knowledge is power" really is power!

What better way to scratchbuild than to be able to have the best possible information about the equipment you own and use on your planes?

What do you think? Thoughts or comments? I'd love to hear them. Send me a note in the "Feedback" form on the Columns page. Thanks!