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Old Jun 13, 2002, 08:12 AM
MrC
Registered User
Columbus, Ohio
Joined Nov 2001
192 Posts
How to test a motor on a field bench?

I thought I posted this yesterday. Seems the computer ate my message

I do know how to measure amps and volts, but what equipment are you using? How do you measure the static thrust and rpms? Is anyone using a computer interface to collect the data?

Do you have any pictures?

TIA

--MrC
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Old Jun 13, 2002, 08:42 AM
Product Manager at Hobbico
GWRIGHT's Avatar
United States
Joined May 2000
5,163 Posts
I made a mount with sort of a parallelogram arrangement so that thrust could be read via pressure onto a digital electronic scale ($25 at walmart,.. but only goes up to 5.5 lbs, fine for 10 cell systems). Many people have said static thrust doesn't tell you a lot, in-flight thrust is what matters, and I agree,.. to a point. If you're flying f5B, you'd probably run something aproaching a "square prop",..i.e. equal diamater and pitch. Since the planes are so "slippery" they will accelerate to a point where the prop is not cavitating and go "up" faster. However, if you want to do 3D style flying,.. (true 3D, not just loops and rolls) static thrust is extremely important since you'll be spending a lot of time flying "on the prop", rather than on the wing. I broke my crude thrust meter quite a while back (wouldn't take the force of even an endo, geared high with a 20" prop ). I've found motocalc to be a wonderfull tool,.. for COMPARISONS. Since I have several established standards,.i.e. gear ratios and props,.. and I know from earlier testing and flying exactly how they perform,.. motocalc does a great job of giving me comparison data. I really don't see much need for a thrust meter any more, although I have connected crude scales to the tail to see how much "pull" I get from various setups. I use an astro wattmeter,.. a cheapie optical tach (I think the one I currently have is the hanger-9 one), and of course a timer during flights. i've plugged in numbers to an excell spreadsheet before to get mph per watt (computed from pitch speed, not actual flight data), and thrust (in ounces) per watt. It's very ease, almost trivial to get HUGE amounts of thrust from very little power,.. but it's very difficult to get lots of speed from minimal power, so,.. other than my kwik-E, I tend to design and build things optimized for lower speed aerobatics since the required power for that realm of flight is much easier and cheaper to obtain.
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