what are people using to get the amps the motor is pulling? I have a multimeter but it doesn't read amps. I'd hate to have to buy another one like a fluke or something they get costly. any cheap suggestions?

I use a multimeter. A decent auto ranging meter is only 30 bucks (assuming that you aren't doing high level electronics repair with it) and is a good investment if you are looking to get heavily into electrics. I don't do electrics, but I have one since I repair electronics (circuit boards, televisions, etc) for people. Just remember that unlike measuring voltage or resistance, current must be measured by breaking the circuit and bridging the gap with the meter. You can't just "probe."

Fluke meters are top of the line. You really don't need one for simple measurements on electric airplanes. Here are some features to look for:

Auto Ranging - Handy if you aren't extremely knowledgable about what's going on in the circuit and don't know what value range to expect.

Continuity Beep - You can check for continuity without having to look down at the meter.

Of course voltage, current, resistance, and diode functions are good.

What about the "Watts up" meter? I have no experience with it. I really only fly glow, electrics are not my thing. Just wondering.


Just went to Tower and answered my own question.

This is the RC Electronics Watts Up Watt Meter with Blue Case.

FEATURES: Works with any electric airplane, helicopter, car or boat model High resolution on all measurement ranges to accurately check battery battery pack cell balance and measure single cell packs Connects like jumper cables and troubleshoots poor performance, crashes, charging problems, battery capacity, ruined batteries, erratic receiver and servo operation and many other common electric model problems Readings are easily reset, even without removing power, by adding an external pushbutton connected to the reset signal of the meter's auxilliary connector, The full user manual (v1.7) at the RC electronics has details on this function. Sets cutoff currents and voltages, compares components and detects wear prior to component's failure Measures eight essential electrical values; Captures Peak Amps, Peak Watts and Minimum Volts events as short as a fraction of a second Current: 0-100A Peak, 50A Continuous, .01A Resolution Charge: 0-65535mAh, 1mAh resolution Power: 0-6500 Watts, .1W Resolution Voltage: 4-60V, .01 Resolution (0V min. using auxiliary receiver battery Energy: 0-6500 Watt Hours, .1Wh resolution Powered by circuit-no battery to change 16 character, 2 row LCD display 8 MIPS microprocessor and DSP firmware for highest performance One year warranty

http://www3.towerhobbies.com/cgi-bin...&I=LXLMV0&P=ML

I use a Sears DC clamp meter. With this you can measure the current (Amps) by clamping a probe around one of the wires coming from the battery. It was about $50. You don't have to unplug anything on the circuit. It senses the current flowing through the circuit - probably through some sort of magnetic property.

For most uses, one of the wattmeters are hard to beat as they give you a pretty good picture of volts, amps and watts. I have both the wattmeter and a clampon ammeter and both are useful at times. The nice thing about the clamp-0n meter is that you can magnify the range by just looping the wire being measured thru the clamp, two loops, twice as high an indicated reading , three loops three times etc. which allows you to measure some pretty small amplitude currents without unduly loading down the circuit being measured. For most measurements on our electric powered planes, I'd suggest the wattmeter though.

If you get a general purpose clamp-on meter, make sure it measures both AC and DC amps. Most of the older ones and some of the less expensive ones only measure AC amps. AC only clamp on amp meters are useless for measuring amps in model airplane motors.
These are handy for other things too, like seeing if your car's alternator is charging the battery after you start the engine.

Wattsup wattmeter especially designed for electric flight.

http://www3.towerhobbies.com/cgi-bin...&I=LXLMV0&P=ML

I have an Astroflight Wattmeter, which is basically the same as the Wattsup, and I like it a lot.

I have also have a multimeter I got from radio shack years ago that does amps, though a lot of multimeters are limited to 10 amps. I''m not sure if that limit is 10 amps at a particular voltage or what, but I don''t think they can handle a direct measurement of larger model (something pulling a kilowatt, for example). You''d need a shunt or something simular.

I don''t have a clamp on meter (though I keep thinking I want to get one for other reasons), but that should work if it does DC.

(it''s 3-phase AC between ESC and motor on a brushless right, but I don''t recall enough about 3-phase to know how to measure it directly...)

Yes it''s 3-phase. Three phase power is AC amps X AC volts X 1.732 X power factor.

The power factor is the cosine of the angle that the current lags or leads the voltage. If the current is exactly in phase with the voltage, then power factor = unity. Power factor will vary with the timing of the esc and since it is an unknown unless you have an oscilliscope, it's best to just measure the DC amps.
Yes, the AC amps can actually be higher than the DC amps if the power factor is low.