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Home-made servo current meter?

Old 04-23-2011, 05:54 AM
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Default Home-made servo current meter?

Is it reasonable, with some simple soldering, to wire a spare servo extension into a "home-made" in-line current meter (used in conjunction with hand-held multi-meter)?

Of course an easy alternative is to simply purchase the Hangar 9 servo current meter, but I want to start setting up my ganged aileron servos today (and maybe also avoid a potentially extraneous purchase).

Anyone done this?

Thanks,

Noah



Old 04-23-2011, 08:04 AM
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Default RE: Home-made servo current meter?

Hi Noah,

Yeah, it's easy to do. You can separate the '+' lead in a servo extension, and put some sort of connector on that that can easily be attached to your DMM. I passed the cable thru a small plastic box and mounted some banana jacks on the lid.

A couple of things to keep in mind is that most DMM's can only measure up to 2A. Some will go higher, or you could also use a 'shunt' resistor in the box, and measure current indirectly by measuring voltage across the resistor. Also, the accuracy of the current measurement might not be great in a cheap meter, but you'll definitely be able to distinguish a "stalled" servo.

John
Old 04-23-2011, 08:13 AM
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Default RE: Home-made servo current meter?

Noah, I made this one because I was having troble with the low sampling rate of the digitals. The switch is for reversing the current when needed. Dan.
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Old 04-24-2011, 02:55 PM
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Default RE: Home-made servo current meter?

I just chopped a servo extension lead in half & use terminals from a terminal strip to connect the multi meter up in series with either the positive or negative wire. You can secure the tips of the meter leads in the terminals so you don't have to hold them.

You can use it to test individual servos or the drain from the whole pack or connect the pos/neg wires to monitor the voltage. - John.
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Old 04-25-2011, 07:36 AM
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Default RE: Home-made servo current meter?

I know this thread is asking for a DIY sort of solution, but I thought to put a plug in for my absolute favorite servo utility:

http://www.vexacontrol.com/xciter_details_1.html

It has a peak current readout so you can fully drive your servo and see both instantaneous and max current values. I use it for absolutely every new plane that gets new radio gear on my bench. It can also use an external servo input (ie from the RX). One feature I absolutely love is the one button touch centering feature (ie 1.5 milliseconds PW) so I can quickly set up my servo arms and check symmetry and other geometries.

About the only drawback I've found is since it runs on a single 9V battery it has a very short life on the large digitals I've been using on my giant scale planes. I may put an external power source option someday to address that.
Old 04-26-2011, 12:58 AM
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Default RE: Home-made servo current meter?

I am very interested in seeing a DIY solution!
Old 04-26-2011, 04:49 AM
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Default RE: Home-made servo current meter?


ORIGINAL: Kostas1

I am very interested in seeing a DIY solution!
What more would you like to see beyond what John and Dan have given?

I posted the Vexa device information because it has memory capability (max current), which perhaps some multimeters would allow also, but the basics of having an inline ammeter have been covered. Beyond that I think you'd need some special circuitry to mimic what the Vexa already does.
Old 04-26-2011, 07:59 AM
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Default RE: Home-made servo current meter?



You might also be interested in seeing the voltage drop at the servo if high currents show up on the ammeter. That would show how efficient the receiver is at passing on the battery voltage to the servos, or what happens when wiring to the servos is of insufficient size. If there is very little voltage drop, but you still have high current, then you know something physical is binding or you have a bad servo.

Joe</p>

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