coomarlin

My Feedback: (1)

I've got a cheap Hobbico Multimeter that is capable of measuring current draw up to 10A but I'm not sure how to do this. Do I hook the leads of the multimeter to the servo leads and then deflect the servos? I'm interested in knowing how many amps I'm pulling.

KW_Counter

To measure current the meter goes in one of the power lines.
I suggest breaking one line between the battery and receiver and inserting the meter there.
Then you can measure the current draw in a static mode and as you move any combination of
servos simultaneously.
Good Luck,
KW_Counter

kgough

KW_counter - Are you saying put it in series?

Another way is to make or buy a shunt.
I wanted to measure a larger current of up to 20 Amps.
I made a shunt per the instructions :
http://www.uoguelph.ca/~antoon/gadge...ts/shunts.html

I placed the meter in parallel to the shunt.
It really helped that I had a known current draw I could use to calibrate.

Geistware

My Feedback: (16)

First I wasn't going to say anything because I can't see lower on the meter.
Most inexpensive volt meters have two or three inputs and one ground.
FInd the input for current and use it.
Not the one for voltage.

J_R

I, also, was going to let this thread go. At the risk of sticking my nose in and getting it bit off, here goes.

If you measure the nominal current draw of the servos, it will indicate whether linkages are binding, etc. It can not be used to project how many flights can be taken. In order to do that, you would need to apply a load to the surfaces (indirectly, the servos) and approach a stalled state for all of the servos. The draw will be significently higher.

I think the typical assumtive draw for a starndard 5 servo system is 250 mah, but I am sure many would argue that. Given that load, you can check your battery voltage and get a semi-accurate reading. That is a better indicator of how much time you have left to fly.

The nominal current draw can give you a good indication of problems with the linkages, hinges, blah, blah, blah.

Wing-Ding

From your picture it looks like you can set your meter for the 500mA scale. Plug the black meter lead to ground (-) and the red meter lead (+) into the appropriate jack to measure using the 500mA scale. I think the current should be about 250mA when operating a servo, so the meter needle should be about mid scale.

As has been mentioned, connect the leads of your meter so that the positive lead connects to the positive side of your battery, and the negative lead (ground), connects to the positive power input to your receiver. If you reverse the connection (i.e., connect the negative lead to the positive side of the battery), the meter needle deflection will be in the wrong direction.

Hope that helps.

KW_Counter

Kgough,
Yes, put it in series if you are using the current function of the meter.
Working with a shunt is a whole different ball game that is especially helpful
when measuring large currents.
KW_Counter

Wing-Ding

Whoops. I realize you have a digital multimeter. In that case, reversing the black and red leads will just result in a negative sign (-) in front of the current measurement. Not a problem.

Looks like you can measure up to 10 Amps with that meter. Let's see, that would be (40) 250mA servos running simultaneously to reach full scale on the meter. Any more than that, you'll have to use a current shunt.

EloyM

My Feedback: (194)

Mostly good advice, BUT.................
Once you are correctly hooked up - in series, when you actuate a servo(s), the digital display will jump around so fast you won't be able to read even an average value. Digitals are only good for steady current drains. For this test you need an analog (needle type) ammeter, which will indicate readable peaks, and if you pulse the servo(s) back and forth, you will get a readable average.
Actually, all these are only approximations, because when you insert the meter in the circuit, you have added a resistance which reduces the total circuit current. Without the meter in the circuit, the current is actually higher.
There are meters with compensation, or in some cases, come with data on how to calculate the true value. The loss is referred to as a "burden voltage" - actually a voltage drop - you don't get this precision or info with the cheapies.
Want to test this? Set up a test with a load, such as a auto light bulb, and read the current on different settings of your meter. They will differ, because the meter adds a different resistance on each range, affecting the current reading.
YOu really didn't want to know all this, did you?????

Wing-Ding

Wow! I didn't realize how much burden voltage can affect current measurements. I found some good information here. Scroll down the page until you get to the burden voltage explanation:

[link=http://zone.ni.com/devzone/devzoneweb.nsf/Opendoc?openagent&0FB8AEBAE30DB15586256E050054C320#6]B+K Precision[/link]

Seems like it would still be possible to identify problems like binding control linkages by comparing current readings even considering how accuracy is compromised due to the burden voltage.

WilsonFlyer

My Feedback: (13)

http://horizon.hobbyshopnow.com/prod...sp?prod=HAN172