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Measuring commanded servo position, is this a no-no?

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Old 03-11-2002, 12:43 AM
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basmntdweller
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Default Measuring commanded servo position, is this a no-no?

I'll start by saying I know just enough about radios and electronics to be dangerous. I am in the process of fine tuning the setup of the pitch and throttle curves on my heli. I have an 8UAFs installed. I went out the other day and set the head speed and pitch for a decent hover. I noted that hover was just below half stick. I am wanting to set up per Ray's manual for hover at 3/4 stick. My first thought was an old device I no longer have called a Datamaster. It would display the pulsewidth commmanded by the TX. I thought that with one of these I could set my stick to where I was actually hovering at and note the PW for both collective and throttle. Then I could move the stick to where I wanted (3/4) and adjust my curves till the PW read the same as before. Unfortunately, I no longer have my Datamaster and don't have the money to spend on anything that will read this PW. I got this bright idea this morning that maybe the vaying PW could be read as just a voltage change on a DVM. I hooked up an extra servo plug I had to my DVM. I hooked the black wire to negative and the white wire to positive. I plugged it into my rx,(aileron) prayed for no smoke, I set the dvm to 2000mv and it read 227mv. I moved the stick full left and it read 280mv and full right read 170. It appears that it's doing what I want to see. So, aside from accidental shorts etc, am I putting my rx at risk? Is it not really doing what I think it is? The Datamaster gave an actual PW measurement, but I'm thinking that as long as I have a reference number that's all I need.
Thanks for you input, Like I said, I know just enough to be dangerous.
,,,basmntdweller
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Old 03-11-2002, 06:40 AM
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flatfour
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Default Measuring commanded servo position, is this a no-no?

It is doing exactly what you think. You are getting an "average" reading of the servo command pulses.

As long as you don't create any shorts, there is no danger to your receiver. The average DVM has an input impedance of 10 MegOhms.
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Old 03-11-2002, 06:55 AM
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flmgrip
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Default Measuring commanded servo position, is this a no-no?

if you just know enough to be dangerous you shouldn't even touch a heli until you educate yourself some more.
what you are saying does not make any sense whatsoever in regards to setting up your heli correctly.
come to the helicopter tread and get some more help...
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Old 03-11-2002, 12:18 PM
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bob_nj
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Default Datamaster

Although I haven't used mine lately, I'm pretty sure it still works. I'm taking it to a flea market next weekend unless you want it. $10 plus shipping and you can have it_Bob
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Old 03-11-2002, 01:11 PM
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Default Measuring commanded servo position, is this a no-no?

Sounds like it works.. you're measuring an average voltage. The only thing I'd be concerned about is does it drop at any given setting as the rx battery voltage drops? Since you're technically measuring time and voltage instead of just time, the voltage is going to be another variable. You'll also get different readings from meters with different sampling rates and A/D methods.

As flatfour said, there's no chance of hurting the rx unless you fatprobe something.
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Old 03-11-2002, 11:04 PM
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basmntdweller
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Default Measuring commanded servo position, is this a no-no?

Thanks guys,
I rigged up the servo plug so it's a direct connect to my meter. I thought about the voltage thing so I powered the rx through a 5 cell pack with a 5.3v regulator. That should eliminate the variable caused by the pack draining. Since I always use the same meter that shouldn't change either. Tonight I'll set it up like I described I'm betting it will hover right on 3/4 stick the first try!
Thanks,,, basmntdweller
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