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Servo current draw

Carps

Veteran

Caterham, Surrey, England

Does anyone have measured figures for the current draw of various servos under controlled load ?
I'd be interested to know just how much digitals suck compared to non-digitals.

Why don't the manufacturers publish these details ? [or maybe they do but I just don't know where ?]

Cheers in advance

02-11-2003 Over year old.
HOMEPAGE  
Galifrey

rrProfessor

Bristol

Some manufacturers quote the servo draw figures for idle, load and stalled..

Have a check on a few websites, I am sure you can find the details..

Don't Email me as I wont reply - PM Only (spam countermeasures)

02-11-2003 Over year old.
z11355

rrMaster

New England

if they published that data, you'd
discover just how inadequate the
wires, connectors and general
power distribution system REALLY is.

S&E Modeller magazine (and I think
the AMA rag) have a report on this sort
of thing every 2 years or so.

In very general terms, analog servos
consume about 20->200mA depending
on load (noload->stalled) and digitals
are often 50% higher (if not 100%)

02-11-2003 Over year old.
Greg McFadden

Key Veteran

Richland, WA

What I would like to know is...

Is it the digital part of the circuitry that takes all that extra power, or is it the coreless motor instead of cored motor...


(the reason I note this is I just switched from all analog coreless to all digital coreless and the load test on the battery after one flight is practically the same)

The silence often, of pure innocence persuades, when speaking fails

02-11-2003 Over year old.
Galifrey

rrProfessor

Bristol

http://www.futaba-rc.com/servos/digitalservos.pdf

just one disadvantage... explains the power consumption issues..

Don't Email me as I wont reply - PM Only (spam countermeasures)

02-11-2003 Over year old.
Carps

Veteran

Caterham, Surrey, England

None of the manufacturers seem to want to quantify it.
I found a very old page with some details of FMA and Airtronics at idle and stalled, but nothing on the current range [ tee hee] of servos

Has anyone out there carried out there own measurements ?

02-11-2003 Over year old.
HOMEPAGE  
Greg McFadden

Key Veteran

Richland, WA

I am going to try to do some non-scientific testing on some of my stuff tonight... sofar I have only gotten through some small electric stuff and a telebee without servo attached... waitin on a larger (more than half an amp ammeter to do the digital servos, and waitin on a 148 for comparison...)

Hitec supreme 8 rx, about 15 ma was what I measured
CS21 microservo 5ma no load, 120 with rapid movement of servo

The silence often, of pure innocence persuades, when speaking fails

02-12-2003 Over year old.
Greg McFadden

Key Veteran

Richland, WA

Well, I got a chance to do some more "unscientific testing" consisting of finding what the load was with no buzzing and servo motion and what it is with a reasonable amount of stick play on free to move servos...

Futaba 148: 5-15ma no load 80-110ma with moderate stick motion
Futaba 9252 15-30ma no load 250-300ma with moderate stick play

I am not going to do stall or load testing as I don't want to mess with my servos that much, and I don't have a good way to measure transient response reasonably.... (that and lack of time)

The silence often, of pure innocence persuades, when speaking fails

02-12-2003 Over year old.
Colibri

Key Veteran

The Netherlands

I've seen in a magazine that a 9250 can draw up to about 1900mA when stalled and about half of that when under the maximum load.

I totally agree with z11355 on our cables, switches and connectors being inadequate.

Tim

02-12-2003 Over year old.
donlynn

Key Veteran

New Zealand

Gidday
Do a search for Augusto, I think he is a servo analysis king.

Regards Don

02-12-2003 Over year old.
Maxx

Key Veteran

Shreveport Louisana

The old anolog servos didn't ramp up to full volt/amps until around 20 degrees of servo movement, which made them "soft" in the center of they're travel whereas the digitals go to fmv/fma in 1/4 of a degree of rotation which is great because the digitals have holding power and full rotational speed under load (up to the torque rating of the motor) in 1/4 degree of rotation...the drawback is that for that holding power and available torque the digital servo motor is at full voltage/amps all the time! And as no one flying a heli has the servos in the center much the digitals are always drawing close to the maximum current regardless of servo load.

I've recently given up on switches in both my SE's after the GEM2000 would go solid green halfway thru my second flight on an 1800 Mah nicad pack but when the switches were bypassed with HD servo wire the GEM went back to blinking thru the third tank of fuel. The switches I removed were JR HD ones not more than 6 months old !
It's just as simple to plug a lead in as to flick a switch and much more difficult to turn the airborne on by mistake and arrive at the field with a low or dead battery! JMO.
Chris

02-12-2003 Over year old.
z11355

rrMaster

New England

fyi,

The makers of the GEM now have some
superduper switch. They 'advertised' it
here on RR a few weeks ago.

02-12-2003 Over year old.
Maxx

Key Veteran

Shreveport Louisana

Z11355, I'm open to anything at this point. Three digital servos (plus one cheap-A$$ throttle servo), a GV-1 and a 601/9151 seemed to be fine as long as the battery voltage was above 4.8...which was the first flight on a freshly charged battery pack. As soon as the pack was at the plateau voltage (4.8) it seemed like the switch couldn't keep up with the flight pack. Not that I had a loss of control; the GEM2000 as well as the voltage display on the GV-1 and the GY601 would go to 4.7-4.5 when the all the servos were exercised after the first flight. Bypassing the switch with the HD servo extention caused the voltage display(s) to go to 4.9-4.8 and stay there for two more flights! My conclusion is fairly simple...the 6 month old switch harnesses no longer have the capabilty to pass enough current at plateau voltage due to internal resistance. So instead of a high $$$ switch harness I now have a low-dollar HD extention with the added bonus of knowing that battery is getting the correct input from my chargers (direct connection), after all...if the switch has a resistance going to the receiver it might too have a resistance showing in the charge loop!
I ran a test of my batts through three flights with an 1800Mah JR Extra pack and three 9252 servos, a 531 throttle servo, a GV-1 and a 601/9151 combo...thru all three tests the airborne was depleted 400-450 MAH per flight (Crappy 3F). though not a lab study, this is what I use as a Yardstick (meterstick in the rest of the world)!

Chris

02-13-2003 Over year old.
Phil Cole

Veteran

Menlo Park CA

My experience with battery discharge rate with digital servos is pretty much the same as what Chris saw.

Average current is something around 2.5 to 3 A. The peak currents would probably be double that.

I use a heavy duty Futaba switch. It is definitely a much better thing than the usual switch you get with a flight pack.

Chris's approach of using a plug in cable certainly has merit, provided you trust it to stay plugged in.

02-13-2003 Over year old.
a_korandr

Veteran

Chicago, IL

stalled 9450 was able to pull 2 Amps when i measured it.

02-13-2003 Over year old.
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Servo current draw

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