Part time servo power - not recommended for aerial vehicles . . .!

Paix

Senior Member
Wishing to operate a micro servo to open a small grating, with one open and one close each day, for a period of up to fourteen days. (approx 90 degrees of servo motion) when the device will be removed from service for potential use elsewhere.

Understandably between operations I don't want to power the servo.

Please be aware that general timing isn't an issue, and neither is the actual positioning, both of which will be determined empirically during development.

How would YOU go about it please? The turning motion on the grating is effectively zero. [it's very light]
The solution would seem to be how to switch the power to the servo, via a gp NPN transistor and relay for the duration of the action?

Code:
#Picaxe 08m2
symbol relay = c.1
symbol grate  = c.2

do
          relay high    ' power to servo
          pause 2000
          servo grate, 75    ' close
          servopos grate,75
          pause 2000
          servopos grate, off
          relay low    ' switch off servo power

           <delay 7 hours>
          relay high    ' power to servo
          pause 2000
          servo grate, 255    ' open
          servopos grate, 255
          pause 2000
          servopos grate, off
          relay low    ' switch off servo power
          <delay 17 hours>
loop
 

eclectic

Moderator
Ian

Quick thoughts

How about adding a RTC? DS1307.

Otherwise, if delays aren't exact,
some very long

Pause100000
For - next loops

And, how about a Takamisawa Latching relay?

PM and I'll explain further tomorrow.

Addit
Bees need Mindz?

e
 
Last edited:

rgooge

Member
If holding the grate in position has very low mechanical loading, then I would just use a power FET in line with the Servo power, the Picaxe can be put to sleep and when awakened to move the grating, powers up the FET before driving the servo. I've done something similar in the past with an x-y gimble mount for small CMOS camera, driven by two servos.
 

boriz

Senior Member
Have you measured how much current the servo uses when at rest? It might be so small as to not be significant. Especially as there is no force on the 'grating'. It might be sufficient to merely stop the servo drive signal. IE: LOW servo.pin, or my personal favorite: HIGH servo.pin
 

srnet

Senior Member
Have you measured how much current the servo uses when at rest? It might be so small as to not be significant
Agreed.

Servos vary considerable in this respect, you really do have to measure each type.

Although with no indication of where the power is coming from or how much, the servo idle current may or may not be an issue.
 

WHITEKNUCKLES

New Member
A magnetic actuator as once used in single channel pulse proportional radio control might suffice. My example uses a centre tapped battery as per the galloping ghost system and once toggled the magnetic force holds that position without power.

Modern equivalents use H bridges and neodymium magnets and although much smaller may have sufficient force.

Dave
 
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WHITEKNUCKLES

New Member
The Rand actuator in that video came a wee bit later and was expensive, in the UK the Galloping Ghost actuator was more likely to be a modified geared Mighty Midget motor.

The Adams Double Ended actuator below shows the pole pieces extending round the disc magnets which were coupled externally and magnetised across their diameters. The centre tapped coil allowed either end to be "pulled down" by a double output receiver where one output or the other was always active.

Dave
 

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