servo control and voltage regulator

[E2005]

I am making a circuit in which I need to control two separate valves with two servos (futaba S3154 mini servo).I am not sure if i should power them with two separate 6V regulators LM7806 (1 amp max output) or a single LM7806. I could not get data sheet on current drawn by these servo except reading somewhere it takes 250 milliamp continuous current for a single servo but I have a feeling the starting current is much higher( probably 1A).
The two servos will need to work simultaneously (both drawing power at same time). The system is battery operated device and I want to make sure the load is not too much for a single regulator for the servos. The microprocessor and other circuit is powered by a separate 5V regulator. Would be helpful if anyone has experience is this. Thanks

 

[controlsdude]

As with using multiple dc power supplies in any system, the only thing that will need is tying the DC common to the same potential.

If you make the DC common the same, you should be ok. Otherwise, you will get some very unpredicable results.

 

[OperaHouse]

Max current limits of any regulator have to take in account how much heat will be dissipated. I don't think initial current will be any higher. Using two regulators will distribute the heat better if you have the room and save an expensive heat sink. Be sure to calculate the watts this will dissipate (Vin-6V)/ .5A Sometimes adding a small dropping resistor prior to the regulator is useful with higher supply voltages an reduce amount of heat sinking necessary.

 

[MikeHalloran]

You do realize that those are digital servos for model airplanes, right? Meaning the input is not a modulated analog voltage, but the modulated width of a pulse train.

The 250mA is credible as a max current, because these servos are not intended for high torque loads: 20.8 oz-in @ 4.8V and 23.5 oz-in @ 6V max. I'd guess they probably _can_ draw more than 250mA, but you'd want the supply to limit or fold back there to avoid damage to the delicate plastic gears.

They're really intended for small control surfaces that push against air, not the devices I call valves. Maybe you have some other kind of valve.



Mike Halloran
Pembroke Pines, FL, USA

 

[ozmosis]

Check out Moog:

http://www.moog.com/Industrial/Servovalves_MotionControl/

they will probably be the best in this technology, by a long way.

 

[E2005]

MikeHalloran ,the valves I am using are specialty rotory valves that do not require a lot of torque and therefor the small servo is able to rotate it( through a four bar mechanism).
My concern was, just not knowing the peak starting torque current for these servos in order to choose a suitable power source( regulator). As suggested by controlsdude and OperaHouse it sure will help to distribute load between two regulators verses one(to avoid overheating)and having common DC ground.The servo ground is sharing ground plane with microprocessor ground and I was concerned when the two servos are running and drawing current , the digital circuit will suffer because of the imbalance in the ground plane ( I have had this kind of problem before)