JR DS8717 at 6.8 Volts

[uluaz]

Does the DS8717 servos handle 6.8 volts ok? These are the regular 8717's not the "HV" ones. Just got a Reactor X2 regulator and want to run these servos at 6.8 volts.

[Pinecone]

Yes, they are rated to run off 4cell and 5 celll (nominally 4.8 and 6 volt) power supplies.

A 5 call pack is around 7 volts off the charger,

And many people are running them off a straight 2S lipo pack without issues (7.4 volt nominal, 8.2 volts fully charged).

[aerocal]

6.8 volts should not be a problem.What may be a problem is that as you increase the voltage the current use also increases.You will want to make sure that the regulator can supply the nessesary current/amps at whatever voltage you are using.
P.S. As a reminder.If your running 8717s at the higher limits of the voltage range it is IMHO nessesary to use more than one servo type connector if that is how you are getting the power into the Rx bus.

[Scottyb410]

Originally Posted by aerocal

6.8 volts should not be a problem.What may be a problem is that as you increase the voltage the current use also increases..

With respect:

As you increase the voltage, the current will decrease proportionality.
Ohms law

Cheers
Scotty

[aerocal]

Originally Posted by Scottyb410

With respect:

As you increase the voltage, the current will decrease proportionality.
Ohms law

Cheers
Scotty

Thats what you would normally expect.As you increase voltage the amperage should decrease proportionally.The actual current in watts should remain somewhat equal.In actual practice this is not always true with servos.

[BarracudaHockey]

Ohms law assums a constant load.

[Pinecone]

Higher voltage means higher speed of the motor. This means an increased load, so current may go up.

[Scottyb410]

Yes interesting point.

I am going to test this in our lab. If you think of it, since the voltage rises, efficiency would rise as well, in turn, current may decrease.

This is an interesting exercise. I will let you know the results.

Cheers.
Scotty

BTW
uluaz, if you feel your thread is being hi-jacked - just let me know and I will start a new one.

S.

[Madryan]

The principle is that the raised voltage uses less current to produce the same power output as follows.

Example: 6 Volt servo drawing 3 Amps and producing 18 Watts of power dissipation.

V/I=R

6 Volts / 3 Amps = 2 Ohms and

P=V*I = 18 Watts Power use

now at 8.4 Volts if you want to produce the same same 18 watts power consumption you do this:

18Watts / 8.4Volts = 2.4 Amps

Same power output...higher voltage, less current, less losses, longer lasting battery and better performing servo during flight.

so in a rounded up fashion...30% increase in voltage provides about a 20% reduction in current usage..

[Sowa]

Resurrecting an old thread.

I recently felt my DS8717's after a flight and they were too hot to touch. Could this be caused by running 2s LiFe straight for rx power?

[Ah Clem]

It very well could be.

I always run mine on 6 volts and they are never warm.

[Sowa]

I hear reports of others running them at 8v coming down at a normal temp. Felt a flying buddies servo after his flight (ds615) and it was warm, but nothing alarming. After 2min in my heli and the servos are pretty hot.

[Ah Clem]

Do you have the settings in the FBL unit set correctly for the 8717's?