How Best to Power Servos?

[FredK]

Hi All -

I just completed setting up my TQ using Phidgets with DVATX. In my present set-up I have the servos powered directly through the Phidgets Servo Controller. I have read elsewhere that the best way is to provide a separate power lead directly to the servos using the "Y" leads to avoid burning out the servo card. That was my original plan but all appears to be working very well powered through the servo card.

Thoughts and experiences are much appreciated.

Fred

[neuman5022]

Hi Fred

This question needs to be addressed to the PHIDGET guys - go to and post it

I read this too - the doco is old, and I guess it was good to those times. I believe the new cards can handle that but I am not 100% sure.

[neuman5022]

http://www.phidgets.com/phorum/

[iwik]

Hi Fred,
i would power the servos fromthere own supply.Noise generated from the motor could cause u other problems.I think the general consenus is to seperate both supplies.
Les

[737NUT]

Hi Fred,
i would power the servos fromthere own supply.Noise generated from the motor could cause u other problems.I think the general consenus is to seperate both supplies.
Les
Then there sure would be allot of r/c airplanes crashing!!!!!!!! ;) Noise is not an issue in r/c servo's.
If properly set-up both mechanically and in software, there is no way you should have a burn-out or card damage.

[737NUT]

Also, as i stated in another post, it is to our best interest to use digital servo's. They dropped by half in price, end points, travel direction and speed as well as many other parameters are adjustable with-in these digital servo's. The programmer for the hitecs is only 28.00! Servo's are 20 to 50ea

[iwik]

Yes ,
providing people know how to do it.Unfortunately a lot dont.If u look at some designers of servo cards ie FSbus, they recommend seperate supply for
Servos.Stalled servos can cause probs on boards to the inexperienced as seen many times on this board.So caution is more to the point.
Les

[neuman5022]

Thank you guys for jumping in.

The question I ask myself is: Does the power connection cause the servos to move because of the incoming current - so I guess all servos will jump. From my experience and from some really keen model-aircraft people - all of them jump in the first power up, some more sme less.

Now if this is not the case (I.E some of you guys have servos that do not move AT ALL at power up) The other option is that the SW attached does not dumpen any unwanted movement. So this may be a SW issue - I know Diego is looking into it.

Switching the cheap servos is a good option - however I will wait to see if it is a SW issue. If not - I guess a better brand cannot harm to try.

Cheers

Isaac

[iwik]

Hi issac,
As i said in your "kicking servo" thread, my experience with three types of servos,Cheap Tower hobbies brand and Hitec and Futaba.The Tower hobbies
would kick with power only connected ie no signal input.The other two did not move at all.This was also confirmed from a friend of mine who used servos for all of his gauges.I do not know what brand he used.I had great concern over this happening when i want to use it for Turn Co ordinator.Or for that matter any gauge that has mechanics that could be damaged.My cheap brand would kick quite a lot,so when testing something,two three powerups would take it to the End of my mechanics munching it up.My friend and i drove the servos from I/O cards servo Modules.
If u want i can try my servos out again and let u know what brands i ahve and if they are completely still.
Hope this helps
Les

[neuman5022]

Hi Les

Thank you for the valuable info.

I did not long ago a "cessna" like simulator - with all the instruments driven with Hitech servos. (SIMKIT GUAGES) Upon connecting the power nothing happens, when loading the sw I recall they moved a bit then went to their zero position defined by the I/O card/SW.

The I/O card was powered the same time as the PC, so it looks like the power itself did not cause any jumping. But I cannot tell you if this is because of the bran of the servos or perhaps the I/O card was dumpenning any unwanted current."


I will test the servos I have with a new version of the SW - hopefully this issue wll be solved. If not, I will get some new HITECH servos and give it a try.

Cheers

Isaac


EDIT:

This is what I got from Phidgets:

"They will usually move when you first apply power. This is because the servo has no position feedback to the controller. If you enable the servo controller output without setting a position, it will choose a mid-point position. You can choose to set your own position before enabling if you know the initial position. This relies on the servo not having moved since power was last disabled. If you need to track servo position when it is not powered, you will need to add some external tracking, or hack into the potentiometer directly and bring out it's signal.