Servo Failure Help!!!

Hi I am using the arduino UNO with servo sheild V5,here is spec sheet for sheild,
http://yourduino.com/sunshop2/index.php?l=product_detail&p=407

I am using the servos mg 996r:

And the Servo Sg90(this came with arduino kit)
http://www.micropik.com/PDF/SG90Servo.pdf

Here is my code, its a sample sweep program that is connected to pin 2(Got it from arduino website, they use pin 9) I just copy and pasted it and just changed Servos Signal pin.

Now when I connect the SG90 to sheild V5, and the shield to the arudino, and finally give the arduino power, as well as connect the V5 to an external 5V DC wall power supply, that servo works fine.

When I do the same thing for the Mg996R which is connected to a robot claw, the power LED light on the servo shield board turns off even though I am not running the board solely off the 5v rail of the ardunio.

Why does the light turn off even though I have the correct power/AMP requirements?
I even tested the 5v dc wall charger when it was connected to the shield an its getting 5.03v.

Why does the light turn off

Because you have a short circuit across the supply, or the current draw is such that the supply is dropping to below 2V.

I even tested the 5v dc wall charger when it was connected to the shield an its getting 5.03v.

Is this with the light turned off on the Arduino? Is this when the Arduino is connected to the shield?

I tested the voltage of the servo sheild while it is connected to the arduino(For your 2nd question). Also I will try to test the voltage of the shield when the light turns off see how much its pulling from the DC power supply.

edit: without the external DC 5v and servo connected, the servo shield is pulling 2.67V from the Arduino uno. When I connect the external that 2.67 goes up to 5v and stays at that level even though the LED on the sheild goes out, when I hook up the mg996r servo. I am measuring this value on the servo sheild Vcc and Gnd input screws(the screws connect to the DC supply). The power light on the arduino also goes off. It's only for this servo, the other servo(SG 90) works fine.

*****But do u think I have to remove the "SEL" pins from the shield v5 when I connect the external supply? If so how would I remove them?

edit: without the external DC 5v, the servo shield is pulling 2.67V from the Arduino uno.

No, you can not pull a voltage from anything, you can only pull current.

So you might mean that the shield is pulling so much current from the Arduino that the power supply drops to 2.67V. What is powering the Arduino in this case?

It's only for this servo, the other servo(SG 90) works fine.

Then the mg996r servo is either faulty or takes more current than the power supply can cope with.

Grumpy_Mike:
So you might mean that the shield is pulling so much current from the Arduino that the power supply drops to 2.67V. What is powering the Arduino in this case?
Then the mg996r servo is either faulty or takes more current than the power supply can cope with.

The arduino is connected to my Macbook Pro USB port. The power supply rating is 5v at 550ma, arduino uno I have no idea how much curretn it pulls at 5v, the servo mg996r rating is
Operating voltage: 4.8 V a 7.2 V
• Running Current 500 mA – 900mA
• Stall Current 2.5 A (6V)

The power supply rating is 5v at 550ma

So it is clear you can not power that servo from the USB nor your power supply.

Note the stall current is briefly drawn when a motor starts.

So what should I do? Get a 5v power supply at 2.5 amps? Or will that current be too much for the servo shield? If that option(5v @ 2.5a) is feasible can I use this power supply?

http://www.amazon.com/ORIGIANL-D-Link-Supply-ADAPTER-JTA0302B/dp/B002FA5WE2

kloud:
So what should I do? Get a 5v power supply at 2.5 amps? Or will that current be too much for the servo shield? If that option(5v @ 2.5a) is feasible can I use this power supply?

http://www.amazon.com/ORIGIANL-D-Link-Supply-ADAPTER-JTA0302B/dp/B002FA5WE2

For testing purposes i often find d cells to be a useful power scource.

Can I have a link? And the D cell you are referring to, its the D cell battery correct?

Yes.

All it needs is a 4 cell battery holder, i normally 'borrow ’ the cells from various flashlights.

Rated for 1A discharge normally but i have had 4A out of alkalines for short periods.

I have LIPO and lead acid available but D cells are probably the ones i use most for motor type testing.

BTW thats a big servo and i am not surprised you have problems, wall warts for this current often do not like inductive loads and will shut down.

EDIT

Looking at the hobby king site the more recent versions of that servo seem to have bad press.

What i would do is use a battery and a servo tester to eliminate the servo as the problem.
But that’s purely because i have access to a tester at my club.

How did u make the housing for the 4 batteries? Or did you just buy a 4 holder?

Purchaced a 4 holder.
Less than 2 UKP at the time.
4 batteries cost more than that.
Useful for lots of things including powering arduino.

kloud:
Get a 5v power supply at 2.5 amps? Or will that current be too much for the servo shield?

You can not have too much current capability from a power source. A device designed for a specific voltage will take the current it needs.

Look at you house mains wiring, you can connect a 7W night light or a 2KW microwave oven to the same wiring and each will only take the current it needs.

BTW do not push your external 5V back INTO the MacBook?

The ground/0v should be shared as a common reference, but the supply rails must be separated unless you know exactly what you're doing!

Huh? Ur saying I can’t connect my arduino to my Mac using the usb port? Cause that’s the only way I connect it? Or do u mean do not connect the 5v wall charger to my MacBook?

I'm saying that you must keep the +V servo supply isolated from the +V USB
The ground and data are fine, but cross-contamination of supplies that are sourced from different places is a recipe for disaster.

The servo supply is from your new 'external' servo plug-pack... the MacBook supply is drawn from its AC adapter or batteries. The arduino is (typically) powered from the USB port (powered by the MacBook) - so you need to stay aware of any place these may connect together.

if the chunky servo 'just happens' to pull 2A from the Arduino or MacBook the results won't be what you're hoping for - and maybe worse if there are other factors.

Yes my power for both arduino and sheild are separate an I'm pretty sure it pulls current from both sheild an arduino. For the d cell battery I only have 1.5v an I can't use that cause for the servo sheild cause I need exactly 5v.

kloud:
Yes my power for both arduino and sheild are separate an I'm pretty sure it pulls current from both sheild an arduino. For the d cell battery I only have 1.5v an I can't use that cause for the servo sheild cause I need exactly 5v. So I'll probably just buy a DC wall charger rated at 5v 2.5 amps cause it's less expensive than buyin 2 1v d cell then I gotta make a battery pack.

kloud:
Yes my power for both arduino and sheild are separate an I'm pretty sure it pulls current from both sheild an arduino. For the d cell battery I only have 1.5v an I can't use that cause for the servo sheild cause I need exactly 5v. So I'll probably just buy a DC wall charger rated at 5v 2.5 amps cause it's less expensive than buyin 2 1v d cell then I gotta make a battery pack.

ref: What..."an I'm pretty sure it pulls current from both sheild an arduino" ?
If you are referring the actual servo motor itself - then 'there's your problem'!

The shield will hopefully have separate power input connections for the servos - unless it's intended for simple low-power R/C hobby servos - which may use the Arduino 5V supply. (the driver chip itself will draw logic power and 0V/ground directly from the Arduino In which case - you may need to look for a 'better' servo (power) shield that supports larger motors / currents.

Keep inmind - if you go up to really heavy duty servos - the Arduino PCB and wiring wount be able to handle the 0V return current from the motor itself. See if you can find an experienced hacker nearby.

I have a link to the sheild in my first post so check it out, it does have power input connects for servos, it has ground, voltage and signal.

Also guys this is the guide I was using for the robotic claw:

This guy used a DC power supply(NOT LIKE THE ONE I USED), the big $60 ones to power the sheild V5. So instead of spending 60 bucks, I was hoping if someone can give me a link to a

5v battery with at least 2.5 amp rating

that I could use instead. If not I will just have to buy a big DC/AC power supply since my options are limited an I dont have access to the things you guys are suggesting like a hacker, or a servo tester, but thx for the suggestions.

That servo looks like a beefy 'hobby' servo, so I doubt it is pulling much current if there is nothing attached to the spindle.(horn) during testing.

OK, your existing supply (USB via the Macbook) may be under-rated for your long-term application, but finding a 5V@2A DC regulated plugpack to drive the shield shouldn't be too hard. (7-11, Supermarket, department or hobby store ? Some discarded mobile phone chargers will do the job.)