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Using a Pololu D36V28F6 with an MG996R servo

Hello all,

Not totally new to servos, but somewhat new to using voltage regulators (at least with servos).

The specs say that the MG996R servo can require up to 3A. I will be using 12 of these servos, not all of them will be moving at the same time - at most maybe 6.

A few questions:

  1. Does this board work with zero issues with the MG996R servo?

  2. The web page says a pull-up resistor is needed. Exactly what resistance and wattage is used?

  3. It says the unit can get very hot. Understood. Is there a specific heat sink that can be used? Should a cooling fan (also) be used?

  4. Will this board work with a 12V input coming out of a PC-650W ATX power supply? (The 12V line can supply up to 30A.)

Thanks for any help!

Mike

Hello, Mike.

I moved your post to the Voltage regulators section of the forum.

It is possible to use an ATX power supply to provide power to a regulator like the D36V28F6; however, most PSUs like that will not output when they are not connected to a computer to give it a signal to power on. There are workarounds for this, but please note that it can be dangerous (possibly even lethal) if done incorrectly, so we do not recommend doing it unless you have the proper experience, and cannot offer any assistance or support.

The D36V28F6 would be okay for powering one of those servos from a 12V input, but not 12 of them. From what you described, each servo can pull up to 3A, and from the “Maximum Continuous Output Current” graph at the bottom of the D36V28F6 product page, the 6V version of that regulator can handle around 4A with a 12V input. The D36V28F6 has over-current and thermal shutdown features which would trigger if you try to power too many of those servos at the same time.

You might consider powering your servos in a couple separate power banks, each with its own regulator. For example, you might be able to use 3 of the #4092 D36V50F6 step-down regulator to power 3 banks of 4 MG996R servos, especially if you can spread the load across all 3 banks (i.e. only 2 or so moving at a time from each bank).

Brandon

Thank you for moving my post to the proper forum section.

I may have mistyped a part or two…

I have purchase an adapter for the power supply that plugs right into the connector, that’s all good. (Previously I had rewired a older P/S to do the same thing, so I’m good with electronics up to that part, anyway.)

Since this would work, I would use a D36V28F6 for EACH servo.

Could you please tell me the resistor value and wattage it requires and also if a heat sink (maybe a link?) should be used or will a fan be ok? If you can tell me those two things, I’ll order a couple

(I’m unfortunately on unemployment right now, so I’ll get a couple at a time.)

Thanks again for your help!

Mike

To clarify, the D36V28F6 regulator is enabled by default and you do not need to add any external pull-up resistors unless you want to use the “power good” indicator pin. If you do want to use that pin, a resistor between 1kΩ and 100kΩ should be fine. It is just a signal line, so you can use a 1/10W or 1/4W resistor.

You should be able to power one of those servos from a D36V28F6 without needing a heat sink. For reference, the testing for the values mentioned on the product page is done in ambient open-air conditions. We do not have any specific heat sinking advice, and generally expect forced airflow to work better for keeping the regulator temperature down, but if you want to add a heat sink as well, the best place to do so would be on the regulator IC (indicated in the picture below):

Brandon

Thank you for that great information sir. I am going to order a couple right now…

Thanks for your replies from some time ago. I have since purchased 17 of these! They are amazing! They barely get above room temperature!

I have a scenario using six MG996R servos with, naturally, six of your 'F6’s.

(This is the part of electronics I forget… Have watched several YouTube videos and none helped.)

Using my Arduino UNO R3, a 650W power supply putting out 30A on the +12V line. if I’m correct with e stall current being 1.5A, I shouldn’t need more than 9A in theory if all stall at the same time.

The problem is, they are all jittering like crazy. I tried numerous values of decoupling electrolytic caps and honestly don’t know what else to do.

Do you have any ideas?

Thank you sir

Mike

Servo jitter is usually caused by an unstable or inadequate supply voltage or a bad signal. It sounds like your power supply should be fine, and the voltage should be stable since you are using regulators. However, to start off, you could try to rule it out by disconnecting the servos one at a time (without changing your code) to see if the problem gets better. You might also try measuring the voltage at the input and output of the regulators while the system is running.

Brandon

Thank you for that quick reply! I actually did try one at a time. I am now wondering if maybe my Arduino is an issue. On a side note, I have another project that uses the same F6’s and they work fine. I tried wapping those out. Still jittering. Very strange. Thank you for the reply! I hope I can figure it out! I have 10 more of your F6’s on the way!

Sorry I forgot to write that I measured the inputs and outputs of all and they’re precise!

You might be running into timing issues from using the Servo library to drive that many servos from the same timer. Do you have an oscilloscope you can use to look at your servo signals? You could try removing or commenting out the code for each servo one at a time to see when (or if) the problem gets better. If you want to make sure you are getting clean signals, you might consider using a separate dedicated controller such as one of our Maestro servo controllers to generate your servo signals. You can use your Arduino to control the Maestro outputs through its TTL serial interface; we have an Arduino library for our Maestro controllers to make that communication easier.

Brandon