Adafruit 16-Channel 12-bit PWM/Servo Driver

For other supported Arduino products from Adafruit: Shields, accessories, etc.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
mr_signal
 
Posts: 5
Joined: Tue Jan 29, 2013 1:34 pm

Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by mr_signal »

What is the max current that can be used on this board? We have 2 6v HITECH servos, and 2 micro servos running off of this board. We place 1500uF capacitor on the board. One of our robot arms was sticking at max torque and pulled the full 3 amps from the circuit. The voltage regulator released the magic smoke. The label on the smd device is FACUO. Can I get the specifications on the voltage regulator?

Thank you,

User avatar
adafruit_support_bill
 
Posts: 88087
Joined: Sat Feb 07, 2009 10:11 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit_support_bill »

There is no voltage regulator on the board. There is a MOSFET for reverse-voltage protection right next to C2. Is that the component you are referring to?

If so, that is an IRML6401:
http://www.irf.com/product-info/datashe ... ml6401.pdf

User avatar
mr_signal
 
Posts: 5
Joined: Tue Jan 29, 2013 1:34 pm

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by mr_signal »

Yes, I stand corrected. Thank you. I can fix the board now. I guess the next question is what would make it release the magic smoke? He device was in system for a full week. The robot was used in a parade where they raised and lowered each arm continuously. It lasted 30 mins +/- and it stopped working. When I checked it out the protection smd was shot. Once I replaced the board, everything worked fine.

User avatar
adafruit_support_bill
 
Posts: 88087
Joined: Sat Feb 07, 2009 10:11 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit_support_bill »

Looks like that MOSFET has a continuous drain current rating of 3.4A-4.3A depending on temperature.
What were you using as a power supply? And which model HiTec servos? Some of the higher-torque servos can pull more than 2A in a stall situation.

M473Y
 
Posts: 2
Joined: Tue Feb 25, 2014 6:43 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by M473Y »

Hello,

i put my question in this thread because i think it will be useful for everyone, and the thread title is appropriate.

Ok, i have 18 Hitec HS635HB servo motors and Arduino Mega 2560 rev3 board.
I want to drive all 18 servos.
With arduino <Servo.h> library i know that
The Servo library supports up to 12 motors on most Arduino boards and 48 on the Arduino Mega. On boards other than the Mega, use of the library disables analogWrite() (PWM) functionality on pins 9 and 10, whether or not there is a Servo on those pins. On the Mega, up to 12 servos can be used without interfering with PWM functionality; use of 12 to 23 motors will disable PWM on pins 11 and 12.
So i want to know, what are the pros/cons if i instead of arduino official servo library use two Adafruit 16-Channel 12-bit PWM/Servo Driver?
Will Adafruit 16-Channel 12-bit PWM/Servo Driver handle current approx. 9A (if all 18 motors locked ~ 36 Ampers).

Best regard,
Matej

User avatar
adafruit_support_bill
 
Posts: 88087
Joined: Sat Feb 07, 2009 10:11 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit_support_bill »

@ M473Y:
Will Adafruit 16-Channel 12-bit PWM/Servo Driver handle current approx. 9A
If Servo power is supplied via the V+ pin on the header, this should be no problem. If supplied via the External Power terminal block, you are limited by the reverse voltage protection MOSFET (3-4A).
if all 18 motors locked ~ 36 Ampers
It would be wise to add a fuse to protect against this condition.

M473Y
 
Posts: 2
Joined: Tue Feb 25, 2014 6:43 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by M473Y »

Thank you Bill for answer about powering the servo motors.
But i still want to ask you, if you can explain me, what are differences if i connect and drive 18 servos with adafuit 16 channel driver
or if i drive 18 servos only with mega 2560 and servo.h library (without adafruit 16 channel servo driver), what are pros and cons if i use adafruit driver?

Thanks :-)

User avatar
adafruit_support_bill
 
Posts: 88087
Joined: Sat Feb 07, 2009 10:11 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit_support_bill »

what are pros and cons if i use adafruit driver?
The driver offloads all of the PWM timing overhead from the Arduino processor. This also eliminates any interrupt contention with timers and frees up timers and pins for other purposes.

User avatar
mr_signal
 
Posts: 5
Joined: Tue Jan 29, 2013 1:34 pm

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by mr_signal »

adafruit_support_bill wrote:Looks like that MOSFET has a continuous drain current rating of 3.4A-4.3A depending on temperature.
What were you using as a power supply? And which model HiTec servos? Some of the higher-torque servos can pull more than 2A in a stall situation.
Sorry for the delay in the thread, but we had another pwm driver board burn up in front of us. The control system is normally encased in a fiberglass shell robot at a children's hospital so we really need to remedy this issue for safety. The Hitech servos we are using is the HS-805BB. The power supply which was attached to the adafruit pwm board was a power-stream 24V to 5V DC-DC converter trimmed up to 5.7V DC 10A.

The adafruit pwm driver is connected to the power-stream supply. Looking at your reply
If Servo power is supplied via the V+ pin on the header, this should be no problem. If supplied via the External Power terminal block, you are limited by the reverse voltage protection MOSFET (3-4A).
which it is using the V+ via the terminal block. Then it should be able to handle the Hitech HS-805BB current draw in excess of 2A at stall. The servo motors are actuating the robotic arms and due to the length of the arms and weight of the hands we need the higher torque servos.

The adafruit pwm board is controlled by an Arduino Duemilanove Atmega 328 via a soldered microfit five pin connector. Side break out OE and V+ --NC. We have now installed the recommended fuses on the motors, but will be problematic to replace as it is encased in the robotic chest. Will probably replace with a auto reset circuit breaker.

My thought is it may be an issue with how we are powering the Arduino with the USB cable and not the barrel connector. The computer is connected to a powered hub, we have placed a diode preventing the hub back feeding the hub barrel connector when the computer is powering the hub.

Two conditions:
On A/C charging: A relay controls the 24 V DC system which disconnects when a cord is plugged in ensuring the robot will not drive when on A/C charging. At this point the computer is powering the USB hub (which is powering the Arduino controlling the adafruit pwm board which parse serial for raising and lowering the servo controlled arms, the joystick dongle, and a separate Arduino UNO w/ no chip for TTL communication with the motor controller), and (the face, an AOC monitor powered off the computer USB port). The pwm driver is powered by the 5.7 V powerstream.

On batteries:
While on the 24V battery system, the hub is powered, which I am assuming will extend the laptop battery life, a speaker system is powered due to the fiberglass robot chest muffles the sound, and supplies the adafruit pwm driver.

Question: If the adafruit terminal block power supply is interrupted for any reason and the load shifts to the side terminals, again with V+ and OE having no connection, what could happen to the reversed polarity protection on the terminal block to fry?

Seconday Question: Is the adafruit pwm driver a production quality module for high torque servos in continuous use environments, or is there another option for this functionality. I really like the adafruit pwm board and haven't looked in detail at the new pwm driver adafruit offers, but we need a stable pwm driver capable of driving multiple high torque, high current > 2amps at stall in a hospital environment.

I am willing to put each servo on its own pwm driver as I2C is convenient. Any Suggestions?

User avatar
adafruit_support_bill
 
Posts: 88087
Joined: Sat Feb 07, 2009 10:11 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit_support_bill »

The Hitech servos we are using is the HS-805BB.
Whoa. Those monsters are rated for more than 0.8A with no load! I'd be willing to bet they pull much more than 2A under load.
Question: If the adafruit terminal block power supply is interrupted for any reason and the load shifts to the side terminals, again with V+ and OE having no connection, what could happen to the reversed polarity protection on the terminal block to fry?
You are powering from both V+ and the terminal block? Can you post a diagram so I can better understand the possible current flow paths?
Seconday Question: Is the adafruit pwm driver a production quality module for high torque servos in continuous use environments, or is there another option for this functionality. I really like the adafruit pwm board and haven't looked in detail at the new pwm driver adafruit offers, but we need a stable pwm driver capable of driving multiple high torque, high current > 2amps at stall in a hospital environment.
I think the PWM signal functionality is fine. The issue here seems to be the current handling capacity of the power bus. The load is clearly more than the reverse voltage protection MOSFET can handle. But the traces from V+ and GND are pretty robust. I will check with the designers about the current ratings on that.

How many servos (and what types) are connected to the board? There are a few approaches to improving power distribution. Worst-case, you could wire power direct to the servos (that might even improve their torque).

User avatar
mr_signal
 
Posts: 5
Joined: Tue Jan 29, 2013 1:34 pm

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by mr_signal »

This may solve the problem or not. My teammate had been using the OE pin on the adafruit pwm board to enable and !enable the servo motors.

Also it was a long post but i mentioned
Side break out OE and V+ --NC
restated we do not use the side connector for OE, which I now know is not the case, and V+ have no Connection. We solely power the board with the terminal block.

I will scribble out a diagram a little later today.

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit »

The driver itself doesnt use any current, it just 'passes' v+ along. i would recommend detatching the red wires from each servo and then just powering all those seperately. i believe we use 24 mil traces for v+ but for huge servos seperate wiring off board may be better for your use!

User avatar
mr_signal
 
Posts: 5
Joined: Tue Jan 29, 2013 1:34 pm

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by mr_signal »

Is there any concern with using the OE to turn off and on the circuit with as you stated I will:
i would recommend detaching the red wires from each servo and then just powering all those separately.

User avatar
adafruit_support_bill
 
Posts: 88087
Joined: Sat Feb 07, 2009 10:11 am

Re: Adafruit 16-Channel 12-bit PWM/Servo Driver

Post by adafruit_support_bill »

It is not a problem. OE has nothing to do with the servo power. It only controls the PWM signal. When the PWM signal is disabled, the servo itself will cut power to the motor.

When wiring power direct to the motor - be sure to connect a ground wire from your power supply back to the PWM board.

Locked
Please be positive and constructive with your questions and comments.

Return to “Other Arduino products from Adafruit”