Using servos with two dual-vnh5019-motor-shields causes one motor to fail

[photodude]

Recently ran into an issue where Using a servo on a Mega 2560 with two dual-vnh5019-motor-shields to drive 4 motors causes one motor to fail.

All 4 motors work fine until servo.write is in the loop then one of the motors will not turn on.

Seems something in the dual-vnh5019-motor-shield library and the servo.h library conflict

[ryantm]

Hi, @photodude.

You are doing something pretty advanced by using two shields and a servo at the same time. I do not think this qualifies as an issue with the library as currently described. Can you post more information about your setup, including your code, on the Pololu forum and we can look into it more?

Ryan

[photodude]

Hi, @ryantm my setup maybe "pretty advanced" but is fairly simple still. (Mega 2560 + two dual-vnh5019-motor-shield + xbee shield + 1 servo) I'm using the dual-vnh5019-motor-shield library, the standard arduino servo.h library, Arduino IDE 1.6.3, and serial3 for the xbee. We found a temporary "work around" for the servo issue by using the old softwareServo library and updating that library for arduino IDE 1.x

I've done a quick search in the forum. According to this tread in the forum ,,, and this thread there is a known issue with timer conflicts between the dual-vnh5019-motor-shield and the servo library when used with an Uno. I believe a similar issue is occurring with the Mega 2560.

Based on this information, I think the best solution would be to provide an optional parameter to switch the timer used by the dual-vnh5019-motor-shield. (switching, changing or modifying timers is unfortunately beyond my arduino skill level at the moment)

Notes about timers:

• Timer0 is used by the functions millis(), delay(), micros() and delayMicroseconds(),
• Timer 1 is used by the servo.h library on Arduino Uno
  • timer5 is used by the servo library on Arduino Mega
  • the Servo library uses timers and interrupts
  • you can't use the pwm pins used for servo timers
  • UNO: when you use the Servo Library You can’t use PWM on Pin 9, 10
  • MEGA: it is a bit more difficult
    • For the first 12 servos timer 5 will be used (losing PWM on Pin 44,45,46)
    • for 13-24 servos timer 5 and 1 will be used (losing PWM on Pin 11,12,44,45,46)
    • for 25-36 servos timer 5, 1 and 3 will be used (losing PWM on Pin 2,3,5,11,12,44,45,46)
    • For 37-48 servos all 16bit timers 5,1,3 and 4 will be used (losing all PWM pins).
• timers for PWM underwrite the function analogWrite(). Manually setting up a timer will/may stop analogWrite() from working
  • You can obtain more control than the analogWrite function provides By manipulating the chip's timer registers directly (note this is very advanced).
• on the Uno Pin 11 has shared functionality PWM and MOSI. MOSI is needed for the SPI interface, so you can’t use PWM on Pin 11 and the SPI interface at the same time.
  • on the MEGA SPI related pins are 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS) so no conflict exists
• the tone(), notone() functions uses timer2,
• Timer 2 has a different set of prescale values from the other timers,
• Timer 0 and 2 are 8bit timers while timer 1, 3, 4, and 5 are 16 bit timers;
• Timer 3,4,5 are only available on Arduino Mega boards,
• The digitalWrite() function turns off PWM output if called on a timer pin
• The Uno has 3 Timers and 6 PWM output pins 3, 5, 6, 9, 10, and 11
  • timer 0 —– Pins 5, 6 (time functions like millis(), and delay() )
  • timer 1 —– Pins 9, 10 (servo library)
  • timer 2 —– Pins 11, 3
• The Arduino Mega has 6 timers and 15 PWM outputs pins 2 to 13 and 44 to 46
  • timer 0 —– pin 4, 13 (time functions like millis(), and delay() )
  • timer 1 —– pin 11, 12
  • timer 2 —– pin 9, 10 (tone(), notone() functions)
  • timer 3 —– pin 2, 3, 5
  • timer 4 —– pin 6, 7, 8
  • timer 5 —– pin 44, 45, 46 (servo library)
• You can "manually" implement a sudo PWM on any pin by repeatedly turning the pin on and off for the desired times

[craig-w-a]

I was wondering if you have a list of exactly what pins to use to connect the two motordrivers to the arduino mega

[photodude]

Hi @craig-w-a I have a fork that is prebuilt for running with two dual-vnh5019 motor drivers on a mega, https://github.com/photodude/DualVNH5019MotorShieldMod3

All the details about pins and stuff for that set up are listed there.

[craig-w-a]

I saw the fork and it mentions the different timers and stuff. idk maybe im looking at wrong file. im new to github and programming

[photodude]

@craig-w-a you should be able to follow the instructions there and use the 3.0.1-dualsheilds release https://github.com/photodude/DualVNH5019MotorShieldMod3/releases/tag/3.0.1-dualsheilds

Everything you need for running with two shields on the mega is contained in the fork https://github.com/photodude/DualVNH5019MotorShieldMod3

[craig-w-a]

@photodude how did u solve this issue of one not running? im using DC motors but still have one that isnt running. i checked the pins and soldering points

[photodude]

@craig-w-a My issue was related to PWM timer conflicts. As noted above "a temporary "workaround" for the servo issue by using the old softwareServo library and updating that library for arduino IDE 1.x"

The other part of the solution was avoiding using the specific PWM pins that caused conflicts. But that all goes beyond just using the library I built to handle running two boards. that library is just about controlling the pins for two boards with single functions.

[kutluky]

I am newbie and I want to build a project that contains two linear actuator that move synchronously. Two of them will lift up and down at same time. I use arduino mega and VNH5019 motor driver. I have thompson electrac ELD linear actuator. I have never tried to synchronize two linear actuator. Linear actuator have encoder output ( it is hall effect encoder -( not absolute. So it cannot keep last position in case of power cut )). Encoder type is hall effect type. Encoder output voltage levels low (logical zero), typical / max is 0.1/0.25 Vdc. Also it has output fully extented/retracted signal. I tested it with H-Bridge motor driver made of 4 SSR relays and push button switches to retract and extract. There is a synchronization problem. How should I solve that synchronozation problem could you help me ? What should I do? How to achieve speed control to run actuators simulatenously and sycchronously

[kevin-pololu]

@kutluky The Pololu forum would be a more appropriate place for your question (the GitHub issues are intended for discussing problems with and changes to this library, and your question is not relevant to this issue).