MassMind BOB PID Servo Motor Control

The BOB PID is a very low cost, but quite capable, PID servo controller, which can replace stepper motors in any standard application, such as 3D printers or CNC machines.

• Serial and step / direction inputs.
  - The serial interface, via any TTL to USB adapter, allows for easy tuning of the P.I.D. constants and setting options like the polarity of the output direction signal. It also supports a bootloader^ for future firmware updates and new abilities / optimisation.
  - The PMinMO Standard Step / Direction input allows it`s use in any application where a standard stepper driver was intended. Our Pololu adapter cable makes plugging it into a RAMPS / GRBL or pretty much any other motion controller very easy.
• Position input comes from a standard quadrature type position encoder, like our non-contact, high speed magnetic ENC connected to the motor shaft. Up to 73,000 edges per second or 18,000 lines per second are supported with the current 0.93 firmware. That supports up to 1,095 RPM with a 1000 line (4k quad) encoder (73K/4K*60), or over 12,000 RPM with our 360 quad ENC2 (73K/360*60).
• The output is PWM speed and direction suitable for any standard "H-Bridge" motor driver. Such as the MassMind.org H-Bridge DC Motor Driver

TEMPORARY: To tune the PID controller for your motor and load, you will need a USB to TTL serial converter. e.g. FTDI friend, etc... Our RLC3 works nicely.

OPTIONAL: +5 volt regulator parts. The BOB PID needs +5 volt logic power from somewhere... But that can come from many sources:

• The USB-TTL adapter can provide +5 from USB while it's attached to your computer for tuning the PID constants. If you have a spare USB power adapter, just plug it into that after you are done.
• Or, if you are using some other driver, and it doesn't put out +5 volts, you can supply +5 volt power form your own source.
• Or, you can order the regulator parts and install them on the BOB PID so it can make +5 from your motor power supply.

NOTE: If these options are confusing, please reivew the Servo block diagram to see how they all fit together.

Assembling the BOB PID

Note: Most components are installed on the underside of the PCB... The side with "U1 PIC"

Motor Driver Output via Z Axis cable

[ ] Install a 10 pin 2x5 header over the Z axis on JP3. On the boards underside, this is the 2nd from the right block of 2x5 pins in JP3 with "Z" just below it. Note that we swapped the standard functions of Step / Direction to support the PIC. For a PMinMO stepper driver, you must swap pins 2 and 3 in the cable. Our MassMind H-bridge driver has those pin swapped, for a straight cable.

Step / Direction input from motion controller via X Axis cable (if desired)

[ ] Install a 10 pin 2x5 header over the X axis on JP3. On the boards underside, this is the far left block in JP3, starting from pin 1. This is PMinMO standard, so our Pololu adapter cable works nicely.

Serial Console: To talk to the controller via USB - TTL serial (Required to set the PID constants):

[ ] Install J2 RLC header for USB / serial communications to a host. The host is used to tune the PID loop, provide motion commands for test or use, and update firmware via the bootloader.  Note that pin 4 TX is data FROM the USB/Host going TO the PID controller. RX is TO Host FROM PID.

Quadrature Encoder:

[ ] Install a 1x6 (or 1x5, pins 6 & 1 share +5) header over the holes for the Z and Y LEDs. (see picture) The polarity tab should be towards the outside edge of the PCB and if a 1x5, it should be slid down to use the square pad toward the lower edge, near "D7" on the underside, of the PCB. See the picture below. This brings power, ground, and data lines originally for those LEDs out for a Quadrature Encoder; we can those data lines as inputs instead. The cable for the MassMind Encoder ENC2 is shown: (see also for ENC1)

[ ] Install C4 (upper right corner, not shown in photo) and C7 (just left of U1 "PIC") to ensure stable power and avoid unexpected resets. Despite the value indicated on the PCB, C4 can be any good sized electrolytic capacitor (e.g. 220uF to 1000uF). Note it's long lead should be installed in the square pad nearest the "+" and just above and right of "C4".

[ ] Install JP4 and JP5 on the under side of the PCB, about an inch from the left, just below U1. See left bubble in picture.

[ ] Install a jumper over the RP2 LED network from STEP Y to the corresponding pin on the bottom side of RP2. See right bubble in picture.

[ ] Install a jumper sideways over RP2 from STEP A to the pin NOT directly on the other side of RP2, but one place over, towards the Y jumper you just installed. See right bubble in picture.

[ ] The PIC 18F14K22 is installed as U1 PIC on the bottom side center left. The notch on one end of the chip should match the notch on PCB and face the U1 PIC text. Be sure it is programmed first (Source code in github). The chip provided with the kit is already programmed and includes a bootloader for future firmware updates.

The PCB can be mounted to any surface with standoffs. The mounting holes are at these locations, measured from the left and bottom of the PCB (right, up)

1. 0.45", 0.10"
2. 2.45", 0.10"
3. 3.55", 0.50" (0.1" from right edge)
4. 0.10", 1.13"
5. 3.55", 2.15" (0.1" from right edge)

Options

ERROR FEEDBACK: OPTION. If you will want error feedback to your motion controller:

[ ] First be very careful that it can accept an error signal on pin 7 of the PMinMO connector. This pin is normally grounded, and so it will make any error much worse if we activate a short to ground. Connect a low value resistor over the "X" just above U1 on the underside of the PCB.

ERROR LED: OPTION. For an error indicator, this LED will light if the controller looses track of a shaft which is spinning too fast:

Install an LED with long lead in the A2D pin of J12 (lower edge of PCB) and the short lead in the hole just right of that. Keep the short lead long, and bend it over to also connect to J12 pin 1 (far right of J12) where a low value resistor (e.g. 330 to 560 ohms) should be installed with it's other lead in one of the GND pads of J11. (see center bubble in picture above)

Operation

TTL Serial 38400 N 8 2 X-ON/X-OFF: Connect a USB (or RS-232) to TTL serial converter to the J2 connector. e.g. FTDI Friend, RLC3 Again, pin 4 "TX" is data FROM the USB/Host going TO the PID controller. RX is TO USB/Host FROM PID controller. Configure your serial terminal program (e.g. Hyperterm, RealTerm, PuTTY, etc...) for whatever COM/TTY port shows up, and 38,400 baud, No parity, 8 data bits, and 2 stop bits. Select X-ON / X-OFF handshaking if available. Video

Note: The pre-programmed chips come with a bootloader installed. On power up, the serial connection will display a countdown in order to give time for the user to go into the bootloader mode if desired. Just wait for the countdown to finish for normal operation. If the screen fills up with "!" the magent isn't placed correctly.

Commands:

• e Enable. On startup the unit will NOT drive the motor, until it is enabled. This also resets any position error, so the motor should not move.
• {space} Disable. To stop the motor at any time, just hit the space bar. This also disables tracking of the hardware input enable line.
• #p, #i, #d Set the constant to the value entered. For example, to set the p term to 14, enter 14p To set I to 0.1, enter .1i. Always use lower case (it's faster) and always enter the value first, then the letter. These settings only last as long as power is on, unless you save them into non-volitile memory.
• 216w Set Direction to positive high, negative low
• 286w Set Direction to positive low, negative high
• 60w Make the motor enable track the step/direction input motor enable line
• 50w Make the motor enable NOT track the step/direction input motor enable line. {space} also does this and disables the motor.
• #s (since v0.92) Set the number of steps per each step input pulse.  e.g. 10s changes the setpoint by 10 positions each step. 1s is a one to one step to position setting.
• #v (since v0.95) Set velocity for move commands from terminal. Like s but internal. Applies v positions per 1/200th of a second from setpoint.
• 321w Save settings / constants in non-volitile memory. Once direction is set, the PID tuning is done, and input enable tracking set, saving the settings allows you to remove the console cable and just operate from the hardware step/direction input.
• #{enter} Move to the location entered. e.g. to move to 100, enter 100 and press enter. To go to 1, press 1. For negative values, put the minus sign at the end, not the start, of the number. e.g. to move to -20, type 20-{enter}. The total range is double... 1.17549435 e-38 to 6.80564693 e+38 with 32 bit precision.

Start by entering very small values for pid. e.g. .01p.01i.01d then hit e to enable the drive and see if the motor moves at all. If not, try increasing p until the motor just moves a bit when you hit space and then e again or when you twist the shaft away from the home position. If you are getting up to 1p and the motor isn't turning, something is wrong with the enable or driver or wiring.

Once the motor starts turning, it may go in the wrong direction, which will make the error get worse and worse. Hit space, then put in 216w and enter then e again. If the motor still just spins, try space, 286w and e. The motor should just jump slightly when you hit e and should hold position loosely. E.g. you should be able to twist the shaft quite a bit and the motor should try to resist you a litte and move back to home. Enter 321w to save the settings.

Now increase p and tweak the motor shaft until it just starts oscillating. Set p to about half that value. Estimate the number of osciallations per second and set d to that frequency divided by 8. Set i to less than the frequency divided by 2. This is a good starting point. Continue with our PID Tuning / Troubleshooting page.

Troubleshooting

On power up, after enable, the motor runs continuously in one direction or the other.

The polarity of the direction signal is backwards. Use the Set Direction commands (above) to make it zig or zag as it should. MD

On power up, after enable, the motor holds position in one direction only. If you push it against the correct position, it will resist, but will then go dead as soon as it moves away from the set point.

The Step / Direction lines from the controller to the driver are reversed. Step is feeding direction and direction is feeding step.

The motor oscillates, moves slowly, shudders/grinds, or generally moves but not well.

Please read and follow our PID Tuning / Troubleshooting page

The error LED comes on, or the serial console shows "!", or the motor looses it's position

1.The encoder is putting out invalid phase A and B signals. The MassMind ENC1 Encoder will do this if it looses track of it's magnet. Recheck the positioning of the magent.
2. The PID controller isn't able to keep pace with the encoder. Please measure the RPM of the shaft if possible and contact us with this information. A firmware update may become available to improve speed.

Movement works ok from the serial console, but the step / direction interface has no effect. Especially when the step and direction signals are open collector

You will need to provide 1K ohm pull up to logic power from each signal.

Firmware versions:

Source respository, Updating the firmware

• 0.90 inital release.
• 0.91 Bootloader
  1. Output motor enable can now track the hardware input enable line from the step direction interface.
     - This is disabled by default
     - Enable with command 60w, disable with 50w or {space} which is still the e-stop
  2. Baudrate is 38400 to match the bootloader
  3. The code can be bootloaded
  4. Add "hello world" message to make it clear when the bootloader is done.
• 0.92 Step size / Faster
  1. A new parameter 's' can be set for the size of each step from the step/direction input. e.g. 10s changes the setpoint by 10 positions each step. 1s is a one to one step to position setting.
  2. The initial versions just used doubles for everything and that was really slow in the interrupt routine for the encoder and step/direction inputs. This code moves to integers (longs... 32 bits -2,147,483,648 to +2,147,483,647) for the position and setpoint which should support much faster rotation and higher resolution encoders; up to 360 line 1440 quad.
• 0.93 Faster! More Sensitive
  1. By increasing the clock speed from 16 to 64MHz, 4x faster operation is possible allowing support for up to 1000 line, 4,000 quad encoders
  2. Fixing a bug in the PWM output routine (was always multiplying PWM by 10) both increased the update speed and improved sensitivity.
     Known issue: Step size parameter is not saved to eeprom.
• 0.94 (not released)
  1. Actually save the step size parameter
  2. Faster processing of step input, slightly faster encoder processing. Just track error, vs Setpoint - encoder_counter.
     Note: Step/Direction input is now relative.
     Calculation of Derivative and Integral terms changed. May need to re-tune
• 0.95 Improved User Interface, Faster!
  1. Just one "!" per encoder overrun; avoid buffer overrun
  2. Add version / status / settings as "?" command
  3. Let the user know they need to enter 321w to save
  4. Past MAX_ERROR, disable and suggest other direction
  5. Movements via serial command have a max velocity 'v'
  6. Setpoint is now relative, always returns to 0, no wraparaound jerk
  7. Smaller datasizes (short long, 24 bits) used for most variables, faster
  8. Derivative and Integral terms changed. May need to re-tune. EEPROM Version '4'
• 0.96 Minor fixes
  1. BugFix: 10 display digits exceeded precision. 9 works.
  2. BugFix: Avoid PIDerror changing during calculations. Can cause small random jerks.

Comming attractions (new features wish list). If you see something you really want, let us know.

• Support for RC servo output (100Hz PWM with zero at 1.5mS, reverse at 1mS and forward at 2mS) so we can support ESC's for BLDC motors. This may not work with all ESCs, but it's worth trying. Some of the new ESC's can manage small movements quite well.
   
• Support for 0 to 10 volt analog output instead of just 0-5v PWM using the relay driver circuit on the BOB PID. This is just a hardware mod. Do anyone have a 0-10 volt input servo driver / motor to test on?
   
• Tuning mode with frequency and oscillation of whatever size the last movement was. E.g. you hit 10t 1000 and it moves back and forth by 1000 clicks every 10 seconds. Then you can just enter tuning parameters and quickly see the results.
   
• Binary error reporting mode / program. This will just transmit a single byte over and over again whose value will be proportional to the current error. A program on the PC will receive this data and plot it, allowing you to see exactly what the error is over time. Combined with the Tuning mode, it will make accurate tuning much easier.
   
• Autotune program. This will use the error reporting and the tuning mode to automatically adjust the PID values for the best movement.
   
• DRO mode. Output of the current position in engineering units on a large display or web page.

See also:

• camphorblue@spam@ at SPAMgmail.com refers to

  /Techref/io/SERVO/BOBPID.htm Another typo on this page: To the right of where it says Step/Direction input from motion controller there is a box labeled X-axis Pin. It reads "Signal from BOB PCB" and it should say "Signal to BOB PCB" I think? I'm curious if the BOB PCB board is getting it's 5 volts from the grbl shield through the PMinMO adapter cable I purchased from you? I don't have your controller board working yet. The grbl shield works to drive steppers with a PMinMO driver in the socket but the drive I built from your kit has no lights lit when powered up. The error light on the BOB PID flashed for a second when motor power is applied. The BOB PID boards error light will also come on if I rotate the motor shaft by hand in either direction.

  James Newton of MassMind replies: I guess it makes more sense to have that say "to" instead of "from", thanks for the feedback. The BOB PID needs logic power from somewhere and it can get it from the DC motor driver, or from the motion controller or whatever.+

  +

• https://youtu.be/qii1SxnRzJw Video showing setup with 0.95 Firmware (existing customers contact us for upgrade)
   
• https://youtu.be/rnwYqGB3bXw Video of the system running from a standard RAMPS/Marlin motion controller, with our MassMind H-bridge driver
    
• https://youtu.be/Wxd9-VgvRpI Running from RAMPS/Marlin with a SyRen 25 Amp Driver or SyRen 50 Amp Driver: (NOT the Sabertooth dual units)
  The trick is to use Option 3 "Analog One-Direction with foward/reverse select on S2" That is, on the DIP switch 1,2,3 ON, 4,5 OFF, 6 ON.
  From the SyRen to our motor connector:
  - S1 to Z axis pin 3 "D", the PWM Drive
  - S2 to Z axis pin 5 "S", Direction signal
  - 0V to Z axis pin 7 "-", Ground
   
• https://www.youtube.com/watch?v=ekbzLTYLiSY The MONSTER servo is a 1 foot square, 5000 oz/in, runs on power tool batteries. Controlled by the BOB PID.
   
• https://github.com/JamesNewton/BOBPID/ Source code for the PID controller.
   
• Full data and Schematic for the BOB PCB
   
• https://docs.google.com/spreadsheets/d/14XrUBmxMQrcOYOkujlJ132LcpPda-IV4-Hq4ntLJoFA/pubhtml?gid=1729284531&single=true
  Layout and usage of PIC pins for PID on the BOB PCB
   
• http://picprog.strongedge.net/bootloader/bootloader.html We use a slightly modified version of this bootloader. (the error LED has been changed)
   

News

Questions:

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