This page's link: "erowbike.com/bogiedyno"

Documentation for Custom Dynomometer to Test Performance of Electric Mobility Devices

The BogieDyno was developed specifically to test the performance of the "bogies" which power Bill James' JPods.

Related Links:
Controllers (3 phase BLDC)
Cycle Analyst (v3)

RPM Measurement

The JPods bogies use solid aluminum wheels with a rubber perimeter, resulting in an effective outside diameter of 8.0 inches. The solid aluminum rollers used on the BogieDyno are 1.25 inches in diameter and use no covering. The bogie wheels are directly fastened to the output motor shaft, and therefore rotate at the same RPM as the 3 phase brushless DC (BLDC) motor. The motor uses internal Hall sensors which are monitored by a Cycle Analyst (v3) to provide an accurate RPM for the motor itself. An 8" wheel rotating at 1,470 RPM would result in a bogie speed of 35 MPH, assuming no slippage on the surface on which it is traveling. An 8" wheel rotating on a 1.25" roller at the above speed causes the roller to spin at a rate 6.4001 times faster, or 9,408.1 RPM at 35 MPH. Using a sensor wheel with 12 magnets (poles), there will be 1,881.6 pulses per second transmitted to the Hall sensor. (0.532 ms/count) For practical testing purposes, the rollers will be limited to a spinning speed of 10,000 (10K) RPM.

freq.README

The "frequency" programs consist of two major categories, the "generator" code and the "counter" code.

Ultimately the "generator" won't be needed because the counts will be generated by hardware sensors, such as Hall Effect modules responding to a spinning magnet wheel.

=================  GENERATOR  ============================

This run on a physically separate pi from the the "counter" pi.

freq-gen-pigpio.py  (1,162 Feb 9, 2016 10:02) <--  Python script which uses the pigpio library to generate a user selectable square wave for testing purposes.

==================  COUNTER ===============================

Make sure the pi has the necessary libraries for the C code to run:
  ---------------------------------------
  aptitude install wiringpi
  ---------------------------------------

The compiled and source code from wanda:/tmp

freq-counter.c    <-- the C source code
freq-counter      <-- the compiled executable for Raspberry Pi
freq-counter2.py  <-- the python script version of the C code above; uses the same arguments

Look at the source for the pin used.
Put the executable where you want it and run it with the right args.

Example:</br>
  ---------------------------------------
  |  root@pi2:~/bin# ./freq-counter     |
  ---------------------------------------
Magnets SamplePerSec and Alpha arguments expected - aborting...

magnets  smple/sec  alpha
                    12         2        .8
  ----------------------------
  |  ./freq-counter 12 2 .8  |
  ----------------------------

Older version is parked on wanda:/tmp ccounter.c and ccounter

=================  HARDWARE  ================================

This applies to the Raspberry Pi ("pi2", 192.168.3.42) which is currently being used to manage the frequency data generated by the BogieDyno.

Use GPIO Pin 17, which is Pin 0 for wiringPi library

-------------- Pi GPIO input pin protection from 5VDC signals -----------------
From: Denny Fox <dennyf@microtimeinc.com>
Sent: May 20, 2015 1:02:17 PM CDT
Subject: RE: Reading flow meter pulses

3.3V
                                             |
                                           __|__
                                             ^
                                            /_\                                              
                                             |
                                             |
  5VDC signal >------/\/\/\/\---------[Input to Pi, clamped to 3.3V]
                        1KOhm
This does the trick...
---------------------------------------------------------------------------------

Raspberry Pi used to calculate RPM and related data (speed)

The pigpio Library

On the Pi you are going to use as a test frequency generator, install the pigpio library as instructed on the page below.
I ran all the tests shown after the install with no errors on an A+ with 256Mb of ram. I like to put downloaded source code in /usr/local/src so I can find it later. Start with cd /usr/local/src then follow the instructions
Download & Install abyz.co.uk/rpi/pigpio/download.html
All the things it can do are listed here: abyz.co.uk/rpi/pigpio/index.html

freq-gen-pigpio.py

Copy the script freq-gen-pigpio.py from wanda:/tmp/freq-gen-pigpio.py to /root/bin on the system that will be the frequency generator.

#!/usr/bin/env python

import time
import sys
import signal

import pigpio

GPIO=18		# Output on BCM pin

if len(sys.argv) <> 3:
  print "Expecting args for Rpm and Magnets - Aborting..."
  sys.exit(1)

Rpm = int(sys.argv[1])
Magnets = int(sys.argv[2])

# Stop waveform and exit on a SIGINT, ^C
def signal_handler(signal, frame):
  #print 'Got SIGINT'
  pi.wave_tx_stop()
  pi.wave_delete(wid)
  pi.stop()
  sys.exit(0)

# Define the SIGINT handler
signal.signal(signal.SIGINT, signal_handler)

#Magnets = 12
#Rpm = 8000
#Rpm = 10
Hz = (Rpm/60.)*Magnets
Period = 1./Hz * 1000000
print "Magnets =", Magnets, "  Rpm =", Rpm, "  Hz =", Hz, "  Period in microsec =", Period
print "Type ^C to exit"

square = []

#                          ON       OFF    MICROS
square.append(pigpio.pulse(1<<GPIO, 0,       Period/2))
square.append(pigpio.pulse(0,       1<<GPIO, Period/2))

pi = pigpio.pi() # connect to local Pi

pi.set_mode(GPIO, pigpio.OUTPUT)

pi.wave_add_generic(square)

wid = pi.wave_create()

if wid >= 0:
#while wid >= 0:
   pi.wave_send_repeat(wid)
#   time.sleep(60)
#   pi.wave_tx_stop()
#   pi.wave_delete(wid)

#pi.stop()

while True:
  time.sleep(1)

freq-counter.c [13 Feb 2016]

freq-counter.c adapted from isr4pi.c - D. Fox 2/8/2016

Ref: D. Thiebaut
based on isr.c from the WiringPi library, authored by Gordon Henderson
https://github.com/WiringPi/WiringPi/blob/master/examples/isr.c

Compile as follows:

gcc -o freq-counter freq-counter.c -lwiringPi

Run as follows:

sudo ./freq-counter

*/
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <wiringPi.h>

// Use GPIO Pin 17, which is Pin 0 for wiringPi library

#define BUTTON_PIN 0

// the event counter 
volatile int eventCounter = 0;

int SamplePeriod, Magnets;
float fEventCounter, fOldEventCounter, Alpha;

// -------------------------------------------------------------------------
// myInterrupt:  called every time an event occurs
void myInterrupt(void) {
   eventCounter++;
}

// -------------------------------------------------------------------------
// main
int main(int argc, char *argv[]) {

// Check for SamplePeriod arg
  if ( argc != 4 ) {
    printf("Magnets SamplePerSec and Alpha arguments expected - aborting...\n");
    exit(1);
  }
  else {
    Magnets = atoi(argv[1]);
    SamplePeriod = atoi(argv[2]);
    Alpha = atof(argv[3]);
    printf("Magnets = %d\n", Magnets);
    printf("SamplesPerSec = %d\n", SamplePeriod);
    printf("Smoothing Factor Alpha = %.1f\n", Alpha);
    //printf("SamplePeriod = %s\n",argv[1]);
  }

// sets up the wiringPi library
  if (wiringPiSetup () < 0) {
      fprintf (stderr, "Unable to setup wiringPi: %s\n", strerror (errno));
      return 1;
  }

// set Pin 17/0 generate an interrupt on high-to-low transitions
  // and attach myInterrupt() to the interrupt
  if ( wiringPiISR (BUTTON_PIN, INT_EDGE_FALLING, &myInterrupt) < 0 ) {
      fprintf (stderr, "Unable to setup ISR: %s\n", strerror (errno));
      return 1;
  }

//Magnets = 12;
  fOldEventCounter = 0.0;
  //Alpha = .8;

// display counter value every SamplePeriod.
  while ( 1 ) {
    fEventCounter = (float) eventCounter;
    eventCounter = 0;
    fEventCounter = Alpha * fEventCounter + (1.0 - Alpha) * fOldEventCounter;
    fOldEventCounter = fEventCounter;
    //printf( "%.1f\n", ((float) OldEventCounter / (float) SamplePeriod ) * 5.);
    printf( "%.1f\n", (fEventCounter / SamplePeriod /Magnets * 60));
    //printf( "%.1f\n", (fEventCounter));
    delay( SamplePeriod * 1000 ); // wait SamplePeriod
  }

return 0;
}

freq-counter2.py [2,725 13 Feb 2016 16:49]

#! /usr/bin/python

# freq-counter.py

# Measure the frequency of a pulse train

# Use an interrupt on the rising (or falling) edge of the signal
# Caluclate the time difference between pulses (period)
# Discard "bad" data and exponentially smooth the period
# Main loop calculates and displays frequency (1/period)

# Denny Fox - 2/5/2016

# Try a different approach - original was too slow - too much going on in the interrupt routine
# Model after the C version
# 2/13/2016

import signal
import sys
import time
import os
import RPi.GPIO as GPIO
GPIO.setwarnings(False)

# Can be used by an /etc/init.d script
PidFile = "/var/run/range.pid"

# using BCM GPIO 00..nn numbers
GPIO.setmode(GPIO.BCM)

# Define GPIO Pins Used
SignalInput = 17

# Set Input with Pullup to read Signal pulse
GPIO.setup(SignalInput, GPIO.IN, pull_up_down=GPIO.PUD_UP)

# Write a pid file
pid = str(os.getpid())
f = open(PidFile, 'w')
f.write(pid)
f.close()

TimeStamp = time.time()

# Define global variables
EventCounter = 0
CurrentEventCounter = 0
OldEventCounter = 0
Alpha = .85
Magnets = 12
SamplePeriod = 2

if len(sys.argv) <> 4:
  print "Expecing args Magnets SamplePeriod and Alpha - Aborting..."
  sys.exit(1)
 
Magnets = int(sys.argv[1])
SamplePeriod = int(sys.argv[2])
Alpha = float(sys.argv[3])

# Cleanup GPIO and exit on a SIGINT, ^C
def signal_handler(signal, frame):
  #print 'Got SIGINT'
  GPIO.cleanup() 
  os.remove(PidFile)
  sys.exit(0)

# Cleanup GPIO and exit on a SIGTERM, from /etc/init.d script
def sigterm_handler(signal, frame):
  #print 'Got SIGTERM'
  GPIO.cleanup() 
  os.remove(PidFile)
  sys.exit(0)

# Define the SIGINT handler
signal.signal(signal.SIGINT, signal_handler)

# Define the SIGTERM handler
signal.signal(signal.SIGTERM, sigterm_handler)

# Handle the signal edge
def either_callback(channel):
  global EventCounter
  EventCounter += 1

# Set up the callback for the Signal pulse
# Comment in the rising or falling callback, the service routine handles either
#GPIO.add_event_detect(SignalInput, GPIO.RISING, callback=either_callback)
#GPIO.add_event_detect(SignalInput, GPIO.FALLING, callback=either_callback, bouncetime=300)
GPIO.add_event_detect(SignalInput, GPIO.FALLING, callback=either_callback)

# Main program loop - loop forever
# SIGINT or SIGTERM terminate loop (handled above)

while True:

CurrentEventCounter = EventCounter
  EventCounter = 0
  CurrentEventCounter = Alpha * CurrentEventCounter + (1.0 - Alpha) * OldEventCounter
  OldEventCounter = CurrentEventCounter
  print ("RPM = {:6.1f}".format(CurrentEventCounter / SamplePeriod / Magnets * 60))
  time.sleep(SamplePeriod)

# make sure all GPIO pins are cleared on exit
GPIO.cleanup()

#Remove the pid file
os.remove(PidFile)

If you don't have a /root/bin directory, create one. I like to keep all my scripts that I'm working on there. I scp'd the python script to wanda:/tmp instead of just emailing it, so the Unix style line endings would be preserved. You need to start the pigpiod daemon before you run the python script. Edit the script Rpm = line for the frequency you want. When you run it, the script will generate a square wave of the frequency defined by the number of magnets for 60 seconds, then the waveform stops. When it starts, the script prints the values of Magnets, Rpm, Hz, and Period so you can see what it is generating. It would be interesting to see how it looks on your digital scope, and what the scope measures the frequency as.
I adapted code from here to create freq-gen-pigpio.py.
http://raspberrypi.stackexchange.com/questions/19765/rpi-gpio-as-a-high-speed-square-wave-generator
I will be following up with the frequency counter script after I tweek the code a little. That will run on a different Pi, the one that will eventually be mounted on your dyno.

PiScope youtube video

King-Meter 12 magnet sensor wheel

A 12 magnet sensor wheel mounted on the dyno rollers feeds RPM data into the Raspberry Pi via a digital Hall Effect sensor which reads the changing magnetic fields from the rotating wheel. King-Meter 12 magnet bogiedyno_magnet_wheel

King-Meter 12 magnet bogiedyno_magnet_wheel

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