Weekly Status Reports

I explored all the motor options in all their fullness of potential. Let me explain what was peculiar with each one:

NEMA17 & L298N (cheap from amazon):

Using the stepper motor library, the motor stalls, as before, but setting the pins directly did not have the motor work. The same code that worked with the fake NEMA 17 and borrowed driver did not work for this motor and driver.

NEMA 17 & L298 hbridge (expensive from sparkfun):

I could not figure out how to get this driver to work, despite trying various wiring configurations. The leds light up for MotorA and MotorB, which is a good sign. I tried hooking up the H-bridge and the motor to separate power supplies and the same power supply. I tried setting different combinations for the enA and enB pins, along with in0-in3 pins. I followed what the datasheet instructed for having a coasting motor. I researched what a stepper motor should be doing and found an article on stepping modes. I manually set the in0-in3 pins according to what the coils were expecting, and huzzah!

I could not get the Full nor Half operation modes to work, but I got the Wave operation mode to work for counter clockwise rotation. Unfortunately, I could not get the stepper motor to rotate clockwise.

NEMA 17 & TB6600 motor driver:

Led indicator told me the motor was asking for more current, but it was asking for more than it was allowed to have according to the datasheet. I found various wiring instructions online, each slightly different. Nathan and I tried all sorts of configurations trying to guess how the motor should’ve been wired up, with little luck. Furthermore, peeling off the cover of the motor driver, I found that the labels on the pcb did not match the labels on the outside of the cover. The pulse pins were mislabeled as enable pins. I gave up on trying this option, but in hindsight, I bet if I fed the motor some more current, it might’ve behaved differently. On adafruit.com the NEMA 17 spec for max current says 350mA, but other sources say the motor can handle more. Weird.

Servos:

The PWM from my Arduino that worked so reliably last week no longer worked this week. The falling edge was not as fast as before, and my servos no longer cooperated with my Arduino.

Furthermore, I realized that PWM from Jetson is not a good idea. The easiest solution for PWM by far is to: connect to Arduino from Jetson TK1, so that your main program running on Jetson decides what the motors should do, and it sends that info to an Arduino that does the actual PWM control. To control motors or servo motors, you can either attach a servo motor shield onto a regular Arduino or use an Arduino clone that includes its own motor controller, so it didn’t need a separate motor controller shield. But if you use a regular Arduino then the easiest solution would be to add a servo motor shield to a regular Arduino. Low-level real-time operations like PWM need consistent “hard-realtime” timing that a microcontroller is much more suited to than a big CPU / Application Processor like Tegra.

DC Motor:

I had actually forgotten that I had a DC motor in my possession until Jing pointed it out. The motor asks for 12 volts, and has incredible holding torque when turned off – I didn’t measure exactly how much, but its more than even Professor Bain’s hands. Reversing the direction of current causes the motor to turn the other direction. I imagine I could probably form an open feedback loop circuit out of transistors to control the direction of the motor using gpio pins. Fortunately, I don’t have to. I can use the L298 hbridge (expensive from sparkfun). All I need to do is reverse the pin settings for in1 and in2 in order to reverse directions, and I can hold both pins at 0 in order to stop the motor.

void ccw() {
  digitalWrite(in1, HIGH);
  digitalWrite(in2, LOW);
}

void cw() {
  digitalWrite(in1, LOW);
  digitalWrite(in2, HIGH);
}

void hold() {
  digitalWrite(in1, LOW);
  digitalWrite(in2, LOW);
}

The jetson should be able to control the motor entirely through GPIO pins since only the enA, in1, and in2 pins on the H-bridge need to be set. And I can share the 12V power supply from the solenoid bolt. The motor draws at most .13A.

TLDR;

I have a motor that turns and I can control it.

I’ll mount the pully system tomorrow so we can show it off at the in class final demo. Next week, we’ll be doing the presentation. I will revise the project paper to according to design review feedback. I will have updated diagrams in the project paper according to system changes.

I used a waveform generator to output a square wave with T = 2.0ms, Ampl = 3.3Vpp, HiLevel = 3.3Vpp, Offset=1.65Vdc, LoLevel=0V, and Duty Cycle between 20% and 80%. The servo seems to work fine, with a few glitches when the duty cycle was low.

However, using the servo library on the Arduino, the pwm output from pin 9 looks funny. Here is a comparison on the oscilloscope:

Yellow is the square wave from the waveform generator, and green is the output from the Arduino using the servo.h library and the sample code provided by adafruit here https://learn.adafruit.com/adafruit-arduino-lesson-14-servo-motors/arduino-code-for-sweep. Upon inspection of the Arduino servo library, it looks like the servo.write() function sets an interrupt. When I set my own pwm using the following code:

void loop()
{
  digitalWrite(servoPin,HIGH);
  delayMicroseconds(active_us);
  digitalWrite(servoPin,LOW);
  delayMicroseconds(period_us - active_us);
}

Hallelujah, the Arduino output has the correct duty cycle and period, but the amplitude voltage is lower. Here is what the output from the oscilloscope looked like:

In the context of the system, I would need to use interrupts to manage the PWM when integrated with the sensors.

I ordered parts for five alternatives because I don’t think we have time for ordering parts for a Plan B. In order of potential, my options are:

1. NEMA 17 & L298 hbridge (cheap from amazon): There are many resources out there using these two parts together and I (almost) had it working with the same type of hbridge last week. 
2. NEMA 17 & L298 hbridge (expensive from sparkfun): I’ve learned from Build18 that cheap parts are not reliable, so here’s an alternative. The hbridge is the same model, but the breakout board looks more enhanced. The heat sink is larger.
3. NEMA 17 & TB6600 motor driver (as recommended by Nathan Serafin). This driver is very heavy duty and reliable, but there are not many resources out there for how to use it.
4. Continuous rotation servo: I feed this a time interval and it spins for that amount of time, but is very imprecise.
5. The original servo: I believe I could hack something together to make this work, but it wouldn’t be pretty. I have better options, and this is only a backup on backups.

If the option that I go with does not have enough torque (which is unlikely), I can use a counterweight to require less torque.

I got through trying options 1-3. Here are my results.

1. NEMA 17 & L298 hbridge (cheap from amazon):

   The motor stutters, but is drawing much less current than the imposter NEMA 17.

2. NEMA 17 & L298 hbridge (expensive from sparkfun): I wired everything, but there is no current flowing. I looked at the user manual and found operating instructions that include the use of ENA and ENB, which I haven’t needed to use before when following other tutorials. I will try more wiring configurations
3. NEMA 17 & TB6600 motor driver: This I have no clue how to wire up (LOL). I will meet with Nathan to figure it out.

In other news, I have mounted the camera and LED to the door. They are both taped on so we can remove or adjust them.

Here is what the camera output looks like:

And with the lights off and LED on:

And I was standing about two feet away:

I’m behind and still working to solve the same problems as last time.

First, I attached the solenoid to the door:

I happened to be in the right place at the right time to overhear Professor Nace say that Ryan Bates from Tech Spark has a box of stepper motors. I talked to Ryan and he let me borrow a stepper motor and L298N Dual H-Bridge Motor Controller. When I followed a tutorial using the same motor and H-bridge motor controller with an Arduino, I couldn’t get the system working.

 

I poked around with an oscilloscope and saw that there is current flowing through the H-bridge, but not a lot. Next, I asked Nathan Serafin for advice, and he said he could lend me a few motors. I tried switching out the motor, but the motor still did not work. I met with Sam to try to get the motor working, and he pointed out that my power supply could not source the amount of current needed at the voltage wanted. He borrowed a bigger power supply from the CMR garage, and the motor didn’t work, so we tried borrowing an identical H-bridge component from another team. The motor moved with the new H-bridge, but the H-bridge was overheating. So we concluded that the H-bridge from Tech Spark was faulty, but that particular H-bridge model is not strong enough to support the stepper motor. Sam suggested I investigate the servo again, which I will be doing. I also talked to Nathan Serafin again and he suggested researching this alternative H-bridge.

In between all the motor things, I found time to do a timing analysis on the integrated machine vision script. I segmented the code into the following blocks: initialization, resizing, converting to grayscale, applying Gaussian blur, calculating frame delta & applying binary threshold & computing contours, tracking where to crop, prediction, and drawing the frame. I counted the number of times each block was executed, the total time spent executing a code block, and the total time for execution of the whole script. I found that image saving, image resizing and drawing things on top of the frame took the most time. Therefore, for the integrated script, I removed the text and rectangle overlays on top of the frames and only displayed one frame. I am keeping the motion detection script separate with all the intermediate frames displaying for the purposes of fine tuning and debugging.

I will be placing orders for alternative motor parts and trying them out. In the next status report, I will detail the pros and cons of each alternative, and why they did or did not work. I’m busy until the start of carnival, which works out well because the new parts will not arrive until Thursday at the earliest. I can work over Friday and Saturday.