3D

Wire bender

/ John Tapsell / Leave a comment

I wanted to bend a large amount of wire for another project.

So I made this, a phone controlled wire bender. You plug it, establish a Bluetooth connection to it, and use the nifty android app I made to make it bend wire.

Details

I had an idea that an 3d printer’s extruder could also be used to extrude wire. So mocked something up:

And then laser cut it.

Mounting

I decided to mount everything to top acrylic, except for the power connector.

Also, I didn’t do much wire management 🙂

The “project box” is actually a flower pot 🙂

One thing I didn’t foresee with mounting everything upside down is that one of the heatsinks on the motor controller fell off. I had to add an acrylic plate on top to hold them in place. Also, I think I need some active cooling. I haven’t had any actual problems yet, despite bending a lot of wire, but I’m sure I’m doing the controllers and motors no favors.

Previous iterations

I actually went through quite a few iterations. Here was one of the first designs, before I realized that I needed the wire bending part to be much further away from the extruder:

I went through a few different iterations. The set of 11 feeder ball-bearings are there to straighten the wire. It’s not obvious, but they actually converge at approximately a 2 degree angle, and I find this works best. So when the wire is initially fed in, the large spaced bearings smooth out the large kinks, and then the closer spaced bearings smooth out the small kinks. Try trying to do it all in one pass doesn’t work because the friction ends up being too high.

I replaced the extruder feeder with one with a much more ‘grippy’ surface. The grooved metal needs to be harder than the wire you’re feeding into it, so that it can grip it well. This did result in marks in the metal, but that was okay for my purpose. Using two feeder motors could help with this.

Algorithm

The algorithm to turn an arbitrary shape into a set of motor controls was actually pretty interesting, and a large part of the project. Because you have to bend the wire further than the angle you actually want, because it springs back. I plan to write this part up properly later.

Software control

For computer control, I connect the stepper motors to a stepper motor driver, which I connect to an Arduino, which communicates over bluetooth serial to an android app. For prototyping I actually connected it to my laptop, and wrote a program in python to control it.

Both programs were pretty basic, but the android app has a lot more code for UI, bluetooth communication etc. The python code is lot easier to understand:

#!/usr/bin/env python3

import serial
import time
from termcolor import colored
from typing import Union
try:
    import gnureadline as readline
except ImportError:
    import readline

readline.parse_and_bind('tab: complete')
baud=9600 # We override Arduino/libraries/grbl/config.h to change to 9600
# because that's the default of the bluetooth module

try:
    s = serial.Serial('/dev/ttyUSB0',baud)
    print("Connected to /dev/ttyUSB0")
except:
    s = serial.Serial('/dev/ttyUSB1',baud)
    print("Connected to /dev/ttyUSB1")

# Wake up grbl
s.write(b"\r\n\r\n")
time.sleep(2)   # Wait for grbl to initialize
s.flushInput()  # Flush startup text in serial input

def readLineFromSerial():
    grbl_out: bytes = s.readline() # Wait for grbl response with carriage return
    print(colored(grbl_out.strip().decode('latin1'), 'green'))

def readAtLeastOneLineFromSerial():
    readLineFromSerial()
    while (s.inWaiting() > 0):
        readLineFromSerial()

def runCommand(cmd: Union[str, bytes]):
    if isinstance(cmd, str):
        cmd = cmd.encode('latin1')
    cmd = cmd.strip() # Strip all EOL characters for consistency
    print('>', cmd.decode('latin1'))
    s.write(cmd + b'\n') # Send g-code block to grbl
    readAtLeastOneLineFromSerial()

motor_angle: float = 0.0
MICROSTEPS: int = 16
YSCALE: float = 1000.0

def sign(x: float):
    return 1 if x >= 0 else -1

def motorYDeltaAngleToValue(delta_angle: float):
    return delta_angle / YSCALE

def motorXLengthToValue(delta_x: float):
    return delta_x

def rotateMotorY_noFeed(new_angle: float):
    global motor_angle
    delta_angle = new_angle - motor_angle
    runCommand(f"G1 Y{motorYDeltaAngleToValue(delta_angle):.3f}")
    motor_angle = new_angle

def rotateMotorY_feed(new_angle: float):
    global motor_angle
    delta_angle = new_angle - motor_angle
    motor_angle = new_angle
    Y = motorYDeltaAngleToValue(delta_angle)

    wire_bend_angle = 30 # fixme
    bend_radius = 3
    wire_length_needed = 3.1415 * bend_radius * bend_radius * wire_bend_angle / 360
    X = motorXLengthToValue(wire_length_needed)
    runCommand(f"G1 X{X:.3f} Y{Y:.3f}")

def rotateMotorY(new_angle: float):
    print(colored(f'{motor_angle}°→{new_angle}°', 'cyan'))
    if new_angle == motor_angle:
        return

    if sign(new_angle) != sign(motor_angle):
        # We are switching from one side to the other side.
        if abs(motor_angle) > 45:
            # First step is to move to 45 on the initial side, feeding the wire
            rotateMotorY_feed(sign(motor_angle) * 45)
        if abs(new_angle) > 45:
            rotateMotorY_noFeed(sign(new_angle) * 45)
            rotateMotorY_feed(new_angle)
        else:
            rotateMotorY_noFeed(new_angle)
    else:
        if abs(motor_angle) < 45 and abs(new_angle) < 45:
            # both start and end are less than 45, so no feeding needed
            rotateMotorY_noFeed(new_angle)
        elif abs(motor_angle) < 45:
            rotateMotorY_noFeed(sign(motor_angle) * 45)
            rotateMotorY_feed(new_angle)
        elif abs(new_angle) < 45:
            rotateMotorY_feed(sign(motor_angle) * 45)
            rotateMotorY_noFeed(new_angle)
        else: # both new and old angle are >45, so feed
            rotateMotorY_feed(new_angle)

def feed(delta_x: float):
    X = motorXLengthToValue(delta_x)
    runCommand(f"G1 X{X:.3f}")

def zigzag():
    for i in range(3):
        rotateMotorY(130)
        rotateMotorY(60)
        feed(5)
        rotateMotorY(0)
        feed(5)
        rotateMotorY(-130)
        rotateMotorY(-60)
        feed(5)
        rotateMotorY(0)
        feed(5)

def s_shape():
    for i in range(6):
        rotateMotorY(120)
        rotateMotorY(45)
    rotateMotorY(-130)
    for i in range(6):
        rotateMotorY(-120)
        rotateMotorY(-45)
    rotateMotorY(0)
    feed(20)

def paperclip():
    rotateMotorY(120)
    feed(1)
    rotateMotorY(130)
    rotateMotorY(140)

    rotateMotorY(30)
    feed(3)
    rotateMotorY(140)
    rotateMotorY(45)
    feed(4)
    feed(10)
    rotateMotorY(140)
    rotateMotorY(45)
    feed(3)
    rotateMotorY(140)
    rotateMotorY(50)
    rotateMotorY(150)
    rotateMotorY(45)
    feed(5)
    rotateMotorY(0)

runCommand('F32000') # Feed rate - affects X and Y
runCommand('G91')
runCommand('G21')  # millimeters
runCommand(f'$100={6.4375 * MICROSTEPS}') # Number of steps per mm for X
runCommand(f'$101={YSCALE * 0.5555 * MICROSTEPS}') # Number of steps per YSCALE degrees for Y
runCommand('?')
#rotateMotorY(-90)
#paperclip()
while True:
    line = input('> ("stop" to quit): ').upper()
    if line == 'STOP':
        break
    if len(line) == 0:
        continue
    cmd = line[0]
    if cmd == 'R':
        val = int(line[1:])
        rotateMotorY(val)
    elif cmd == 'F':
        val = int(line[1:])
        feed(val)
    else:
        runCommand(line)

runCommand('G4P0') # Wait for pending commands to finish
runCommand('?')

s.close()

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Unity vs Unreal Engine 4

/ John Tapsell / 1 Comment

I implemented two medium-sized projects, one in Unreal Engine 4 and one in Unity 5.

Unfortunately these were both for clients, so I can’t talk about any specifics.  I do, however, want to give some general thoughts on the comparison between them.

Pros and Cons:

  • Unreal Engine 4 seems to have a lot more advanced features.  But I didn’t personally use any of these advanced features.  They didn’t seem easy to use.
  • Unity 5 was much more intuitive for me to use.
  • The Unity 5 asset store was so much nicer to use.  I could buy an asset and import it into my game with a couple of clicks.  With UE4 it seemed so much more difficult.
  • UE4’s VR support simply didn’t work on a Mac.  This sucked because my artists all use Macs.   More annoyingly, it didn’t say why it didn’t work, it just simply disabled the Preview In VR button, giving no reason.   And the reasons were written up in an Internal bug report (UE-11247 apparently) that the UE4 developers constantly refer to, but users aren’t actually allowed to view or see the status of!
  • I much preferred having a managed language (C# or javascript) in Unity than the C++ support in UE4.  Mistakes in C++ code meant crashing the whole app.  It also led to long compile times.   But a mistake in C# meant just having an exception and the app being able to easily recover from it.
  • I tried really hard to get on with UE4’s Blueprint, which is basically a visual “programming” language.  But implementing in a fairly simply mathematical formula would result in 20+ nodes.  Implementing a simple polynomial like  $latex  y = 3x^2 + 2x + 5 $  was incredibly painful in dragging out nodes for each operation.

untitled-46b8493

Blueprint quickly becomes a mess. This is a random example from the web.

  • UE4’s blueprints become particularly annoying when users are asking questions about them.  They’ll paste a screenshot of their blueprint saying that they have a problem.  Someone else then has to try to decipher what is going on from a screenshot, with really no easy way to reproduce.  Users who want to copy a blueprint have to do so manually, node by node..
    I would really love for UE4 to mix in a scripting language, like Javascript.
  • UE4 has lots of cool features, but they are really difficult to just use.  For example, it has a lot of support for adding grass.  You can just paint grass onto your terrain..  except that you can’t because you don’t have any actual grass assets by default.
    The official UE4 tutorials say that to add grass, you should import the whole 6.4 GB Open World Demo Collection to your project!
    But then, even that isn’t enough because it doesn’t have any actual grass materials!  You have to then create your own grass material which is quite a long process.  This was really typical of my experience with UE4.  Why not just have a single ‘grass’ asset that could be instantly used, and then let the user tweak it in more complicated ways if they want to later on?
    Compare this to Unity.  You go to: Assets > Import Package > Terrain Assets  click on the tree or grass that you want, and that’s it.  You can then start painting with that tree or grass immediately.  If you later want to make your own trees, it comes with a tree editor, built in!
  • Unity’s support for Android was much better than UE4’s.
  • UE4 taxed my system a lot more than Unity.  For my beefy desktop, that was no problem.  But the artists had Mac laptops that really struggled.
  • I really like Unity’s GameObject plus Component approach.  Basically, you make a fairly generic GameObject that is in your scene, and then you attach multiple components to it.  For example, if you want a button, your button GameObject would have a mesh, a material, a renderer (to draw the material on the mesh), a hit box (to know when the user presses it) and presumably some custom script component that runs when you hit it.
    And because your custom scripts are written in C# or javascript, you get lovely automatically introspection on the class variables, and any variables are automatically added to the GUI!

Overall, I guess I’ve become a unity fanboy.  Which is a shame, because I started with UE4 and I really wanted to like it.  I have been with UE4 for 2 years, and was a paying sponsor for a year.

I feel that the trouble is their different audiences.  UE4 is obviously targeted towards much larger studios, who want advanced features and don’t care about built in assets etc.  Unity on the other hand is targeted towards Indie developers who want to make quick prototypes and cheap products easily.

This has resulted into a sort of stigma against Unity projects, because there is a glut of rubbish games produced by novices in Unity.  Unity charges about $1,500 per developer to remove the start-up Unity splashscreen, resulting in most indie developers not paying that fee.  Only the good games which sell well can afford to remove that splashscreen.

The result being that if you start up a random indie game on steam greenlight, for example, and see the Unity splashscreen, you know that the game is unlikely to be that good.  Hence a stigma.

Flight aerodynamics simulator

/ John Tapsell / 4 Comments

I wanted to have a modern aerodynamics simulator, to test out my flight control hardware and software.

Apologies in advance for a very terse post.  I spent a lot of hours in a very short timespan to do this as a quick experiment.

So I used Unreal Engine 4 for the graphics engine, and built on top of that.

The main forces for a low speed aircraft that I want to model:

  1. The lift force due to the wing
  2. The drag force due to the wind
  3. Gravity
  4. Any horizontal forces from propellers in aircraft-style propulsion
  5. Any vertical forces from propellers in quadcopter-style propulsion

Lift force due to the wing

The equation for the lift force is:

L = C_l \cdot A \cdot .5 \cdot r \cdot V^2

I created a function for the lift coefficient, C_l, based on the angle, by calculating it theoretically.  To get proper results, I would need to actually measure this in a wind tunnel, but this is good enough for a first approximation:

micron lift coefficients

The horizontal axis is the angle of attack, in degrees.  When the aircraft is flying “straight”, the angle of attack is not usually 0, but around 5 to 10 degrees, thus still providing an upward force.

I repeat this for each force in turn.

3D Model

To visualize it nicely, I modelled the craft in blender, manually set the texture space, and painted the texture in gimp.  As you can tell from the texture space, there are several horrible problems with the geometry ‘loops’.  But it took a whole day to get the top and bottom looking decent, and it was close enough for my purposes.

 

I imported the model into Unreal Engine 4, and used a high-resolution render for the version in the top right, and used a low-resolution version for the game. screenshot2

textured_micron_screenshot

Next, here’s the underneath view.  You can see jagged edges in the model here, because at the time I didn’t understand how normal smoothing worked.  After a quick google, I selected those vertexes in blender and enabled normal smoothing on them and fixed that.

ue4_2(1)

and then finally, testing it out on the real thing:

Screenshot_20180626_232400

Screenshot_20180626_232350

Architecture

The architecture is a fairly standard Hardware-in-loop system.

The key modules are:

simulator

  • The Flight Controller which controls the craft.  This is not used if we are connected to external real hardware, such as the my controller.
  • The Communication Module to the real hardware, receiving information about the desired thrust of the engines and the Radio Control inputs from the user, and sending information about the current simulated position and speed.
  • The Physics Simulator which calculates the physical forces on the craft and applies them.
  • The User Interface which displays a lot of information about the craft as well as the internal controller.

The low level flight controller and network communication code is written in C++.  Much of the high level logic is written in a visual language called ‘Blueprint’.

User Interface

From the GUI User Interface, you can control:

  • The aerodynamic forces on the wings
  • The height above ground to air pressure curve
  • The wing span and aerofoil chord length
  • The moment of inertia
  • The thrust of the turbines
  • The placement of the turbines
  • The PID values for the internal controller

Result

It worked pretty well.

It uses Hardware-In-Loop to allow the real hardware to control this, including a RC-Transmitter.
In this video I am allowing the PID algorithms to control the roll, pitch, yaw and height, which I then add to in order to control it.

 

 

PID Tuning

I implemented an auto-tuner for the PID algorithm, which you can tune and trigger from the GUI.

 Hardware

I used two arduinos to control the system:

overview

And set up the Arduinos as so:  (Btw, I used the Fritzing software for this – it’s pretty cool).

neva arduino_bb(1)

 

And putting together the hardware for testing (sorry for the mess).  (I’m using QGroundControl to test it out).

And then mounting the hardware on a bit of wood as a base to keep it all together and make it more tidy:

20140822_202401.jpg

I will hopefully later make a post about the software controlling this.

ESC Motor Controller Delay

I was particularly worried about the delay that the controller introduces.

I modified the program and used a basic UFO style quadcopter, then added in a 50ms buffer, to test the reaction.

For reference, here’s a photo of the real thing that I work on:

The quadcopter is programmed to try to hover over the chair.

 

I also tested with different latencies:

 

50ms really is the bare minimum that you can get away with.

These are manually tuned PIDs.

I did also simulate this system in 1D in Matlab’s Simulink:

simulink_roll

A graph of the amplitude:

matlab estimated transfer function sin

And finally, various bode plots etc.  Just click on any for a larger image.  Again, apologies for the awful terseness.

Flash Furniture Website

/ John Tapsell / Leave a comment

I had an idea for website that would let you design what you want your kitchen to look like, while immediately getting a material quote for the work.  The idea is to act as a middle man between kitchen-fitters and customers, charging the kitchen-fitters a small fee per customer.

So I put together a flash website:

The actual furniture is based on the dimensions that the the company “Howdens” produces.  The 3D models and textures are entirely procedurally generated.  Getting the plinths and worktops to be calculated correctly took far more time than I’m willing to admit 🙂

The helper girl at the bottom is my 5 year old daughter.  I got her to point in different directions 🙂