PlotBot: Building the Gondola

Next stage of the build is to work out how to hold the pen. Some people call this the gantry or holder, I’ll be calling mine the gondola.
I decided to use lollipop sticks for this, they have a similar length to whiteboard maker pens, reasonably light weight and at only 50p for a pack of 50 sticks and it was an obvious choice!


Clamping the Sticks for drilling

Having cut a few sticks down to size I then clamped them together to drill a thread hole through them using my trusty dremel.


Lining them up for gluing.


First one clamped down.

With the first side clamped in place and the wood glue drying things are starting to take shape.


Sides nearly finished.


And the finished gondola! look forward to a video of the first test draw in a couple of days . . . things are a bit shaky!

PlotBot: Building the Machine

With the research all done, I started thinking about how I wanted to build my PlotBot.
Having looked at the other designs, I found they were either mounted on a wooden frame and then a piece of paper is taped onto the wooden panel, or they draw directly onto a surface like glass or a wall. Given that the aim is just to make something that catches peoples eye, rather than making posters or drawings for people, I think the best course of action would be to use a whiteboard. I can get one reasonably cheaply, and the mounting is pretty much already sorted.

the Mountings

The whiteboard and mountings.

Once I had bought a whiteboard (600mm x 450mm) I started lining up the parts I had as to how I would mount them.
I had also bought 2 Pololu 1204 Stepper Motors and an Adafruit Motorshield v2 (AFMSv2). I did have a few concerns with these parts combined together, in that the motors only draw 600mA and the motorshield provides 1.2A per channel, therefore the motors might get a little hot if they start drawing more than they should – but we’ll see how it goes!

rough positioning

Roughly lining up the parts on a sheet of acrylic.

To mount the acrylic sheet to the whiteboard I used two of the mounts supplied with the whiteboard secured on the top of the sheet. These then hook onto the edge of the whiteboard, and the mounts on the side are adjustable to “lock in” the sheet to the sides of the board. Finally I decided to neatly mount the arduino and AFMSv2 in the center of the acrylic sheet.
Drawing up where to cut

Whiteboard Mounting     Arduino Mountings

IMG_20140813_134431     IMG_20140813_110556_1

I picked up two remote control car wheels at a local hobby store, along with 50m of fishing line, which would form the basis for my reels.IMG_20140819_220854

I found some nuts in the garage that fitted the inside of the wheel, and used Araldite (metal glue) to fill the gap around the stepper motor shaft hoping that this wouldn’t go wrong.



Araldite’s in, I was a little bit messy dripping it everywhere!

 With the luck of the gods, after leaving it 24 hours to cure I was able to punch the stepper motor shaft out of the nut, leaving a nice shaped hole. The advantage of this method being that I can very easily remove the reels and use the steppers in other projects.  


IMG_20140819_221038  IMG_20140819_221322

Now that I have the reels mounted on the steppers, I was able to complete the main build; mounting the steppers onto the acrylic sheet, and winding the fishing line onto the wheels – happy days!


IMG_20140903_141638  IMG_20140903_141609




Digibury Discussions

So the other day, for the first time, I went along to Digibury, a event for people interested in technology in the local area. At the monthly meetings you can normally expect to 3 different talks.

The Digibury Postcard

The Digibury Postcard (Slightly crumpled)

At this months meeting we heard from Joe Webb, a PhD researcher in Cultural Studies. He is conducting an ethnograph about how “computing professionals” have learnt to use computers. He has started to see some very interesting generational differences in how people learnt to use the computers.

Next up on the schedule was a talk from Deri Jones, from SciVisum.
At SciVisum they specialise in load testing websites and web applications. From the data that they collect and analyse they can advise a business’s technical team so that they can adjust the companies website to be more efficient and capable of coping with the expected load. It also means that SciVisum can advise the less technical directors as to if there is a something that the companies technical team can do when their website has a fault.

The final talk of the night was from Chris Atherton, a user experience architect. She was talking to us about the recognition rules that humans apply to the world around them, for example that a chair has 4 legs and a back, or that a wheel is circular and has spokes. She then asked that we apply these rules to showers and to microwaves, and we all came to realise that these products do not have any standard user interface. Eventually after some discussion we even decided that showers do not offer enough control for the temperature of the water, only cold or hot, whereas microwaves offer too much functionality above and beyond heating a dish for a set amount of time.

All in all I really enjoyed the evening of talks, and am looking forward to next months set of talks on interfaces.

The PiBow Case

After all the festive activities, I have a new case for my Raspberry Pi, the PiBow. Found at, it is a durable acrylic layered case for the raspberry Pi. The case offers access to all the ports and the GPIO pins via a ribbon cable.

The PiBow finished and ready to use.

The PiBow finished and ready to use.

When completed it protects the main board and has engraving on the top and base to mark the function of each port.
Held together by 4 nylon bolts, it is very easy to modify, especially as there are expansion layers available for things like a camera module, VESA mount, and electronic prototyping.

The PiBow Case for my Raspberry Pi is finished

The PiBow Case for my Raspberry Pi is finished

PiBow - Step 7

PiBow – Step 7

PiBow - Step 6

PiBow – Step 6

PiBow - Step 5

PiBow – Step 5

PiBow - Step 4

PiBow – Step 4

PiBow - Step 2

PiBow – Step 2

the RPi placed on the PiBow

the RPi placed on the PiBow

The first part of the PiBow

The first part of the PiBow

the Base of the PiBow case

the Base of the PiBow case

the Raspberry Pi as taken with the new camera

the Raspberry Pi as taken with the new camera

Solving Quadratics

So to start off a new area of discovery I have decided to start to learn Python.

To start off this undertaking I downloaded Python 2.7.3 from python/download and started to play around with IDLE, python’s Integrated DeveLopment Environment (IDE).

As a project to work on to learn this new language I decided to make a simple console application that try’s to calculates the value of X for a given quadratic.  To do this it will use the quadratic formula


So to do this I first need the values of a, b, and c as per the formula.    Image

for example a = 1, b = -9, and c = 20.

The first step logical step was to cut the equation into 3 chunks:

  1. The Discriminant (Δ); b^2 – 4ac
    1. sqrB = pow(b, 2)
      AC = 4*a*c
      Delta = math.sqrt(sqrB – AC)
    2. the “pow(x,y)” function returns the first term to the power of the second, i.e. b^2
    3. the math.sqrt is a function of the math module which square roots the contents of the brackets, or to use the technical name, parentheses.
  2. The Numerator; -b +- √Δ
    1. NumeratorPlus = -b + Delta
      NumeratorMinus = -b – Delta
  3. The Denominator; 2a
    1. Denominator = 2*a

Then with the necessary components the values of X can then be calculated by:

XPlus = NumeratorPlus / Denominator
XMinus = NumeratorMinus / Denominator

and then be outputed on the screen using the print command:

print (“Your answer is, X = “), XPlus, (“Or X = “), XMinus

notice the comma’s after each component which are needed.

And so the final step was to allow the user to enter in values:

print (“Please separate the quadratic equation into aX^2 + bX + C = 0”)
a=input(“Please Enter the Value of a : “)
b=input(“Please Enter the Value of b : “)
c=input(“Please Enter the Value of c : “)

The “input” function is important as it prints the given prompt to the output and then reads in the data entered by the user and assigns it to the variable.

This is different to the “raw_input” function which is not syntax sensitive.

And so the final code looks like:

import math
from time import sleep

print (“Please seperate the quadratic equation into aX^2 + bX + C = 0”)
a=input(“Please Enter the Value of a : “)
b=input(“Please Enter the Value of b : “)
c=input(“Please Enter the Value of c : “)

sqrB = pow(b, 2)
AC = 4*a*c
Delta = math.sqrt(sqrB – AC)
NumeratorPlus = -b + Delta
NumeratorMinus = -b – Delta

Denominator = 2*a
XPlus = NumeratorPlus / Denominator
XMinus = NumeratorMinus / Denominator

print (“Your answer is, X = “), XPlus, (“Or X = “), XMinus



Converting a old PC psu

Most decent workbench power supplies cost quite a lot, at least for a student. Whereas I have and old computer PSU lying around, so I figured I’d have a bit of fun converting it.

Taking inspiration from various other projects including the DIY Bench Supply from TG’s builds and the RepRap PCPowerSupply I’ve ordered a MIC2941AWT from Micrel, this is a 1.2A Low-Dropout Voltage Regulator that I’ll be using to supply a variable voltage. In addition to the variable supply I’ll be including terminals for the voltages supplied directly from the old psu.