Portal Gun Build - Choosing Components Part 3

Portal Gun Build

Choosing Components Part 3 – Motion!

For Part1 – sound and Part 2 – lights see my Facebook page https://www.facebook.com/BlueRoseCosplay/

Ok so you want your prop to move. Well before you can choose what sort of motor you want to use you need to work out how exactly you want your prop pieces to move relative to each other. For the portal gun this is pretty simple, I want the barrel to slide in and out of the body of the device when it fires. I want the movement to complete in around 0.5 to 1 second. Now most motors spin, they don’t slide. The type that do slide are called linear actuators. This was where I looked first but I was unable to find one that would be fast enough and small enough for the task. They are mostly built for slow high force applications. So I went back to looking for a spinning motor.

Now if you have ever looked for little motors you might have been surprised by the number of different types available, and the jargon can be a bit daunting. The standard hobby motor of the sort you find in remote control cars and even your electric toothbrush is a dc motor.

Look familiar anyone?

DC stands for Direct Current which means a steady flow of voltage and a DC motor is one which will just work if you attach it to a battery as you would a lightbulb. AC motors are designed to be driven by the same type of power as your wall socket provides, though I wouldn’t recommend just plugging them in. This is Alternate Current and it has a constantly changing voltage that if you graphed looks like a wiggly line. It looks a little more complicated and it is, for hobby applications DC is fine and simpler.

AC and DC voltages

However there is a big but here which meant neither of these would do for me. These motors are either on or off. You can control the speed by changing the voltage you give them (e.g. two batteries instead of just 1) but you cannot tell them to move only a certain amount or turn to a certain position. So if I want the barrel to move outwards a little then inwards a little then stops, I need another option or a kind of doorstop for the motor when it reaches its final position.

Luckily there are motors out there that you can tell to move a certain amount; Servo Motors and Stepper Motors. Servo Motors have a thing called feedback which means you can even ask the motor what position it is currently in. However but you cannot tell servo motors to move more than a single full rotation. There is a way to modify them for continuous rotation but that involves taking the motor apart and doing some hacks and ain’t nobody got time for that! Actually it’s pretty simple but I'm too lazy and you still can’t tell them to move more than 360 degrees at once. Stepper motors can be told to move any amount but you have to assume the start position is where it was last and that nothing will block the motors while they turn. Still better than a DC motor so I bought one of them.

Even when you narrow it down to Stepper type motors there is still a lot of choice

Which one? Adafruit has a several page long article about choosing a stepper motor. It starts from the basics of how they work and goes into everything you might want to consider. You can find it here: https://learn.adafruit.com/all-about-stepper-motors/what-is-a-stepper-motor

For my abridged look there are four things to consider with stepper motors, speed, size, resolution and torque. Speed and size are easy to understand, although speed is often given in RPM. If I want the full portal gun motion to take place in under a second I need between 60 and 120 RPM. I got 50 because I had to compromise a little for size and torque but it's close enough.

Torque is a measure of the strength of the motor. The one I bought had 2kg*cm holding torque per phase. Sound a bit confusing? Well finding out how many phases sure is. Turns out it can be worked out with how many wires and whether the motor is bipolar or unipolar. This one is bipolar and has 4 wires so must have 2 phases. Adafruit’s article on stepper motors has more on determining how many phases your motor has. To understand the torque then just imagine you connected a 1cm (the cm in kg*cm) radius wheel to your motor. You put it on the ground and tell it to hold position (holding torque). You need to apply the equivalent of 2 kg * 2 (the number of phases), so 4kg to make it move. I want 4cm range of motion so I will use a 2cm radius wheel. So look at the measurement like 2cm*kg, per phase. It will be able to hold 2kg with this setup. Plenty to move the barrel of a portal gun but not much to stop it shifting if someone bumps it. I will still need to add a lock for when it is not moving. Note there is a gotcha using this maths, Stepper Motors have their highest torque at their lowest speeds so you will want to get one with more torque than you calculate to be just enough.

Finally resolution is how smoothly it will turn. A resolution of 200 steps per revolution is pretty common and will look smooth at almost any speed, lower resolutions need to be turning at faster speeds to look smooth.

All that and it eventually lead me to choose a motor: this one https://www.adafruit.com/products/324 

Since there was quite a lot involved in motor decision I will make the next post about driving it. I'm looking forward to testing it out!

Crayon Art - Rainbow Heart and Birds

Just a short post for now while I work on another project. This is something I did a while ago for some cheap colorful and fun wall decor to brighten up my room. I got three boxes of these crayola crayons because I was planning on more crayon art. A bit of PVA glued them to a canvas in a heart shape, getting the shape right was probably the hardest part and laying out the crayons before gluing them is pretty much a must. To keep the inside of the heart white I used a bit of paper cut into the heart shape and some blu-tack as a barrier to block melted wax.

Once the crayons were glued it was pretty much just a matter of applying the heat. I borrowed a hairdryer and a spare pair of hands from my boyfriend and set to work. It took a bit of experimenting but we found that the best way was to tilt the canvas and focus on melting a small section of the heart at a time. It is best not to angle the hairdryer along the crayons as this can cause small drops of way to fly off the crayon ends instead of running smoothly, although this effect can be used to advantage as well. A small stick can be used to draw the wax into a line and encourage separate tracks to form along with using the air flow from the dryer to push the melted wax along the desired direction. Also note this is best done somewhere with plenty of mess protection as wax can get everywhere.

And this is the finished result. So bright and cheerful!

But I couldn't stop there. After a heart I had to see what else I could make. I have a bit of a thing for birds so came up with these.

I peeled the wrappers off some of my leftover crayons and used the trusty pocket knife to cut them down to more manageable sizes for the smaller canvasses and then to cut them in half lengthwise. I sharpened the ends as well just to help the crayon flow more smoothly as it melted. I also saved the shavings, more about that later. These crayon fragments were glued along the base of the wings and tail. It is worth noting that the wax will spread a lot so the crayon fragments don't need to be very long. I think the longest one was less than half the original crayon length. More blu-tack and, this time, insulation tape was used to mask the areas where I did not want wax. some wax managed to seep underneath the insulation tape, this was just carefully scraped off and painted white but in future I would use a blu-tack barrier around the entire shape.

Using the blade of the pocket knife to gently start tracks as before and applying heat at the low setting finished the wings and tails. For the bodies I wanted a mottled feather effect, remember those shavings I saved? I sprinkled those into the body and head of the birds (making sure there were no oversize chunks) and melted them. The first attempt was the red bird, I used the hairdryer to blow directly on the shavings and they just melted and ran together except for a few chunks of yellow which took longer to melt.

For the blue-green bird I decided to try a different approach and hold the canvas up high and level and use the hairdrier to heat the canvas beneath the shavings.I also made doubly sure the shavings were very fine. This took a surprisingly short time to melt and didn't disrupt the already formed wings and tail. I am really pleased with the result.

As I mentioned there was quite a bit of wax seeping away from the borders but a little white paint and a couple more layers of white paint and it is barely noticeable. I also used a orange pen to mark in a small beak for the blue bird. One now hangs on my wall and the other went to the boyfriend for all his help and design input. They seem to remind me of fire and water respectively... maybe a light blue/white and a brown/yellow one should follow.

Just for interests sake, the heart is on a 40x50cm canvas, and the birds are both on 15x15cm canvasses.

Mini Cardboard Drawers

Hmm looks like I chose the wrong time to start a blog... next time I will wait until AFTER the 50% electronics assignment is due. But back on track now, and here *cue drumroll* is my first project.

I needed something to tidy up the mess inside my sewing box, solution - mini drawers. Cheap solution, fabric covered cardboard mini drawers! Basically it consists of four cardboard boxes like this:

They make awesome storage for all my thread (for the moment - actually I will need to up-size soon), and could be used to store any small items, from sewing notions (buttons, zips, ribbon scraps etc), to paperclips and similar stationary or even jewellery.

I started by making the three drawers, I used corrugated cardboard which was fairly stiff and not too thick, I wanted them to feel reasonably sturdy. An abandoned shoebox and another box which once held canned drinks were sacrificed for the cause. Here's the pattern I sketched out, any dimensions should do, but the important thing to add 0.5cm to the width and depth, and 1cm to the total height of all the drawers for the larger container box so that they fit snugly inside.

After making the small drawers I covered them in some fabric that I managed to score from my Nana last time she was cleaning up her cupboards. Nanas are good like that. I like the patchwork look of using different patterns for each part. I used PVA diluted with water and cut out a small finger hole as shown here:

I lined them with plain white paper cut to the same pattern as the drawers and trimmed to fit.

The large box was made much the same way, I initially left it unlined as the drawers hide the inside surfaces, but then I found I would often take the drawers out completely when using them. I had recently found some adhesive drawer liner at the closest dollar shop for just under $4 a roll and tried it out. Slightly easier to use than paper but it was still a little bit fiddly getting it inside which resulted in a couple of air bubbles. Flatten them out and you can hardly tell though.

 The finished article all fits together like this. I was surprised at how well the drawers work without anything to support them from underneath, I can slide one almost entirely out without the ones on top falling down. And aren't they cute!

Add an $8 picnic basket from the salvation army store and a few other miscellaneous boxes, and I have a much tidier sewing kit with room to grow. This is a big improvement on what was essentially a shoebox. After several years of shoebox storage I feel I am finally moving up in the world! I also picked up a couple of sewing patterns because at $1 each... why not.

Now I just need to think of a better way to store my fabric scraps...

 

For my first post I suppose I should give you an overview. Pretty much anything that involves making something pretty I will give a try. I sew a lot, I am very lucky to be the proud owner of both a sewing machine and overlocker, and make sure neither of them ever feel rejected. I have been making jewelery for a few years, and when the occasion calls I enjoy making handmade cards and scrapbooking. Unfortunately the last two don't happen quite so much now as in the decision for which piles of hoarded treasures I could bring to my flatting life the cards and papers lost out, though my scrapbooks have found their way here.

I also like to make art. Especially art that hides the fact that my drawing skill still have a lot of room for improvement. In fact anything that looks amazing with little skill required is in my opinion a winner. On this line crayon art is great, and Photoshop is pretty fun too.

I live in a tiny flat in a room that I would like to think screams personality, however it also often screams "you need a bigger room". While trying to think how to keep it all controlled I turned to trusty Google, and several hours later turned back with some severe crafter's envy but a lot of ideas. Now my room is a bit more manageable (at least until next study rush when everything will be covered in sheets of paper again).

I will try to document each project I do step by step with photos, however for some I will be migrating old projects from facebook and the depths of wherever they happen to be hiding. I hope you enjoy seeing what I come up with.