For this year's Big Bang Fair, Rapid's Education Manager Chris Calver (right) collaborated with TV presenter Stefan Gates on his live show. The brief: to build a sugar-spinning, Malteser firing, thermal imaging robot. This is the first part of how he did it.
I think it is fair to say that this is one of the most bizarre robot
builds I have done but at the same time, also one of the most interesting.
Stefan Gates, perhaps better known as The Gastronaut, is a television
presenter, author and live performer who describes himself as a Food
Adventurer. To find out more about Stefan, check out his
website.
Stefan does a live stage show at the Big Bang Fair each year. His shows
are well known for providing an energetic, exhilarating yet hugely educational
experience and 2016 was no different. This year’s show was entitled
Gastronaut
and the Quantum Mechanical Chocolate Factory and Stefan decided it would be
cool to incorporate some robots into the performance.
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| Stefan Gates & 'Shirley' |
I got chatting with Stefan at the Bett Show in January and we
worked out a couple of ways that we could incorporate a robot into the stage
show. What we needed was a robot that could fire Maltesers, spin sugar and give
the audience a thermal imaged view of the world ...
It was harder than it sounded. This is how I built the robot that came to be known as 'Shirley' ...
The design
Stefan had pretty much left the design up to me. There were some basic
criteria with size and he also sent me a knife steel which needed to be
incorporated for the sugar spinner. Other than that, I was on my own. I wanted
to make the robot look as much like a large
VEX IQ robot as possible and I was
also keen to use the VEX IQ motors to make the wiring simpler. However, the
size of it and the fact that it needed to travel well and be relatively
maintenance-free meant that I would build the bulk of the frame out of VEX
aluminium and screw it all together with nyloc nuts.
The first task was to screw together the basic metal chassis so that I
had a basis to design all the rest of the parts to. It’s made from 7 pieces of
standard 1x5x35 hole VEX aluminium C-Channel and bolted together using nyloc
nuts. I also bolted a couple of pieces of IQ plastic to the chassis just to
check that it was going to be easy enough to interface the VEX IQ motors with
the VEX EDR metal.
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| The chassis |
Next job was to take the knife steel and work out a way to rotate it at
approximately 45rpm as requested by Stefan - this forms the sugar spinner
of the robot. It’s fairly weighty so I needed to come up with a way to support
the steel at either end of the handle.
Conveniently, the knife steel that Stefan provided has a nice square
profile on the handle which will make it easier to clamp to and rotate it. The
clamp part is mounted to a VEX IQ turntable.
I then built a frame to house the whole of the handle of the steel and at
the other end of this frame is another IQ turntable. I drilled a hole in the
centre so that the blade of the steel will protrude through and this will
provide a perfect rotatable support.
What to do with the camera?
Next, I
started to look at how to house the thermal imaging camera on the robot. The
camera I am using is the
FLIR i3, partly because this is what I had to hand and
partly because it can be used as a USB webcam. This will allow us to connect it to a
laptop and ultimately, to the large screen at the back of the stage. A quick
test at my desk was looking good so I set about working on a way to mount it on
the robot.
Now the FLIR i3 is a rather unwieldy beast and not really the ideal
camera for this application. However, I like a challenge so I stuck with
it!
It’s too big to use as one of the robot’s eyes, so I decided to give
the robot a wide mouth and have the camera there instead. This also means I could hide the long handle of the camera in the neck area.
The first job was to build a frame around the camera that held it
securely and could then be used to mount it to the robot. Once I had a secure
frame, I then needed to make it a little bit more like a face so added some
eyes using VEX IQ wheels and temporary eyebrows. I’ll change them for coloured
plastic later and also add a mouth once it is fixed to the robot and everything
is working.
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| Shirley's thermal imaging mouth |
So back to the sugar spinner - I now needed to mount this to the robot. The whole thing is pretty weighty so I decided I'd use 2 VEX IQ motors using a fairly substantial reduction gear ratio to raise and lower the arm.
The shoulder joint pivots on an axle with two 60-tooth gears mounted to
the frame of the arm. These 60-tooth gears will be rotated by a 12-tooth pinion
giving a gear ratio of 5:1 at the shoulder.
To make sure there was plenty of space for the head mechanism at the
top of the robot, the two motors that would actually control the raising and
lowering of the arm were mounted in the bottom of the robot’s body. The two
motors are connected together with a pair of 36-tooth gears and then chain and
sprockets are used to transfer the rotational movement up to the shoulder. This
uses an 8-tooth sprocket at the motor end and a 32-tooth sprocket at the
shoulder end giving a first-stage gear ratio of 4:1. This means the total gear
ratio of the whole mechanism is 20:1 which will give it plenty of grunt.
When in use, the arm needs to stick out at 90 degrees in front of the
robot and when rested it sits at approximately 20 degrees so with the 20:1
ratio, it will take approximately 2.3 seconds to raise and lower.
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| The sugar spinner |
Look out, here
comes the maths part!
A VEX IQ motor has a maximum output speed of
100rpm. Our gear ratio is
20:1
so the speed at the shoulder is
100/20 = 5rpm.
5rpm is equal to
1800 degrees per minute
(360 x 5) or
30 degrees per second (
1800/60). Our arm needs to move through approximately 70 degrees in total and
70 / 30 gives us
2.3 seconds.
In reality, it will be a bit slower than this as the motor won’t hit
100rpm under load but it will be fast enough for me!
Now to make the head move.
It doesn’t need to rotate left and right,
just raise up and down so that Stefan and his team can aim the camera at an
object in front of the robot. I needed to keep the motor out of the way of the
handle of the thermal imaging camera so it didn’t block its path as it swings
through. To do this, I created a chain of three 36-tooth gears. The first gear
in the chain is driven by a 12-tooth pinion which is connected to the motor. The
third gear shares an axle with another 12-tooth pinion forming a compound gear
which drives a final 36-tooth gear giving a total gear ratio of 9:1. We don’t
need much torque here so I’ll control the speed by slowing the motor down in my
program.
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| About halfway through the build |
In the next blog I will tell you how the rest of the build went, and what happened when Shirley took to the stage!
