RS IoT Blockchain Demonstrators Part 2: Mechanical Build
The design and build of Internet of Things Blockchain demonstrators for Electronica 2018.
This series of posts looks at the design and build of a set of demonstrators for the bi-annual Electronica trade fair and conference, which show how blockchain technology can be used to create a secure, de-centralised data platform and more for the Internet of Things.
This post covers the mechanical design and build.
Each unit needed to clearly display its function and, where possible show the key components being used. As well as being functional they need to look attractive, be a suitable size and robust enough to transport to the exhibition.
The units needed to have a unified appearance so should have similar construction, colour schemes and consistent labelling.
Having used 2020 aluminium extrusion in previous projects it presented itself as a good choice for these demonstration units. It is often used to construct the frames of 3D printers, as well as display cases and exhibition stands. It comes with a variety of fittings, such as internal and external right angle brackets, which lend themselves to the construction of sturdy box frames. Possibly the best-known version is made by Bosch Rexroth (466-7219) . It comes with both 6mm and 5mm slots, which accommodate appropriately sized fittings, so you do have to make sure you match the extrusion and the fittings correctly.
Having decided on the frame material acrylic sheeting was the obvious choice to complete the construction. It can be accurately cut using a laser cutter, can be bent if needed and comes in a good variety of colours and clear options, so is ideal for display.
As previously mentioned, the working parts and key components that will be used — such as Raspberry Pi and Pi hats — would be on display, so these would need to be neatly arranged and cabled. Some controls would need to be accessible to the public and some would need to be hidden, as they are only for use by those managing the exhibits.
The units featuring a Raspberry Pi would also need discreet access to its SD Card.
Designs for the panels were carried out using Inkscape and prototypes were constructed in MDF and/or cardboard.
Cardboard is quick to cut and can be bent if needed. Where something more rigid is required, to test the mounting of heavier parts, for example, MDF is ideal. Both can be laser cut.
The aluminium extrusion to construct the frames is cut on a band saw with the appropriate blade. Any swarf on the cut ends of the lengths is then carefully removed using a fine file.
IoT Blockchain Units
There are five units in total. Two of them needed a 5-volt power supply, two required 12 volts, and one 24 volts. To avoid any potential mix up in power supplies the inputs were colour coded using Binder 720 Series connectors, that come in a range of colours and provide a good snap-in connection. The power input fuses and reset buttons were placed out of sight on the back of the units, using a consistent layout on each to make life easier for the people managing the exhibits.
A small hand wash sink was sourced from a catering supplier and this is supported on an aluminium frame.
Copper pipe and the waste trap are only there for appearance – no real water is involved. The flow of water will be represented by a string of addressable LEDs.
A Raspberry Pi is mounted on the base and power input and controls such as Blockchain Reset and Reboot are on the rear panel out of sight.
A front panel was added to provide the interactive element of the demonstrator, this features a big red button to press to trigger the leak, and LEDs to indicate flow of data to and from the Blockchain.
This unit possibly posed the biggest challenge. A number different ways to illustrate a collision were considered. Initially a pendulum of some sort was planned but it was felt this would be difficult to make robust and durable enough and could be complicated to construct. Then a catapult of some sort was considered, but again it was felt this had the potential to break easily.
It was decided to let gravity do the work and a ramp was constructed that a model car could be run down to collide with a stationary vehicle placed at the foot of the incline.
Various prototypes were built from cardboard to get the best angle for the slope and devise a way of keeping the vehicle on track.
Then an MDF and acrylic version was put together on an aluminium frame.
The screws originally intended to fix the model cars to a plinth for display were replaced by longer ones that went through a slot in the runway to keep the vehicles in place.
Again power input and controls such as Blockchain Reset and Reboot are on the rear panel out of sight.
In the final version matt black acrylic was used for the runway to give the look of a tarmac road.
The miniature conveyor belt we sourced to demonstrate the “Machine Failure” use case was also constructed from 2020 aluminium extrusion. It was the slightly different 5mm slotted version, so it was decided to use that for the construction of the case too.
Health and safety concerns given the conveyor belt is moving constantly while the unit is on display, lead to the decision to fully enclose this demonstrator.
On testing, it was felt that the continuous noise of the conveyor could become irritating under certain circumstances, so a run/stop switch was added to the back panel. This necessitated re-cutting the panel to add the appropriate hole and some re-wiring.
As this demonstrator was simulating a factory process, an industrial look and feel were achieved by the use some of the larger aluminium brackets and the exposed DIN-rail blocks and terminals.
A small 12-volt refrigerator is used for this demonstrator. This is mounted on 5mm acrylic sheet, which is in turn mounted on an extruded aluminium frame.
The rubber feet were removed from the base of the ‘fridge and the resulting holes left by the self-tapping screws that had secured them were used to screw it to the base.
After some experimentation, it was decided to mount the Raspberry Pi on a bent acrylic structure to give it a good viewing angle.
It was observed that condensation could build up in the base of the fridge, so the original fabric insulation on the temperature sensor cable was removed and replaced with heat shrink sleeving, so as to avoid moisture wicking along it and coming into contact with electrical components. A groove was filed in the door frame of the fridge to accommodate the sensor wire.
This was the only unit that did not utilise an aluminium frame. An Intel NUC mini PC motherboard is mounted on a laser cut acrylic base. A clear acrylic top supported by four 60mm stand-offs and features a fan with a dust filter, indicator LEDs and a reboot button. Two small upright pieces of acrylic hold the power input at the back and the Blockchain reset button at the front.
An additional Ethernet connection is provided by a USB Ethernet adapter that is sandwiched between the top and a small piece of acrylic held in place by 15mm stand-offs. The open back provides direct access to USB, built-in Ethernet and HDMI.
On all the units, apart from the Miner, some of the wiring runs under the base and is held in place by cable ties routed through holes in the acrylic. To avoid any risk of wires being accidentally snagged an additional base was added to the underside of the extrusion. This not only kept the wiring safe it gave the demonstrators a neater appearance.
Other posts in this series
The design and build of the demonstrators is covered over the course of a total of five posts:
- Part 1: Introduction
- Part 2: Mechanical Build
- Part 3: Electronics
- Part 4: Blockchain Network
- Part 5: Host Software