Carlitos’ Contraptions

I built a bedside table for bunk beds from a pile of wood I found in the garbage and some flat nylon rope.

The Main Goal
I wanted to build a bedside table for the top bed on a bunk bed but I did not want it to become a head-banging hazard for those sleeping under it. So the table has to be rigid as seen from the top and mobile for those under it. My solution: a folding bedside table.

The Materials

• Wood (six 6.8 cm x 60 cm pieces)
• Flat nylon rope
• Three cabinet-door stoppers
• Three bolts with nuts
• Staples
• Varnish

Putting it Together

By stapling the nylon rope to one side of the wood pieces (as shown in the picture below) they become linked in a way that is rigid when applying force from the top, but can be folded easily if the force comes from the bottom. Note that the staples must be very close to the wood’s edge, otherwise, the structure will become a sort of ladder since the pieces can freely hang from one another. The original SVG is also available for download for those wanting to have more precise measurements.

In order to attach the bedside table to the specific bed it was meant for, I used some more nylon rope and another piece of wood.

The wood is used to hold table since it fits very tightly under it (as seen on the right) and the rope acts as an extra safety in case the table should fall (as shown below). Of course, I wanted to have the least destructive approach for fastening the table to the bed, otherwise, I would have only used screws. Also, I added a slight upwards curve to the table by using rubber door stopper in the middle joint so the objects stay on the table instead of going sliding down. Finally, I applied a think coat of varnish so the table is easier to clean and nicer to the touch.

An advantage of this table is that it can be folded away so it is not very intrusive and of course does not hurt anybody’s head. The downside, on the other hand, is that if it is folded while something is sitting on it, the object might at best get smashed or at worst go flying around the room.

Project

I found a nice breadboard in McGill’s garbage a while ago and decided to convert it into an electronics bench. My main goal was to have a powerful power supply with regulated outputs combined with a breadboard and some useful connectors so I can build circuit prototypes easily. Also, I needed a new bench power supply since mine was lost in the Lunar Excavator shipment.

Materials

• A nice breadboard found in the garbage
• A computer power supply
• An ATX motherboard power connector
• Two LEDs with resistors for current limiting
• A switch
• Some cables

Putting it Together

I wanted to build a modular system so I can replace the pieces easily, especially the power supply (since it comes from an old computer and may not work for very long).

I connected a switch and two LEDs (actually, my switch comes with an integrated light so I used only one LED) to the PS ON, 5V SB, and PWR OK pins so I can have an indicator of the power supply (PS) being plugged-in (D1) and another for the PS being turned ON (D2). The diagram below illustrates the connections.

I also connected the 12, 5, 3.3, 0, -5, and -12 V lines to the bottom-left banana connectors in order to have easy access to the power lines. Now, I can connect any ATX power supply to the box and it will work, which makes replacing a defective power supply very easy.

After making the electrical connections, the switch and LED(s) have to be mounted to the box by drilling appropriate holes.

This was a fairly easy build, with the only difficult part being to find the appropriate materials in the garbage.

I may add a USB hub or some USB connectors as well in order to have more ways of connecting things to the box.

Project, Tools

I received many questions about the circuits driving the LEDs in many of my projects, especially for the Iron Man’s repulsor.

LEDs are pretty neat devices. You make some current flow forward through it and you get some light as a result. Nevertheless, since they are diodes, they can allow an infinite amount of current to flow (which in practice means a lot of current) and this can be problematic since, as any electrical device, it cannot handle that much current. In order to prevent them to pass too much current, a current limiting circuit is required (usually implemented as a resistor in series).

When you buy an LED, you (should) get two very important parameters, the voltage drop across them (say, V_LED), and the maximum continuous current (I_LED).

So, for the trivial case where we have a battery (V_bat) in series with a resistor (R) and an LED, the value of R must obey the following inequation:

If you decide to place many (say, n) LEDs in series, the inequation becomes:

Finally, if the LEDs are in parallel (as is the case for the repulsor), the inequation becomes:

This result can be obtained by applying Ohm’s law (V= RI) to the circuits described above. The proof is of course let as an exercise for the reader .
This page has a very nice LED calculator which makes life really easy when calculating resistor values: alan-parekh.com/led_resistor_calculator.html

WARNING: the repulsor circuit may cause the LEDs to fail sooner or later. I’ll post an update as soon as I have one. Thanks to Tim for the hint.

For those interested in the repulsor circuit, below you can find a diagram describing it. It is the same as the circuit with many LEDs in parallel but with a potentiometer added to regulate the light intensity. The only requisite for the potentiometer is to be large enough to attain the dimmest light according to your needs.

Project

I found a little stool lying around in the garbage lately and decided to give it a new life. It turns out the stool comes from some kind of hospital and is actually pretty old.

In order to refurbish the stool, I simply applied a coat of anti rust spray paint, oiled the screw holding the seat, and put in some new rubber feet. My grandmother, who was visiting (from Argentina) was kind enough to make a new cushion for it.

This build was really simple but resulted in a nice, modern looking stool for almost no cost.

Project

I was lucky enough to help my friend Stephen and his team to build a lunar excavator to participate in the Regolith Excavation Challenge, sponsored by NASA.

We put lots of efforts and many hours to get the robot done in time and we managed to get it running before it had to be shipped to California (from McGill University in Montreal).

Unfortunately, despite the awesomeness of the lunar excavator and the fact that it was going to completely own the challenge, the UPS shipment went wrong and the robot could net get to the competition on time. Now the fight with UPS has begun to get a full reimbursement (~2000$) and the robot back.

UPS incompetence aside, I worked in putting all the electronics system together in the electrical box. This meant, I had to build two boards: one for the power management (transforming the provided 24V into a 12 and 5V in order to power the many devices and turning the latter ON and OFF), and one for the logic (interfacing the main computer with the various motor controllers and sensors).

This task was done using perfboards and lots of solder since we did not have enough time to consider designing and fabricating proper PCBs with nice places for all the components.

Note the nice (and very classy) wood finish of the electrical box interior as shown in the picture.

I will not give away any details about the excavator since it will compete next year, provided there is another Regolith Challenge.

Project