Thursday, November 28, 2013

LED Dress

About six months ago my Sister told me that she was going to a Taylor Swift concert and that she would love me to make her an LED enhanced outfit to wear. Taylor specifically asks her fans to get out their glowwy things such as cellphones so I took this as an opportunity shine... Ahem.

A quick check of the conditions of entry didn't say anything against going to concerts covered in red LEDs.

Skip to the middle if you just want to see the final result.
What could possibly go wrong?

Having done this kinda thing in the past I was only too keen to do something similar. As she is sometimes wheelchair bound due to having dysautonomia I decided that her wheelchair had to feature in the outfit too.

She had a red cocktail dress that was to be the basis of the creation. We ordered some cheap waterproof red LED strips, and LED controllers from eBay along with a rather chunky LiFePo4 RC flight battery from Hobbyking.

Battery, Power
electronics and controller.

The battery is 19.8V and 4.5A/h and I use a switchmode buck converter to supply a constant 12V dc to the LED controller.

LED Controller: $4.80 from eBay, Bargain.

Sudden realisation as to
how much of my hair
has fallen out recently.
At the end of my most recent contract with VUW I organised to make a trip up to my sister's place and begin creating...

 I measured out the the strips to fit the bodice and the skirt. Mum then stitched the strips on with invisible thread.

Ready for wiring.
I then began the rather painstaking task of stripping and soldering some 22 joints to each of the LED strips. The strips are just paralleled LEDs, that is they all glow at the same brightness.

Due to using hot glue to reinforce all of the joints, I made doubly sure to test every joint and avoid nasty dark strip surprises later. The dress is impressively bright with all the strips running on 12V (about 25W)

With the strips all wired it was time to test...

25% power.
100% power.

It would be rude to not do any light painting with a creation capable of such ludicrous luminous flux, the results are rather breathtaking.

Battery Belt:
Sketch of the net for the pouch.
Needing a place for the rather large battery and the electronics to live I set about measuring everything up and devising a "net" or pattern for the battery pouch. The design is a basic "cereal box" with a lid that's held down by velcro. The sketch roughly shows the dimensions with a 10mm seam allowance around the edges.
Not everyone uses vernier calipers for sewing projects.

I then transferred the sketch to the fabric stiffened with iron on interfacing. Then cut out all the notches which give the corners clearance.

It's red on the other side.

After a bit of fun with the sewing machine the pouch was done. I made a velcro belt from the same fabric.

Battery pouch with electronics hidden inside.

Update Friday 29th November: I have received an email from the touring company and they are going to allow the dress at the concert! Thank you Frontier Touring!
Update Monday 2nd of December: My sister got into the concert with no trouble at all and had a great time :D

Patiently waiting for the doors to open.

Wednesday, November 13, 2013

Closed Loop CNC 4th Axis.

My friend has an Abene 3-Axis CNC machine, it's capable of lifting 1000kg on the table... Pretty grunty. I've used it for making Tesla coil parts, making custom camera accessories, and even teaching his 12 year old stepdaughter CNC programming.

Due to making such things as the centre plate for a twin plate car clutch, and because it's well cool. We decided it was time to build an addon rotary 4th Axis.
The controller, a Heidenhain TNC 155b which despite being as old as me is still capable of driving 4 servo axes with 1 micron positioning accuracy. It's even capable of 3D graphics!

 The controller outputs 0-10Vdc which is fed into a dc servo amplifier for each axis.

Left to right: XYZ

The amplifiers then output up to 100Vdc to the DC brush motors which drive the ballscrews on the axes.

The servo motors have a tachogenerator mounted to the opposite end of the shaft: This generates a DC voltage proportional to the speed of the motor. This signal is fed back to the servo amplifier for the speed control loop.

On the linear axes the position control loop is closed by use of linear glass scales which output a quadrature signal of two sinewaves back to the CNC controller.

The 4th axis is a little different. Mechanically it's a rotary table that would normally be used for manual indexing of parts on a milling machine.

The table is driven by a 1000w dc servo motor with a 3:1 belt drive reduction. When the servo is at maximum speed (3000rpm) the table rotates at around 10RPM, a little exciting when there is a large part in the chuck.

Due to the machine originally being only 3 axes with an optional 4th axis, we had to add an extra servo amplifier.

The servo we used has a higher voltage tachometer than the amplifier was designed for. Not wanting to allow many dollars worth of smoke out, I modified the "Personality Module" of the amplifier slightly to allow a higher input voltage.

If only humans came with such a module.

The mechanical loop is closed in this case by a Heidenhain rotary encoder which is connected to the input shaft of the rotary table.

The encoder is held in place by a large block of aluminium machined to suit. Inside there is a flexible shaft coupling between the encoder and the input shaft of the rotary table.

Electrically the 4th axis is pretty simple:
A small proximity switch is used for the initial homing of the axis on startup.

All the connections are made inside a tiny electrical enclosure, all the holes were CNC machined of course :)
The lid carries the encoder connections.
The base carries the motor and
tachogenerator connections

All the parts are mounted to a 12mm thick aluminium base plate that was also machined in the CNC.

Mounting bracket for the servo motor.

It took a couple of evenings working till way past midnight but the result was well worth it.

The video below shows a test piece being machined with the 4th axis mounted horizontally and then the clutch centre plate being machined vertically.

Using a touch probe to set the X zero point.
Drilling the edge of the clutch centre plate.

Monday, November 11, 2013

Opening Lego Mindstorms batteries with a CNC milling machine.

Working for Victoria University of Wellington, we use Lego Mindstorms for teaching some of our robotics papers as part of our Bachelor of Engineering. (yes we get paid to play with Lego)
The Mindstorms battery packs have been wearing out lately. In the interests of being environmentally friendly we are repacking them with cells from Battery Space.
The cases are held together with aluminium rivets which have to be drilled out to get inside.

With around 20 battery packs to open: I wrote a quick program on one of my friend's CNC machines to do the drilling for me. Each pack took less than 30 seconds to open as a result.