Broken tray gear wheel

The gear wheel is split, and has dropped off the motor drive. Here is a close-up of the gear:

Closeup of gear

Because the gear had shrunk a little (probably why it cracked), simply epoxying it together at the crack didn’t work: this made the hole too small and prevented the gear from going back on to the drive shaft. I carefully bored the hole out a tiny amount, then used epoxy to glue the crack and the gear back onto the shaft: I clamped it there for 24 hours.

Next problem was a broken belt for the platter itself: to reveal this involves removing a plate underneath the turntable tray:

Broken belt on motor

The belt had disintegrated, leaving a rubbery mess over the turntable and the motor capstan – removed fairly easily with rubbing alcohol. I ordered a replacement belt, and fitted it by feeding it through from the top of the turntable. It was a bit fiddly, but I’d read somewhere it was a nightmare – I didn’t find that.

Now the turntable tray moved in and out, and the turntable turned. The next problem was that the stylus trays were not moving. These trays move linearly across the deck. There is a clever mechanism with worm gears and a slotted metal disk and opto-transistors that move and detect where each stylus arm is. Here is the mechanism:

Stylus trays mechanism

Just visible at the back of the mechanism is a rubber belt – of course this turned out to be worn and was slipping on the motor and not moving the mechanism. I replaced it with a rubber belt I happened to have in my parts box and fit very nicely. Now the whole mechanism worked. Here is a video of it in operation, showing the switchover to Side B from Side A, which involves the turntable motor reversing direction.

The fitted stylii are by AudioTechnica. The Sharp part number is STY133.

AudioTechnica Stylus

Although the turntable now works, it initially played several LPs without issue, it has now developed a random periodic click/thump, almost as if the record is scratched. This is a little peculiar and hard to understand. To be continued ….

Sharp Optonica RP-117H and Sony CDP-X555ES

Anyway, here it is!

Figure 1: Celestron motor drive

After assembling the Celestron and fiddling about playing around and understanding the EQ mount, I realised that the supplied tripod was going to drive me nuts: it wobbled and swayed even if I breathed on it. I tried tightening everything up as much as I could, but it still wobbled – it was far too flimsy.

Figure 2: Celestron PowerSeeker 127EQ Newtonian Reflector

So I decided to make something a little more sturdy using bits and pieces I had in the garage. Here are the parts I collected:

• 1 Circular piece of 3/4″ thick plywood, diameter 24″ – base board
• 1 Circular piece of 3?4″ thick plywood, diameter 12″ – scope platform
• 1 5ft length of 4″x4″ wood stock – pillar
• 4 shelving brackets
• 4 3″ steel brackets
• 3 screw thread furniture feet
• 3 nuts to fit the feet
• 4 3″ lengths of 2 1/2″x3/4″ wood stock

Step 1:

Find the centre of the 24″ diameter circular base board: drill a pilot hole through the board there. Place the end of the 4″x4″ pillar upright at the centre of the base board, position the four shelving brackets against the sides of the pillar, mark screw hole positions in the base, and then screw the brackets in place on the base board.

Step 2:

Remove the pillar from the base board, turn the board upside down, then place the base board on the top of the 4″x4″. Drive a long screw through the board, into the 4″x4″, then drill a couple more holes nearby, and drive long screws into those, too.

Step 3:

Turn the board and pillar right way up, carefully supporting the pillar. Now attach the brackets to the pillar with screws, and tighten all screws very tight.

Step 4:

Take the four 3″ steel brackets and attach each to each of the 3″ lengths of wood stock with screws. Then loosely attach each combination to each side of the top of the pillar so that they are centred and level. These will act as spacers so that one can gain access to the nut at the centre of the EQ mount to tighten it.

Step 5:

Using a jigsaw, cut a circular hole in the centre of the scope platform board, of the same diameter as the circular part of the Celestron tripod platform (see Figure 3).

Figure 3: Celestron tripod platform, with new holes drilled at the top of each spoke

Step 6:

Remove the legs from the Celestron tripod, leaving the platform for the EQ mount, and put the threaded rods and nuts that secured the legs to one side. See Figure 3. Drill a hole through the top of each “spoke” of the platform: these will be used to pass the rods through and tighten the platform to the board.

Figure 4: The scope platform showing the spacers and brackets attached to the pillar

Step 7:

Place the scope platform board on top of the spacer/brackets, mark and drill pilot holes through the board into the spacers, and screw tightly in place. Then firmly tighten the brackets against the top of the pillar. See Figure 4.

Place the tripod mount on top of the platform, centre it, and carefully mark the positions of the three spoke holes, using an awl. Before drilling through, make sure that the positions are clear on the underside of the board, and wont foul any of the platform supports.

Step 8:

The platform board should be fairly horizontal at this point, but it’s not critical as there will be adjustable feet added to the base board. These will require captive nuts. Turn the whole mount upside down so that it is resting on the scope platform. Using the centre of the base board, and a protractor mark positions for the three feet at 120 degrees from each other, about 2″ in from the edge of the board. Find three nuts that will fit on the screw feet. Using e.g. a Forstner bit, drill large diameter holes just bigger than the diameter of the nuts, part way through the base board. Find a drill just smaller in diameter than the screw thread on the feet, and drill through the centre of the holes to the other side of the board. Test to make sure that the feet than be screwed in and out of the holes. See Figure 6.

Step 9:

Using a two part epoxy, glue the captive nuts into the holes, taking care that the nuts are centred and that no glue gets into the threads. Leave the epoxy to set. See Figure 5.

Figure 5: Captive nut and adjustable foot

Step 10:

Sand all surfaces, clean with a rag, and then spray paint your choice of colour. (I had a bunch of Rustoleum Navy Blue indoor/outdoor aerosols left over from another project, so I used those.) Leave to dry well.

Figure 6: Mounting the captive nuts and adjustable feet to the base board

Step 11:

Mount the Celestron tripod platform to the scope platform board, using the threaded rods and nuts that came from the tripod. Screw in the three adjustable feet at the bottom of the base board. The platform is now ready to use.

Figure 7: Painting the mount

Here is the finished mount (Figure 8) with the PowerSeeker 127EQ attached. There is a minor problem: the counterbalance for the scope touches against the scope board for low inclinations to the horizon. This will simply require the scope board to be reduced in diameter by taking a circular cut around it – but I haven’t bothered since the viewing area is surrounded by high walls anyway.

Figure 8: The completed home made mount, with Celestron PowerSeeker 127EQ

Hantek DSO8060

The screen can be saved to a .bmp file. Here is an example: this is measuring the output of a 416Hz triangle wave signal from a Droid X running my “AudioTool” application:

AudioTool output: signal and FFT on the DSO8060

This also shows the FFT (in blue). There are cursors which can be used to measure features of the channel signals or the mathematical functions, manually or automatically.

Overall, I am extremely impressed so far. The operation is very straightforward and intuitive. i shall be comparing it to my benchtop Tektronix 7844 in the next few days.

A couple of things I haven’t been able to work out: can the FFT data be averaged (the time domain signal certainly can), and how to change the vertical (dB) scale for the FFT.

The Metaloid Field Detector application on Android Market

The Metaloid application has about 20,000 downloads of which 31% are still installed, so about 6,200 active users. The AdMob idea is that you get revenue every time somebody clicks on an advert. Since adding this “feature” (I use the word cautiously), I have earned a grand total of $3.50 for a total of around 80 clicks on 117,000 adverts shown. I shall buy myself a Double Tall Mocha.

Here is the breakdown by day:

A couple of days later, we fired it up again, this time using scrap wood and barbecue charcoal bricquets. After a couple of hours or so it had reached a temperature of 550F. The outside walls of the oven steamed as the water evaporated away, and some hairline cracks appeared around the door – this is normal (they closed up when the oven cooled).

After removing the larger pieces of wood, and making enough space to cook a pizza, we cleaned the oven floor’s surface using a damp towel nailed to a long stick. That created a lot of steam! We were careful to remove all the sand and ash from where we wanted to bake – nobody likes a sandy pizza. Then we used some of Trader Joe’s fresh dough to make a simple pizza, and placed it inside – it cooked in a few minutes, and we had to turn it a few times to stop it burning.

(Normally we make our own pizza dough, but for this first experiment we liked the convenience of pre-made.)

The taste was amazing – especially the crust, which had a characteristic aroma and taste particular to pizza from a good Italian restaurant. There must be some chemical change associated with the very high temperature, that you don’t get in a domestic oven.

We cooked a couple more pizzas, and then removed all the charcoal and wood by scraping them out into a metal container partly filled with water. Then we put a small loaf of bread dough in to cook, closed off the door of the oven. It was ready after about 40 minutes. This also turned out to be delicious … with a slight hint of smokiness in the crust.

First pizza cooking – it’s only small

First we bought and laid 21 red bricks on a 1/2″ layer of sand, making sure to get them even and with small gaps. We could have just used the existing brick oven base, but we wanted something very flat, which it wasn’t. There’s nothing worse than catching your peel on an uneven surface when trying to extract a pizza.

21 bricks laid flat on a bed of sand

Next we marked out on the bricks where the wall of the adobe oven would go: both the inside and the outside edges, using a sharpie. We had bought five 50lbs bags of medium sand, most for the oven wall mix, but some for the oven mould – basically a mound of wet sand like a sandcastle.

The mound needed to be 16″ high, so we first cut a stick to that length and positioned it in a small mound of sand at the centre of the oven bricks.

Then we started to build a sandcastle around the stick, trying to keep the sides of the sandcastle as vertical as possible, and making sure that the sides followed our outline of the inside adobe walls we had marked on the bricks.

Once we had our sandcastle made (in the shape of a dome, reaching the top of the stick), it was time to go digging in the garden for subsoil – the stuff under the topsoil that contains the most clay. We dug about a 3′ deep hole and then extracted a wheelbarrow full of soil.

The clay soil needed to be mixed in one part soil to two parts medium sand. To mix it, we made a ring of four buckets of sand, and put two buckets of the soil in the centre. Then we set about sprinkling it with water and treading it all in to mix it. In fact we found that we had too much sand, and ended up using six buckets of soil to the four buckets of sand.

We checked that the mixing was good when a golf ball sized piece of the mixture, when squeezed tight, and then dropped from shoulder height, didn’t crumble when hitting the ground, but rather just squashed to an oblate spheroid.

At this point we were ready to apply the mud to the sandcastle former. First we placed sheets of damp kitchen paper over the former – this is so that, when we come to remove the sand, after the mud had been applied and set, we could tell when we were at the edge.

16″ measuring stick

Preparing to mix the clay soil and sand, on a black plastic sheet

The well trodden sand and clay soil mixture

We made an oven door from a piece of old wood. Shaped like an arch, it had to be 12″ at the base and 10″ high. We folded a sheet of paper in half, drew half an arch against the folded edge, cut along the line with scissors, then unfolded the sheet to use as a template on the wood, which we marked around the paper’s edge. Then we cut the wood with a jigsaw.

The door was placed against the front edge of the sandcastle, before we started placing the mud. Then we started packing mud around the sandcastle, being careful not to press inwards on the castle, and trying to maintain a mud thickness of 4″ all the way around. After we had surround the sandcastle with mud, we smoothed out all the bumps, and patted the surface down with a flat paddle made of wood, for an even finish.

Now we need to wait for the mud to dry – after which we will remove the door, and scoop out the sandcastle.

To be continued ….

Packing the mud around the sandcastle. Note the oven door.

Finishing the mud packing

The design I’ll use is based around an Arduino Duemilanove processor, and is called an AeroQuad. Here’s what I ordered, for a total of around $250:

Motors, Speed controller and Propellors

Four TowerPro BM2410-08T / 18A BEC / 9×3.8 Prop Combo

According to the HobbyKing table this motor should run at up to around 8900rpm at full voltage (10V). Plugging the size of the propellor (9 inches with a pitch of 3.8 inches) into this static thrust calculator, the thrust from each motor should be a maximum of 0.6kilos, so a total thrust of 4×0.6 = 2.4 kilos.

Battery

One Turnigy 2650mAh 3S 20C Lipo Pack

At around 11 Amps for each motor, maximum, the total will be 44 Amps. This battery should give a minimum operating time of (60*2.65)/44 = 3 minutes.

Radio Control Transmitter/Receiver

One Hobby King 2.4Ghz 6Ch Tx & Rx (Mode 1)

The “Mode 1″ refers to how the controls are laid out. Apparently in the USA, most pilots use Mode 2. Mode 1 looks like a more logical layout to me, and since I am not a pilot, is what I chose. The Transmitter/Receiver works at 2.4 GHz. One idea I have is to put an X10 RF Spycam I have on board the quadcopter: this also operates at 2.4GHz, but in analog, so there should be no interference. I also have an ICOM IC-R3 handheld I will be able to receive the X10 video stream on:

One Hobby King 2.4Ghz 6Ch Tx USB Cable for Win2000/XP

This interface cable allows the Transmitter to be controlled from a laptop/desktop.

Processor

Arduino Duemilanove with ATmega328

Sensors

One 5DOF add on board (X,Y,Z, Roll and Pitch)

One Dual Axis Gyro

The concept is that the sensors detect the position and orientation of the quadcopter, and the Arduino board runs software that uses this information, together with motion control signals from the Transmitter, to adjust the power going to each of the four motors. This in turn affects the thrust from each of the propellors, which produces the desired (or not!) motion of the quadcopter.