Projectiles - Building a blow gun with laser sight

I thought I'd build a blow dart gun with a laser sight.

It turned out to be a total success.

It works well, and is much more fun than regular darts of the non-blown variety.

I started with a couple of pins, some string, some cotton, and a thin pipe. A broken car aerial works well, so does a pen casing. Even a drinking straw works at a pinch. The longer the better, and it's best to avoid flexible things as your pipe. Drinking straws tend to be a little less accurate.

I started by piercing the string so I had four strings stuck to my pin.

 I taped up the strings so they wouldn't move when I started to wrap them.

This next bit is really important.

Add a loop of cotton running the length of the pin.

Take some cotton and wrap it tightly to make a binding along about a third of the length of the pin.

I also made one where I used electrical heat shrink instead of cotton binding. It worked well, and was much faster to make, but didn't look as nice as one with binding.

Trying to tie off  the end of a binding is difficult unless you have that loop we added.

To finish your binding, pass the loose end through the loop.

Then pull the back of the loop all the way back. This will draw in the lose end, and secure it by tucking it under itself... under the binding.

That's really important string tech. As long as you plan it beforehand and add that loop it's easy, but without the loop, it's next to impossible.

 The end result looks something like this.

Next I took another pin and frayed the string.

Wool would work better, but I didn't have any.

When it's fully frayed, it looks like this.

You can us it like this, but it was a little slow, and not very accurate.










I trimmed mine down a bit.











The point of the tail is to create drag so it flies straight, and with the sharp end up the front where it belongs.

If you have even one thin strand longer than the others it can cause trouble.

A long strand will make your dart turn off course a bit, and can also get stuck between your lip and the tube, resulting in a blowing noise but no shooting.

An easy way to trim it is to put it into the blow pipe and cut any excess with scissors.

Next, I found my container full of prototyping plastic. I explain it in this post about it's possible use in making hand made fishing lures, but basically it's stuff that gets soft at 65 degrees centigrade or so, and sets hard once it cools.

Next, I got hold of a laser pointer ($15 or so), then it was a simple matter of heating up some prototyping plastic, and wrapping it around both the tube, and my laser pointer.

I added three screws that sit through the plastic so I can tighten them against the laser to adjust where it points in relation to the tube. That way, it's easy to adjust and make certain everything lines up properly.



I shot some video while I was sighting it. I placed the laser sighted blow dart gun in a clamp, and repeatedly shot it, and adjusted the screws to get it more accurate. A simple matter of firing, then moving the dot to the same spot as the dart hit.

Stirling engines - Slow motion balloon power piston

I made a few adjustments to my little tin can Stirling engine. It now spins twice as fast, at a rate of around 210rpm. Not that that means much because the more flame you put under it the faster it goes. But it's around twice as fast as it was originally. Quite a success as far as bettering a terribly inefficient Stirling engine goes.

If you ask me.

The main adjustment I made was to replace the two sections of shaft that make contact with the supports. The original shafts and bearing surfaces were made of galvanised fencing wire.

I replaced them with a thinner grade of stainless wire. Actually it's welding wire, and is the same stuff I use whenever I mention stainless wire in the construction of my fishing lures or anything else on the blog.

Pictured here in this uncomfortably framed, but interestingly red image, is the new wire, the old wire, and a match.

The thin stainless wire makes a huge difference. It even runs without the 8g counter weight now.

The counter-weight is there to mirror the weight of the displacer, so without it, the power piston has to lift all that weight on it's own.



With the counter-weight and a minimum sized flame, it can now tick along as slowly as only 32 rpm.

Stately.

To run as slowly as 32 rpm, I found it also needed a small drop of very light lubricant (fishing reel/sewing machine oil). But it's important to note that the shaft for the displacer - the one that goes through the small hole in the can, should not be oiled. The oil burns, and leaves a sticky residue which will stop the engine.  As seen by the improvement by the slight reduction in friction, the smallest extra friction will kill these little engines. Use graphite, or just leave it with nothing.

If you did lubricate the displacer shaft, it's also possible that oil or Vaseline could get into the displacer container, and being flammable, might eventually find it's way to igniting if everything was just right.

Everything is very rarely just right, and a Stirling engine is a very safe thing to make and use because there are no pressurised containers. The making involves some sharp bits of tin can, and should probably not be built by kids, but as a finished item, it's as safe as any small candle is, so probably qualifies as relatively child friendly.

Lets say... As child friendly as a birthday cake.

Anyway, it looks like this in slow motion (sorry for the poor picture quality)...

[edit from the future - Opps, for some reason the video wasnt dropped into place.] Here it is...




Even more stately.

It's currently clunking away on my desk, running at around 60rpm on these two little flames, and has been doing so for an hour. One flame is about the size a birthday candle, and the other is around half the size of a birthday candle.

My point is it isn't using much heat compared to the last version.





I find it's sounds...

oddly soothing.



K-chunk K-chunk



120 Things in 20 years thinks that if ever I disappear, it might be because I'm off on a Stirling engined bike trip around Australia... in slow motion.

Stirling engine ver 2

I made a few changes to My little home made Stirling Engine.

Change is always required when your engine seizes after only 55 seconds.

This one ran until the plastic bits caught fire.

Much better...

The original displacer popped itself to bits when it got hot enough, so this new version has a different design that's open to air travelling through it.

The autopsy also shows why my little engine stopped so suddenly. There is only around a quarter of an inch of air above and below the displacer when it's at it's extremities, and the bottom popping off made the displacer touch the bottom of the can it was in.



I replaced the can surrounding the displacer because I had to use a can opener to get the displacer out, and reattached the power piston balloon.

In the process of building the new displacer can, I discovered a new way to drill a hole that suits my personality perfectly.

You punch a hole with a nail, then rip a circular hole with pointy nose pliers in much the same way as opening an old style tin can of fish that the eater would open with a key.





If you aren't old enough to know what I'm talking about it, count yourself lucky and get on with it. You haven't missed a thing.

I drilled a few large holes in the top and bottom of the displacer, and packed it full of stainless steel, kitchen scrubber pad.

Apparently this works, and acts as a thing called a regenerator.

A regenerator can often be found on a Stirling engine and acts to store heat between the hot and cold sections as the air moves between the two.



The regenerator material collects heat from the freshly heated air inside the can the displacer is in. As the heat is displaced from the hot section to the cold section, some heat is removed and stored in the material. This is a good thing, because we want the cold side of the equation to be as cooled as possible. When the cooled air returns to the hot end, it picks up the heat it dropped into the regenerator on the way through, making it heat up more rapidly.

It's not by magic that the heat knows when to sit and when to be picked up, just that the air is hotter on the way up from the heated section, and has cooled a bit at the top before coming back through the regenerator.

I put the new displacer in it's tin can, and threaded it's wire through the bottom of the top can that holds the crank shaft.










In the process of de-constructing the first version, I bent the shaft a little, and it never ran quite as smoothly again. The little Stirling engine took a lot more heat to get it going this time, but I'm not sure if it was due to the new design of the displacer, or just due to the fact that every thing was a bit warped.

Friction really kills these things, so making sure the shaft is straight is a must.

It does run, and it's going a lot faster than the first version, but I suspect that has to do with all the extra heat from using a gas burner rather than a candle, and not some gain in efficiency.

I think I now know a little more about these interesting engines, and a little more about the universe in general, and I think I'll have another go at building a better one. I'd really like to make one efficient enough to run on the waste heat from my wireless router so it could just jig around all day for free.



120 Things in 20 years is finding the universe yet more interesting as a result of building this version 2 of my first, working, home made Stirling engine.

Electronics - Aquaponics - Demand feeder hits

It turns out the fish have been hitting the lever, but the switch hasn't been working.

It should be an easy fix, but for the time being, this will have to do.

[edit from the future - I fixed the switch and got a few proper hits with feed delivered within a few hours]

Aquaponics - Healthy silver perch feeding

It seems my fish have totally recovered from whatever it was that was troubling them, and are now growing so fast that I think it's time to eat another.

Since I lost a few a while back to some mystery problem, the remaining six have been getting more food each. And one in particular is getting much more than the others just because it's the biggest.

Eating more than your share is normally an excellent tactic for success in the wild, but in my little system, it just draws attention to yourself, and makes you stand out as a likely candidate for the plate.

They are now looking around for more food than I can give the system.

In aquaponics, it's important to fed the system rather than the fish. If you keep feeding the fish as much as they want, when they get bigger, there may come a point where the system cant process the amount of feed you are putting in. So always thinking in terms of feeding the system rather than feeding the fish is a good idea.

All you need to do is keep checking your water with a test kit until you start to see the first signs of it being overwhelmed. If you start seeing ammonia or nitrites, it means you have reached your systems limit. take note of how much feed you are putting in and then back off just a little to be sure.

Then never feed your fish more than this amount in a day.

If the fish want more feed than you can give them, it's time to eat some, or sell some if you are growing a variety not for the plate.

My fish look like this at the moment, with the biggest being around 25 cm in length.






120 Things in 20 years, where the greediest of your Aquaponics - Healthy silver perch feeding, tend to be the first to hit the BBQ.

Electronics - DIY waterproof switch build

It's a funny thing, but of all the wacky little inventions I've come up with since starting this blog, my DIY waterproof switch is the one I'm currently most proud of.

Here's how to build one.

I spent a long time trying to figure out a nice material to make a water proof, domed button out of.

I searched all over the place for ages until I decided to make myself a drink and found this inside my soft drink bottle.

I figured it would be perfect.

It already looks a little like a button.

I cut a 20mm hole in the end cap of the 90mm PVC tube that will house the electronics package for the demand fish feeder.

I needed to create a dome shape by pre-tensioning the gasket so I started by sticking the lid under the project temporarily with some tape.

This would allow me to press the button from the other side and hold it in place.

I added a large ball bearing to introduce a dome shape, and held it in place with vice grip pliers.

And the drink I'd made earlier.

And a box marked "Adjustable head magnifying glass".

Presumably, packaging for a device used to magnify heads.

I glued it in place and drank my drink through a straw until the glue set.












I figured with the ball bearing giving pre-tension, the glue should hold the gasket in it's new bubble shape to some degree,.

And it did.

This is the finished product from the inside.

Now when I mount a small tactile switch behind it, I should be able to press it from the outside so I can keep the electronics safe in a water proofed section of PVC.


It even works (if you can call that colour selection working (I was in a hurry))....





120 things in 20 years  Electronics - DIY waterproof switch build


All button pressing by Mrs 120ThingsIn20years. 
Mrs. 120ThingsIn20years is highly skilled at pushing buttons, and in the interests of domestic harmony, this should never be attempted at home.
Only one soft drink bottle was harmed in any way during this video production.
My drink was delicious 

Electronics - DIY water proof switch

Here's my home made water proof switch working, but I have to go out to dinner and don't have time to explain my switch.

And it isn't really a home made switch, just a DIY water proofer.

It looks like this, and I'm very proud of it...





120 things in 20 years - Not just an Electronics - DIY water proof switch that I'm very proud of

Aquaponics - Self cleaning swirl filter

Some stuff is better than other stuff.

This test is more like other stuff.

But it does illustrate the kind of thing a swirl filter might do if it were designed a bit better.


The first scene shows water entering through the thick black pipe on the bottom right of screen. The water exits the pipe via an elbow that directs water to the right so that a gentle whirl pool is set up.

You can see that the solids (these are real fish solids from a sieve I put under the inlet to the grow bed) do indeed collect in the centre and once they are there, they quickly sink to the bottom. Much of the stuff that looks like its going down into the standpipe (black centre) is actually an optical illusion. 95% of that is too low to be sucked in, but just appears distorted by the lensing that occurs with the water shape at the top of the tube. In the final product, a bell would sit over the top, so that wouldn't be happening, but that's the exit pipe back to the grow bed, so that's where we want the solids to go anyway.




After the bell siphon magically appears (I must learn how to do better scene transitions), we see the siphon kick in and most of the solids get sucked in, to return to the grow bed.

I add the same solids back again after collecting them with a spoon from a sieve.

The clear plastic tube on the left is where clean water would be drawn off to feed the NFT tubes. Water only exits via that tube for a few seconds at the top of each cycle. The length of time that water flows can be varied by the flow rate allowed through the tube. If you have a flow rate that takes a lot of water, it takes longer for the siphon to kick in. The exit flow could also be adjusted by simply moving the tube down a little from the rim. I placed it high because my little bucket was never going to be deep enough, so I was trying to get the most out of what little depth I had.

All in all, I guess this test was a success, even though it didn't work as well as I would have liked.

I Think it works well enough for me to have a go at making a bigger, better one.

Aquaponics - The bullwinkle sequencer build

I thought I'd put all this in one place to make it easy to link to.


Some of this is covered in previous posts, but it will be easer to follow if its all wrapped into one post.


The aim here is to make a device that will transfer water from an aquaponics fish tank, or sump tank, to different grow beds in turn. This means you can avoid dry fish. A condition fish hate.


There are existing methods to do this (I've made two other versions myself), but this is the simplest and most inexpensive way I could come up with. It also looks like being very reliable, and could probably be made from scrap. 


The device works by creating a free moving but balanced tube that fills with water. There are holes in each end to let the water out, but there is a float inside that restricts the water in an interesting way. 


When the tube is empty, the float rests in the hole, and blocks it. When a pump on a timer is switched on, the tube fills until it becomes top heavy. The device then tips, and the float drops out of the hole that is now tilted up, and comes to rest on the water until the pump is turned off. The float then settles in the hole at the other end of the device, and the process is ready to repeat.


So the float in this case is used, sometimes as a thing that floats, and sometimes as a thing that sits on the bottom, and blocks a hole. I wasn't completely certain that I understood the universe in this respect but thought it should work. I testing it like this...





Then confirmed it was worth building with this proof of concept.



Which worked a bit, but the float got stuck on my professional brown tape sealing technology.


But I made a proper one. It's called a Bullwinkle sequencer, and it looks and works like this [Edit from the future - When you watch this next video, make sure you have captions turned on, there is a stack of extra info in the captions]...

To build one, you need some PVC parts. I used 90mm storm drain fittings...


You will need...


a T-junction
2 short lengths (50mm or so) of 90mm tubing to fit your T
4 end caps
a 500mm length of 90mm tubing


You will need a ping pong ball, a drill, a length of stainless steel or wood to act as the axle for the device to pivot on, and a way to cut PVC tubing. I used a hacksaw and an electric jigsaw.


I also used a stainless steel ruler, but any long thin weight with a hole for the axle to go through would work.


I cut two holes a bit smaller than a ping pong ball, and used a hole cutter saw for this as described bellow. Another way might be to drill a hole and then enlarge it with a file. It might also be possible to buy a PVC component that is an adapter for one size pipe to the size down from it. This might negate the need for cutting holes at all.

To start with, drill a hole in your T-junction from both sides as shown. 


This will be where your axle goes through. 


Another, perhaps better method might be to glue two washers where I have drilled the holes. This way you could avoid the holes and therefore avoid have a metal bar running through your T-junction. With the washers, a bar could be placed into the washers from each side to achieve the same result. The washer would act as a seat for the axle.


I've used an iron axle for this demo because I had it handy, but its probably better to use stainless or plastic or even wood to avoid contaminating the water and harming your fish unless you use the washer method mentioned above. If you used the washers, the water wouldn't come into contact with the axle at all.

I used some lids from a powdered sports drink container for the flow control caps, but normal PVC end caps would be fine.


The only reason I used these is because I had them and didn't have the end caps.


These caps control the flow out of the device, and as such, it's important to drill the correct size hole. 


I was planning on testing this with my very tired little pump that only puts out 70LPH so that is why the holes are so small. These holes represent the exit flow from the device, and need to roughly allow the flow of the same amount of water that your pump delivers.


The device is quite forgiving with different flow rates, but you still need to make these holes so that they drain water at roughly the same rate as water comes in from your pump.


For this reason, I would recommend you drill a small hole to start with, and only glue them in place after you have established they are correct. It might even be possible to make an adjustable one, but I'll talk about that a bit later.

The flow cap fits over the cap that hold the ball. 


It's important that there is enough clearance, and that the ball can seat freely in the hole in the float seat cap without hitting the flow control cap. To this end it might be useful to add another pair of spacers (a short length of 90mm PVC.


I didn't bother with the spaces. but I would if I wanted to glue it all in place and not have any leaks. You actually need a spacer here to make a proper join between these same diameter parts.

I cut the holes for the ping pong ball with a hole cutting set I bought for around $7. It looks a little like this. There is a central drill bit and some different sized rings that are made of saw blade.

You clip the required sized saw to the disk attached to the central drill bit, and you are all set to cut a hole.

I can now make PVC eggs

I cut holes in each end cap so that a ping pong ball would sit neatly in them. These need to be a reasonable fit but it doesn't matter if they leak a bit. 


Any leaks just flow into your grow bed and only for a few seconds before it tips.

It might be possible to add rubber seals to stop leaks, but I wouldn't bother, even on a real world device I was intending to put into use.

PVC tubing cuts really well with a standard hacksaw, and I cut Two short sections (around 50mm long) of 90mm PVC tubing to act as joiners and spacers from the T-junction to the end caps.


The final assemble order looks like this.


T-junction
50mm spacer (with the ball in it)
Float seat cap
[This is where the optional spacers would go]
Flow control cap (with seeds written on it)




The length of those spacers isn't critical, but they are needed to make the device more forgiving, and to fit the end caps to the T-Junction. When the device is flowing freely, and adding water to the grow bed, the height of the water in this tube (defined by the length of the spacers) gives rise to a condition where the water level finds its own comfort zone. It's important for your water to be comfortable. It does this by regulating it's pressure by it's height in the tube. Remember the tube is sitting on an angle once its committed to a side. If there is more water flowing in than flowing out, this makes the water level rise within the tube. This could be a bad thing because it would overflow if not for an interesting fact. 


When the water level rises, the pressure at the exit point also increases. This means that, within reason, you can vary the amount of water flowing in, and the system will cope. A higher water level in the tube, means higher pressure, and therefore higher flow from the exit through the flow control cap. This is the bit I'm most proud of. The longer the spacers, the more forgiving the device will be. You still have to match the hole in the flow control cap roughly so that it will cope with the input from your pump, but the spacers make it so that you don't have to be accurate.

The size of the hole in the float seat cap determines the maximum flow that can pass through the system. 


These holes are around 25mm but that is only because I'm using a ping pong ball as a float. 


If you needed a bigger flow, all you have to do is get a bigger float, and cut a bigger hole. It might also be possible to use a PVC fitting that reduces from one pipe size to another smaller pipe size, rather than drilling holes at all. 


I found large foam balls at a craft store, but you might find them at a fishing tackle store, or even inside a Christmas decoration if you do Christmas where you live. A child's toy ball might also work. Ask first. The last thing you want is a cranky child when you are trying to make a water diverter.


Almost anything can be used as long as it's fish safe. It doesn't really need to seal all that well because any leaks just flow into one or the other grow bed. As soon as the device tips, the float is no longer acting as a seal, so any leakage not only goes to your grow bed, but it only lasts a few seconds.

This is what it looks like from the outside.

Next we need to make one of these. This is the extension gutter, and is there to bias the weight.


This bit is also very important to have, but it doesn't need to be all that accurate. I didn't measure any of my cuts or drilling on this prototype and it all worked first time. Even without being glued together. Its actually the pressure applied by this gutter than held the entire thing in place.


When you first start the flow, the ball is sitting at the bottom, under water, held in the ball seat cap hole by water pressure from above. If the ball displaces enough weight of water, the device will get top heavy when it fills, and tip as required. If the ball is too small, and the device is on say a 45 degree  angle, water might start to flow from the hole in the flow control cap at the top end, before the device has become top heavy. If it never gets top heavy it will never work. The extension gutter holds water and creates weight in the section that is uppermost at this stage. This means that, as far as the water is concerned, the tube is always longer on the side that's in the air. All the water on the down facing end drained away ages ago, so the extra water held in the gutter creates the desired top heavy weight bias, and decisively tips the device to switch to the other grow bed.


I made my gutters quite long, because I wanted to run my Bullwinkle sequencer, so that it would only rock 20 degrees or so. I would stop it going further by placement of the gutters that would take the water to the grow beds. This would mean my very tired pump would only need to pump water to around 150mm higher than it does now.


I think that if the gutters were shorter, it would need to be allowed to tip to a greater angle to hold enough water to create the top heavy bias required. A steeper angle might mean the sequencer would have to be raised higher and the pump would need to work harder. But then again it would be shorter so who knows. 


Only a small fraction of the length of the gutter fills with water before the device tips when it's operating to the angles shown on the video. I didn't experiment with changing the gutters because it worked the way it was. 


Basically, the gutter helps to make a Bullwinkle sequencer more forgiving of different operating parameters.

The gutter was made by cutting a 500mm length of 90mm PVC down its length.

This is done so you can slide a 90mm pipe over other 90mm fittings.

Then I made two cuts in the middle about 120mm apart that went approximately half way through the PVC pipe.

I was very casual and did all this by eye, but I guess if you were building one to use for ever, you might want it to look a little neater.

I'm not so good with neat, so I'll leave that bit up to people who are.

This cut out needs to be just big enough to fit the T-junction. It would be easy to make bigger if needed.

Next, I drilled two holes at the bottom of the cuts, to allow me to get the jigsaw in.

I cut the sections out and removed them.

You could use tin snips, or perhaps even a sharp knife or scissors.

Pry apart the gutter a little and force the T-junction in. 


Make sure you have already fitted the spacers, and float seat caps. 


I left the flow control caps until last.

Keep forcing the T-Junction along the cut gutter.


Remember none of this was glued, so it doesn't really matter. I'd leave everything un-glued until it was tested. Partly I left it unglued so I could pull it apart and take photo's, and now that it's in pieces I'll just reuse the parts for something else.

Until it falls into place.


Now all that's left to do is add the axle, and the flow control caps.

I also added a stainless metal ruler when I put the axle through. 


When the device has finished it's cycle and the pump is off, the ball drops down into the float seat cap's hole. Because the ping pong ball is so light weight, the device can almost come back to a balance position. This could give rise to a condition where, say because of the way the water came in a slight angle, it might make the same side trigger twice in a row. By the addition of the ruler, the device stays where it was when the pump was switched off. Perhaps a better way would be to add a marble in a sealed tube*, or a sealed tube filled with water. This could be attached on the side or underneath running the length of the device. All that's required is that there is a weight to hold the device where it was when the pump turned off, and that weight will shift to the other side when the device tips. If the ball was heavy enough that would probably do. The ideal would be a ball that only just floated. 


Even the pig pong would be enough if you added the water right in the middle, and kept the device out of the wind.


As it is, if a bird landed on the device, or it was subjected to a strong wind, it might upset the balance.  It would correct itself, and it starts again from such a condition, but if it happened at just the right time it could make the device water the same bed twice in a row. For this reason I'd put it in a box and put a lid on it, if I was making it for real world use and cared for perfection.

Lastly, the flow control caps need to be put in place.


If it happens that the holes that seat the float are the correct size for your flow, these would not be required, but I find its always good to have a component that's easy to adjust and or replace to set your final flow. 










You could use a tap on the exits to set the exit flow rate, or you could make two holes in 2 disks and rotate them so they don't quite align to make the size of the exit hole adjustable.


It might also be of use to mount the exit hole high. This might trap some water once it was all glued in place and negate the need for the ruler or marble tube, to bias weight and hold the Bullwinkle sequencer in the position it was in when the pump stopped.


If I was making one for real use I would definitely explore that before committing to the ruler, although the marble would be pretty easy to implement. Simple is good though.


As mentioned, this Bullwinkle sequencer is designed to switch sides every time a timer turns off the pump, then turns it back on again. But it can also be used with a pump that is always on. The only difference is that you need to adjust your flow with a little more accuracy. If the flow matches the holes in a way that allows only a tiny amount more water out than is coming in, your Bullwinkle sequencer will gradually drain and eventually the float will rest in the draining hole, and it will fill with water again, and tip to the other side. The time it takes between swapping sides, is set by the time it takes for the tube to empty and thus, the time it takes for the float to block the outlet.


 It turns out that it's not as difficult to set up as you might think, and I had no trouble making it work. As long as you can adjust the flow going in, or adjust the flow coming out, its very easy to make work.


As far as I can tell, this device is an original design. 
Its my intention that this design should be freely shared with the world. 
I ask that if you make a design based on this, that you also make the improved design freely available to the world. 
That being said, feel free to make, it duplicate it, improve it, sell it and profit from it, or do whatever you wish with it. 


Also, if you make one, please let me know as I'd love to see it use. 


I would really enjoy some feedback on this one. Suggestions, critiques, derisive laughter, whatever. It's as big as my "how to" handmade fishing lures - how to get the most out of your printer. And like the fishing lure post, I feel there is a little more room in my head after getting it out. 


I hope it's useful, and thanks for reading.




*thanks for the marble idea mofish (idea suggested for a previous sequencer design seen here)


[edit from the future - There is some additional material on sequencers. ]