Replacement electronics for the Quacker

The current electronics are not robust enough. In moving the components over to the new housing, things are coming apart, soldered connections are failing, etc. There’s not really enough space in the box so everything’s crammed in and nothing has any strain relief so the cramming-in is causing failures.

There are two options:

  • Replace the current nest of wires with a custom-made shield.
  • Replace the entire thing with a standalone Arduino – one board that includes all the supporting circuitry

Either way, I think I should also move away from the two relays currently used to control the bang and the siren and just use transistors instead – I’m not sure why I didn’t do that the first time.

The schematic I have is not actually right as the indicator light has a voltage doubler to bring it closer to the required 24V. I should make a new one.

No data sheet for the central locking actuator and nothing much came up on googling. Attempted to measure peak curtent with multimeter that has no peak function… the highest value I saw was about 2.5A, so let’s assume 3A@11.1V. This probably requires a MOSFET to switch.

Siren is 350mA@12V according to the datasheet.

 

Improvised wet-vac

We have cats. And they piss in the wrong places. It’s very annoying.

Cute furry weeing Unit 1.0
Cute furry weeing Unit 1.0

Recently, a bit of a patch started to emerge in the hall. We cleaned up the best we could, but it’s very hard to get it all out, and the regular abuse of this bit of carpet had started to mount up. I thought a good wet-vaccuming might be the solution!

Unfortauntely wet-vacs are expensive, and big, and we only have a small flat. Also, improvising one seemed like a fun project for a Saturday afternoon. In the end, it only took about half an hour!

To start off, I picked up this ultra-cheap vacuum cleaner from my local Argos. It was only £20 then, it seems to have gone up. I also grabbed some big tupperware boxes, which we needed anyway.

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I cut the hose, leaving a little length to connect the box to the cleaner, and marked a hole on the lid of the box.

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I drilled the hole using a conical bit (which is one of the best things in the universe) and stuck the hose in.

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And then did the same with the other end of the hose:

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Ta-dah! Wet-vac. I thought I’d have to seal the hoses in but it turned out that a friction fit was fine – perhaps because the hose is quite flexible plastic, and the low pressure probably causes them to bulge a bit. I hoovered up a mug of water and all seemed well.

To the hallway!

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I made up a weak solution of floor cleaner, poured it over the evil cat patch, and scrubbed a bit. And then hoovered it up. (Note: under the carpet, the floor is concrete, so I wasn’t too worried about the neighbour below.) It worked fairly well:

I didn't save the PSD, so I can't make the text brighter.

Judging by the naaasty water that came back out of the carpet, less bad stuff is there than before:

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The water trap was not perfect, however:

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I think quite a bit of water ended up going through the motor. This suspicion was a few days confirmed later: after about half an hour of total wet-vaccing, it gave up the ghost. An autopsy revealed significant corrosion:

Corrosion

If there is ever a version 2, I will design the water trap differently. Learnings:

  1. When the vac is on and sucking air, there is a lot of disturbance in the water in the trap. It goes all over the place. This tupperware wasn’t nearly tall enough to guarantee enough clearance between the top of the disturbed water and the tube connecting it to the cleaner.
  2. Even with a better designed box, I think some water will always get through. It would probably be sensible to have a second water trap, or to add some foam baffles to reduce the amount of atomised air getting into the motor

Mysie thought box the vacuum cleaner came in was the best bit. She might be right.

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Notes on making a tricopter

Making a Quad- or Tri-copter is a project I’ve been tempted by for a long time. Ever since I got an RC heli, which I’ve since abandoned. The Heli was too hard to fly, and there wasn’t much motivation to persevere — having learned, all you can really do is aerobatics, which I’m not very interested in. A quad, on the other hand, is easier to fly and much more flexible: I could add cameras, sensors, telemetry, code it to do interesting things, etc. And lots of people have done this so it’s an easy thing to Google about.

The tricopter seems the most appealing so far – interesting build, nice balance of stability and maneuverability.

Interesting things so far:

I’ll update this post with more stuff.

Design notes

Frame

I thought there would be maths (shuddder) about frame size vs prop size vs motor power and all that sort of thing, but this FAQ says the main considerations are maneuverability and stability. A smaller frame is more nimble but less stable, and vice versa.

Since I’m a beginner, a larger, more stable frame seems like a good idea. It also seems plausible that it’s a better platform to develop from: I could perhaps add bigger motors/props to increase lift, for example, without having to change the frame. (Guess).

The RCExplorer v2.6 arms are 480mm, which seems a good place to start. I think I’ll also use the frame design from RCExplorer as it’s well proven and designs are available.

Some tips from this thread:

  • Prop wash over the arms causes vibration. Try to mount the props at least as far above the arms as the prop radius.
  • ESCs (unsurprisingly) work better if kept cool. Perhaps worth mounting them in the prop wash?

Props

Not much headway on this yet. RCExplorer (again!) recommends the smallest props you can as smaller props are lighter and have less air resistance, making them more stable.

Trial and error seems a sensible approach here, as long as the prop doesn’t overwork the motor.

Control board

From this table, Arducopter seems both very functional and reasonably priced. Lots of resources for it too.

Beyond (advanced) features (that I won’t need for ages, if ever), I still don’t have a clear idea what the pros and cons of the various boards are, though. For example, noob-friendliness, ease of repairs. The KK board does have a screen to guide you through the process, which might make it preferable to start with. And it’s cheap, so easy enough to replace with something more feature-rich later.

ESCs

There are so many important bits of information in the big tips thread that it’s not really worth reproducing them here. Just go read it.

Use NiMH mode even for a LiPo battery, because the low-voltage mode engaging (to protect the LiPo) causes flips (eek).

Motors

RCExplorer uses these for the v2.5. Mentioned elsewhere too. Is 750kV enough? What are the considerations?

Batteries

TBC

Video

Not planning to do this immediately, but from reading so far, there is stuff worth noting.

Apparently, the only legal frequencies for airborne video tx in the UK are 2.4 and 5.8GHz. These are very short wavelengths with poor penetration and are limited to 10mw and 25mw respectively. This sounds totally dreadful, but people do claim that they can get decent range (up to a mile) with a high-gain antenna. A significant number of other people are (unsurprisingly) completely flouting the law. It does seem a bit OTT.

Obtaining an amateur radio licence makes no difference as they do not include airborne transmissions (out of date but probably still accurate: Amateur Radio (Foundation) Licence Terms, Provisions and Limitations Booklet BR68/F, para 2(6)). Possible exception: higher power 5.8GHz transmitters at 250mw rather than 25mw.

It seems that to stay legal you can only use 2.4GHz or 5.8GHz. My transmitter is 2.4GHz and I don’t want to replace that with an (obsolete) 35MHz transmitter. So it seems it’s 5.8GHz or bust.

Telemetry, sensors

I’ll think about these later.

Transmission of telemetry data is permitted on 433.05 to 434.79MHz up to 10mw.

 

Making PCBs at home

I’d like to start making PCBs instead of using stripboard. Stripboard is horrid.

I think the easiest approach for me will be to expose the board to UV through a transparency printed on an inkjet. Because there’s an inkjet in the house, and I think that’s how we used to do it at school.

It seems fun to make my own UV box for this, from LEDs. Useful things about that:

On the subject PCBs in general:

I will need:

I already have a printer, Sodium Hydroxide and acetone.

New project: suitcase Airsoft prop

I’ve still a few bits to do on Captain Quack, but in the meantime, I wanted to jot down some notes about the next project. I’m going to make a defusable suitcase prop to use in Airsoft games. I’d like it to be quite flexible: it should suit lots of scenarios, from being the main event in a filmsim to being an objective in a quick skirmish game.

It should look the part. This will be used in skirmish and filmsim, not milsim, so I think there’s some licence to make it look a bit “Hollywood” rather than being realistic (which would be dull). Google image search found some useful inspiration.

Of course, it also needs to play well, so I’ll make a prototype to test the basic idea. This will consist of a small box with connector for pyro, a removable lid which will expose some cabling of various colours, and a countdown display. In the game, the timer will be set to a countdown value appropriate for the scenario. Players will have to defuse the box before the timer reaches zero. When the timer reaches zero, it will detonate the pyro.

Players will defuse the box by cutting the right cable: there will be many to choose from, and their number and purpose can be selected to suit the game. Some may be dummies. Some will defuse the box. Others will immediately detonate the pyro. (Possible future enhancement: wires which add or remove time on the countdown). Wire cutters may be next to the box, or may be issued to (some or all) players.

In the game, players will need to find out which cable they need to cut. Or, if they’re nearly out of time, take a chance! Again, this can vary to suit the scenario. In some games players might just be told which is the right cable. In others, there may be a puzzle they need to figure out. Or they might need to find intelligence, which could be a separate scenario.

As before, this will be an Arduino project and I’ll build something pretty after testing the game on the prototype. Feedback and ideas welcome!

MCOM – version 1 – Captain Quack goes bang

So, the MCOM worked great. Much fun was had by all, and the box (due to its rather odd siren) was christened: Captain Quack.

It’s a 600x400x400 box built from softwood and 6mm ply, with aluminium edging and stainless steel corner covers. I was pleased with the look. Inside, I had a steel-lined chamber at the bottom of the box with vents between it and the outside. This is where the pyro was loaded, and also where the siren was mounted so that the sound could escape better.

The upper chamber contained the rest of the electronics, and enough space to put other game objectives if desired. There was a removable panel at the bottom so that the steel-lined chamber could be accessed to set the pyro. This was secured using cupboard magnets that I enhanced with some neodymium disc magnets for a more secure hold.

Unfortunately, I forgot to take a picture of it when I finished, and during its second outing, a slightly-more-powerful-than-I-expected pyro did a bit of damage.

Captain Quack took some damage

Anyway, hopefully, you can tell from that picture how it looked before its misadventure!

It performed really well. The first game day there was an annoying bug where the timer would stop itself running. I’m pretty sure that the cause was a short, or some kind of capacitance effect. The box housing the electronics is a metal one, and although I lined it with tape, I think the pins at the bottom of the boards were poking through. Adding better insulation to the boards solved the problem.

The housing for the electronics, with controls mounted

After that, the electronics have worked flawlessly: before and after the pyro that blew it to bits 🙂

For the next version, I’m going to make the steel lined chamber more robust by getting rid of the removable panel and securing the top of the chamber more robustly. The top was completely forced off its mounting: the force of the explosion managed to push out eight 3/4″ screws, as well as blowing the ends and bottom off the box. To secure those, I’m going to screw them to the frame rather than pinning them. I’m also going to replace the vents at each end with a mesh screen.

Panels removed to fix damage. Main siren visible at the left, and the new mesh vent at the right.

Hopefully, a more robust steel lining combined with more ventilation at each end will allow the pyrotechnic’s gasses to escape at each end without doing any damage.

The pyrotechnics are quite serious

Since seeing it in action, I’m also going to add some new safety features: there’ll be a new piezo siren to sound when the explosion is 10 seconds away, the button will be disabled at that point, and we’ll brief players to stand clear when they hear the change in tone. I’m also going to add warning notices at the ends of the box.

Introducing: the airsoft M-COM station

I’ve been playing Airsoft for about a year now. And I’ve been a gamer for a lot longer than that. I was a big fan of Battlefield 2: Bad Company. One of the game modes from BF2BC is Rush – where one team of players has to destroy a box of electronic gear (the M-COM station), and the other has to defend it.

The gameplay is pretty simple – attacking players have to approach the box and hold down a key. That activates a timer, which detonates the box when it expires. While the timer is going, the box sounds an alarm and flashes a light. If defending players can reach the box before it explodes, they can hold down the key to disarm it. This felt like an pretty good thing to take out of computers and put into an airsoft game!

I thought through some of the gameplay and chatted it over with Viking Airsoft (my regular site) and decided it would need to be a bit different from BF2BC.

The game’s timer is quite short – about 30 seconds. This wouldn’t work at all well in an airsoft game. In order to start the timer, the attacking team would have to hit all the defending players. Those players would then need to walk to their base in order to regenerate their life and come back into the game. That’s a round trip of a few minutes, at least. So, in order for them to have a chance to disarm the M-COM and win the game, the timer needs to be long enough for them to regenerate and get back into the game. 10 minutes is probably about right.

In the game, you hold the button down to arm the box. I decided that for the first version, just pushing the button should be enough. Holding the button down would make it quite hard to arm and disarm the box, as keeping good cover and avoiding being shot is rather harder in real life than in a game. This should make the game more dynamic and avoid situations where it’s so hard to arm or disarm the box that players get frustrated.

With all that in mind, I decided to make a prototype to see how hard the electronics would be. I’ll write that up in my next post.

PS: Since starting the project, I’ve discovered that Gunman Airsoft have beaten me to it — they regularly run (awesome) M-COM games. Their approach is a bit different from mine, but definitely fun. Knowing that the game works has definitely spurred me on!