YAPP idea - MOB alert system

[AngusMcDoon]

25m is a problem

25m is the range at maximum transmitter power. There are 3 lower levels of transmit power configurable on the victim unit.

If two handed then then in the time it takes to go below press the GPS MOB button and get back on

Not required on this system. It records the last known position automatically and gives a range/bearing back to that location. Also it is intended to send a MOB message on a Seatalk system, although that is not tested yet.

Everything you say about MOB prevention is true. This is only a hobby project, although I will make sure it works properly to the best of my abilities.

 

[JohnGC]

So no countersinks with that method. I could use pan head machine screws, but not quite as neat. What is it likely to cost?

Cost depends on the material used, time to tool-up, time it takes to do the job (related to material and tool travel distance) and the quantity.

Create a DXF file of the design, specify the material and ask for quotes. Google "laser cutting" and check out fabricators & "engineering" firms local to you. Steels are easy to cut so cheap, plastics are done but you need to make sure the company you choose can do the matarial you select.

It is also worth noting that laser cutting combines very well with sheet metal folding and powder coating. As an example; I have a Netbook based plotter mounted on a sheet metal bracket I designed. The bracket is made up of 2 laser-cut and folded sheet metal parts and is powder coated. Made from mild steel, 1 off cost me aprx £50 including the tooling.
https://dl.dropboxusercontent.com/u/84858928/Tray%20folded.pdf
https://dl.dropboxusercontent.com/u/84858928/SAM_4761.JPG
https://dl.dropboxusercontent.com/u/84858928/Tray.pdf
http://www.shermaynes.co.uk/

If the material is thick enough, countersinking can be done as a separate process after cutting either by the fabricators or by yourself.

 

[nigelmercier]

>Doing some tests I have found that the range of the radio transceivers I tried is about 25m.
25m is a problem. ...

All good advice, but why is a 25m range a problem?

[Later] Note to self, check for a further page when replying

 

[Graham_Wright]

If you're thinking of machining a flat plate then you could also consider NC laser cutting. 2D only but very clean finish and very small internal radi. Lots of different materials can be cut now.

You couldn't do the sealing lip with laser;- as you point out, 2D only. For the other features - fine, but I couldn't compete with £6 even for quantities.

 

[AngusMcDoon]

You couldn't do the sealing lip with laser;- as you point out, 2D only. For the other features - fine, but I couldn't compete with £6 even for quantities.

If machining was the way to go then the lip would not be required assuming that the lid that comes with the box can be machined. It has that feature already. It would just need the LCD cutout, buttons, beeper and LCD bolt holes cut - 1 rectangle (rounded if necessary) and 7 round holes. I expect a hobbyist 3D router (that can be bought for £600) would do the job fine. What I need to find is someone who has one who would like to recoup a bit of the cost with a small amount of work.

If I could sell enough I would buy one, but I am limited by trading standards because of my lack of CE marking to sell "just a few" to interested hobbyists as open source kits, although they wouldn't say how many "just a few" is.

 

[AngusMcDoon]

Angus, I was thinking, a plugin to OpenCPN to drop a MOB marker when the alert goes off. I did a quick test on OpenCNP on Navigatrixsend in Shift+Space using the X11 TEST method (xdotool and xsendkey.c) but so far not working. I think a plugin would be be the right way to do it anyway. Any thoughts?

I'm not familiar with OpenCPN plugins, but if you investigate it, it could perhaps be something to incorporate.

 

[Graham_Wright]

If I could sell enough I would buy one, but I am limited by trading standards because of my lack of CE marking to sell "just a few" to interested hobbyists as open source kits, although they wouldn't say how many "just a few" is.

Are you sure about the CE requirement? I researched this for the MastaClimba and was advised that "as it was not a ladder - even one with a moveable rung" (!), CE marking is not necessary. The MastaClimba is defined as "an aid to ascending" and is not safety critical.

I think your MOB alarm might be in the same category?

 

[AngusMcDoon]

Are you sure about the CE requirement? I researched this for the MastaClimba and was advised that "as it was not a ladder - even one with a moveable rung" (!), CE marking is not necessary. The MastaClimba is defined as "an aid to ascending" and is not safety critical.

I think your MOB alarm might be in the same category?

It's an electronic device and virtually all such devices need CE marking. This one is also an intentional electro-magnetic energy radiator.

I had a very informative discussion with trading standards who were generous of their time considering I am a virtual non-entity to them. They said that commercially sold devices like YAPPs would need CE marking, most commonly for EMC reasons. The law states that it applies when "put on the market" in the EU, and they suggested that it was this phrase that has some flexibility that applies to what I am doing. They said that a hobbyist selling to another hobbyist is sharing a hobby, and not putting the device on the market. There's no hard and fast law on this, or even case law that they knew about, but by following a few guidelines they would be happy and would not prevent me (or many others like me) doing this kind of activity. These are the guidelines that together they suggested that indicate a shared hobby and not a business:

- open source and design
- unpaid community involvement in specification, design, advice, implementation, manufacture, test and distribution
- not my main or only source of income
- essentially non-profit making. Buying development equipment with any profit is allowed.
- small production numbers, although they wouldn't give me a definite number, but I got the indication that a few dozen small devices would be ok
- no advertising or marketing. My own website and announcements and discussion within interested groups of other hobbyists allowed.
- EBay selling to non-hobbyists would indicate a business and not a hobby.
- not creating devices that could fall foul of other legislation or certification, i.e. aviation related, powerful transmitter etc
- and probably in practice the biggy... not giving any purchaser any cause to contact or otherwise bother them, i.e. offer full refund if anyone is unhappy

In light of my contacting them for advice they indicated that this bode well for me if there were any problems or infringements as it indicates that I wish to act legally. They said that if there were any problems they would first of all advise or warn rather than prosecute to give me time to comply or cease selling. They also strongly indicated that these were just guidelines, not law, and a court would make a final decision if it went that far. So far, no complaints.

 

[nigelmercier]

3D printing works out at £6 a lid. I'd prefer a machined lid as I have to buy it anyway, ... The only online quotes I have had have a starting price of £600. I could buy a small 3D CNC router for that price and do them myself.

Have you done any research into this?

I've been thinking of buying a CNC router. If I had a project like this that I could use to subsidise the cost a little, I would go for it. Perhaps we could come to an arrangement ...

 

[KellysEye]

>All good advice, but why is a 25m range a problem?

I took it mean metres in which case a MOB would be out of range of the radio in 9.7 seconds if the boat speed is 5 knots and if the boat speed is 6 knots 8.1 seconds, if it's miles it is not a problem. If the transmitter is under water there will be no signal.

 

[nigelmercier]

>All good advice, but why is a 25m range a problem?

I took it mean metres in which case a MOB would be out of range of the radio in 9.7 seconds if the boat speed is 5 knots ...

That is the whole point!

 

[AngusMcDoon]

>All good advice, but why is a 25m range a problem?

I took it mean metres in which case a MOB would be out of range of the radio in 9.7 seconds if the boat speed is 5 knots and if the boat speed is 6 knots 8.1 seconds, if it's miles it is not a problem. If the transmitter is under water there will be no signal.

It's metres. At the lowest transmit power it's about half that. No received signal raises the alarm. Perhaps you misunderstand how it works.

 

[AngusMcDoon]

Have you done any research into this?

This sort of thing.

http://www.ebay.co.uk/itm/CNC-3040-...900?pt=LH_DefaultDomain_3&hash=item1e69827bac

I doubt it's really in Portsmouth and is probably as electrically safe as a dodgy sewing machine.

 

[JohnGC]

You couldn't do the sealing lip with laser;- as you point out, 2D only. For the other features - fine, but I couldn't compete with £6 even for quantities.

I have a customer who gets stainless plates laser cut. They are of a similar size to the MOB YAPP. I've just asked what they expect to pay, it's around £6 each if the steel is free issued and £10 ish if the laser cutter supplies the material. This is for 20 to 50 off including tooling, Ex VAT. So more than printing but not crazy. It's with these people who I have used myself for laser and folding.
http://www.lasercuttingfoldingmachine.co.uk/

 

[Rum Run]

This sort of thing.

http://www.ebay.co.uk/itm/CNC-3040-...900?pt=LH_DefaultDomain_3&hash=item1e69827bac

I doubt it's really in Portsmouth and is probably as electrically safe as a dodgy sewing machine.

I have done some research into these cheap desktop CNC machines for work use and the consensus seems to be that they are OK-ish mechanically but the driver board is pretty bad and needs replacement quite early. They are not thought suitable for professional use due to the unreliability, though if you had a full stock of spares and the knowledge to use them it might help.

Having given some though to the base unit enclosure design, I wonder about using a bought-in case with a a transparent lid so that the display is visible without cutting an aperture, thus leaving only holes to be drilled. Something like this -
http://www.rapidonline.com/Mechanic...Clear-Lid-115-x-65-x-40mm-7200-Series-30-5709
This one may be too small but it shows the principle. By using this type, then using panel-sealed buttons like this -
http://www.rapidonline.com/Electronic-Components/Black-Round-IP67-Mom-Switch-Solder-Term-78-1835 the base unit enclosure would be much better protected against drips and splashes.

Also I wonder if, in order to make sure the victim-unit triggers during a tethered MOB drag alongside the boat, making its' enclosure deliberately water permeable might cause the Tx to stop once it had become wet?

cheers

Rum Run

 

[AngusMcDoon]

I had an informative talk with people from here yesterday...

http://www.3dprint-uk.co.uk/

and they think that their process will be ideal for this application - accurate enough, sufficiently strong and a shape that will work well. They only downside is the plain white colour, but the material gives the best shape and strength results and it can be painted. They have a video of someone trying and failing to break a 3mm thick item with their hands; I am going for 3.5mm thickness. They will cost about £7.00 each in small numbers.

I have used transparent cases before and the visibility is not great, especially after a while as the outer surface becomes scratched.

When I finally get to making them I will be happy for people to take the boards with no case at all and mount them in their enclosure of choice for both the victim and central units. Just waiting for the PCB's to arrive now which will be a couple of weeks yet.

 

[VicMallows]

When I finally get to making them I will be happy for people to take the boards with no case at all

That's good to hear. I was starting to think that for most people the appearance of the unit was more important than the function.

 

[ShinyShoe]

3. I have included some water sensors to trigger the victim unit. This is because of the possibility of crew being tethered to the boat and still falling over board. I wouldn't want to be dragged along with the boat whilst everyone else thinks everything is all OK!

Assuming you are conscious and can get to it get it out your pocket and throw it away. £12 cost to call for help.

>All good advice, but why is a 25m range a problem?

I took it mean metres in which case a MOB would be out of range of the radio in 9.7 seconds if the boat speed is 5 knots and if the boat speed is 6 knots 8.1 seconds, if it's miles it is not a problem. If the transmitter is under water there will be no signal.

You need to add a 30 second activation delay. 34 seconds actually as it only radio's in every 4 seconds.

 

[AngusMcDoon]

You need to add a 30 second activation delay. 34 seconds actually as it only radio's in every 4 seconds.

The 30s value may be reduced during testing. It's just a starting value to avoid false alarms. I was thinking about reducing it to 16 seconds.

 

[nigelmercier]

The 30s value may be reduced during testing. It's just a starting value to avoid false alarms. I was thinking about reducing it to 16 seconds.

Shouldn't this be as low as possible?