Help with project

stereo_steve

Not sure if this is the best place to post this, so feel free to move it.

I have a college project which I have to make but I'm not sure how to make part of it! Hopefully someone can help me, I know gadget and daveirl seem to know their stuff, they helped me before with something.

The problem is, to design a system that will carry cargo to the bottom of a swimming pool and then automatically come back up once it gets to the bottom.

This is what I have in mind, to bulid something which is more dense than water. It will therefore sink. I have a little circuit which will detect when it is in the water and activate a timer (~10seconds) which will turn on four motors, which are connected to tilt switches to make sure it propels itself up straight!

The problem is, I have absolutely no idea how to build a timer!

1. Is it easy to construct? The system will be running on ~27volts,so I can use any voltage under that.

2. The water sensing circuit will be sending a 9volt signal to the timer. Again I can use any volage under that.

3. The water sensing circuit will send a continuouas signal of xvolts to the timer, not a once off pulse. Will this keep reseting
the timer? cos after the ~10seconds I want the motors to stay on.


I realise I'm asking alot here, but any advice/help would be great. Thanks a million.

Gerry

For a timer you should look at circuits based on the 555 chip, which is quite a simple device. At least have a look until someone comes up with a better suggestion

Dr. Dre

Yeah I'd say a 555 is the way to go, probably use it in conjunction with a relay. My first port of call would be Peats or Maplins they can sometimes have kit projects which can be a great time saver.
It's late and i can't quite get my head around what you plan to do, I'll have another look tomorrow and see if I can think of anything else

PS Tilt switches ?? I haven't heard of them in a while !!!:D

K!LL!@N

Do you have to use motors to propel the thing back to the surface?
Why not use cans of compressed air to fill balloons which could float it back to the surface.
You could also try making the thing bouyant and using water as ballast to cause it to sink.
When it gets to the bottom realease the ballast and it should float back to the surface, right?
By the way, what's the project for?

Killian

yellum

This sounds cool, I'll sticky it for now

Occidental

Do you dispose of the cargo once you reach the bottom. If so then I don't see why you need motors or timers. Just use something with a few balloons attached, which will sink when carrying the cargo, but will float when the cargo has been released. For a release all you need is something at the bottom of the device which will eject the cargo on contact with a surface(bottom of the pool). Probably being a bit too simple here. If you really want to go to town I can lend you a PLC and do up some ladder logic.

longword

Originally posted by Dr. Dre
Yeah I'd say a 555 is the way to go, probably use it in conjunction with a relay.

A 555? FFS! Why not stick a PIC12CE519 in there! Way better value for your eight pins and probably happier with a wider voltage range

Seriously though, for a fixed timing interval you can use a capacitor and a resistor or two. Here's a link to a simple DIY project that demonstrates the concept: http://hop.concord.org/amu/amu.core.html

(Yes, I'm a programmer, yes I'd go with the PIC )

stereo_steve

Wow people are really taking a interest! I'll post pics up so, It sounds great in theory but really its just going to be a dirty old lunch box with arms holding motors!

For those of you that suggested using pressure and weights for the project, we can't. Its for an electrical engineering project and we've been told that it has to be electromechanical. Also the project must stay intact. None of us fancy jumping in the pool to collect the pieces!

Because everyone is interested, I'll go into a bit more detail about it. The water sensor is one that I actually had lying around the house. I'm gonna rip off buzzer and connect the wires that should have gone to it to the timer circuit.

The timer circuit is going to turn on 4 24volt( :eek: its gonna fly) motors. Hopefully powerfull. They're all gonna run off the same battery! And each motor will have its own tilt switch so it will level the system as it travels up in the pool.

Back to the problem though, I like Longwords idea of using a resitor capacitor circuit. Its basic and seems like the easiest to construct. Can't see much going wrong with it.

I'm gonna look into it. Does anyone have any advice? I've never built one! also i'm gonna have a continuouas DC source going into the time, will the timer just turn on for a second then turn the motors off untill the capacitor charges again? Is there a swith you can get that will turn on once it recieves the signal once from the timing circuit? Cos that would solve the problem!

Once again, thanks for any help that I get.

Dr. Dre

Steve, would there be any chance of you posting the brief for the project ?
...just so that we all know exactly what "we're" ( you like that ? 'we're' taking over Steve so stand back !!! ) dealing with.
Obviously we don't want to be coming back saying "you should do it like x" or "like y" but you might get a lot more advice and suggestions this way.

Cheers

daveirl

This post has been deleted.

longword

Originally posted by stereo_steve
Back to the problem though, I like Longwords idea of using a resitor capacitor circuit. Its basic and seems like the easiest to construct. Can't see much going wrong with it.

Don't dismiss the PIC12C509A approach! Especially if you've already got access to a programmer device, and definitely if you can corner a coder who can already speak asm or C.

You need only the one 8-pin device, bugger all support. All it asks of you is a power supply of anywhere between 3.0V and 5.5V. It has internally its own 4MHz clock, and an internal timer so you don't have to count cycles yourself. Despite the miniscule 8 pin DIP package, you get 5 input/output pins and one input-only pin. Enough for independent control of each of the four motor relays and two sensors before you even think about multiplexing (or more likely a bigger PIC chip with more I/O pins )

BTW, I notice on that Maplin page for the water sensor it suggests that people who bought this also bought a 150W DC-AC inverter. Should we be worried?

Dr. Dre

Originally posted by longword

BTW, I notice on that Maplin page for the water sensor it suggests that people who bought this also bought a 150W DC-AC inverter. Should we be worried?

Heh, I saw that too, it was only when I woke up this morning I went what the f*** ? Very much a Fr. Dougal moment ! :rolleyes:

stereo_steve

Sorry for the delay in writng back, we had a rag trip in college. 24 solid hours of drinking, traveling around the country on a bus!!!

I saw the inverter too and for a couple of seconds I actually thought about it! Don't really want to electrocute anyone, might loose some marks!

I realise I started this thread to ask for help with a timing circuit. But the project has to be in in ~3weeks and we (I'm making it with two others) have loads of work to catch up on. So we decided to scale back the project. Instead of the water sensor and timing circuit, we are going to just have four push switches under the lunch box. Odds are one of the switches will get hit when the lunch box gets to the bottom of the pool. That will activate the motors.

But there are still some probs I need advice on, has anyone ever tried to waterproof a motor!! I was thinking of the little plastic things in kinder eggs with silicon around the holes for the wires!
Also is it possible to buy water proof push switches?


BTW We connected the motors up to the power supply in the lab on wednesday, Cranked it up to 24v. Tow of the propellers snapped!! :eek: I figure though that their will be more resistance in the pool though.....hopefully no more snapping!

ST

How about mounting the motors in the lunch box with the propellors underneath the lunch box. The upside down lunchbox should remain full of air and therefore keep the motors dry.

To start the motors you could use a momentary push switch which would activate a latching relay to start the motors and keep them running. You could connect the water sensor to the relay and mount it on the top of the lunch box so that when it gets to the surface it would reset the relay, switching off the motors and the box would sink again....etc. going up and down until the battery ran flat.

You could build a variable voltage regulator circuit to reduce the power going to the motors if they are too powerful.

JohnBoy

Do you really need all this complexity?

4 motors with the tilt switches?
is this part of the brief.

It'd be real easy to make the unit self righting. just put the weight (batteries) in the bottom and one motor on the top.

good ole gravity will keep you level. maybe put a bit of buoyancy at the top if nessecary.

to give a contolled descent you could run the motor @12v on the way down and @24v on the way up possibly.

just some ideas.

John

po0k

Assemble everything in a vertical config, more streamlined. The motor(s) would be best located at the top.
Mount the (non-momentary) push switch inside, use connector rods/prods to hit the switch, prehaps having it attached to a plate to ensure it gets hit.
It'll be like a bit chunky whirring pog stick.
Two contra rotating motors would be best to stop it spinning in the water, I haven't thought about this long enough to consider 4 atm.
Get steel props, or larger props spining slower. don't need to ahve them angled steeply.
Is this thing supoosed to make it to the surface inside some particular time?
The trigger can be made with a single AND gate. When the push switch is hit it'll give the second logical 1 needed to output the 1 to the motor circuit.
No need for PICs at all
2 motors, box, power supply, power circuit, and gate, push switch.

Low component count, it'll work and provided the construction goes well should have you singing