Help For School Project

We're building a remote-controled nitrogen-based mobile cannon as a school project. My responsibilities is the electronics, the wireless system aswell as the servo-motors and so on.

The thing is, even though we had a great amount of time in the beginning I suddenly find myself having only two weeks at my disposal for this project.

Now, this has led me to give up certain ambitions about this project. At the beginning I aimed at getting a pretty good general knowledge of this antenna-building process as well as the whole implementation of the motor-system and so on, but now I'm only looking for the very basic skills from the fields of knowledge this whole project cover.

Now, I've got this USB-based controller from school and to it I've thought that I would add a self-made transmitter to one of it's digital outputs.
On the cannon-wagon I've to build a reciever that can recieve data from the transmitter with atleast 15-20 metres range. This data should then be able to be translated and used to control three servo-motors.

Now, perhaps this is too vauge to give any real answer to, in that case please ask for the information you lack. My question, or my purpose with this post was to get some general pointers toward which I could orient myself to pick up the sufficient skills to build these things. So this is not so much a question of you doing my "homework" for me but rather gently guiding me with your acquired experience and knowledge of these concerned fields! : ))

Something that would be very helpful would be a general description of how you would go about in the construction of this wireless system aswell as the translation of the data to motor-instructions at the recievers end and what I would need to read up on to be able to complete this thing.

Perhaps a quite unstructured post but unfortunately there is some other things that I've procrastinated and needs to be dealed with this evening and that I'll need to attend to as fast as possible.

kthxbye

lol RC airplane transmitter/receiver...?

yep ...
that sounds like the fastest out for procrastination .
seriously , in two weeks time i don't believe you could learn , design , implement and debug what is needed . something has to give .

ps ... "dealt" is a better choice than "dealed" .
composition on/in/of the project write-up will count .

I'm not comfortable with the idear any rudimentary or hacked together wireless system being used on a device like this without seeing some mention of a positive fail safe safety system.

That being said, the amount of work that would go into a full wireless safety isn't trivial and would pretty well (in this case) bring the project down to a hard wired switch or interlock that would arm the device for a short duration countdown and wireless firing. As this would already mean a wire tether, is there any point in another wireless beyond the minor cool factor?

I would actually say that a wireless system would be down right dangerous for a high school project "mobile canon". Sorry to be cynical but there are just too many variables that could inadvertently trigger the canon, potentially injuring or even killing someone.

To give you an idea:

• You would have to make sure your communications system was secure and clear (i.e. that noise or other RF 'traffic' was not interfering).
  
• You would also have to implement a fail-safe system that by default locks out the canon completely, rendering it inoperable.
  The only real safe way this can be done is by a hard-wired power kill switch that disables everything by removing power and that can be activated immediately, should something go wrong.
  
• This list isn't exhaustive, there are heaps of other things to consider too, though I won't dive into that.

The reason why a "normally open" kill switch controlling the power is hard-wired is that it won't be influenced by RF interference or a crash in the programming of the canon, so if there is sufficient interference from other sources (or for instance an infinite loop condition arises) and you need to kill your canon, the fail-safe won't be compromised, it simply turns it off.

You have essentially no control on what signals are out there and even though there is a microscopically small chance of anything untoward happening, I wouldn't bother, any risk of complete wireless control would be too much of a risk in the school's eyes.

Look on the bright side: you'll get more brownie points from your assessor for deciding to keep this key safety consideration in mind and keep it separate and independently operable of the wireless control system.

I want credit for these ideas too. My fee is $500 per hour.

So that's about 5¢ per idea... is there also a "postage" fee?

Nah, I'll be nice this time and throw postage in for nothing.

OP, by kill switch I mean one of these: http://cgi.ebay.com.au/NEW-Isolation-Switc...#ht_1609wt_1165

Make sure it has "NC" or "Normally Closed" contacts so that when the button is hit, it will open the electrical contacts and break the circuit, therefore disabling the cannon. You twist it back up to reset it. A key operated one (so you can lock it until everyone is out of the danger zone) would be better.

Nice and colourful so that it's easy to spot and it's meaning is universal. Red and Yellow means "Oh SHI....."

i agree ...
this can be a lethal project .
there are too many variables with the security of a wireless firing system .
a hard wired system is the best bet .
make sure your final link to the device that actually "fires" the cannon (i am assuming a dump valve) requires "high level" actuation .
low level circuits , as previously mentioned , are prone to interference and erroneous triggering .

an even safer method would require the use of two arming switches independently operated by two observers/operators .
locate these on opposite sides of the control panel .

@ TB : you are really being generous by throwing in the postage .