Rock the house... I'm looking at using a cap small enough to fit inside a .20 ID tube, if yours is anywhere near that then mine should have runtime issues
the biggest problem I had was finding large enough caps with small diameters... All the small ones were way too small... and the ones with enough capacitance were too large. the cap I have is 8mm diameter (.315 in) and 3F. at 2.5V it stores ~9.3J of energy, but only about 7.8J of that is recoverable if the motor requires 1V to run. If the motor needs a higher voltage this recoverable portion gets smaller.
I used Digikey's capacitor filter menu... it lets you weed out the too big and too weak If you go to their website and type capacitor in the search blank, it'll send you there. If you already know about it, sorry for wasting our time I looked at either one big one, or several small ones in series. After I'm done focusing on the spring-powered launcher for V-106, I'll do more research on powered torps, assuming you haven't got one invented by then I have a feeling that David will build a Kitakami and I'll be treated to seeing 'the wall' (In Navy Field, a huge swarm of torps fanning out from a ship or ships is called a 'torp wall' or simply 'the wall')
yeah, I have been using digikey. Remember, capacitance of caps in series is analogous to resistance of resistors in parallel as far as the math is concerned. caps in parallel increase capacitance, maintaining max voltage rating, caps in series increas max voltage while dramatically reducing capacitance.
from rough estimation on my part we will need between 1-2 Joules of recoverable energy... hopefully less, but margin is good.
I figured 8-15 seconds, depending on the speed. Ideally both speed and runtime would be settable so that folks can easily adapt them to different rules formats or to different navy's. E.G. the Japanese long lance torps would run fast for a very long time but the american torps would run not quite as fast for a much shorter time.
How many different types of torps/speeds are you planning? With all of the different torps from different countries, it might be more trouble than its worth to subdivide them that much. In my 1/72 rule set I'm working on, I've restricted all torps to just 4 types. One size and maximum speed for all torpedoes in pre-1900 ships, all post-1900 ships with 18" or smaller torpedoes, all ships with torpedoes 18+" to 21", and all ships with 21+" torpedoes. I chose to only restrict maximum speed and leave range open to the individual captains' choice... fast, shorter ranged torps or slower, longer ranged torps. Given the small scale involved, I think it would be very difficult to make torps conform to rigid speed/range specs for each different navy.
Since it is pic controlled, the speeds/ranges would be set in firmware. It is infinitely flexible so long as you have a board with pogo pins to reprogram the pic....
How big is the pic? Archer183, I think your really on to something with you drive setup... but I still fear that size and weight will be too great for a scale torpedo... What torp dimensions are you planning?
the pic I am looking at is ~4mm x 4mm. Right now I am just trying to get a functioning drive system going. I am hoping that the cap (8mmOD X 20mm) + the board (8mm * 12mm is what we are going for) will be sufficiently small. I have not figured out the warhead yet, and that will probably drive the size more than anything else.
Well, I have one board cut, and as far as I can tell, I did it right. But now the hard part... soldering a 10 pin uMAX package boost converter... my brain hurts a bit on that one. SOT 223 easily, but this one has me a bit confounded... only thing I found small enough, but damn, it is small... I do need to get a new schematic made up... I have a hand sketch or two... but I need to get it on paper before I forget. The short and skinny of it... assuming I didn't get something routed wrong (first proto, we'll see): 2.5V supercap runs motor, is pulse width modulated to control throttle, with a fixed run duration and speed, changeable in firmware. microcontroller and fet's are run off a voltage converter to eliminate need for second cap... Charge to no more than 2.5V... will run until the cap is down to ~0.7-0.8V, which ran one of my test motors (hooked directly to cap) for over a minute with load...
Well, part of the circuit works... down to ~.7VDC on the cap. the little uMAX regulator there upconverts to 5V nicely so I have a nice stable sufficiently high voltage to run my pic off of. I have not put the pic chip on yet (and I don't plan to till I get the code working). uMAX form factor is a real pain to solder, especially when all one has is a fatty iron and some solder wick... but it worked out... note picture does not show everything hooked up. the resistor is a current limit I use to prevent high currents from the cap. the middle board is a pair of Low dropout regulators from microchip that will drop up to 16V down to 5V (left one) and 2.5V on the right. the 2.5V one I am using to charge the capacitor, at ~50mA (limited by resistor). Takes a while to charge, but I figured better slow for now then sorry. the left is a motor/battery I tracked down to play with. no idea of battery capacity, but it is small. more to come when I get a chance to continue. I still have to solder the fets to the board...
Since I realized recently that I have an input on the pic used (if I install a resistor) that does not need to be used at all, there are additional possibilities for this. I could solder on a lead from a receiver and make it a throttlable drive for tiny craft using the tiny lipo battery in the picture... could prove even more interesting
folks, I think I may have it... still have to put it all together... but this is close.... this chip is tiny. I get one byte sized variable and one word sized variable... Runtime limits should be doable and making it read a receiver signal for throttle should also be very doable, meaning it could be used to power a really tiny craft off a lithium battery while having the required low voltage cutoff.
Got it. Still not certain that this tiny motor will drive much of anything or that it will be possible to power it from the capacitor sufficiently. This code does work to run the motor at a constant speed for a while and then terminate the run. As a bonus this has me thinking about how to monitor a pump for vaporlock or blockage and control it accordingly. I have some really slick hall effect sensors laying around. I switched to a new chip. much easier to code for due to more internal space...
I have no idea. I have not seen if they will even work in water yet. But the theory is sound, now it is just finding the correct motor/cap or battery. I could also replace the adcin with pulsein and read a servo signal to set the hardware pwm. capacity can be expanded by using the tiny fets to drive bigger fets... -Greg
