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Dec 03, 2014, 06:21 AM
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Build Log

Destroyer Project

Hi all, I'm combining all my threads into one. I started a build log in 2008 in scale boats section of this forum (1:35 Dd), that has the hull construction and a bunch of tangents, steam powered turbine that never went far among others. It's basically a 10 ft long 1:35 scale model approximately resembling a WWII destroyer, two electric motors for propulsion.

I plan to use an arduino mega to control it and have a good chunk of the program ironed out. Comm is one of the main items left, I'm currently planning on using xbees and a laptop to pilot it. So far no gui (graphical user interface) so keyboard at this point. It has had it's maiden voyage using an RC radio that was several years ago though.

Another issue is the finish, it's all wood, fiberglassed hull but the superstructure is made of thin plywood and I'm afraid it will all curl up when it gets wet. I've "painted" the insides with Zpoxy, just need to go over the entire thing and make sure it's all sealed. Any ideas on this would be helpful.

I has two 12v lawn tractor batteries, and I calculated a displacement of approximately 125 lbs. Features:

Anchor winch; having used hall sensors for the tachometer, I'm thinking I might attach a small magnet near each end of the anchor chain to indicate when it's fully retracted and fully paid out so I can do away with the friction clutch. The control issue being how to know when the anchor is fully in or out and not pulling the anchor through the hawsehole. I have not cast the anchor yet but have the wax dummy I will use for the mold. Magnets on the anchor chains is a bit iffy so we'll see. Any ideas on that would be helpful.

Air compressor; The forward compartment has an air compressor. The main use for the compressed air will be to fire the K guns, six of them along the sides of the aft deckhouse. The K gun lobs a depth charge out to each side of the ship a few hundred feet (inches in this case) to increase the size of the depth charge pattern. I don't plan to litter the lake with dummy depth charges (except maybe I'll make some biodegradable). Have yet to install pressure tank, I have some high quality surplus solenoid valves (three) that will be used to fire them using the compressed air.

Bilge pumps; Have two RULE 12v bilge pumps, one forward, one aft, connected with scratch built float switches, theoretically these would pump out the water if there was a major leak, hoping they do not need to demonstrate their function. I will wire up a sensor that will let me know if they go on, maybe a siren of some sort.

Control compartment; The second compartment under the bridge (had previous mechanical gun director) has one of the two batteries and will have all the electronics, the mega, xbee, if I use that would probably be mounted up higher, relays etc.

Mast; Not built yet the mast will be there, it will have some lights, a rotating radar probably and the fixed radar mesh at the top. I'm waiting on this for last because by the time I get there I expect to be able to pick up a breakout board for functioning radar....

Fogger compartment; The third compartment has the second battery and will have the dreaded fogger. There will be a fogger, whether I buy harbor models version, make my own or throw lit cigars in a box. Both funnels are accessible from this compartment. There is a ventilation (computer fan) at each end of the deckhouse. There is the main fuse box, a 5v buck converter to power all the 5v stuff, leds etc, 12v-24v step up converter for the occasional k-gun solenoid operation and whatever else.

Spotlights; I have a spotlight on each side of the forward funnel, ultra bright led in a cheap flashlight cone (parabolic mirror), they will be fixed at this point.

Gun director and 5-5" gun turrets; I have the contorl of the director and guns all ironed out using the arduino mega, darlington arrays and stepper motors. The director has 360 degree + rotation. Once pointing at a "target" whatever turrets can operate at that angle will rotate to match the directors angle, if not they return to the 0 or 180 position. The guns elevate. But alas, no BB's pellets come out, have to save that for another model, or a later modification.

40mm Bofors; There are 5 double 40mm bofor rotating gun platforms, I'm weighing whether to animate these with the little 5v geared stepper motors, I got enough extra motors to replace the 5" gun elevation servos with these and do the bofor guns.

Quintuple torpedo mounts; There are two of these and at this point they are not animated, they are probably a bit big for the little 5v geared stepper motor, so they may remain non-animated, no working torpedos on this either.

Motor compartment; The fourth compartment has the two 12v electric motors. The motor turns the propshaft with timing pulleys and a belt. The two ESCs will be put here. There are two water pumps for cooling the motors which I wrapped with copper refrigeration tubing. There is one outlet and one inlet each side of the hull. The inlets may be prone to clogging, anyone have problems with that? I stuck a temp sensor on each motor with JB weld and they will contorl the cooling pumps. The ESC's may need cooling more than the motors so I may tap off the plumbing for that. There are the prop shaft tachometer sensors of course. The three K gun solenoids are mounted above the prop shafts. The compressed air tank(s) probaby will go in above the cooling pumps.

Fifth compartment; This is small, has one access hatch and so far contains just the 5th 5" gun turret stepper motor.

Sixth compartment; Even smaller contains the steering gear and giant scale servo. The hatch for this has the aft machinegun tub attached to it.

I'll attach some updated photos.

After learning the arduino and how to use it I see the light at the end of the tunnel on this project, thanks to Blutoh for recommending I get one and give it a shot. I to recommend everyone get one to play with they are easy. Anyone who can build an RC boat can figure out how to use an arduino.

You can have an arduino on your boat and still use your standard rc radio it will read the PMW signal from how ever many channels you have, see threads by others. Cap
Last edited by capricorn; Dec 04, 2014 at 07:20 PM. Reason: continuing
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Dec 04, 2014, 08:33 PM
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Spotlights; I had standard ultra bright leds in the spotlights but found 8mm 1W leds that fit perfect and are considerably brighter so I pulled the old out and put in the new ones. At three volts, 100mA (in the pictures it's pretty bright), at 4.5v, 250mA it's blinding.
Last edited by capricorn; Dec 04, 2014 at 08:45 PM.
Dec 05, 2014, 01:25 AM
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Hi Cap,
Nice LEDs but I have to ask - are you controlling or limiting the current in any way?
People are often unaware that these devices are current fed and not voltage driven like an incandescent bulb. You feed them a current and they drop a characteristic voltage. With bulbs you feed them a voltage and they draw a given current.

White LEDs are very stark and "clinical" - they are weighted towards the blue end of the spectrum unlike incandescents which are more towards the red end. The white is from a phosphor and not the actual LED emitting light. The base LED is usually blue or UV and this energy is used to trigger the phosphor and hence the cold look.
Now for a geek like you why not consider RGB leds? Three colours each driven by PWM and you can dial up any colour you like. Should keep you off the streets a bit longer.....

Dec 05, 2014, 06:51 AM
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Too late David, One of them was hungry and ate too much current. How did you know? The voltage and current values I gave? I realize I was over 1W now I was multplying .25Ax3V when I should have used 4.5V, not only that but they might be .5W leds. Does one use something other than a resistor to operate led's? I would consider the RGB but I want to limit the number of wires....
Dec 05, 2014, 07:31 AM
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Most LED applications have some form of ballast circuit to limit current. The simplest is that in a key ring torch - it relies on the internal resistance of the battery. Then there are resistors, constant current (really current limiting) circuits, and careful use of PWM. There are high voltage LEDs that can be used rather like incandescent bulbs, but these are usually a fairly normal LED with a current limiting circuit built into the package.
Dec 05, 2014, 06:29 PM
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Hi mfr02, Thanks for joining in. Gee I thought the spotlights would be easier, I thought they just needed a resistor, I guess that is on your list of ballast options. I used the ammeter to measure the current, at that time I wasn't using a resistor (or was using the battery as the resistor), just starting with lower voltage. So, if it is 1Watt, if I use 5v, that is 0.2 Amps, and 5v/.2A = 25 ohm resistor correct. And the resistor uses 25 ohms x .2A^2 = 1Watt. If I use 12v power I get .083A, need a 144 ohm resistor and it also uses 1 Watt. Does that sound right? There will be more lights on it so it would be good to get it started right. Thanks, Cap
Dec 06, 2014, 12:09 AM
Registered User
Hi Cap,
It was that hot, semiconductor smell that alerted me.
LEDs vary in voltage drop depending on colour with red being around 2v (depending on doping) up to blue/white LEDs around 3.6v. The drop will vary with current somewhat but is basically a fixed forward drop.
A resistive feed is usually sufficient. Take your supply voltage and subtract your LED's forward drop - this is the voltage your resistor has to drop. Work out what current you want to run at (in Amps) and divide the voltage value derived before by this value to give you the resistance.
For example - you want to run a white LED at 200mA off a 12V supply.
12v - 3.6v=8.4v. 8.4v/0.2A = 42R. A 39R or 47R is probably close enough.
Now keep in mind the resistor will get hot - it's dropping 8.4V at 0.2A = 1.68W.
The LEDs too get hot and often they're rated with a laminated aluminium heatsinked pcb and will need to be derated if just used soldered to a simple pcb. Check any data you may have about the LEDs.
You can run several LEDs in series. For example you could use 2 LEDs in series in the above examples. Both LEDs will be drawing the same current but the total drop is now 2x 3.6v or 7.2v. With your 12v supply the resistor now only has to drop 4.8v at 0.2A so now becomes 22R and only produces 0.96W. Check your datasheet - you may be able to run a third LED in series but you're running out of ballast headroom. You may find that at the lower current needed to keep the heat down for free air mounting you can run the 3 in series but they will vary more in brightness as your 12v goes from full supply down to cut-off value.

Dec 06, 2014, 05:46 AM
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What he said. Be careful with resistor wattage. I had an amusing (after the smoke had cleared and the smell had gone away) experience. An application with not much room needed a bunch of 2 watt resistors. We had a bunch of miniature vitreous enamel coated 2.5 watters of the right resistance. So far, so good. With the lid shut and more than one in use, there was enough temperature to start melting wire insulation. Lesson - a resistor with a larger surface area, dissipating the same power, will run cooler.
The voltage dropped across a LED over a range of currents is constant enough that they have often been used as a souce of reference voltage in things like constant current sources.
Dec 06, 2014, 03:59 PM
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Okay, I think I'll need to check the voltage drop and use probably a 47 ohm with 12v and the led would use about .72 watts sounds like. And check it to see if it gets too warm, don't want melted wires or fires, so large surface area. I was sort of wondering about the wire, I used the smallest I had, 30 or 32 ga. About the size of the old fashion radio earplugs, it did not seem to get warm.

Since I'm on lights I need to figure out how many and where they go. I know there is a green(stbd) and red (port) light on the sides by the bridge. I see a few lights on the main spar in photos, one each spar tip and one in front. I don't know if they typically have a white anchor light at the top of the mast somewhere. Cap
Dec 07, 2014, 06:46 PM
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Long hours of wiring, socket connectors and soldering, I have the turret control hooked up. With all those wires some troubleshooting was inevitable. The main glitch is I currently have the 1 and 5 turrets unpluged, The darlingtons have a .5 amp limit, that is about exactly what one motor alone is drawing and two together (1&2 and 4&5) fried the ic, fortunately I got extra (it made a very distinctive "pop". So no promotion, still an electricians mate lowest class, should have checked my data sheets.

So aside from the need to separate the paired motors, which probably wasn't a good idea to start with I'm happy with it, it appears to work well.

I started the video 10deg, 20, 30 40 50 60, but then lost count somehow. Once all 5 turrets are up and running I'll try to get a better video. Still have the gun elevation wiring to do.

The number 2 turret set screw was loose so it got "lost" part way through but not worth a new video

turrets (0 min 53 sec)
Last edited by capricorn; Dec 16, 2014 at 05:34 AM.
Dec 16, 2014, 05:55 AM
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Still working on it. More darlingtons on the way. The motors operate right at the limit of these ULN2803 IC's. I am very close, I have fried 3 of the 4 chips I bought troubleshooting bad connections without using a resistor to reduce the current. As you suggested David I need low ohm resistors (not just to soften the steps), I may need to vary the size depending on the turret, the aftmost turrets have longer wires so don't need as high a resistor. 2-5 ohms for the back, 5-10 ohms for the front. Too high and the motors don't have adequate torque.

If it turns out the 2803 is not going to work I'll have to switch to a different driver, any suggestions? Something with exactly the same pins as the 2803 would be great (just plug it into the existing socket) but doubtful. Or I think they could be doubled up, one 2803 for each motor, evidently you can split the current between two, not sure how evenly it splits. Has anyone ever seen an IC socket adapter that allows you to plug two IC's into a typical socket for one IC? Cap
Dec 16, 2014, 02:11 PM
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Or I think they could be doubled up, one 2803 for each motor, evidently you can split the current between two, not sure how evenly it splits. Has anyone ever seen an IC socket adapter that allows you to plug two IC's into a typical socket for one IC? Cap
Back when I worked for a living, one of my mates used lots of these for their intended purpose. He also knocked up a speed control for one of the other guys (back in the days when Bobs Boards were high tech) which worked by switching elements in using an R/2R resistor ladder. The only limit seemed to be the chip limit for power dissipation - if memory serves, you couldn't have more than half switched on simultaneously.
Two chips, one holder. That brings back memories of mods on the TRS-80. I think (memory, again) that if you wanted access to the full set of characters that you had to piggy-back the extra chip to get the extra bit for the character generator. So piggy-backing is viable, but whether the chips would be able to dissipate the heat.........?
Dec 16, 2014, 03:16 PM
Registered User
Hi Cap,
Sounds like you're living on the edge there and you may want to check the current your motors are pulling. Killing the chips could be one of two things - excessive current or excessive power. The chip uses Darlington driver configuration so they have poor saturation voltage which in turn means high dissipation at high current.
You could measure the resistance of a single motor phase and calculate the current it will draw. If you're using half step then it will be double that when two phases are driving.
Whilst not as convenient to use you may be better off with some small logic level power FETs. Most are in an SMD format which may be a problem for you.

Forget trying to parallel chips - they don't share nicely.
Do a Google for logic level FETs but as warned - most will be TO-220 style which is too big and others will be SOT-23 which is a small SMD part. A TO-251 style may be suitable and offer quite high current capability. Some years back there was a FET equivalent of the Darlington parts but it seemed to die off for no obvious reason. Hopefully others can add something here.

Dec 17, 2014, 06:41 AM
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Thanks guys, I have measured the motor current, have more fuses on the way too for the ammeter(s) They seem to have a similar limit at 500 mA., one has a 10A range but not much resolution at the low end. I think they'd like about 600-700 mA. I measure 12 ohms for the #5 turret, 10 for #2. Will research sharing.... I don't think they need to share equally as long as it works. I thought about mosfets, or fets or similar, I would need a lot of them. Why would T-220 style be too big? I used similar circuit for the last fogger attempt, plenty of capacity, 10A or more.

I'm not sure heat dissipation (out of the chip) is the problem, it's not like the motors ran for 5 minutes then burned out. They will be intermittant use as long as I don't run them back and forth rapidly. Dealing with heat dissipation could be a problem because the chips are completely blanketed in wires (not much air circulation) but a little blower strategically placed would help. SMD format?

TRS-80.... That was the first computer I used, a handmedown from cousin. I did not attempt to modify it, however when it's time came I disassembled it. Cap
Dec 17, 2014, 07:10 AM
Registered User
Hi Cap,
Is that 12R and 10R per phase for the steppers you're using? If you're running 12V then that's 1A or just over if the Darlington's were fully saturating (which they won't).
BJT's ar not very forgiving in overload (secondary breakdown) whereas FET's will tend to get hot before they snuff and also handle inductive spikes better (avalanche mode). If you can fit TO-220s then go for it. I use them for PWM brush motor control and a single FET without heatsink is OK for around 30A continuous and 50A peaks. If they switch fully then there is very little heat.
SMD? Surface Mount Device.


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