RC-conversion of the 1930s river tug 1:100

[akremedy]

Wow - the results are incredible. I'm amazed that Lutz was able to stuff all of the necessary electronics into the hull of the tug and still achieve bouyancy *and* what appears to be perfect balance.

Adam

[Gharbad]

Very nice!
Really makes me want to try some electronics in a few models!

[Leif Ohlsson]

Can't resist a final post, showing the builder's, Lutz, and the maiden voyage of the little paper tug. All went well, and no assistance from a nearby rescue vessel (also RC) was needed.

Incidentally, the author has published a YouTube video of the trial run.

All relevant technicalities here at Kartonbau.de (all in German, though).

[Lutz]

Now that this model is finished, I would like to add a few comments and explanations myself.

First of all, thanks to Leif for reporting here about my project.

For those of you, who are interested in how I've built this model, I would first recommand to take a look at the thread in the German forum. I posted a lot of pictures, which document the construction pretty well, even if you don't understand a single word of German.
Now for those things, that aren't in the pictures:
The most important question is probably: "How did I get it waterproof?"
Well, I did two things: First, I coated everything on the inside of the tug with pore filler (Porenfüller), the stuff usually used by buildrs of rc airplanes to treat balsa wood.
On the outside I used "Lukas Sprühfilm", a varnish usualy used by artists to protect water color paintings. This is a very thin varnish, so you usually don't get any varnish runs.
I applied about 5 layers of this stuff.

The servo is a normal, cheap mini-servo.
The propulsion engine once was a cheap standard servo: the servo electronics serves almost unchanged as the motor controller. I just shortened the pcb and had to reconstruct one conductor path and the suppression capacitor.
I also exchanged the 5 kOhm potentiometer, which usually gives the feedback of the servo position, with a smaller one of equal resistance.
But if you have the room, you can simply use teh servo electronics as is for a motor controller.

The batteries originally used (1/3 AAA) proved to be too weak for the maximum measured current of about 1 Ampere. So I replaced them with 1/2 AAA cells (GP33AAAH from GP). These last for about half an hour.
Had I not already glued in 20 grams of lead balast, even normal AAA cells might have fit.

The electronics for the lights are based on a PIC12F675 micro-controller. It measures the length of the pulse from the receiver. This pulse can have a length from 1 to 2 ms. 1 ms means full deflection of the controller in one direction, 1.5 ms is the middle position, and 2 ms is full deflection in the other direction.
So if the pulse is longer than 1.6 ms, the normal navigation lights are switched on, if the pulse is longer than 1.8 ms, the lights for a tug & tow are switched on, and if the pulse is at least 2 ms long, an additional light for a tug &/ tow over 200 meter length is switched on.
If the pulse is shorter than 1.4 ms, the light for long tug & tows is switched off, if the pulse gets shorter than 1.2 ms, the lights for a tug & tow are switched off, and if the pulse is not longer than 1.0 ms, all lights are switched off.

In addition, I also implemented an undervoltage warning. The voltage across a 2.4 V Z-diode is measured and compared with the input voltage. If the input voltage falls below 4.8 V, all lights start to blink.

The circuit diagram and the source code for the µ-controller program are also in the German thread.

Also remember that this was my first conversion of a cardboard kit to a swimming rc model, so my techniques aren't necessarily the best.

That's it for now. If you have any further questions, don't hesitate to ask.

Lutz

[Lex]

Thanks for the info Lutz!! I wonder if it's easy to connect the electrical circuit? Or knowledge of electronics are required for the part?

[Gharbad]

Thanks for the info!

[Bluenoser]

The results are fabulous and speaks for itself.

[Lutz]

Originally Posted by Lex

Thanks for the info Lutz!! I wonder if it's easy to connect the electrical circuit? Or knowledge of electronics are required for the part?

Well, you don't have to understand it, if you want to build it.
But you should be able to tell the different pins of the ICs apart and to route the connections between the components.
If you are not that experienced when it comes to soldering, you should probably be a bit more generous with the size of the circuit board and put the z-diode and the resistor R1 also on the front of the board and not under the PIC, like I did.
You can also leave these 2 parts off, if you don’t want the undervoltage alarm. This might be a good idea anyway, because you need to change a value in the µ-controller program to calibrate this function, depending on the real values of your components (which can vary quite a bit). In this case, one must delete the undervoltage detection part from the program. (This is simple, so I can post the program without this part here, if you like.)


You should also use sockets for both integrated circuits.


One important thing are the values of the LEDs:
I used “superbright” LEDs with the following values:
White: U=3.5V, I=20mA (=0.020A)
Red: U=1.85V, I=20mA
Green: U=3.3V, I=20mA
Yellow: U=2.0V, I=30mA
If you use LEDs with different values, you must also use different series resistors R2-R8.
The values can be calculated with the following equation:
R >= (Usupply-Uled)/I,
where R is the smallest allowed value for the resistor, Usupply is the absolute maximum of the supply voltage (better a bit more, to be on the safe side, e.g. 6V for 4 NiMH-cells, which have a nominal voltage of 4,8 V, but quite a bit more when fully charged), Uled is the voltage used by the LED and I (in Ampere) is the largest allowed current through the LED. Your supplier should be able to tell you these last two values.
Example: White LED:
R>=(6V-3.5V)/0.02A=125Ohm
The next larger available resistor is 130Ohm, so I that’s what I've used.
The other ic (ULN 2003A) is just an amplifier, since the PIC can’t provide enough current for all the LEDs.


The biggest hurdle for the “normal” model-builder will probably be the programming of the micro-controller. For this you need a computer and a programmer (e.g. the PICkit 2 from Microchip, the manufacturer of the PIC µ-controllers). Such a programmer is not that expensive (about 37 Euros + s&h). But that would still be a bit over the top for just one project.


I can send you a programmed PIC12F675 (preferably without undervoltage control), if you find a reasonable way to compensate me for my expenses (i.e. the price I have to pay for PIC plus the actual postage). Not necessarily money, but maybe some specialty from your part of the world. I don’t want to make a profit from this, but I’m just not in the mood to give out freebees to everyone who comes across this site.
Since this is just a hobby, I can only keep up this offer, as long as the number of requests remains fairly low. I also can’t guarantee that the micro-controllers will work in your application.

[Don Boose]

This is a very evocative model and a real inspiration.

Don