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Top RC-Gun

R/C Model Airplane Combat System

This project shows you how to build an aerial combat system for your R/C model airplane. Successful "kills" are marked by a temporary loss of motor power and audible alarm.
"Top RC-Gun" Shoots down the enemy!

Note: There is an updated version of this project that has exciting new features. It can be seen here: Top RC-Gun AWS Project.

A series of discussions on the popular eZone forum lead to the creation of this project. The goal was to provide a low cost combat system that could be installed on a small electric Radio controlled (R/C) model airplane. The success of the Top RC-Gun combat system is due to an off-the-shelf R/C model combat module. And some magic hacks, of course.

Main features of Top RC-Gun:

  • Low cost, under $30 per model.
  • Easily moved from model to model.
  • Can fire weapons using the throttle or a spare R/C channel.
  • Momentary motor loss on the attacked model identifies successful kills.
  • Can be used as a lost model finder (audible beacon).
  • Low power consumption. Operates off R/C system battery.
  • Small size and weight (1.3 ounces).

What's All That Noise?

The project uses the amazing HobbyZone Sonic Combat Module. Although available for on-line purchase, your local R/C hobby store probably carries these little $25 wonders. They work by using high frequency sound waves that are extremely loud. Enough so that you just may want to cover your ears if you are near one that is being fired indoors. The sound is similar to those personal alarm products that joggers carry.

HobbyZone Sonic Combat ModuleHobbyZone's Sonic Combat Module was designed for the proprietary "X-Port" configured HobbyZone model aircraft. If you own one of their models then it is a Plug-N-Go installation. However, generic models will need an interface to allow them to work with a typical AM or FM R/C system. Nothing too serious is needed, but you do need to warm up the soldering iron.

There are two versions of the project. One uses the throttle channel to fire the sonic cannon and the other uses a spare channel. The latter has an extra servo cable on it, but other than that they are nearly the same. Just choose the one that works best for your R/C model. Frankly, I prefer the version that uses the throttle channel, but the choice is yours.

By the way, you must use a model aircraft that has a typical ESC (Electronic Speed Control) for motor control. Servo based throttles will NOT work.

Out with the New, in with the Old

Sometime in 2004 HobbyZone changed the design of their Combat module. Sadly, their new module does NOT work with this project. But, if you have the old original Combat module then you are in luck. Otherwise, new module owners will need to build the Top RC-Gun AWS Project system

Old vs. New Combat Modules

By inspecting the grills used on the module you can tell them apart. The new module, which is incompatible,  has a mesh screen and silver chrome ring around the ultrasonic transducers. The older module, which is the one you need, does not have these identifying features. The photos on the right should help you out:

If you are still not sure, then you can inspect the module's circuit boards. Here is what you will find:

Old HobbyZone Module

The Original HobbyZone Module looks like this.

The new HobbyZone Module cannot be used.

Let's Go Shopping

The custom interface uses very few electronic components. They are not critical devices and substitutions are possible. The sources shown below include part numbers; the indicated Radio Shack parts may be discontinued, but some stores may still have them in stock.

Bill-of-Materials: (*) denotes discontinued part









IC, CD4011B

276-2411 (*)





POT, 47K/50K ohm

271-283 (*)

531-PT6KV-47K 3306F-503



Resistor, 10K 1/4W






Perf Board


You will also need a female servo connector (or 3-pin header) and one or two male servo connectors. Optionally, you will need a 4-pin header to connect the Sonic Module, but it can be hard wired if you want.

Construction: Hard Hat Zone

Perfboard construction works well The project is built by reviewing the schematics, which can be downloaded at no charge. The links to the CAD files are shown further down this page.

The circuitry can be assembled using nearly any technique you wish. Mine was built on phenolic perfboard and point-to-point wired using 30 gauge insulated Kynar wire (Radio Shack #278-503). I did not use an IC socket since they tend to cause reliability issues. I recommend a 40 watt or less soldering iron (700° tip).

The photo above shows the version that uses the throttle channel for firing the weapons. The 3-pin header on the right connects to the model's ESC and the servo cable partially shown above it connects to the throttle channel on the R/C receiver. If you build the version that uses a dedicated R/C channel for weapons firing then there will be another servo cable wired to the board.

Also, you may have noticed that I used a 4-pin header connector for the Sonic Module's cable. This convenient method is recommended but not necessary. I did not add a decoupling cap across the power buss but you can do so if you like.

The perfboard looks a bit messy under the covers.The bottom side is a bit messy. Despite the low parts count, there are a lot of wires to solder. Be sure to double check your work BEFORE applying power. Sure, some smoke would add a realistic touch to your weapons system, but in this case I believe it would really ruin your day.

Once you determine it is working you should protect the board with heatshrink tubing or plastic tape.

Set Up and Adjustment:

I will assume that you will be sharing your throttle channel with the Top RC-Gun device. Just plug the servo cable (ref J2) into the R/C receiver's throttle channel and connect the ESC cable into the other connector (ref J3). In other words, the board is in series with the R/C Receiver/ESC connections.

The Top RC-Gun's firing position is adjusted using the Pot. Adjust the 50K pot for maximum resistance. Turn on the R/C transmitter and apply receiver power. Verify that you are able to correctly control the model's motor.

Now adjust the pot so that the combat module fires only at the highest throttle stick position. Please note that the sound lasts only a few seconds; to shoot again the firing mechanism requires "reloading."

So, once it has fired you must reduce the throttle between shots to "re-cock" the weapon. During the adjustment phase this can cause confusion. I found that moving the pot back to maximum resistance and then trying again helps identify the pot's best sweet spot.

If you built the version that uses a spare R/C channel (the gear channel works well) then the operation is nearly the same. Just plug the J1 cable into the R/C channel that will fire the weapon and perform the pot adjustment as explained above.

There aren't any adjustments required to setup the throttle cut that occurs when your model is fired upon. To test it out you will need another combat system -- just fire the sonic cannon at a model on the bench and verify its motor shuts off for a few seconds.

Design Documents:

The technical details are available as file downloads. Please be aware that the information is copyright protected, so you are not authorized to republish it, distribute it, or sell it, in any form. If you wish to share it, please do so only by providing a link to the RC-CAM site. You are granted permission to post links to the web site's main page ( Please respect this simple request.

Top RC-Gun V1 Schematics Schematic Files: Throttle Sharing Version. PDF file of the Top RC-Gun circuitry for use with the throttle channel. Rev A, dated 06-27-2003
Top RC-Gun V2 Schematics Schematic Files: Dedicated R/C Channel Version. PDF file of the Top RC-Gun circuitry for use with a spare R/C channel. Rev A, dated 06-27-2003

The Small Print:

If you need a part then please consult the sources shown in the project (see schematics download). I do not work for, nor represent, ANY supplier of the parts used in Top RC-Gun. Any reference to a vendor is for your convenience and I do not endorse or profit from any purchase that you make. You are free to use any parts source that you wish.

All information is provided as-is. I do not offer any warranty on its suitability. That means that if you build and use this device, you will do so at your own risk.


If you have technical questions or comments about this project then please post it on the rc-cam project forum.

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