| Introduction | | | | which would broadcast on the allowed |
| What do we need to reliably and safely | | | | surface frequencies. There would still |
| fire our model rockets? Well, the | | | | be no way to avoid the problem which R |
| minimalist approach is simple enough as | | | | Cers face when two people want to use |
| presented by G. Harry Stine in the | | | | the same channel. |
| Handbook of Model Rocketry (excerped | | | | Of course, the battery and controller |
| here) and available through the basic | | | | base could stay near the rocket |
| Estes Electron Beam® launch controller. | | | | (presumably in a small field box) and |
| A small step up is a simple launch | | | | only the handheld unit would need to |
| controller using an external 12v battery | | | | have a long connection to the controller |
| such as the AeroTech Interlock™ launch | | | | base. This means one could use a |
| controller. | | | | low-current signal to trigger a relay in |
| Things which might be desired beyond | | | | the controller base allowing a more |
| this are: | | | | convenient physical connection. Low |
| Higher power battery for quicker, more | | | | current, low voltage (12V) signalling |
| reliable ignition | | | | like used in telephone lines are perfect |
| Removal of the continuity lamp to avoid | | | | for this. Telephone cords come in many |
| firing exotic igniters | | | | flavors, coiled and with built-in |
| Easier-to-manage connection between | | | | retractors. And, it's much easier to |
| hand-held unit and actual controller | | | | handle than lamp cord. |
| Computer interface for launch controller | | | | Also, since telephone cord comes in 1-, |
| | | | 2- or 3-pair conductors (and data cable |
| There is a nice home-brew launch | | | | in 4-pair) you could have additional |
| controller system, designed by Michael | | | | communication channels. The most |
| Moncur. This seems very close to what is | | | | interesting one is to drive a continuity |
| mentioned above. He uses relays instead | | | | indicator on the handset. A handset |
| of a transistor circuit for the | | | | could control up to 7 ignitors (without |
| continuity check, but otherwise the | | | | handset continuity indicators) with a |
| systems are very similar. Another | | | | 4-pair wire (using a common ground). A |
| interesting one-piece system by Robert | | | | trade-off between continuity indicators |
| Bright supports three ignitors at once. | | | | and number of ignitors could be made |
| There are some commercial controllers | | | | here. For example, using 4-pair wire, |
| listed below which already address some | | | | one connection could control 3 ignitors, |
| of these problems. | | | | including continuity indicators. Or |
| Ideas for a Better Launch Controller | | | | 2-pair could control one ignitor and |
| Below are ideas for solutions to the | | | | continuity indicator. |
| improvements suggested above. These are | | | | Note that using telephone wire and |
| designed for minimal hardware ability. | | | | direct signalling such as described |
| Luckily there are many pre-made units | | | | above requires no special tools or |
| for prototyping embedded systems which | | | | knowlege and should be 100% reliable. |
| provide useful functionality. | | | | Noise won't affect the signal. RF won't |
| Higher Power Battery | | | | create a strong enough current to switch |
| For the best results use a motorcycle | | | | a relay. You can't launch someone elses |
| battery. Lead-acid batteries can source | | | | rocket without the physical connection. |
| a large amount of current, will launch | | | | Computer Interface |
| many rockets on a single charge and can | | | | Why would you want a computer interface? |
| be recharged. Sealed motorcycle | | | | Well, if you have to ask you probably |
| batteries (unbiquitous in R/C airplane | | | | don't. Suffice it to say that if you |
| field boxes) are also relatively small | | | | have more than one hobby, the temptation |
| and light. | | | | to combine them is great. |
| Apparently NiCd batteries are also good | | | | Of course, there are real reasons to |
| for this use since they will put a lot | | | | have computer control as an option: |
| of current into a short. A large NiCd | | | | Synchronization of multiple rockets or |
| pack might be the best answer. | | | | multiple engine rockets |
| Motorcycle batteries have also been | | | | Overall control of a launch site to |
| regularly used for starting R/C airplane | | | | prevent multiple simulataneous launches |
| motors and have never presented problems | | | | Synchronization of launches with |
| doing so. | | | | external events |
| Of course, if you have a source of A/C | | | | Synchronization of on-board instruments |
| power, you could use a standard A/C | | | | with launching |
| brick to get a quick 12VDC (or 6, 9, 15, | | | | There are several obvious approaches to |
| 18V) power source, however if you want | | | | computer integration: |
| to keep your setup totally portable, A/C | | | | An external controller which |
| power and car batteries aren't options. | | | | communicates to the computer through an |
| Lantern batteries apparently can't | | | | RS232 interface |
| source the necessary current, have short | | | | An custom internal (PC card) controller |
| lives at high current levels, and aren't | | | | A digital I/O card with solid state |
| rechargable. | | | | relays |
| Removal of the Continuity Lamp | | | | (It is assumed that the PC can't source |
| This can be done using a simple | | | | the current for launching, therefore it |
| transistor circuit so that the current | | | | is only controlling relays for an |
| leakage across the ignitor is minimal. | | | | external launch controller.) |
| Some ignitors (flashbulbs and electric | | | | Commercial Controllers |
| matches) will fire at low current levels | | | | The Estes Estes Electron Beam® launch |
| (< 60ma) so keeping continuity lamps | | | | controller is venerable (known to |
| buzzers from passing significant current | | | | old-timers as the "Estes Solar"). Estes |
| through the ignitor is essential. | | | | doesn't have a web site, but these can |
| Easier-to-manage Connection | | | | be found in any hobby shop or through |
| The best connection would be wireless. | | | | HobbyLinc in their Estes section |
| There have been arguments not to use | | | | (starter kits). |
| wireless communications because stray | | | | The first step up seems to be the |
| noise or interference could trigger the | | | | Aerotech Interlock™ launch controller. |
| launch. Ideally, the units would use | | | | This unit connects to a motorcycle or |
| digital communication including matching | | | | car battery for power with large |
| serial numbers to avoid noise | | | | aligator clips and provides higher power |
| interference or launching someone else's | | | | than the penlight battery-type |
| rocket. Unfortunately this eliminates | | | | controllers. |
| standard R/C controllers (except maybe | | | | Pratt Hobbies Offers a nice launch |
| PCM) for an off-the-shelf solution. Most | | | | controller which looks like the best of |
| surface R/C radios use AM (since they're | | | | the currently avaialable "box and wires" |
| generally over short distances), but | | | | controllers. More information on the |
| Futaba makes a PCM car radio (the XXX) | | | | Launch Box is on their site. |