Comment

Comment by Carl Houtman on June 19, 2012 at 8:58pm

Here are some pics.It is just a series of nipples, tees, and reducers.  As noted before, we use a spring, a latch and a ball valve to release it.  The string running to the right is about 10 feet long, so we can be well out of the way during launch.  The only small problem with this system is that the stop tabs on the ball valve handle get bent after about hundred launches, or so.

Here is a detail of the bike pump and hose connection.  We started with a standard Schrader valve connection to the pump, but it kept coming off, so I used a air hose connection. 

I'm not sure that more pressure will do the trick.  When we increase pressure over 100 psig, the rocket don't go any higher.  One thing we have noted is that longer rockets go higher.  It likely has to do with a longer impulse.  We also experimented with the diameter of the launch tube, and found only a slight improvement with bigger diameters.

Comment by Dan Bramos on June 19, 2012 at 7:51pm

Carl,

I'm very interested in the galvanized steel version. One of the guys at work has built his own UAV and asked me about an automated launch system. I think would do the trick if we can boost the psi just a bit more to compensate for the added weight.

Thanks, Dan

Comment by Carl Houtman on June 11, 2012 at 11:07pm

As a chemical engineer who designs piping systems,  this design has always worried me a bit, PVC does not take cyclic loads well, neither do PET soda bottles, but this is another story.  While a bit more expensive, I built a launcher out of galvanized steel fittings, which are rated to 300 psig.

As to the bike pump,  mine has a built in pressure gauge, which allows us to reproducibly pressurize the tank.  We have found that 80-90 psig is pretty good, 4-500 ft elevation, depending on the rocket design.

Finally, we used a spring-loaded 1" ball valve with a latch on a 10 foot string instead of the sprinkler valve.  This works well and there isn't batteries to go dead.

I guess I could post pictures if anyone is interested.

Comment by James Floyd Kelly on June 10, 2012 at 8:00am

I don't have any suggestions for modding the rockets, but one of the problems I've had with the rocket launcher is that the kids get so excited that they often run straight to the rocket, tripping over either the wires from the push button to the launcher OR they trip over the air tube of the pump.

I'm going to try and come up with a wireless launching device -- maybe using the XBee devices. I'm hoping to make them modular so I can remove the XBee when it's not needed as these are a bit pricey for permanently assigning to the launcher.

I have a question, too -- pumping with a foot pump is a bit inaccurate in the pressure measurement.  Anyone know how to determine just how much pressure this thing can handle (with good seals) if you use Rick's measurements of the tubes as a starting point?  I'm really just wondering how much pressure PVC can handle -- or will the air hose burst first if someone tries to pump it up to much?