Reminiscing: read a post on altimeters and it occurred to me that today's goodies are unimaginably far ahead of the electronics used back in the mid-90s when I started. Back then many fliers used motor ejection, even on large rockets, simply because of the cost of (and probably unfamiliarity with) electronics, which weren't extremely common in the early and mid 90s. One of the early manufacturers I do recall was Adept; their altimeters started around $100 (almost $200 today). Until around 1997 all altimeters used pressure sensors for altitude detection. I don't know which, if any, units had dual-deploy capability, nor what that capability cost. (any Oldguys™ who want to chime in with more info?)
The only thing I bought from Adept was a bare-bones timer kit for about $25. No launch detection, no battery holder, no screw connectors, just a small board with a 555-based timer. If memory serves, resistors were used to set the time. (Never used it, it got thrown away when they cleared out my lab
). You had to solder a battery connector and figure a way to start the timer.
Some units had electronics that would detect launch; on others you had to figure a way to start the unit such as pull-wires or a broken or burned-through wire. I recall seeing one or more that had a spring-loaded microswitch with a spring-loaded lever that supposedly wouldn't activate the switch except on strong acceleration. For a while, one approach was to have a microswitch that would bear against the launch rod (no rails back then); when the rocket cleared the rod the switch would snap open/closed, starting the unit. Use of that method ended when (I think) someone used it on a pad that had a rod slightly too small for that switch, and it "detected launch" on arming... Mercury switches to detect apogee were already on the way out.
Most of the early altimeters had no "mach" inhibition, though that changed as more and more fliers were attempting high-altitude machbuster flights. Newer units could be set to ignore the pressure change at mach, often by simply ignoring any pressure change that occurred in the first 2-3 seconds. I recall at LDRS in Amarillo, a full-scale Arcas flew on an N motor. Either the altimeter didn't have a means of inhibiting ejection firing through mach, or it wasn't set properly. The main came out around 760 mph...
I bought the first accelerometer-based altimeter that came out. The Cambridge(?) was about 38 mm wide and 200 mm or so long, and retailed for about $200, or almost $400 today. I don't recall whether it had dual-deploy capability but I don't think it did. As it used an accelerometer, mach inhibition wasn't needed. After using it successfully on several flights I trashed the first one by using it just as an altimeter (no e-ejection) in a rocket that had a bonus delay. Bought another and destroyed it on its first flight by mounting it upside down. Stupidity was really expensive back then...
Today: altitude-only units, some of which fit a BT-5, for as little as $25. Which also buys a dual-deploy altimeter kit no bigger than your little finger. Flight computers handle multiple events and can be activated or accessed by phone. Altimeters that don't require e-matches. Affordable GPS transmitters and receivers. Onboard transmitter/receiver for live readout of altitude, deployment etc. Inexpensive tilt sensors. Chute release that doesn't require BP.
One wonders what the future will bring.
Best -- Terry
The only thing I bought from Adept was a bare-bones timer kit for about $25. No launch detection, no battery holder, no screw connectors, just a small board with a 555-based timer. If memory serves, resistors were used to set the time. (Never used it, it got thrown away when they cleared out my lab
). You had to solder a battery connector and figure a way to start the timer.Some units had electronics that would detect launch; on others you had to figure a way to start the unit such as pull-wires or a broken or burned-through wire. I recall seeing one or more that had a spring-loaded microswitch with a spring-loaded lever that supposedly wouldn't activate the switch except on strong acceleration. For a while, one approach was to have a microswitch that would bear against the launch rod (no rails back then); when the rocket cleared the rod the switch would snap open/closed, starting the unit. Use of that method ended when (I think) someone used it on a pad that had a rod slightly too small for that switch, and it "detected launch" on arming... Mercury switches to detect apogee were already on the way out.
Most of the early altimeters had no "mach" inhibition, though that changed as more and more fliers were attempting high-altitude machbuster flights. Newer units could be set to ignore the pressure change at mach, often by simply ignoring any pressure change that occurred in the first 2-3 seconds. I recall at LDRS in Amarillo, a full-scale Arcas flew on an N motor. Either the altimeter didn't have a means of inhibiting ejection firing through mach, or it wasn't set properly. The main came out around 760 mph...
I bought the first accelerometer-based altimeter that came out. The Cambridge(?) was about 38 mm wide and 200 mm or so long, and retailed for about $200, or almost $400 today. I don't recall whether it had dual-deploy capability but I don't think it did. As it used an accelerometer, mach inhibition wasn't needed. After using it successfully on several flights I trashed the first one by using it just as an altimeter (no e-ejection) in a rocket that had a bonus delay.
Bought another and destroyed it on its first flight by mounting it upside down. Stupidity was really expensive back then...Today: altitude-only units, some of which fit a BT-5, for as little as $25. Which also buys a dual-deploy altimeter kit no bigger than your little finger. Flight computers handle multiple events and can be activated or accessed by phone. Altimeters that don't require e-matches. Affordable GPS transmitters and receivers. Onboard transmitter/receiver for live readout of altitude, deployment etc. Inexpensive tilt sensors. Chute release that doesn't require BP.
One wonders what the future will bring.
Best -- Terry
