Wireless Rocket Motor Analyzer Tests Rockets, Saves Fingers

Testing rocket motors is a dangerous business, as they have an annoying habit of releasing all of that energy a little quicker than you might like. [Jeff Hopkins] knows this, so he made his own wireless rocket motor analyzer that allows him to trigger, test and monitor rocket motors from a safe distance. This involves more than just pushing a button and watching them go whoosh: his platform measures the thrust of the prototype over 90 times a second and transmits this data to him remotely for logging and later analysis. His current prototype can measure engines with up to 400 lbs of thrust. That is a lot, so it is a good thing that his rig can also remotely arm, fire or safe the motors, all over a 70cm wireless radio link that keeps him safely out of the way. It is also built of cheap parts, so if a RUD (Rapid Unplanned Disassembly) does occur, it won’t cost him much to rebuild and start again.

This project is part of a bigger plan: [Jeff] is looking to build a high-power launch platform that can launch an electronics platform high above the earth. Could this be the beginning of the race to be the first hacker in space? We shall see…

17 thoughts on “Wireless Rocket Motor Analyzer Tests Rockets, Saves Fingers

  1. The igniters still need quite a bit of current to fire, by utilizing a super capacitor discharge via transistor switching. The microcontroller needs a serial command with arming code to arm and fire. All in all, very safe.

    The igniter is still not added until the motor is safely in place.

    1. That came off sounding a little strange…

      The igniter needs a decent amount of current, a super capacitor is charged only after the system is armed with an arming code via the wireless serial link. After arming and a brief period of charging, the capacitor can be discharged via another serial command.

      The likelihood of a misfire is akin to a ultra bright LED lighting itself off an empty capacitor.

      Even so, a multimeter is used to insure there is no voltage prior to attaching the igniter.

      1. Both came off fine.
        Are these solid fuel engines made by you? What process is used to make them? That as it happens was the biggest problem faced by the people behind Estes here, and the folks who eventually provided a reason for their existence. Especially since your static test stand is simply amazing.

        1. They are solid, utilizing a sugar fuel (65/17/18 potassium nitrate/sugar/corn syrup). Check out Richard Nakkas site for ideas.

          I’ve had over 30 successful static tests, the largest producing 180lbs thrust.

    2. Hell of a lot better than what I had as a kid.

      I used a Radio Shack garage door opener remote and module to launch my rockets as kid. I used a small motorcycle(?) battery as the power source (caps were still a bit of a mystery at the time).

      The entire thing, launch pad and all, was made into a sort of backpack so I could carry the whole kit out to a field. I used the remote because I tended to launch my rockets West of a creek and the higher launching rockets tended to land East of it. I couldn’t set up Eastward because I didn’t have enough space for them to land. If I stayed westward, I would lose sight of the landing due to a slight rise. So I would set everything up and walk as far as the remote could reach and launch. Of course I didn’t realize adding an antenna would give me greater distance. Then I would race across the creek and climb the rise before the rocket would land… hopefully.

      Thankfully, I realized at leastsome of the danger presented with my setup and took great pains to physically disconnect the battery before setup and used a long cable (about 5 feet or so) to set the battery away in case it did launch while connecting the battery.

      Ah… the dumb stuff we did as kids…..

      1. And I should clarify here, I’m using ematches which do a have a relatively low ignition current by igniter standards. But I can’t even set it off with the full source/sink specs from the microcontroller.

        If I can trust the microcontroller to light an LED when it’s supposed to, I can trust it to do this.

        But to be safe the igniter is wired prior to insertion into the motor. So even if after I’ve checked voltage on the line, and attached the igniter, it would ignite before being inside the motor.

        There are several club based wireless launchers, plenty safe.

    1. I’m a bit confused,isn’t the load cell and analogue sensor and he is using the ADC on board the trinket pro? I’m pretty sure the ADC can at full resolution more than 90 times a second. Or is it a limitation of the load sensor?

      1. I’m using the HX711 with onboard amplification and ADC, not the the Tricket’s ADC. I can run at either 1Hz or 80Hz. The clock source isn’t too accurate and ends up running a bit faster.

    2. Are you sending time stramps with your logging? Mine will average 11 ish ms between sampling. Noise is an issue at lower thrusts, but is working great in my 80-200lb range

      1. Yeah. I’m currently writing xy pairs of time offset from start of logging and force.
        My next unit will likely not be based around the current hardware (HX711 + arduino pro mini), but a teensy.

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