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# simple voltage circuit for my rocket

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#### cynic

##### New Member
Confession - I do not know what I am doing but the best way to learn is to jump in and build something

I've purchased this board - **broken link removed**

A breif description of the sensors is here - Theory of Operation - Paparazzi

I'm using this board to control a rocket motor mounted to a gimbal and make it fly straight up.

As near as I can tell the sensors are shorted out for lack of a better description. I supply the sensors with 3.3 volts in; easy enough I can wire that up. The sensors (I am guessing) provide differential resistance based on temperature readings.

I then get a variable voltage out somewhere between 0 and 3.3 volts with 1.65 volts telling me that the sensors have an identical temperature reading.

Thus, 0V - 1.64V would mean I need to actuate a servo to the right and 1.66V - 3.3V would mean I actuate the servo to the left.

I do have a small flight computer which I could use to monitor the voltage and run a program to actuate a servo but... I think this will be far to slow to control a rocket motor.

I believe a circuit could do the same thing. If I could create one that activates a switch based on the voltages described then I would get the response time I need and it would be far more simplistic. I suppose that might mean I need 2 circuits for each of the two servos.

I have no idea how to build this other than I probably need a comparator.

Help?? Suggestions??

Thanks!

As near as I can tell the sensors are shorted out for lack of a better description. I supply the sensors with 3.3 volts in; easy enough I can wire that up. The sensors (I am guessing) provide differential resistance based on temperature readings.
If they are shorted, then how can you use them?

When operating normally they sense the temperature difference between the earth and sky.
I then get a variable voltage out somewhere between 0 and 3.3 volts with 1.65 volts telling me that the sensors have an identical temperature reading.

Thus, 0V - 1.64V would mean I need to actuate a servo to the right and 1.66V - 3.3V would mean I actuate the servo to the left.

I do have a small flight computer which I could use to monitor the voltage and run a program to actuate a servo but... I think this will be far to slow to control a rocket motor.

I believe a circuit could do the same thing. If I could create one that activates a switch based on the voltages described then I would get the response time I need and it would be far more simplistic. I suppose that might mean I need 2 circuits for each of the two servos.
Controlling a rocket motor gimbal to stabilize a rocket is far from trivial. Feedback control systems are inherently unstable and need a proper feedback loop for stability. You will need a PID loop such as described in your reference or, if using a computer a Fuzzy Logic loop might be simpler. In either case, you will need to tune the loop experimentally to get stability. I would expect a lot of rocket crashes before this is achieved.

A normal microprocessor should be able to do this, particularly if you use a Fuzzy Logic Loop, but if not, an analog loop using op amp integrators and differentiators would be faster.

A bang-bang system using comparators would be difficult to stabilize.

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