Roll Control Questions

[cagz]

Hi all, hope you are well.

Toying with the idea of building simple avionics that maintains the rocket's roll angle so that video capture does not spin like mad. Two questions:

1. Is this as simple as a single-axis gyro driving a servo? Or are there any major complications I am missing?

2. Then comes the probably lame question: I know how to use gyro in a "receiver -> gyro -> servo" scenario. However, there is no RC here, hence no receiver. In this case, I suppose I need something to generate the PWM waveform, at least to keep the servo centred permanently and gyro modulates this further up and down. If this is correct, what is a practical yet lightweight way of driving the servo ? I've considered either using a small, so-called servo tester or building a 555 based PWM generator myself. Both options sounded like workarounds, is there a better way of doing this ?

Many thanks

 

[waltr]

Hardware can be designed and built (555's etc) but it is cheaper and more versitile now to use a processor and write a bit of code.

Look at the Arduino IDE to write software.
It has libraries to generate and control Servo signals and to read sensors like Gyro chips.

I recommend going to Adafruit's web site and read their tutorials on the various breakout boards for processors and sensors. These tutorial are excellent and the best to get started.
Adafruit also has libraries for Arduino IDE for almost all the processors and sensors they sell.
I'm pretty good at circuit design and writing code but use Adafruit stuff since it is just so easy to use.
https://www.adafruit.com
There are a few control systems built for rocket in this forum. Do a forum search and some reading to see what others have done.

 

[OverTheTop]

Use Ardupilot. All the hard work has been done (firmware written).
www.ardupilot.org

You might be able to use one of the smaller (cheaper) flight controllers as you don't want any fancy functions, although you need to get a FC with 2MB of RAM if you want to run LUA scripting, which is what I use for flight status and mode-switching the control during flight.

Will link to my system when the Aus Rocketry website is not broken.

Note also that Ardupilot is open-source so you might be able to see how they have done their control system and code that part into yours.

FYI

 

[OverTheTop]

AusRocketry website is finally back online. For a look at my Vertical Trajectory System here is the link:
https://forum.ausrocketry.com/viewtopic.php?f=56&t=6632
Note that roll control would be very straightforward and not need any of the LUA scripting or other complex electronics. Just the flight computer, power supply, and probably two servos. You can try and get clever and use one servo, but two make for simpler mechanics with less backlash IMHO.

You will be surprised how little canard area is required for roll control, especially as the velocity goes up.