Then @Nv7 you can get up to 16G on that sensor:
https://forums.adafruit.com/viewtopic.php?p=776214#p776214
https://forums.adafruit.com/viewtopic.php?p=776214#p776214
I plan on making a new flight computer with the Bosch BHI260AP which supports +/- 16g in sensor fusion mode, however, I am very busy with school so I don't have time to develop that for a while.@Nv7 what accelerometer are you using? I know some of the stock LSMs I've used default to a lower magnitude of measurement to get more accuracy, but I was able to reconfigure mine to do up to 12G (which is still mostly insufficient for HPR, but has done well for MPR and less). Before you go buy new hardware, check if you can modify the configuration of the accelerometer to get larger magnitudes.
- I understand that simulations are a close approximation, and normally my simulations are pretty close to reality (+/- 5m). However, in this flight they were significantly off from reality (20m). If they are this far off they are no longer usefulSorry for the response delay, I've been fighting a virus.
- Simulations are just that, a close approximation of what is reality. You use your real time data to make improves in the simulation calculations, not the reverse action.
- Solid propellant batch to batch burn rates vary. A ±100 ms variation in burn time is not unusual.
- Your 4G accelerometer rail severely limits knowing what is occurring above that value for burn time and velocity calculations. You need to record the actual acceleration values and not a simulated acceleration from a thrust curve.
- Check your servo response speed to understand the servo response delay. This value is given as a time/degree movement, usually 0.1/60° or 0.1/90°. My cheap SG90 test servos are rated at 0.1/60°, but my 90°movement test was 0.2/90°.
- Your canards are producing drag, just not the drag values I would expect.
Yes, but sensor fusion is not supported, and I need orientation data to measure vertical acceleration accurately (otherwise its difficult to account for gravity)Then @Nv7 you can get up to 16G on that sensor:
https://forums.adafruit.com/viewtopic.php?p=776214#p776214
Almost looks like the fin tip is on fire from the rocket motor…you don’t really see it until it just clears the pad then the thrust looks like it catches right as it leaves the pad…..no loss of clear coat or paint I assume or tell tale signs of paint burn?Did a launch today on our new F35-8W motors, but unfortunately it ended up going a lot lower (not sure if it went vertical, hard to tell from POV) and because of that the delay was way too late so parachutes ejected at a very high velocity. Because of this the ring that attaches the parachutes to the payload tube broke. Then, the payload tumbled and the egg mount broke upon impact. Finally, the parachutes got tangled and failed to open so the fin can broke. Here is an image of every part that is broken (which is every exterior component):
View attachment 628579
Luckily the electronics, egg, and motor were completely unharmed (all the delicate and expensive components)!
View attachment 628582
In the video you can see there is a line coming off the fin of the rocket. This follows the rocket throughout its flight and starts when the motor ignites. What is it? Did it cause the rocket to go lower? Here is the video so you can take a closer look:
View attachment 628585
I have also attached the flight data but its not too useful because the fins didn't tilt since it went so low. However, I can see the rocket's oscillations until it tilts over as it approaches apogee. It seems like it flew straight though, until it tilted as the effectiveness of the fins reduced.
View attachment 628588
Torque At 3.7V | 3.6 kg-cm / 50.0 oz-in |
Torque At 6.0V | 5.5 kg-cm / 76.4 oz-in |
Torque At 7.4V | 6.6 kg-cm / 91.7 oz-in |
Torque At 8.4V | 7.1 kg-cm / 98.6 oz-in |
Speed At 3.7V | 0.20 sec / 60° |
Speed At 6.0V | 0.13 sec / 60° |
Speed At 7.4V | 0.10 sec / 60° |
Speed At 8.4V | 0.09 sec / 60° |
Nope, plus this has happened on the same fin can for the past 4 flights and nothing visible has happenedAlmost looks like the fin tip is on fire from the rocket motor…you don’t really see it until it just clears the pad then the thrust looks like it catches right as it leaves the pad…..no loss of clear coat or paint I assume or tell tale signs of paint burn?
The area per fin for the canards is 4.95, and for 2 fins that comes out to 9.9 square inches.Here is your Blue Bird BMS-115WV data:
Torque At 3.7V 3.6 kg-cm / 50.0 oz-in Torque At 6.0V 5.5 kg-cm / 76.4 oz-in Torque At 7.4V 6.6 kg-cm / 91.7 oz-in Torque At 8.4V 7.1 kg-cm / 98.6 oz-in Speed At 3.7V 0.20 sec / 60° Speed At 6.0V 0.13 sec / 60° Speed At 7.4V 0.10 sec / 60° Speed At 8.4V 0.09 sec / 60°
I used a simple beam break opto-coupler jig to measure the rotation time. I had to install wheel encoders on an old robotics project to keep the servos rotating evenly and the robot traveling straight.
Solid propellant motors are a Total-Impulse device. The thrust and burn time are affected by internal and external variables that you have no control over. The two most important parameters you can measure are time and acceleration. Limiting your acceleration to 3 g's produces an accumulative error in acceleration, velocity, and position. If your position is in error, I would assume your Euler angle is also in error. Real time calculations of Euler angles or quaternion vectors requires processor power on the order of ESP32 or Teensy 4.1 at my sampling rates of 500Hz - 860Hz. So, I do post flight calculations. The 6DoF ICM-20649 and the 9DoF LSM9DS1 are working for my applications. I took a quick look at the Bosch BHI260AP parameters, very interesting.
The 15% drag increase due to the canards is an interesting area. I also do not understand this value. Working with university students, they used a variable iris that extended drag panels out into the slip stream to reduce the velocity. The increased frontal area was ~2X. What is your canard area to stability fins area ratio?
I wouldn't worry about the rotational speed of your servos. Not a critical parameter. Your drag increase spikes are approximately 100 ms.The area per fin for the canards is 4.95, and for 2 fins that comes out to 9.9 square inches.
The area per fin for the bottom fins is 7.8, and for 3 fins that becomes 23.4 square inches.
The Bosch BNO055 has a builtin ARM chip that is doing the calculations necessary. I also have some of those encoders and I will see if I can find time to test the rotation rate.
Yes, I have a future PCB planned that will greatly increase the power available to the servos but I haven't gotten a chance to make it yet. However, I think that the servos are working due to the dip in altitude from a high pressure zone created by the canards, the bump in acceleration, and because the rocket goes lowerI wouldn't worry about the rotational speed of your servos. Not a critical parameter. Your drag increase spikes are approximately 100 ms.
What could be important is your servo drive voltage. The available torque increases with drive voltage. Fluctuations in the drive voltage over the 100ms could indicate torque issues.
@Nv7 --If I activate the fins too early, they correct too much and the rocket goes too low. If I activate them too late it goes too high. In addition, as I test different weather conditions all of them need different fin activation times/P values otherwise they go too low or too high. How do I solve this?
The acceleration in the thrust phase exceeds the 4g limit of the accelerometer. Because of this, it cannot be integrated to get the correct velocity so instead I am obtaining this value from the simulation. However, a future design I have made will have a 16g accelerometer so that I can just integrate acceleration for the whole flight.@Nv7 --
Why not integrate acceleration during the thrust phase too ?
IOW, where do you get velocity after burnout ?
-- kjh
You can see in the "temp" column of the flight data it was around 21 C. My barometer corrects for temperature, but I am not sure about the P-Nut altimeter (which is what the TARC competition uses).@Nv7 --
Are your reported barometric altitudes corrected for site temperature and site altitude ?
If your site temperature was above 15C / 59F the corrected barometric altitude will be a tad higher ( and vice-versus ).
See @ihbarddx's Post #45 - in the recent "Altimeters vs. GPS?" Thread where he linked Dan Wolf's Article from the January / February 2019 issue of Sport Rocketry magazine.
Another method for site temperature and site altitude correction is on Richard Nakka's Experimental Rocketry Web Site ...
HTH !
-- kjh
p.s. I like your color scheme !
@Nv7 --You can see in the "temp" column of the flight data it was around 21 C. My barometer corrects for temperature, but I am not sure about the P-Nut altimeter (which is what the TARC competition uses).
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