+70G flights with Raven 3

[T34zac]

Since Adrian's inbox is full I figure I might as well ask everyone else this question:

I am wondering if the raven 3 will behave differently than what it's supposed to do if the accelerometer gets maxed out during flight.

I understand that I will not get accurate speed or acceptation data due to this, but I just want to know if there is risk of early deployment.

Any and all help is appreciated, thanks!

 

[COrocket]

I would honestly just use Baro based apogee deployment so you don't have to worry about the accelerometer at all. If you need the data you would need to get a 250G version.

 

[T34zac]

I would honestly just use Baro based apogee deployment so you don't have to worry about the accelerometer at all. If you need the data you would need to get a 250G version.

I didn't know he had a 250g version. Yeah the data is what I'm trying to get (was planning on using a Pico AA1 for data, raven for deployment). Thrust curve tells me an I800 will take an 8oz rocket to Mach 2 at 168Gs. Plus the rocket depends on accelerometer based deployment as there is one static port hole.

 

[cvanc]

I honestly don't know for sure. I've pegged the accel data records briefly on mine, but only under conditions best described as 'catastrophic'

The way to mitigate your concern is to use the baro data to control all trigger events.

 

[T34zac]

But again, I don't want to use baro if I'm flying at Mach 2 with one static port hole. That's why accel is necessary. But I might get a 250g raven since I do need a second one anyway.

 

[T34zac]

But as luck would have it, it's out of stock...

 

[dixontj93060]

I have done this a few times on extreme flights and shared some of these results with Adrian. In each case, the g-scale was pegged, but once back within the operating window, measurements continued for the duration of the flight. And, although I am sure there may be a scenario where you would damage the accel, all my modules have worked fine on future flights.

 

[T34zac]

I have done this a few times on extreme flights and shared some of these results with Adrian. In each case, the g-scale was pegged, but once back within the operating window, measurements continued for the duration of the flight. And, although I am sure there may be a scenario where you would damage the accel, all my modules have worked fine on future flights.

Thanks for the info. The flight I'm planning will be sometime next flying season so hopefully a 250g version will be available before then. That way I won't have to worry about damaging the one I have.

 

[UhClem]

You are very unlikely to damage the sensor with so pedestrian an acceleration. To know for sure consult the data sheet for the sensor in question. (The device should have a visible part number.) Just as an example, the data sheet for the ADXL78 lists an absolute maximum acceleration of 4,000Gs.

On the other hand, deployment will be early. Because the altimeter is integrating the area under the acceleration curve, clipping off part of that curve will result in the integrated velocity being lower than reality. So as the rocket coasts, the integrated velocity will reach zero before the rocket reaches apogee. Perhaps well before. See Figure 9 in my 2004 R&D report for an example.

You can estimate how early by making a reasonable guess as to the area missing from the integration. For example, assume actual acceleration exceeds the measured value by 100Gs for 0.5 seconds. That is 100G * 32ft/sec/sec/G * 0.5sec = 1,600ft/sec of velocity. So when the altimeter things its velocity is zero, it is really 1,600 ft/sec. Ouch.

On the other hand, the ADXL001 says that it is velocity preserving under overload but that seems to be a pretty uncommon feature. And I don't think anyone uses one in an altimeter.