Does a rotating accelerometer moving linearly measure linear velocity?

[Nugatory]

The accelerometer is fixed 3 axis attached to the plate. It has a separate gyroscope that has no effect on the accelerometer from what I see.

The separate gyroscope is what allows the accelerometer to calculate and report accelerations along fixed x and y axes, the ones that make sense to us watching this whirling device. Without it would be reporting constant acceleration in the direction of the centripetal force, which does not change relative to the orientation of the accelerometer.

 

[A.T.]

That is what I was wondering earlier. If it measures deceleration then I believe you can determine instantaneous velocity.

This won't be very accurate though. If your object is disk-like, you will have lift and drag. And part of the aerodynamic force will be along the z-axis (spin axis), where it is the constant component, while the double frequency sinusoidal variation is likely the wobble mentioned in post #15.

But at least you can get the current flight direction in local space, which might help you to correct drift errors, when using integration of the gyro data.

 

[A.T.]

The separate gyroscope is what allows the accelerometer to calculate and report accelerations along fixed x and y axes,

I doubt the device is actually doing this, but @FGD should check the documentation, just in case.

Without it would be reporting constant acceleration in the direction of the centripetal force, which does not change relative to the orientation of the accelerometer.

The data does have a constant offset and a sinusoidal variation on top of that.

 

[Nugatory]

I doubt the device is actually doing this, but @FGD should check the documentation, just in case.

These little (and ridiculously inexpensive) accelerometer devices are used in drones, an application which really cares about orientation in space and accelerations relative to the earth's surface so I wouldn't be that surprised. But yes, the documentation will be authoritative and I'm speculating.

 

[FGD]

This won't be very accurate though. If your object is disk-like, you will have lift and drag. And part of the aerodynamic force will be along the z-axis (spin axis), where it is the constant component, while the double frequency sinusoidal variation is likely the wobble mentioned in post #15.

But at least you can get the current flight direction in local space, which might help you to correct drift errors, when using integration of the gyro data.

Yeah, I will have to take into account lift, orientation, etc. But then it should be better than what kalman filters can do alone atm. Just need to make sure it is actually deceleration causing the sin wave.

 

[FGD]

These little (and ridiculously inexpensive) accelerometer devices are used in drones, an application which really cares about orientation in space and accelerations relative to the earth's surface so I wouldn't be that surprised. But yes, the documentation will be authoritative and I'm speculating.

Yeah, it is a fairly cheap acclerometer. The z gyro saturates past 4000dps. The x and y gyros actually give a fairly similar sin wave to the accelerometer data. Here is an image of the accelerometer and gyro data plotted together. So, after seeing this would you conclude the sin wave is from decelleration, wobble, or something else? I actually don't know why I am seeing the sin wave in the gyroscope.

 

[A.T.]

So, after seeing this would you conclude the sin wave is from decelleration, wobble, or something else? I actually don't know why I am seeing the sin wave in the gyroscope.
View attachment 349178

It could be from the wobble. If you look at the video below you notice that the angular momentum vector (which is parallel to the angular velocity vector) is fixed in the inertial frame, while the vertical body axis revolves around it. In the body frame it is the other way around and the angular velocity vector revolves around the vertical body axis, so its X and Y components are sinusoidal with quarter period phase offset.

It might seem weird that the XY-gyro frequency (related to the wobble) is the same as the XY-accel frequency (spin_frequency), and not twice as much like Z-accel (wobble_frequency). But this is because when you transform the wobble_frequency (= 2 * spin_frequency) from the inertial frame to the rotating body frame, you have to substract the frame rotation (spin_frequency), so the wobble_frequency in the body frame ends up the same as the spin_frequency.

The Z-accel doesn't transform like that. because it is linear acceleration along the frame spin axis, so it shows the same wobble_frequency, as in the inertial frame. If your object is disk-like and wobbling, the variation in the Z-accel is likely due to the changing angle of attack, which can lead to big changes of the aerodynamic force direction (lift/drag ratio), especially at small angles of attack.

How does the Z component of the gyro look like?

 

[FGD]

That makes sense. I am going to try and model this but need to make sense of the data. It looks like from the model in the video that the foot of the bear (logo) is pointing down on the right side and then pointing up on the right side so there must be a rotation around the axis. (Like the video says.) The orientation of the sensor according to the datasheet is as the following diagram shows.

I guess when the x axis (gyro) rotates it would effect the linear value of the y axis (accelerometer) which would be 90 degrees out of phase. And the Y (gyro) effects the X (accelerometer).
So I guess the linear accelerometer would just get a centripetal force acting on it from the rotation? But offset also somehow needs to be accounted for.....