I apologize for what is likely an ignorant question, but I am fairly new to electronics and have little confidence. I am working on a personal project where I am using a servo motor to move a rod back forth 90 degrees (not exactly, but this analogy should suffice), and I am interested in measuring the instantaneous (angular?) acceleration (I want to use it to calculate torque). Surprisingly, I have come across trouble while researching online for a sensor to do this. My understanding now is that an accelerometer is only capable of measuring linear acceleration (which means the object can't be rotating, right?), while a gyroscope only measures angular velocity when an object is spinning about an axis. Technically, the rod in my project isn't spinning-it's just rotating back and forth between two angles (0 and 90) on the XY plane. Is there a simply way/sensor to do this? More broadly, am I completely misunderstanding the uses of gyroscopes and accelerometers? I hope I explained the issue properly…
Edit: Sorry about the confusion. I am using a servo to rotate a rod back and forth and need to measure the instantaneous torque. While the rod is moving, there will be times at which a force acting against the rod/servo is applied, which means that the torque shouldn't remain constant between experiments.
I thought of a couple of ways to do this, and one idea I had was using calculating the torque using: torque=I (moment of inertia)*angular acceleration. To get the angular acceleration however, I figured I need a sensor. I thought an accelerometer might work, but don't know how I would implement it in my system or if it would even work.
Best Answer
A gyro measures angular velocity, and is relatively insensitive to other movement. You would need to differentiate to get angular acceleration. An accelerometer measures acceleration. Period. It will respond to reorientation with respect to gravity (as gravity is an acceleration). It will respond to linear acceleration. If offset from the axis of rotation, it will respond to centripetal acceleration, which will be related to angular velocity (though if motion is sinusoidal, you will need to keep track of tangential accelerations).
If you can orient the accelerometer to be right on the axis of rotation, you can easily track the orientation with respect to gravity (that is, Z), but not so easily in the xy plane (if that is the earth plane in your system)
Your situation may be easier to use some sort of absolute or relative encoder, which will give you angular position without worrying about drifts and offsets associated with integration.
With your improved description, you might want to die toy measure torque! http://www.omega.com/googlebase/product.html?pn=TQ513-514-FOOTMOUNT&gclid=Cj0KEQiAtZWkBRC9ibSfhoKEyLYBEiQA5fDxkcDLSo3_jC7_lsm5amhIy02A4MfjEriBgxXRaW5BxcYaAgOy8P8HAQ