My goal is to compare the accelerometers on different mobile phones. I figure the easiest way to do that would be to build a simple pendulum, strong enough to swing 250-300 grams back and forth.
Yes–provided you don’t make the pendulum arm excessively long. Servo’s aren’t very fast so depending on the magnitude of the acceleration you want to measure, it may or may not provide the velocity you need.
I’ve never used the Servo Trigger but I don’t know that it has a timer to periodically toggle the direction automatically. Something like the example in the SFE video would work.
What do you want to measure about the accelerometers? Are you interested in what angles the gravity vector produces with it’s components? Of are you interested in the accuracy of the acceleration values? Mounting the phone to a subwoofer and shaking it with low frequencies is another way, using movement in 1 axis at a time. If you know the amplitude of movement and the frequency then you can calculate the forces and acceleration on it.
Valen:
What do you want to measure about the accelerometers? Are you interested in what angles the gravity vector produces with it’s components? Of are you interested in the accuracy of the acceleration values?
Thanks, Valen, for your reply! I’m interested in the accuracy of the detection values. I figure that a pendulum would be close enough to approximating a human arm in walking movement while holding the phone.
I like your idea of the subwoofer! I had an idea along the same lines, but much more crude: mounting different horns, with one part flattened, onto a continuous servo and laying the phones on that and letting the flat part trigger the accelerometer with the ‘bump’ it would make.
MonsterBot:
Yes–provided you don’t make the pendulum arm excessively long. Servo’s aren’t very fast so depending on the magnitude of the acceleration you want to measure, it may or may not provide the velocity you need.
That’s definitely a worry of mine, as the pendulum arm will be a bit over 2 feet long. I’ll make it out of aluminium so the weight won’t be increased a LOT, but I know the longer the arm is the more torque I’ll need.
MonsterBot:
I’ve never used the Servo Trigger but I don’t know that it has a timer to periodically toggle the direction automatically. Something like the example in the SFE video would work.
Please forgive me for being dumb, but could you link this SFE video you’re mentioning? I’m failing to find it.
Oh, I’m so dumb. I did see that video, but didn’t understand that SFE stood for Spark Fun Electronics
Rather than use the Servo Trigger, I decided to pick up an Arduino Uno R3 SMD to control the servo instead. I just placed the order and I’m super excited!
If you are still working in this project you might try this: Use a free swinging pendulum, mount a photocell to detect the passage of the pendulum which then triggers a short burst from an electromagnet properly positioned to give the pendulum a nudge to keep it swinging. No microprocessor and just a few analog components.
