Eccentric cams will not work in this application.
I would say eccentric cams are the simplest and cheapest way to do this. A solenoid would have to be very big to move such a weight through such a distance.
Also the release time of a solenoid is probably not going to be fast enough to allow you true free fall at the rate you are looking for.
This is the part I guess I need help with. Can the plunger not move freely through a de-energized solenoid?
How big a solenoid and what kind of currents will you need to work with? That might be where the real problems lie.
This requires a lot of precision machined parts, which causes these devices to cost thousands of dollars.
Put a magnetic head on the solenoid to lift the hammer. Have the hammer restricted to only lift 40mm. Your solenoid has a stroke of 62mm, but after 40mm of lift the magnet will detach and the hammer will freefall.
That's not the worst idea I ever heard.
The problem that comes to mind is dropping the solenoid plunger back down to pick up the head again would cause a secondary impact that might screw up the test results.
Quote from: kf2qd on Jan 10, 2012, 12:02 amHow big a solenoid and what kind of currents will you need to work with? That might be where the real problems lie.Indeed. The solenoid I linked to would work with 80 Watts in (voltage anywhere from 35 to 340), which isn't too awful, but getting that from an off the shelf solenoid drive IC is probably asking for trouble.Perhaps I can use the arduino to drive a MOSFET directly and control PWM duty cycle in the code. Any reasons this wouldn't work?
You can set the solenoid to drop so that it doesn't drop onto the hammer but rather stop just a little short so the magnetic attraction lifts the hammer. Or simply put a piece of felt on top of the hammer to deaden the click.
You may find that with the usual diode connected across the solenoid, the solenoid doesn't switch off quickly enough. If so, you can speed up the current decay by using a second mosfet to switch the diode out of the circuit when you turn off the solenoid, together with a resistor to limit the back emf. Preferably, you should measure the inductance of the solenoid so that the speed at which the current decays can be calculated. If the current doesn't decay fast enough, the motion of the still-magnetised plunger leaving the solenoid will generate more current and there will be a braking effect.