- Tue Feb 28, 2012 3:17 pm
#140446
While on the topic of a stalled motor ... I like the idea of controlling the motor speed via PWM. But you do have to be a little careful not to deprive the motor of enough "umpf" to be able to finish compressing the spring. If the spring takes more torque to compress than the PWM is giving to the motor, it'll stall (stop moving). A stalled motor sucks a lot more current down than a running motor and it's more common to burn out a stalled high-power motor than a stalled low power motor. My guess is your AEG motor would not survive. The kewl thing is that, given your current sensing, I think you could slow the low torque portion of the cycle down quite a bit and recognize when the sector gear engages the spring/piston and ramp up the PWM accordingly. There's something the Extreme guys can't do !
And on the topic of slowing down the motor ... what's the thinking re: a single shot vs burst vs full auto ? A selector switch makes it easy but in keeping with your original concept not to have that, even with a switch (vs a potentiometer), here's a thought off the top of my head (FWIW). Since the cyclic rate is probably too high to allow a person to easily squeeze off a single round at full speed, you could slow the 1'st shot down so that a person could squeeze and release the trigger before the 2'nd shot cycle happens. If the trigger is still depressed the logic switches to burst mode and checks to see if the trigger is still held after the 3'rd (or 5'th, whatever your burst length is) and then goes into full auto mode. I guess a delay after #1 shot would work as well. The question is then if the extra 100-200 msecs delay to get into full auto is annoying enough to warrant a separate selector switch and whether any switch bounce will complicate the scheme.
StaticDet5 wrote: I'm eyeing a car battery in the corner, but I'm wondering if that will destroy things... Here's where that lack of electrical confidence comes in to play. At my heart, I know a volt is a volt is a volt (and an amp is an amp is an amp), but hooking that massive brick up to something like this... dunno. Somewhat intimidated.The car battery will be something like 12.2 - 12.8 V and the LiPo was ... 11+ V ?? So the voltage is a little higher but I doubt that would make much of a difference to the motor, it's not that big a % increase. But the car battery will supply 100's of amps upon demand, the LiPo somewhat less. So IF the motor stalls and IF the LiPo not supplying enough amps to fry it was the motor's saviour (I doubt this to be the case), then the car battery would surely fry the motor under that condition. I'd not worry about it, there's a fuse for that ... isn't there ?
While on the topic of a stalled motor ... I like the idea of controlling the motor speed via PWM. But you do have to be a little careful not to deprive the motor of enough "umpf" to be able to finish compressing the spring. If the spring takes more torque to compress than the PWM is giving to the motor, it'll stall (stop moving). A stalled motor sucks a lot more current down than a running motor and it's more common to burn out a stalled high-power motor than a stalled low power motor. My guess is your AEG motor would not survive. The kewl thing is that, given your current sensing, I think you could slow the low torque portion of the cycle down quite a bit and recognize when the sector gear engages the spring/piston and ramp up the PWM accordingly. There's something the Extreme guys can't do !
And on the topic of slowing down the motor ... what's the thinking re: a single shot vs burst vs full auto ? A selector switch makes it easy but in keeping with your original concept not to have that, even with a switch (vs a potentiometer), here's a thought off the top of my head (FWIW). Since the cyclic rate is probably too high to allow a person to easily squeeze off a single round at full speed, you could slow the 1'st shot down so that a person could squeeze and release the trigger before the 2'nd shot cycle happens. If the trigger is still depressed the logic switches to burst mode and checks to see if the trigger is still held after the 3'rd (or 5'th, whatever your burst length is) and then goes into full auto mode. I guess a delay after #1 shot would work as well. The question is then if the extra 100-200 msecs delay to get into full auto is annoying enough to warrant a separate selector switch and whether any switch bounce will complicate the scheme.