Author Topic: accurate & reliable way to launch stuff at a certain speed ?  (Read 379 times)

tob.s

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accurate & reliable way to launch stuff at a certain speed ?
« on: December 04, 2016, 04:36:31 am »
Hi,

tinkering on ballistics again, atm i have troubels getting my jet-driven projectile to accelrate nearly instantly to a certain variable speed (desired vfront between 50 and 150 ) - atm im using a pid and a counter ( maths operator&multiplexer ) to shut the jet off some 10th seconds after launch and/or as the desired speed is reached. In theory the pid shouldnt alow the projectile to get faster than its setpoint, but if the kp is to high, the initial thrust is so high that the projectile reaches speeds above the setpoint - if the kp is to low though, the projectile doesnt reach the desired speed fast enough. With some trial & error i reached a good precision when using a fixed velocity. However i want to optimise the projectiles flightpath for an relatively flat arc ( so instead of lauching almost straight up when a target is close, the projectiles launch speed should be reduced until a launch at 45° would hit the target )

I also used fast pistons  to toss grenades before, but it doesnt seem very precise / affected by framerate

any ideas ?

tob.s

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #1 on: December 04, 2016, 07:01:37 pm »
changed the design of my launcher a bit so it uses a larger rocket with fins. Also now using a fixed launch angle of 45° and instead just varrying the missiles speed based upon distance ( d=vē/g   if launch at 45° and startpoint and impact point at the same height ). Tends to shoot a bit too far at high distances, but hits accurate at distances around/below 500


cupid_the_conqueror

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #2 on: December 05, 2016, 05:06:32 am »
Take a look at my AutomaticBallisticRocketTurret the rocket should be easy enough to separate from the rest of the turret. the jet just has a thrust of 2,000 and I turn it off after velocity = 2,000

mind you my speed is so fast I don't really worry too much about getting that ballistic drop until the range is REALLY far.
At the end of the day, love conquerors all.

MarvinMan

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #3 on: December 05, 2016, 07:55:41 am »
For small missiles it may be possible to use plasma cannons as a form of propulsion to deliver a fixed impulse.

On planets, missiles will always overshoot at long ranges due to the low gravity at high altitudes and the curved ground dropping away beneath them.

You could try not being especially accurate with the launch and always overshoot the target, then use an air brake/reverse thrust to switch to a more accurate final trajectory when close to the target.

tob.s

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #4 on: December 05, 2016, 12:38:59 pm »
Also thought about adding reverse thrust to that missile, set the lauch to double speed ( so the flightpath should have its highest point directly above the target ) and stop the missile midair when directly above the target, so it will fall down at the target from directly above ( maybee even accelerating as soon as pitch hits -90 )

in the meantime i tried using a hypercannon

edit=vd
« Last Edit: December 05, 2016, 12:41:02 pm by tob.s »

z26

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #5 on: December 05, 2016, 02:22:12 pm »
I cannot see the video in the last post, "This video is private"

Btw i have no solution to your problem, but you inspired me to give another go at a failed project of mine.  Thanks for that :p
« Last Edit: December 05, 2016, 04:37:17 pm by z26 »

tob.s

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #6 on: December 05, 2016, 05:03:28 pm »
video should be public now

z26

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #7 on: December 05, 2016, 05:18:15 pm »
Haha, playing fetch with an hypercube, thats clever.

MarvinMan

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #8 on: December 05, 2016, 08:26:16 pm »
Is there any articular objective for these missiles?

If adding some reverse thrust for trajectory changes is a workable solution, it wouldn't take much more to have a couple of control surfaces to constantly adjust the flight path.

If it's acceptable to have the missile spinning, it could be possible to steer with a pair of fins and a single elbow/motor.

tob.s

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #9 on: December 06, 2016, 01:21:54 am »
basicly, i just added the fins to make the missile turn accourding to its flight path ( without, the missile would just keep the angle at wich it was launched as theres no air resitance) , so its mainly decorative and to see how much of a differnce the drag would make. One benefit though is that the missiles always hit with the grenade first, while without fins they would crash their rear into the ground short before the target, sometimes even making them bounce of target - as seen on this old bot

MarvinMan

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #10 on: December 07, 2016, 07:55:48 am »
Once it's in a stable flight path, you could have the grenades separate from the propulsion system to continue to the target in a regular ballistic arc.

tob.s

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Re: accurate & reliable way to launch stuff at a certain speed ?
« Reply #11 on: December 07, 2016, 12:41:31 pm »
that idea seems promissing,, will give i a try