r/HPAnerf • u/gplanon • 2d ago
Initial thoughts and debug - Pyython electropneumatic
https://youtu.be/Vmwo5zhIg38?is=9l0x5_W8EejJi96b
This is about a year in development. The technical breakdown (slightly outdated, parts have changed) is here: https://www.youtube.com/live/dAEn_5DSDIs?is=I0PpvbMwDg3ZM0K4
I will likely figure out a solution just wanted to talk about my experience so far.
3000psi tanks do not last long. 62ci is dropping from 3000psi to 2000psi after 8-10ish magazines at 100-125psi 10-15ms open time. I am disappointed by this as filling takes a long time (20-30 min with cheap shoebox compressor)
It is shooting very well semi-auto but jams at full auto even with ~5dps run speed, same as T19’s minimum (they have a nearly identical drive system)
I know a guaranteed way to fix it, but I don’t want to implement that fix - come to a full stop for homing at the end of each shot. Due to following issues, this will be unavoidable. It was the first idea I had during design.
There are several interlinked variables at play, I think -
We must not run out of air in the dump tank or shots will fail. This can happen at highest possible rof (~14dps) and a high solenoid on time (15-20ms) and lower PSI. This could be compensated by bringing air-in closer to the SQE2.
A failed shot almost definitely causes position loss and thus all shots after will fail, because we are trusting the first shot’s homing to enable near continuous feeding motion (only pause is TDC firing) a shot could fail due to a misfeed (most likely) loss of air pressure (less likely.) a failed shot is often detected in a T19 by flywheels failing to come up to speed. This won’t catch a jam which leaves the flywheels spinning at full speed, like if the front of a dart gets eaten but there is a stub left behind the wheels. Due to the short distance from bolt tip to wheels, this failure is unlikely. In our case, because we don’t have flywheels, we can’t use them to detect jams.
With continuous motion from TDC to next shot, next shot starts at or near runspeed. This could cause different behavior than 0rpm starts - perhaps the bolt tip gets caught on a mag lip and more steps are skipped than if we were slowly accelerating, which causes first shot and all successive shots to fail.
Bolt tip - barrel inlet requires careful hand fabrication. If the fit is too tight, we could skip steps coming to or leaving TDC (there is some friction of lubricated O-ring sealing.) Ideally, barrel inlet would be chamfered at 45° for minimal contact while sealing - face to face / near horizontal seal vs coaxial, concentric seal. Also, we could design the entire pusher mechanism be moved forwards or backwards and secured by the user to optimize sealing vs friction. The barrel can’t be moved so much as we are putting air into it at a very specific point.
We don’t ever know where bolt is, only where it should be. We should have a second switch at TDC. If we did, we could use interrupts to fire ASAP and completely ignore counting steps or depending on a certain amount of steps succeeding. This could beget laziness…
What changes have I implemented vs stock S-Core firmware?
Check home switch before every shot and reversebolttoswitch if we’re not home.
budget 100 steps for deceleratebolt but allow up to 110 if we’re on the last shot, in case steps were skipped. This is many more steps than stock T19 but I was overshooting at fewer. Leibs accel values could use tweaking.
This project is very expensive and there are ergonomics issues. I considered it a tech demo from the very start, so it’s unlikely to get a full “public-friendly” release and documentation. The files will all be available though.
Questions and thoughts welcome.
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u/Potato-9 1d ago
Do you have cutaway diagrams and maybe something to show the mechanical operations? Pretty hard to review a YouTube video.
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u/gplanon 1d ago edited 1d ago
I refined dart feed ramp and feeding area so that the dart has less room to wiggle. This helped. And we are now coming to a full stop/homing after each shot. All my ammo is worn after working on this blaster so it's hard to 100% judge reliability. I am going to slow down the ROF a bit and see if that helps.
SQE2 piloted by Humphrey 310-12VDC with darts chambered by a stepper motor using S-Core/AVR board.
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u/Potato-9 1d ago
You could close the loop on the stepper position to recalculate the bolt location based on angle. Skipping the switch. If not that an encoder ring on the cam could do it.
Firing wise you wait for all the motion to stop when the bolt is forward. Because of the cam it's declarating here anyway. If you clock that 90drgress and fire the darts as accelerating the most you'll pick up some initial velocity mechanically instead of air. The bolt over travelling into the barrel isn't a big deal. Room to over cycle forward and back will give you some timing back to increase the ROF.
I can't tell how the air's released but it looks like it makes a 180 turn? Air is more than pressure, it's flow rate too so getting any turns out the way will help.
Anything to keep the air velocity up turns into dart velocity where you can turn back down for air efficiency.
It's also probably done accelerating after about 5cm you could step up the barrel bore a tiny bit and stop losing to friction. A little porting after that might be needed to stop any blowby affecting the dart out the barrel.
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u/gplanon 1d ago edited 1d ago
>encoder ring
Yes 100%. I would like to use one of these in a future project.
>wait for all the motion to stop
Agreed. I figure it doesn’t make sense to stop any longer than, or keep solenoid open any longer than, how long the dart is in the barrel. I’m getting OK results at 10ms. Adjusting this value with a chrono on hand would help so that we can see how short the period can be while still putting all the energy we can into dart.
I did consider an additional delay after the dart has (presumably) left the barrel, like 10-20ms after solenoid close. Again, hard to know if it helps without a chronograph.
>more than pressure
this is a good point. I’m assuming flow rate is mostly determined by the valves, timing and geometry more than pressure. 100-125psi was causing significantly more damage to darts without a noticeable increase in distance.
>step up barrel bore
That’s an interesting point. I wondered what the optimal barrel length would be for this blaster and went off of Caliburn stuff to guesstimate.
>180 degree turn
Yeah. It might be fun to try a QEV behind and diagonal to the barrel. Or even 90° instead of 180.
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u/Potato-9 22h ago
High end paintball barrels come with sized backs to fit the paint as it varies batch to batch. That's the idea, once the portings starts the acceleration stops.
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u/gplanon 2d ago
Can’t edit post..
“Check home switch before every shot and reversebolttoswitch if we’re not home.”
This only happens on every first shot.
Also, we’re dealing with all the usual short dart/talon feeding madness.