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Stampede voltage upgrade issue

Bump firing even after fix

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#1 Keola88

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Posted 02 August 2013 - 06:17 PM

I recently modified my Stampede for a small amount of size reduction and a voltage upgrade. It's currently running around 16.8v. When I first put it back together, it bump fired quite a bit. Bump firing means that it continues to fire even after I let go of the trigger. I opened 'er back up, and went to this thread here: http://oznerf.forumo...t-your-cure-now

I did what they said, I increased the strength of the spring for the switch under the orange cover next to the white piece. I also attached a spring to the same white piece and stretched it to a place to secure it, to give it more resistance overall. Yet it still bump fires. I really need some help, and I cannot figure this out. Anyone with any ideas? Thanks in advance!

I did not bypass any switches at all in this blaster. Yet.

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Edited by Keola88, 02 August 2013 - 06:20 PM.

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#2 Mully

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Posted 02 August 2013 - 06:21 PM

What kind of spring are you using?
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#3 Keola88

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Posted 02 August 2013 - 06:30 PM

What kind of spring are you using?


One of the tiny springs from one of the tactical rails on the blaster.
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#4 Mully

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Posted 02 August 2013 - 06:44 PM

One of the tiny springs from one of the tactical rails on the blaster.

Whoops! Should've been more specific, I meant for the main spring, ie OMW spring, 3b spring...
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#5 Keola88

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Posted 02 August 2013 - 07:15 PM

Whoops! Should've been more specific, I meant for the main spring, ie OMW spring, 3b spring...


Oh, haha. All good. It's the stock combined with this one: http://www.ebay.com/...=item20c4680a55

I really need some help with this guys, I don't want this thread to get flushed until I get some solid assistance here :s

Edited by Keola88, 06 August 2013 - 05:52 PM.

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#6 T da B

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Posted 15 August 2013 - 02:34 AM

When you add those springs, you end up putting a tremendous amount of friction on the plunger tube from the white piece. I suspect what's happening in your situation is that the friction from the white piece is slowing down the plunger tube from retracting fast enough, failing to reset the firing cycle in time. Does the plunger retract at all after the first shot? If not, the plunger is not returning fast enough. Lube always helps as well.

Other things to check:
1. Trigger catch activator spring
2. Make sure black return spring isn't caught somewhere
3. Make sure the breech isn't getting stuck in the receiver (caused my brass breeched Stampede to bump fire)
4. If you can hear the gears spinning, but the plunger isn't being pulled then your gearbox may be F-ed in the A
5. Make sure the trigger catch is in the right way
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#7 azrael

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Posted 15 August 2013 - 09:24 AM

I'm running my Stampede with a 16.8v LiPo battery, using an 9kg SGNerf spring and a stock retaliator spring. Used a stronger catch spring, too. Catch return spring or whatever was fine. Make sure all your springs are aligned correctly.
I still ended up getting bump fire or runaway stampede syndrome or whatever.
I ended up shaving a mm or two off the top of the white piece that moves. This prevented it from bouncing onto the trigger switch. Just keep shaving off tiny amounts, you want to take off the minimum amount necessary. Sand, then test. Rinse, repeat.
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#8 MAV13

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Posted 15 August 2013 - 01:14 PM

I'm running my Stampede with a 16.8v LiPo battery, using an 9kg SGNerf spring and a stock retaliator spring. Used a stronger catch spring, too. Catch return spring or whatever was fine. Make sure all your springs are aligned correctly.
I still ended up getting bump fire or runaway stampede syndrome or whatever.
I ended up shaving a mm or two off the top of the white piece that moves. This prevented it from bouncing onto the trigger switch. Just keep shaving off tiny amounts, you want to take off the minimum amount necessary. Sand, then test. Rinse, repeat.


Replacing all the small springs in the blaster with similarly sized, stiffer ones from a Home Depot variety box, coupled with a stiffer spring on the switch got rid of all of my bump-firing. I'm running 16V NiCd batteries and a 25lb Home Depot Handyman spring.

The spring on the switch was the only thing that fixed it for me after I had replaced all the other springs and lubed everything real good. Shouldn't cause any undue friction since the trigger is still pushing the lever the same distance, it just prevents the recoil from making the lever bang against the switch enough to keep firing.

Edited by MAV13, 15 August 2013 - 01:19 PM.

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#9 azrael

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Posted 16 August 2013 - 02:04 AM

Did you cut down that spring? How is the compressed size of that thing even catching haha.

Your white pin spring replacement is the a different solution to the same problem I had. The white think needs to catch on the bolt as late as possible. With the weak spring, or with how tall it is, it catches on the bolt far too easily.
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#10 Keola88

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Posted 19 August 2013 - 03:18 PM

Did you cut down that spring? How is the compressed size of that thing even catching haha.

Your white pin spring replacement is the a different solution to the same problem I had. The white think needs to catch on the bolt as late as possible. With the weak spring, or with how tall it is, it catches on the bolt far too easily.


Apologies, I have not been on nerfhaven in a while. The first shot will always get off, but it either fires about two more and then quits feeding, and just continues to fire, or fires only one dart. Should I just reduce the spring weight, and keep only one spring? Should I reduce the resistance on the white piece? The swtich's spring was replaced with a heavier one, and a return spring was added to the white piece as you can see.
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#11 azrael

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Posted 19 August 2013 - 05:47 PM

Unprotected trustfires, right? Did you remove the thermistor? I forget where it's located though.
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#12 Keola88

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Posted 19 August 2013 - 07:09 PM

Unprotected trustfires, right? Did you remove the thermistor? I forget where it's located though.


Protected Ultrafires, 18650 I believe. And I did not remove the thermistor.
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#13 azrael

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Posted 19 August 2013 - 07:36 PM

You'll want to bypass the thermistor and remove the protected PCB from the trustfires. It's quite easy. Carefully cut the label off, and peel away that plastic cover. You'll see a PCB pad on the flat side. Just rip it off.
I order the wrong kind of Trustfire for testing, and had to do that.


The reason being that at stall, for heavy spring loads, the Stampede will ask for a lot of current. Protection circuits severely limit the burst current a battery can provide. Just don't over discharge your battery (installing a voltmeter can help with this. I'll be posting a guide at some point with some electronic blaster accessories like that.) and it will be safe.
Thermistors also limit the current flow, increasing their resistance as greater and greater currents travel through them, as heat dissipation of power causes them to increase in resistance. This chokes your current flow.

Motors pull a lot of current when working to the max of their torque, like when you start one up. This is called stall current.


Your blaster sounds like it's working, but then the thermistor kicks in and limits the current flow to the motors.
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#14 Keola88

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Posted 19 August 2013 - 09:37 PM

For an unprotected i cant charge it for too long? That is necessary if that is the case, because I cannot sit there and watch my batteries. And sadly, we have no voltmeter. Would I just lower the springload and bypass the thermistor?
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#15 MAV13

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Posted 19 August 2013 - 10:05 PM

Most decent chargers will shutoff when a battery is full, so you should be ok there. If you can't install a voltmeter in your stampede to monitor their charge, just pay close attention to the rate of fire as it will quickly drop off when its time to recharge your batteries; probably from shooting normally to not firing at all in the space of a couple minutes I'd bet.
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#16 MavericK96

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Posted 20 August 2013 - 01:59 AM

I HAD to cut down that white piece to get my modded Stampede (9kg spring and 14.4v battery packs) to stop auto-firing. I think it ended up being about 60% of the thing cut off for me before it worked.
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#17 azrael

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Posted 20 August 2013 - 11:33 AM

Ya, that was the final straw for mine to work on 16.8V.

Keola, you don't need to reduce the spring load. Should be fine once the current is flowing properly.

And when I mentioned the voltmeter, I meant a simple LED one from eBay. Costs like 5 bucks, and is powered by the device it is measuring.
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