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Voltage Modded Stampede problem... It keeps going, and going, and goin


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#1 stoicclown

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Posted 22 April 2014 - 06:46 PM

Hey guys. Got a weird issue with my recently modded Stampede. Not sure if anybody has encountered this before, so here goes.

I did a basic voltage mod to my stampede, connecting a run-of-the-mill 8 "AA" battery holder from RadioShack into the battery tray. When I load it with 8 standard alkaline "AA" batteries (for a total of 12v), it runs just fine, no issues. However, when I up the voltage by replacing some of the standard batteries with "AA" Trustfires, the darn thing just won't stop firing. I slide the battery tray into the blaster, and everything seems fine. I pull and hold the trigger and it rattles off the rounds like a champ. But when I release the trigger, it doesn't stop firing. The trigger itself isn't stuck in place, it physically releases into it's "relaxed" position, but the motor keeps churning. If I only replace one standard battery with one Trustfire, it will eventually wind down and stop firing after several seconds. But if I replace 2 or more standard batteries with 2 or ore Trustfires, then the thing keeps firing non stop. I have to physically pull out the battery tray from the gun to get the motor to stop cycling.

Any body seen this problem before? Any suggestions?

Thanks!
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#2 snakerbot

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Posted 22 April 2014 - 07:19 PM

First off, don't mix battery chemistries, that's a dangerous practice. They're going to drain at different rates, so you will end up draining some of them too low and venting them. Second off, trustfires are shit batteries for our purposes. They have very little capacity and terrible discharge rate, so you will have slower rate of fire and response time. Use something for the RC hobbyists, like NiMh with a good discharge rate.

Now, since I didn't answer your question, here we go. That's a normal problem with Stampedes. There is a spring-loaded cam that is part of the cycle control system, and when you up the cycle rate too high, the cam doesn't have time to move out of the way before the bolt is already forward again and into the next cycle. Either lower your battery voltage or upgrade your spring.
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#3 Xenomorph1320-D

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Posted 22 April 2014 - 07:20 PM

I know EXACTLY what the problem is and how to fix it. under the catch there is a pushrod that releases the catch when the breech is fully closed. the spring that returns said pushrod is weak and will become stuck. remove the pushrod and simply replace the spring with one from one if those ballpoint pens with the clicker or something of the sort. that should fix any issues


-Xeno

Edited by Xenomorph1320-D, 22 April 2014 - 07:21 PM.

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#4 azrael

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Posted 22 April 2014 - 07:31 PM

Did you replace the spring? Using the stock spring will usually give you a Runaway Stampede.
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#5 Mully

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Posted 22 April 2014 - 07:55 PM

How many Trustfires are you using? If you're filling up the tray, there's your problem. It could also be the pusher-rod under the catch, the direction in which you've placed the catch (if you removed it while modding), or your stampede could be cycling to quickly. If it runs fine at twelve volts, the first two issues can be eliminated; your problem is probably how fast your stampede is cycling.
When you pull the trigger on a Stampede, a white lever coming from the trigger compresses a switch, engaging the motor, which moves the plunger. The plunger holds down the switch until the cycle is completed; holding the trigger down will make the cycle repeat itself, which is what gives the Stampede the ability to fire full-auto. If the system is running to quickly, the switch-lever can't move back to it's original position, which causes the runaway.

Edited by Mully, 22 April 2014 - 07:58 PM.

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#6 stoicclown

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Posted 22 April 2014 - 09:31 PM

Thanks to all you guys who weighed in. I'm a self-taught tinkerer, which means I know a little bitty bit about a lot of things. But I am by no means an expert, especially when it comes to the inner workings of electronics. I'm learning as I go. snakerbot, I found myself particularly educated in the ways of batteries by your post. Thanks for that. A little knowledge is a dangerous thing, so I'm just that much more dangerous now.

azrael, though I do have an upgraded replacement spring (for the plunger), I haven't put that in the gun yet.

snakerbot, Mully, and Xenomorph1320-D: Thanks much for pointing out the bit about the pushrod switch that works with the trigger. To your question Mully, I was trying a maximum of 2-3 Trustfires with all the other slots filled with standard "AA"s. So I wasn't going crazy with those.

Xenomorph1320-D, I tried your suggestion of replacing the spring that operates the pushrod switch. Unfortunately, none of the ballpoint pens I have around here were big enough in diameter to fit around the pushrod. BUT, out of curiosity, I scrounged around and came across a spare tactical rail lock button from a section of tac rail that I removed from the stampede as part of an exterior mod to the shell. That button spring was just about the same diameter and length of the spring that came off of the pushrod, but had a stiffer tension than the original pushrod spring. Soooo... with a little finagling I managed to put that button spring on the pushrod and get the little locking clamp back on to the rod. And what do ya know... it friggin' works. I can use 2 Trustfires in the battery configuration and it stops firing the way it should. 3 Trustfires are still too much, making it run too fast for the new switch spring to shut it off. But the ROF from 2 Trustfires + 6 standard ""AA"s is pretty sweet.

Maybe I'll get my grubby hands on a NiMh battery eventually that I can use to improve and clean up the battery configuration, but for now, the Trustfires are doing the trick.

Thanks again everybody.

Edited by stoicclown, 22 April 2014 - 09:35 PM.

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#7 azrael

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Posted 23 April 2014 - 01:11 AM

Well, FWIW, Trustfires are crap for this application. Better batteries will make it run better. BUT. For many people, there is a bit you need to shave to make it work with better batteries. It's a whole thing to get into. So in that respect, Trustfires can work here.

I can run mine off 4s/16.8v, with a LiPo battery, with around 9-11kg spring resistance, FWIW.
You're absolutely going to need to put in the upgraded spring if you up the voltage. That will honestly probably solve your problem. Run is 3s, with the new spring.
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#8 stoicclown

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Posted 23 April 2014 - 08:06 AM

Thanks azrael. I'll give that new spring a try. My replacement spring is one of the 6+ kg upgrade springs I ordered through Orangemodworks. Also, taking to heart the advice you and snakerbot gave on using better batteries than Trustfires, I went ahead and ordered a new battery holder, one that will hold 10 "AA"s instead of 8 (and has the 9v battery clip connector so I can just change it out with the 8 battery holder while using the same wires I've already attached to the battery tray). Unfortunately my Radioshack doesn't carry anything with a greater holding capacity than 8 batteries, so I had to go shopping on Google. I figure using all standard "AA"s will be safer in the long run (and I've got tons of them lying around), and 10 "AA"s should give me around 15v instead of the 12v I can get from 8 of them, which isn't that far below the roughly 17v I was getting from 6 regular "AA"s + 2 Trustfires. We'll see.

Edited by stoicclown, 23 April 2014 - 08:07 AM.

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#9 azrael

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Posted 24 April 2014 - 12:56 PM

It's not all about voltage, remember. You need a decent current discharge, because as you increase voltage, there is a proportional increase in current demand.
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#10 Langley

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Posted 24 April 2014 - 02:58 PM

An interesting experiment would be to run your stampede off of a bench-top power supply. Run it at the voltage you're planning for and see how much current it draws. Then hook up a multimeter and monitor how many amps the stampede is actually able to get out of your trustfires at that voltage.

I ran my Rayven off a bench top power supply just to see how much current it drew, but it was well within the max for the R/C car battery pack I run it off of.

Don't forget the motor torque is related to current. If your batteries can't source enough current, that may account for a larger drop in RPMs after each shot. I'm not an engineer so I can't really back that up but it is consistent with my crude understanding of electronics and motors.

Edit: Whoops, forgot which gun we were talking about. If you don't have enough current, your motor isn't going to be able to crank through the cocking phase as quickly, as the peak current draw will be when the most force is applied, right before the plunger is released. I was thinking of a flywheel gun when I was talking about RPM drop after each shot.
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#11 PBZ

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Posted 29 April 2014 - 09:13 AM

As several have stated, definitely don't mix your batteries- you came back and said you "weren't going crazy with it"- mixing is bad news, period. even just one trustfire in a stack of AA's can cause problems. moving on.

i don't understand why everyone in this particular thread is hating on trustfires, its what i have used in my stampede since day one. I don't think I've ever actually fired a stampede with D's in it... I run 4 unprotected 14500's and have never had a problem. they charge in decent time and have a great run time. to combat your gun continuing to fire, there are two options that work pretty well and are easy to do:
1. modify the trigger mech (easier): there is a white lever that runs up from the back of the trigger to the bottom of the plunger tube. when the gun fires, it rotates counterclockwise and holds the trigger switch /on/ until the plunger tube retracts, enabling single fire. simply cut or sand the nub off so that it stops interacting with the plunger tube.
2. move the trigger switch (more involved): if you are a little more inclined to doing stuff and things to the internals of your blaster, take out the white lever explained above and its housing. underneath you will find a switch- move this to right behind the trigger and dump in some hot-glue to hold it in place. you may have to re-solder some longer leads to the switch, i don't remember if it will reach with stock wiring but my guess is no. while doing the soldering, un-solder all of the other electronic locks and improve the response time and fire rate of your blaster as well.
both of these options will solve your problem- however, it also means you need to learn to use the gun again. if you hold down the trigger for too short of a time, you will load a dart and not fire. this can quickly lead to jamming issues. simply practice firing until you learn how long to hold the trigger down to fire- remember to have a loaded clip as dry firing with the voltage mod can severely harm the blaster.

hope this helps.

edit: a few little things.

Edited by PBZ, 29 April 2014 - 09:16 AM.

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