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Author Topic: Stampede Gear Question  (Read 1246 times)
Briguy52

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« on: June 22, 2012, 05:51:01 pm »

So, the main issue that I'm having here is that when the plunger tube assembly moves forward, it gets stopped about halfway by the gears in the gearbox. I tested many different "rotations" of the white gear inside the gearbox by manually priming the blaster but it always gets stuck about halfway. When I lift the plunger tube assembly up a little bit from the shell (so that there no longer is any gear contact), the barrel/ breech assembly is able to reach the dart tooth area just fine. From comparing my internals to pictures on SG Nerf's website, they seem more or less the same. (3rd picture here: http://modworks.blogspot.com/2010/07/nerf-stampede-internals-guide.html)

Additional info:
-When firing normally (ie with batteries, etc. instead of manually priming) it makes a really scary grinding noise similar to if you sampled the firing sound of one shot from the stock Stampede and continuously looped it with no pause between shots
-Also when firing normally, the dart does not leave the clip and the breech/barrel does not move forward either
-I originally popped a Home Depot Handyman spring I borrowed from my Nite Finder which caused the dart to move a little bit. I also somehow placed the plunger tube endcap (the circular piece with the square hole in the center and the white ring around it that screws onto the back of the plunger tube with 2 silver screws) upside down but I quickly fixed it after the 1st test fire
-In order to reinforce for the Home Depot spring I was planning on using, I added a foam pad (from a BBB arrow), filled the plunger rod with hot glue (I used a X-acto knife to clean it up so it doesn't catch on stuff), and I have a 3x4.2 volts (12.6 volts) Li-Po battery setup. Right now, I got rid of the Home Depot spring and have everything else the same (but I fixed the end cap of the plunger rod of course).
-When removing the ARs, I did not have a drill bit long enough so I had to pipe cutter the bolt apart at the seam (between the orange and grey plastic tube sections before the plunger tube) but I have since sealed it back and cleaned it up so it won't catch on the plastic ring guide that holds the black return spring back.
-I have tried moving the gear inside the gear box around with a flat head screw driver, but no matter what orientation it starts off with, it doesn't seem to work when manually priming. If I lay the Stampede down and look at it from the top (where the jam door is) I can see a white gear with two halves. The bottom half is all teeth while the top half is about half teeth and half no teeth. If you imagine taking the circumference of it out and laying it flat like this:  _______________^^^^^^^^^^^^^^ , should I rotate the gear so that the toothy part sticks out when un-primed or the flat part?

*If pictures would help, I'd be more than happy to post them. The reason I didn't yet is because after comparing my internals to SG Nerf's internals guide, I can't discern any major differences other than the parts on the plunger where I had to cut to get the ARs out.

Thanks for any advice/help/suggestions!
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torukmakto4

Inhuman Resistance

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« Reply #1 on: June 22, 2012, 06:26:37 pm »

So, the main issue that I'm having here is that when the plunger tube assembly moves forward, it gets stopped about halfway

Your gearbox is blown.

I already replied in other thread but this answered a few of my questions. Go ahead and post some images of the sector/rack area just in case you have something improperly assembled but I am almost certain you should be shopping for a gearbox.

When you get your new one, you should split it, pull apart the 3rd gearset which is 2 piece, flip the input gear over so the solid side is against the pinion, and maybe CA it down to prevent walking-off of the spline which will eventually cause rounding and failure.

You also didn't mention the 3s lipo, or the test fire with the Everbilt clone spring and a dead catch due to the reversed end plate. It's clear what triggered the kaboom now, although I still maintain that your gearbox abuse just shook out a time bomb that could have cost your your brains. A healthy GB should take stalling a 360 motor against a dead catch on only 11.1v just fine. The aforementioned 3s lipo and everbilt clone spring are in no way unsuitable, in fact I would consider that a decent rig if maybe a little low on cyclic rate, and I would recommend 4s, if not 5s depending on motor variability.

EDIT: FYI, the rest position of the sector gear does NOT matter as long as it doesn't mesh with the rack in the wrong place which will cause a single short-stroked shot and jam the first time it is fired after repair. Set it so that the sector teeth are NOT visible outside the GB or meshed with the rack when assembling, and you are good.
« Last Edit: June 22, 2012, 06:34:05 pm by torukmakto4 » Logged

CT-2406
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Briguy52

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« Reply #2 on: June 22, 2012, 06:54:27 pm »

Thanks a ton! It turns out that it's the second gear from the left that got eaten a little bit.
Also, the reason it would stop half way was one of the nubs got lodged in the big gear on the far right causing it to get stuck.
Should I go online or to a hardware store to buy replacements?

« Last Edit: June 22, 2012, 07:32:58 pm by Briguy52 » Logged

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torukmakto4

Inhuman Resistance

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« Reply #3 on: June 22, 2012, 08:26:44 pm »

A little bit? That 2nd pinion is missing about half the teeth, OUCH. First time I have actually seen a 2nd gearset failure, although it is supposedly the second most common failure point behind the 3rd. You will not be able to get these parts at a hardware store. Look online. You may have to just get a new gearbox if no one happens to be parting one out. Having a spare 3rd gearset is always a good idea anyway, and if you want to reuse this one you need to thoroughly clean and check all of the remaining gears from it for damage since they were exposed to debris from the failure.
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CT-2406
Quartermaster of the Florida 501st
You are now entering the Dart Zone

Quote from: Ross_Varn
Rabid squirrels are not an approved special weapon on any campus
hawkdanop


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« Reply #4 on: June 23, 2012, 03:32:27 am »

What could someone do to prevent the gears from stripping? I was thinking about drilling some holes and putting a fan in to blow some air onto them. Would it even help?
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torukmakto4

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« Reply #5 on: June 23, 2012, 10:19:11 pm »

What could someone do to prevent the gears from stripping? I was thinking about drilling some holes and putting a fan in to blow some air onto them. Would it even help?

No appreciable heat is generated in one of these.

It's odd you mention heat, though. High temperature (externally generated) seems to greatly increase the risk of gearbox failure. Never fire a gun that is noticeably hot or has been baking in the sun or left in a hot car until it has cooled. Higher spring loads obviously mean more care is required here. Normal usage doesn't seem to pose problems, not even here in Florida.

My slipping 3rd was the result of picking up a swarmpede that had been cooking in the sun and firing it.

If you are looking to prevent gearbox failure in general, you don't have that much besides common sense. Try to avoid abuse like action lockups, munched darts, late catch timing and bolt hits on mags. All of these shock load or abnormally load the GB. Be sure your springs are not stacking solid and your catch operates before test firing. Don't shoot a hot gun until it cools. Also, perform preemptive service on the 3rd gearset by flipping the spur over and gluing the assembly together. Keep your GB clean and lubricated - they are open and can collect garbage and grit.

Finally, cross your fingers and hope you are in not in the unlucky 1% who will have a failure for no identifiable reason.

Also, as a final note, there is a company producing cast bronze gearsets, in Australia. If you must nip it in the bud once and for all, it's worth a thought.
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CT-2406
Quartermaster of the Florida 501st
You are now entering the Dart Zone

Quote from: Ross_Varn
Rabid squirrels are not an approved special weapon on any campus
hawkdanop


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« Reply #6 on: June 23, 2012, 11:17:21 pm »

flip the third gear? why and looking at it right now, not sure how
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torukmakto4

Inhuman Resistance

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« Reply #7 on: June 23, 2012, 11:27:11 pm »

flip the third gear? why and looking at it right now, not sure how

3rd is 2 piece with a rectangular spline drive between the pinion and the spur. The spur gear is a molded part and has one side solid/flat, and one side webbed. Pull the spur off the pinion, flip it over so that the solid side faces the pinion and reinstall. The solid side is stronger and reduces the chances of stripping the drive.

I also recommend cleaning/washing the drive area to remove oil from the surfaces and gluing the assembly back together with CA, which will prevent walking/disengagement of the drive which can result in damage.
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CT-2406
Quartermaster of the Florida 501st
You are now entering the Dart Zone

Quote from: Ross_Varn
Rabid squirrels are not an approved special weapon on any campus
hawkdanop


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« Reply #8 on: June 23, 2012, 11:50:56 pm »

Like so?

http://i.imgur.com/r7IIS.jpg
« Last Edit: June 24, 2012, 12:18:03 am by hawkdanop » Logged
torukmakto4

Inhuman Resistance

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« Reply #9 on: June 24, 2012, 01:05:31 am »

Correct.
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CT-2406
Quartermaster of the Florida 501st
You are now entering the Dart Zone

Quote from: Ross_Varn
Rabid squirrels are not an approved special weapon on any campus
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