DMR Build Probs

[Mad Magpul]

So I finally got all my parts for my DMR threw them together and the motor wouldn't pull the spring back. When I pull the trigger all I hear is a beep from the motor and the wires will jump from the current.
SETUP
Systema M150 Spring
G&G Standard Ratio 18:1 Gears
Lonex A2 Titan Motor
Extreme-Fire Cheetah 2N MOSFET
11.1v 3300mAh 25c Battery

So I have no clue what could be wrong because i'm almost positive the battery and motor are strong enough. Help is greatly appreciated!

[Star_folder]

You hear a beep from the motor when you pull the trigger? Have you tried resetting the mosfet?

Does the motor click, or beep? Perhaps the connectors are backwards if it is clicking?

[Mad Magpul]

The motor is beeping but I think it is because an overload of resistance. To test I put it back together but with an M120 spring and I had to use a 11.1 25c lipo to pull it back successfully, a 10.8 couldn't do it. Due to this I think my shim job might be the culprit.(I don't know what else could be giving the motor this much resistance)

[Star_folder]

Most likely your shimming is too tight. Can you give us a few more details on how you shimmed your gearbox?

[Mad Magpul]

I do exactly like Dom does in his video starting with the spur and then moving to the bevel and sector. Then I see how it matches up with the piston rack and the pinion gear. Finally I put whatever shims are needed on the top of the gears. I think what happened was I ended up mixing shims between gears because these seem to have a LOT of play so I ended up having about 5 shims just on my spur gear and the pesky things don't like to stay on! But to conclude I will shim it again tomorrow and get back to you if something still is not working out and hopefully have it up and running Saturday to see how it preforms!

[Dominum]

You also have to check to see if the pinion is meshing well with the bevel, because the bevel could be too low or the motor mounted too high. Did you close the GB with everything in it except the spring and try to spin the gears to verify that it was not too tight? With the powertrain you've listed, something must be causing some undue duress for it not to be functioning.

[Mad Magpul]

Yeah I did all that and I put a lighter spring in it and was shooting it on full auto for about a second and a gear broke so I'm now in need of new gears. I would like higher torque gears but I would still like decent trigger response. What ratio would you suggest and what brand is both strong but not $150?
Thanks for all the help guys!

[Dominum]

For that you don't need higher torque gears. Buy some SHS standard ratio ones.

[Mad Magpul]

Don't know if it would matter but the spring guide has about 9mm of bearings. But yeah I'll probably get the SHS ones.

[AngryBear]

Here is a shim guide i have heard good things about.

http://www.youtube.com/watch?v=1F0zpkmNux4

[Mad Magpul]

So right now I have gotten the SHS 18:1 gears and they are shimmed but now I have seen my piston is moving up in the gearbox by about a millimeter at most and has caused problems. The sector gear has now carved a line in the pick-up tooth. It's not enough to render the piston useless but without the piston staying down there is no way the piston will move. The gears just simply keep spinning without picking up on the piston. I have no idea if it is the piston or the gearbox shell. I don't even know if anybody has ever had this problem! Sorry for all the trouble!
Thanks
P.S. The AOE has been corrected. And if needed I can provide pictures!

[Star_folder]

Hmmm, I once had that issue with an SHS piston that I had Swiss Cheesed too much, the piston body deformed enough so that the teeth of the sector gear would skip on it. I doubt you've done that.

What gun is this? I didn't see it mentioned when skimming the thread, but I feel like you are suffering from poor tolerances, causing the teeth to skip like that. You can try to put a spacer at the top of the gearbox to push the piston down, but that may or may not work, and you risk it coming off and falling in the gearbox if you don't secure it well enough.

[Dominum]

Check and make sure your bushings haven't had a groove worn into them so that the sector gear sits too low.

I have had this happen in an ICS before (split GB+poor tolerances were the culprit), I ended up having to order a piston with abnormally long teeth to get it to work. I like Star_Folder's idea of making a special spacer on the top of the piston. Make it out of POM, and be sure to make it fit very precisely. This will take some time. It will actually have to be made in two halves, one for each side of the shell and the tolerances will have to be very specific. I recommend using a quality epoxy, or maybe a cyanoacrylate to affix it. Polish the portion that will be rubbing on the piston and lubricate it with a viscous lubricant like what you would put on your gears/bushings. I had to make a piece like this for my DSG P90's tappet plate. Due to having to trim 11mm of it (DSG) and the design of the V6 shell itself, it was deflecting off the sector gear. I followed this procedure and it works flawlessly.

[Mad Magpul]

The shell is a Modify Torus 8mm and the piston is a Bravo blue polycarb piston.
The gears seem to be fine. I think I'm going to get a Lonex red piston and then if that doesn't work then I will do as you are saying Dom. Something seems a little skew about the Bravo piston anyway...

[Star_folder]

If the Bravo piston isn't working for you, just skip picking up the Lonex piston. The Bravo piston is a rebranded Lonex.