Gearbox Lockup Solutions

[rail008]

On my gun I've been having constant lockup issues, running a m120 spring by SHS, had gears replaced and shimmed at a local airsoft store, replaced motor with Systema A to Z using 7.4v LiPo. Shoots fine but after a while it would lock up, had motor height adjusted too then after a while back to square one and had to replace pinion gear once already. moved on to m130, now total lock up everytime even on 11.1v and blows fuses right away. After days of searching for solutions, I came up with short stroking the piston by one tooth on the rear end of the rack and regreasing everything with "Dow Corning 33 Extreme Low Temp, Bearing Grease"(had like a gallon bucket already on hand) Shoots like no tommorow.... but what I'm getting at is was this a good solution? Its been a couple a days since I did it without any failures yet.

[CommieHunter]

If it's shooting well, it's probably a fine solution.

My guess for lockup if you have the gears shimmed well is that there's an improper spring tension / gearset torque / motor power combination.

If you have a stiff spring without a high torque motor, it's like trying to start riding your bicycle uphill in the tallest gear. The Systema motors are good, but are designed for 12v, which is where they get all their power. A Systema motor is not ideal for use with a 7.4v battery.

What you have done is increase the voltage to get all of the power out of the motor, as well as short stroke the piston, which reduces the amount of spring tension on the gears at full load (which is usually where it locks up).

The only other 'better' solution would be to use a higher torque ratio gearset, but you can't much argue with results. If it's working now, it works.

[Spartanacus]

By short-stroking the piston, I assume you took a tooth off the sector gear as well, right? And by moving up to a M130, then short stroking, you were effectively reducing the FPS back down. A simpler solution would have been to put the M120 back in.

As far as batteries go, you can't compare a 12v nimh battery to a 7.4v lipo in terms of power output without more information. Modern Lipos universally outperform 12v nicd and nimh batteries in terms of amperage. A decent 7.4v lipo should have no problem pulling an M130 given the rest of your gearbox is setup properly.

If you were blowing a fuse each time it meant your motor was working harder than it should have. I'm guessing your shimming is too tight. There should be about a tenth of a millimeter play with the gearbox fully assembled and screwed tight.

[rail008]

Okay before i modded i did noticed that shimming was right on everything except the bevel gear. I dunno if the technician did it on purpose or not but there is a lot of slop going downwards had like one shim on it but it was to the extent that you could see a good portion of the axle protruding thru the bushing.

[Spartanacus]

Sounds like lazy shimming, allowing the bevel to 'ride' on the pinion.

[rail008]

Sounds like lazy shimming, allowing the bevel to 'ride' on the pinion.

i take its not supposed to?

[CommieHunter]

The motor pinion gear will push on the bevel gear once it's installed. If the bevel gear has play in one direction, the motor prevents it from slipping there anyway.

Some, such as Spartacus (and myself) usually prefer to shim the bottom gear in place anyway. Is it necessary? No. But it feels safer.