Problem with Modify gearbox

[sab567]

Hi ASC community,

I just bought a Modify Torus gearbox from airsoftparts.ca and instal it in my custom M4 (use a G&P body, some madbull parts and a mixt of CA and SRC for the other internal parts).
There is my problem:
First I shim the gear, all look's to be correct I assemble the gearbox, but when I pull the trigger all jam and after some try the fuse blow up.
I ask a frien who use the same gearbox and he tell me he has a lot of problem to install it and shim it correcly. He has tried different gear set to find one that work correcly and shim it.
So I try again and reduce the shim, screw the gearbox to be sure shimming is perfect. It's now "work" better, but jam when the piston is back and after some try the fuse blow up.
I tried to remove all shim from the gear, juste to test it, and assemble it again. Now it work, complete the cycle, BUT it sound really bad, like a bad motor ajustment (I tried to ajust it, but never get better). A little grinding sound.
So there I don't know what to do. It's pretty hard to shim and when it's look good in shimming, the AEG don't work proprelly, without shim it work but badly. I don't know if someone had the same trouble or if someone has a solution (maybe a special gear set for this gearbox) or i don't know.
If it's continue on this way, I'll try to find a good guntech near Montréal, maybe he will be able to find a solution.

Thanks a lot

[lurkingknight]

are you using bushings or bearings?

if you're using bushings you might be able to sand the inside face of the bushing to create more room for shims... be super careful otherwise if you don't sand it evenly, the shimming won't work. Also, how are you shimming the gearbox? are you shimming the bevel first to the correct motor height or are you starting somewhere else?

[sab567]

Originally Posted by lurkingknight

are you using bushings or bearings?

if you're using bushings you might be able to sand the inside face of the bushing to create more room for shims... be super careful otherwise if you don't sand it evenly, the shimming won't work. Also, how are you shimming the gearbox? are you shimming the bevel first to the correct motor height or are you starting somewhere else?

I have Bearing into the new gearbox.
I start as I learn with the spur gear, after the sector gear and finaly the bevel. As I look, it seem to be at the right place.
But as I said, it doesn't work with shim in place. I'will try to shim just a little bit and to start with the Bevel gear.
Can you tel me, to be sure, how I can recognise if the bevel gear is perfecly shim to fit with the motor?

[lurkingknight]

you have to take the half of the shell that gives you the best view of the bevel gear when it meets the motor... install the pistol grip on that side of the gearbox and put the motor in. You want the motor in position where it would be if it were fully assembled... and you will need to raise the bevel to meet it, then you shim the others to that adjusted gear. That way your motor pinion will be properly engaged without the bevel being too high or too low.

Here's a video of someone from ASM explaining it with a gearbox that's cut away so you can see how it's supposed to be.
Bevel Gear to Pinion Gear Explained - YouTube

Best Shimming Tip For A Beginner Tech - YouTube

one more
The Art of Gearbox Shimming - YouTube

[sab567]

Ok there is some news.
I reshim with the Bevel gear first, it's don't change anything.
I put out the bearing, and put them in again, one look's to be in angle, So I try again, nothing move. I have the idea my battery is dead... Damn right, I try a 11.1V and it's work proprely now shoot fast and all.
But I hope it's not only because I have a bigger battery (other one was a 7.4V) so It's on charge now.

But a problem still, when I pull the trigger and let the gun fire in full auto (about 50 times I think) the fuse Blow up and the mosfet is hot. I have to say, I blow up my last 20A fuse in the last shimming process so I replace it with a 15A for the actual problem. I'll go afternoon take some 20A fuse and I will see. And let you inform.

Hope this time will work

[lurkingknight]

if something is mechanically binding, overpowering it should not be the solution. That just puts the load on other components.

what motor and spring are you using?

anything under a 120 spring should not need a super powerful battery to turn it over. If it won't turn over unless you're using a 11v or super high discharge battery, you have a problem.

[Kos-Mos]

Sounds like you might have a "defective" piston or mechbox shell.

Not the end of the world, but it means that it might require more than just put parts together to have the mechbox working.

I have a TORUS too and it works perfectly, with shims of course.

What is the thinest shim you have? Maybe it's just because you don't have the right shims. Did you buy a new shim set when you planned on replacing the mechbox shell/gears?

[sab567]

Originally Posted by Kos-Mos

Sounds like you might have a "defective" piston or mechbox shell.

Not the end of the world, but it means that it might require more than just put parts together to have the mechbox working.

I have a TORUS too and it works perfectly, with shims of course.

What is the thinest shim you have? Maybe it's just because you don't have the right shims. Did you buy a new shim set when you planned on replacing the mechbox shell/gears?

Yes I have a shim set with 0.1 and 0.2 and a lot of 0.4 or 0.5 from other gearbox.
I'still working on it, but it look's to work correcly on my last try

[Kos-Mos]

Then you might have to look for tweaks in the mechbox shell or piston rails.

First step is making sure that the outside walls of the shell are perfectly straight. Then check the rails and guides for the piston inside.

You will have to do the same for the piston. It can be warped or demolded too fast, and it's not straight or just too wide as some points.

Also, are you using a bearing spring guide along with a bearing piston head? You don't need both, and if your spring also have a high coil count, it can bind and cause your issues.

[sab567]

Originally Posted by Kos-Mos

Then you might have to look for tweaks in the mechbox shell or piston rails.

First step is making sure that the outside walls of the shell are perfectly straight. Then check the rails and guides for the piston inside.

You will have to do the same for the piston. It can be warped or demolded too fast, and it's not straight or just too wide as some points.

Also, are you using a bearing spring guide along with a bearing piston head? You don't need both, and if your spring also have a high coil count, it can bind and cause your issues.

I have both, spring guide and piston head bearing.
I look for some imperfection to the gearbox and all seem to be good at naked eyes

[ThunderCactus]

Take the cylinder/piston parts out of the mechbox, just leave the gears in.
install all the screws.
Then reach in there with your finger and try spinning the sector gear, it should make 3-6 rotations with a good spin.

If the gears do not spin freely, you could have;
-shimming issue, either gears are touching or shims are too tight
-axle misalignment
-jammed bearing

If the gears do spin freely you might have;
-sector gear may be pressing against the tappet plate, test by pushing the air nozzle back when the mechbox is together, it should move back and forth freely
-bevel gear may still be shimmed too far into the motor
-piston might be jamming in the guide rails
-spring may be too powerful for your battery (which sounds like the case)
-wrong gear ratio for your spring/motor combo
-could very well have a bad motor

SO if you're blowing out a 20A fuse, but the mechbox works with an 11.1v lipo, it means either your motor doesn't have enough torque to move the mechbox, or you have way too strong a spring on high speed gears.

so what exactly is in your mechbox? spring and gear ratio?
and what kind of motor do you have?