M4 Motor Bouncing/clonking

[EscapisT]

Hey guys, I was testing my Umarex 416 today. It's almost fully custom built. Everything operates, but not smoothly. It feels like every time I fire the motor is clonking around inside the grip.

I tried running it with a piece of styrofoam (from a styrofoam dish) inside the frontside of grip to tighten the fit, but it doesn't help. The height is properly adjusted as I can barely hear the gears engaging. Also, the wires are routed behind the motor in the back of the grip.

Ever since I could remember I've always had this issue.. Every time I'd try out other people's m4's they felt much smoother than mine; All I would feel is the light vibration of the motor and the soft thump of the piston as opposed to the motor is bouncing and clonking around in the grip which makes my gun feel cheap and flimsy.

I was reseating the motor today, trying to fix it, and on the 5th attempt, I gave up.. Then I decided to fire it to test for heat (with a barrel plug, to simulate the compression of a BB in the barrel). The grip started heating up but the wires, connectors and battery remained cool. All normal.

Suddenly, it feel like it started to run smoother. Like the clonking gradually disappeared, and it did. It felt like it just magically "broke in". But, simultaneously, it also started making a screeching noise with every shot and got progressively worse. Turns out the cylinder did not have enough lube and the o-ring was sliding dry. The last thing I wanted to do at that point was take it apart now that I had it in that sweet spot. But I couldn't let the piston cycle dry. I re-lubed it and put it all back together and now the clonking is back.

This is soooo frustrating >:[

[MaciekA]

You are going to need to step back and address each issue one by one.

If you are new at this, then the symptoms you are reporting are going to be confusing and may lead you down the wrong path. There's a way to fix this, and a gun doctor will find it fairly fast. If you want to figure it out yourself though, it'll take a bit of time since you may have multiple issues. If it's true that this gun is "almost fully custom built" and it is exhibiting issues like the ones you describe, it seems likely that at least some of the parts were poorly selected, matched, and installed.

I am unsure what your skill level with mechbox maintenance is, but some of your statements above contradict each other and suggest some very weird stuff going on.

For example, there is no way your motor should be "bouncing and clonking" if it's the case that the "height is properly adjusted".

Screeching noises are generally a sign of improper motor alignment and either incorrect shimming or lack of shimming. Your o-ring could be as dry as the desert, but if your shimming and motor height are correct, it will sound absolutely fine.

In general, you should not be placing any styrofoam or anything of the sort into your grip. If you are able to do this and actually impact the placement of the motor, then something is probably wrong. The grip in a V2 setup typically functions as a guide for the motor -- once you have the grip closed, it is essentially like a V3 motor cage -- your motor should NOT move much, if at all, because if it could this would spell trouble for your pinion and bevel gears.

Off the top of my head, here are some possibilites:

• Your grip's height adjustment plate might be missing.
• Your motor is the wrong length.
• Your motor's pinion is too high or two low on the shaft and/or has been paired with a grip that is too different in spec.
• You are not closing your grip correctly.
• You are routing the wires through your grip incorrectly.
• You haven't screwed the grip in all the way to the mechbox or used screws that are too long.
• Your grip can't contact flush with the mechbox due to fitment issues, and there may be a gap between the grip and the mechbox's pinion-hole face (this issue is far more common than you might realize).
• The "clonking" is in your head. You have a bevel gear with a very small number of anti-reversal teeth (i.e. G&P's bevel gears are like this). After firing a shot, your bevel gear reverses a bit and you hear a "clonk". VERY common. I have a teammate's G&P rifle on my work desk this week that exhibits this quirk. Completely normal.
• You have an anti-reversal latch issue. Something similar to the above point.

Some of the things you've said in your post raise some alarm bells and make me wonder if you went too far with your custom build before learning the basics. For example, I don't recommend firing an AEG with a barrel plug to "simulate the compression of a BB in the barrel". If you manage to pull off this kind of compression simulation and the plug is unable to eject, this is an excellent way to strip a piston.

What you should do next is do a basic test for us: Fire one full mag of BBs out of this gun in semi and tell us if it at least works properly. Do a few bursts too. Count the BBs or ideally try to chrono the gun. At that point, if you're still unhappy with the sound and vibration of your motor, I suggest posting a video or audio recording of the gun in action so that we can assist you in troubleshooting this issue.

Hope that helps

[EscapisT]

Originally Posted by MaciekA

You are going to need to step back and address each issue one by one.

If you are new at this, then the symptoms you are reporting are going to be confusing and may lead you down the wrong path. There's a way to fix this, and a gun doctor will find it fairly fast. If you want to figure it out yourself though, it'll take a bit of time since you may have multiple issues. If it's true that this gun is "almost fully custom built" and it is exhibiting issues like the ones you describe, it seems likely that at least some of the parts were poorly selected, matched, and installed.

I am unsure what your skill level with mechbox maintenance is, but some of your statements above contradict each other and suggest some very weird stuff going on.

For example, there is no way your motor should be "bouncing and clonking" if it's the case that the "height is properly adjusted".

Screeching noises are generally a sign of improper motor alignment and either incorrect shimming or lack of shimming. Your o-ring could be as dry as the desert, but if your shimming and motor height are correct, it will sound absolutely fine.

In general, you should not be placing any styrofoam or anything of the sort into your grip. If you are able to do this and actually impact the placement of the motor, then something is probably wrong. The grip in a V2 setup typically functions as a guide for the motor -- once you have the grip closed, it is essentially like a V3 motor cage -- your motor should NOT move much, if at all, because if it could this would spell trouble for your pinion and bevel gears.

Off the top of my head, here are some possibilites:

• Your grip's height adjustment plate might be missing.
• Your motor is the wrong length.
• Your motor's pinion is too high or two low on the shaft and/or has been paired with a grip that is too different in spec.
• You are not closing your grip correctly.
• You are routing the wires through your grip incorrectly.
• You haven't screwed the grip in all the way to the mechbox or used screws that are too long.
• Your grip can't contact flush with the mechbox due to fitment issues, and there may be a gap between the grip and the mechbox's pinion-hole face (this issue is far more common than you might realize).
• The "clonking" is in your head. You have a bevel gear with a very small number of anti-reversal teeth (i.e. G&P's bevel gears are like this). After firing a shot, your bevel gear reverses a bit and you hear a "clonk". VERY common. I have a teammate's G&P rifle on my work desk this week that exhibits this quirk. Completely normal.
• You have an anti-reversal latch issue. Something similar to the above point.

Some of the things you've said in your post raise some alarm bells and make me wonder if you went too far with your custom build before learning the basics. For example, I don't recommend firing an AEG with a barrel plug to "simulate the compression of a BB in the barrel". If you manage to pull off this kind of compression simulation and the plug is unable to eject, this is an excellent way to strip a piston.

What you should do next is do a basic test for us: Fire one full mag of BBs out of this gun in semi and tell us if it at least works properly. Do a few bursts too. Count the BBs or ideally try to chrono the gun. At that point, if you're still unhappy with the sound and vibration of your motor, I suggest posting a video or audio recording of the gun in action so that we can assist you in troubleshooting this issue.

Hope that helps

Thanks for the response,

For the barrel plug thing, I'm positive it's not making so much compression that the gears pre-engage the piston.... but enough to keep the piston from slamming the cylinder head so hard. It seems to work well for testing the gun.


I just fixed some wobble between my upper and lower receiver by bending the tabs on the lower to tighten its fit with the link on the upper. And now that that's fixed, i noticed less "clonking" when I fired it.

It feels a lot more solid now, and there's less vibration resonating through the gun when firing... The "clonking" feeling when firing is definitely coming from the gearbox... It isn't necessarily bad.. Everything functions normally. It's very subtle, but I can basically feel all the moving parts in the gearbox through the pistol grip (stock) and I don't feel it as much in other people's guns.

I think it might be gearbox cycle slightly over-spinning when I let go of the trigger from the residual electricity still in the circuit. It just doesn't "cut" smoothly...
I guess that's what AB mosfets are for?



Internally, stock parts are the GB shell, the trigger+switch assembly, tappet+nozzle, cylinder+head and the motor. Everything else is custom.


Also, I just did some reading and suspect having a non-ported cylinder in combination with a short inner barrel might cause problems. Apparently because the compression is more gradual on a non-ported cylinder, the BB might be exiting the barrel before the piston reaches the end of the cylinder, resulting in a loss of compression and the piston accelerating slightly before hitting the cylinder head. I think this might be a contributing factor to the vibration when firing.

I'm running KA 13:1 gears and the stock motor.... Perhaps if I got a torque motor I'd have a sharper "cut off" and less overspin? Or maybe I should just make a youtube video and see what you guys think I should do.

[MaciekA]

Originally Posted by EscapisT

It feels a lot more solid now, and there's less vibration resonating through the gun when firing... The "clonking" feeling when firing is definitely coming from the gearbox... It isn't necessarily bad.. Everything functions normally. It's very subtle, but I can basically feel all the moving parts in the gearbox through the pistol grip (stock) and I don't feel it as much in other people's guns.

I think it might be gearbox cycle slightly over-spinning when I let go of the trigger from the residual electricity still in the circuit. It just doesn't "cut" smoothly...
I guess that's what AB mosfets are for?

This is all good data.

This is starting to sound more and more like a tiny bit of reversal after a shot happens. Perhaps you're getting a little bit of overspin followed by the gears reversing on the bevel until they hit an AR tooth. You mention below that you have the SHS/KA 13:1 set, so I'm not sure how likely this is since the reversal wouldn't have to go very far to catch a tooth.

I wish I could show you my teammate's G&P I have in my workspace here this week, I'm guessing you'd recognize the "clonk" right away and this would put you at ease.

Internally, stock parts are the GB shell, the trigger+switch assembly, tappet+nozzle, cylinder+head and the motor. Everything else is custom.


Also, I just did some reading and suspect having a non-ported cylinder in combination with a short inner barrel might cause problems. Apparently because the compression is more gradual on a non-ported cylinder, the BB might be exiting the barrel before the piston reaches the end of the cylinder, resulting in a loss of compression and the piston accelerating slightly before hitting the cylinder head. I think this might be a contributing factor to the vibration when firing.

There are some tables you can look up somewhere on the net that give you a good match between barrel lengths and cylinder types. Make sure to double check your matching with some calculation, since tightbore barrels can throw the volume matching off.

I'm running KA 13:1 gears and the stock motor.... Perhaps if I got a torque motor I'd have a sharper "cut off" and less overspin? Or maybe I should just make a youtube video and see what you guys think I should do.

A video would be helpful.

With 13:1 gears, especially if you're using LiPos for your power source, you generally want to be combining them with a high torque motor. It will give you far better trigger response anyway. Make sure to get a neo motor.

As far as AB MOSFETs go, they're very nice and will stop your motor in its tracks immediately, but you have to balance that against expected motor wear.

[EscapisT]

RIGHTO!!

I just got my SHS high torque motor, installed it expecting everything to operate normally... It's just a motor swap right? Wrong. It fails. Somehow, the SHS high torque is unable to pull the piston all the way to the back of the gearbox and it jams up...

I took the SHS out and put the stock back motor in, picking the piston up where the SHS left off, and it cycles normally... What the hell?? How can a torque motor not be able to pull while the stock motor could?? I tried different heights for the SHS to no avail.

One thing I noticed is the Pinion on the brand new SHS high torque is not down the shaft all the way. The pinion itself has a screw in it to hold it to the shaft (unlike my stock motor, where the pinion just slides off). On the SHS, the pinion looks like it still has ~1.5mm to move down the shaft towards the endbell, but I can't loosen the pinion screw cause I can't figure out how.... Like I can't see what kind of head cause it's so small.


I also thought the SHS high torque was purple?? I got a black one... The labels are the same, with the wolf and all... and it definitely has neo magnets cause it goes apesht whenever I set it next to my tools XD




EDIT:

Scratch what I wrote about the gap on the pinion... I guess it's normal


Judging by that picture, my motor is fine... There's that gap between the pinion and the silver thing that the spring sits over..

But my motor still fails to pull the piston all the way while the stock one can do it no problem... WTH? Torque motor my butt!!!!

Also, the SHS is a little longer than the stock motor... oddly, by ~1.5mm.. perhaps because of the gap below the pinion?



EDIT 4:

Solved. Thanks a bunch MaciekA! The motor actually feels really different! And on full auto there's almost no spin-up time!!

[MaciekA]

Originally Posted by EscapisT

Solved. Thanks a bunch MaciekA! The motor actually feels really different! And on full auto there's almost no spin-up time!!

Nice work. What did you end up doing to make it work?

The silver thing is actually kind of a giant bushing / shaft guide, and in many cases at the top it contains a standard bushing, sometimes with ball bearings. It usually is able to move relatively freely, up and down.