KWA SR7 + Perun V2 Hydrid switches off in auto with blinking red light. (Motor Block)

[iNKu]

Hi there, I recently put a new piston (15T Steel SHS) and a new piston head (Maxx CNC Aluminum double o-ring), along with a Perun V2 Hydrid drop in mosfet.
 



The tech who worked on the rifle did the shimming, and said he was forced to shim it a little bit high for one reason or another, but I got it back and did some testing. It's making a very high pitched whine when firing, and in auto it's very high pitched. (Can attach video if necessary.)
 



When firing in auto, occasionally it will just stop and have a flashing red light coming from the mosfet, which is a "blocked motor" according to the mosfet's programming aide.



Could this be that the motor is old and dying? Could the high shimming have caused it? Please help, as I don't want to spend money on a new HT Motor for no reason.
 



Thanks in advance!


NOTE: To my knowledge, the only modifications that have been done are the ones listed above, and a 6.01 tight bore. The rest is all stock.

 

[concretesnail]

Id start by droping the gearbox out of the receiver and then offering up the motor mounted in the grip. If you have a window in the gearbox watch how the motor meets the gear. something is too tight of not sitting where it should. If it were the spring being too heavy id expect excessive motor heat before horrible noise.

 

[Adolf Hamster]

looking at the perun manual the blinking red light is a high current draw, which sounds like the motor's being made to work too hard.

wondering if either the shimming is tight, a box can seem nicely shimmed until you tighten up the case on final assembly and that little bit of compression makes the whole thing tight.

other possibility is the pinion engagement is bad/motor has been set too tight, which would do the same thing.

if it's neither of those then it could be something else like the rack on the piston is tight against the sector or is tight against its guide rails, which would be unusual but by no means unheard of.

 

[iNKu]

@Adolf HamsterApologies, I didn't receive any notifications so I assumed my post got ghosted. 

The tech did mention he shimmed it quite high because he was forced to make a decision to either shim it too tight or too loose, so he chose to shim it too tight. The red blinking light says "Blocked Motor" on my end, but I suppose it can be interpreted the same way. It does get super super hot when using it for a little while, so that sounds consistent with shimming it too tightly, yes?

 

[Adolf Hamster]

yeah this place can be funny for notifications, maybe your settings,  @iNKu 

overheating in the motor is also a symptom, it's all pointing to a tight shim job.

have the gears been changed? if not then i'm curious what on earth this "forced to make a decision" business is about, i'd be contemplating getting a second opinion on that one, that is if you don't feel confident to pop it open and have a crack yourself.

 

[concretesnail]

With that little bit of clarification of your intended meanings, to high being too tight, it could/would be cause of the issues you are having.

A little play is nearly always better than binding, and a good tech being forced into shimming too tight, I doubt it, they should have found another way unless there is something odd going on in the gear box.

Either open it up yourself or take it somewhere else unless you have a vested interest in the tech you've used.

 

[Adolf Hamster]

I doubt it, unless there is something odd going on in the gear box.

the only time i can recall having a similar issue was a set of shs advanced (the ones with the bearings in them), i think that particular set had been assembled incorrectly with the bearing pressed into the wrong side meaning you had to raise the bevel/sector much higher than normal which led to a tight meshing.

needless to say the solution to this problem is to use a different set of gears.....

 

[concretesnail]

needless to say the solution to this problem is to use a different set of gears.....

 Bang on. Turn down a face a hair, get some finer shims, dress the gearbox surface, or bind the gears.

 

[Adolf Hamster]

 Bang on. Turn down a face a hair, get some finer shims, dress the gearbox surface, or bind the gears.

in that case couldn't turn down the face due to the bearings, however yes that would work on normal gears if you had access to a proper lathe.

 

[iNKu]

@concretesnail @Adolf Hamster

so I got the sound sorted out, I haven’t had a chance to test if the motor is still overheating. 
 

the shimming was tight, and that is sorted out now I believe, but the mosfet is still switching off for some reason. 
 

Edit: that is, it’s switching off the battery and blinking red light coming from the mosfet indicating some type of motor block. Really frustrated. 

I think the stock piston was a 14T, and I put a 15T piston in. Could that be an issue?

 

[Adolf Hamster]

I think the stock piston was a 14T, and I put a 15T piston in. Could that be an issue?

@iNKu

it could be if it's catching on the pickup, depends on what kind of attention was put towards the aoe, hard to say without seeing it.

if it isn't cycling could be the sector is hitting at the wrong point and jamming, it's also possible the sector body is rubbing on the rearmost tooth, which would give a similar effect to tight shimming (and also make it a pain to put the box together)

it could also be that the aoe is ok, but the piston is too tight on the gearbox rails and/or has been misaligned on assembly (ie the piston is getting squeezed by the gearbox).

generally when i'm assembling the box, having gone through the shimming i'll tighten up the casing with just the gears in, check they're spinning (holding it at different angles lets you know if the gearx have enough play to bind), then repeat with the piston (no spring) to check how easily the sector can pull it back (easier on v3 boxes to turn the sector) and also how freely the piston slides in general.

 

[iNKu]

@Adolf Hamster @concretesnail



View attachment 81475
@Adolf Hamster @concretesnail

note though, it doesn’t consistently lock up in the same place. Sometimes it will lock up further back. 
 

I don’t have precocking on, I’ve tried enabling it and I’ve tried turning on and turning off active breaking. 

 

[Adolf Hamster]

@iNKu

video doesn't seem to be working?

 

[iNKu]

@Adolf Hamsterseems to be working for me…

 

[Adolf Hamster]

@Adolf Hamsterseems to be working for me…

@iNKuit kinda pops in when i load the page then turns into a normal link, but clicking on it gives me a "can't find the file" page.

tried turning off me adblockers but that hasn't fixed it

 

[iNKu]

@Adolf Hamsterokay so I believe I found out what the issue was with the rifle. It had nothing to do with the shimming, which fair enough was a bit high anyways. Had nothing to do with a motor dying, or a piston too long. 

IT WAS THE BATTERY. The battery's C value was too high, I swapped down to a 20C and now it's working 100%. The battery I had was a 45C battery, which the hobby shop nearby had lead me to believe was fine.

 

[Adolf Hamster]

@iNKu i would be very very careful about that.

if the motor was drawing too much current on the original battery (enough to trip the mosfet), then swapping to a battery with a lower current rating is a very bad idea. the last thing you want is for the gun to be trying to draw more amps than the battery can handle.

what capacities (mah rating) and voltage ratings are these 2 batteries you're using (original 45C one and current 20C one)? did the shop do anything else to the gun besides "try a smaller battery"?

 

[Lozart]

@Adolf Hamsterokay so I believe I found out what the issue was with the rifle. It had nothing to do with the shimming, which fair enough was a bit high anyways. Had nothing to do with a motor dying, or a piston too long. 

IT WAS THE BATTERY. The battery's C value was too high, I swapped down to a 20C and now it's working 100%. The battery I had was a 45C battery, which the hobby shop nearby had lead me to believe was fine.

That's...not how batteries work.

Chances are that the lower C battery is limiting the motors speed which is what the actual problem is. A battery will only supply either as much as it can or as much as the load requires. Running a battery at 100% isn't really the best route, addressing why the load is drawing too much current is a much better method. Fix the cause, not the symptom.