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Getting rid of overspin

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Hello,

 

SHS High Torque

SHS piston assembly that weighs 19 grams and has been SS'd two teeth

SHS 18:1 gears, also SS'd two teeth

SHS M130

11.1V 15/25C 1200mAh Li-Po

 

The problem: on semi the setup overspins about a half a piston stroke, very rarely does a two round burst, I am going to upgrade the motor to a Lonex A2 and I would like to hear some of the suggestions how to get rid of the overspin NOT by shortstroking, but any other methods, example, messing with cutoff timings, trigger troleys etc.

 

Any given feedback will be greatly appreciated!

Have a nice day!

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You should be getting around 27rps on that motor /gear combo, but your battery may well be reducing that. It's capable of supplying 18A continuous which is close to what the motor will be demanding, and it's burst rating is considerable below the start up current.

Short stroking won't do anything to reduce over spin, but at that ROF the heavier spring and the short stroke to bring the fps back down is good insurance against premature engagement.

There are two ways you can approach this. One is to reduce the motor speed and increase the resistance it operates against. Moving to a suitable capacity 7.4v lipo and 13:1 gears with a 16TPA motor is a good solid set up with great trigger response, excellent reliability and probably around 23rps with virtually no overspin. The slightly lower ROF also means you can go back to a full stroke piston and an M120 spring.

Plan B is to put an active braking Mosfet into what you've already got. An AB Mosfet is the quick and easy solution, building a system that doesn't need one is probably the better solution.

The Lonex A2 is outperformed by cheaper motors these days. They're pretty hard on their brushes too. For almost the same money you could get an ASG CNC 30K, which is an excellent motor. And to be honest there's nothing wrong with the SHS if you've got one from the good batches, especially once the brush braid is soldered to the brush housing rather than just jammed under the end of the brush spring.

Edited by Hangtight

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If you have a true M130...that should be a major factor in preventing over spin.

 

Trigger contacts have no direct correlation to over spin.

 

Cut off level will not stop over spin either. nor the nub.

 

All three items have no direct bearing on over spin.

 

Nub holds back the nozzle a fraction of a sec longer.

Trigger connects the circuit for electricity.

Cut Off level mitigates SA fire of the gear sets.

Overspin is due to the gears continuing to turn against a weak spring to push the gears part way into the next firing cycle.

Now if you provide the FPS of your AEG with 2 teeth removed and a M130 I can help narrow the cause down.

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There aren't any mods you can do to the cutoff lever that will change its timing.

You could potentially regrind the cutoff cam on the sector gear, but the chances of doing this with anything less than CNC equipment so it actually works? Virtually nil.

There may be a sweet spot in the engagement of the trigger shuttle with the contacts, but the most likely result of trying to modify this is semi auto jams caused by an incomplete cycle.

The reason these are "not so known methods", is because they're not going to fix an overspin problem. I'm fact the most likely outcome is a gun that won't work at all.

Edited by Hangtight

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If it worries you then simply cycle the gun on a 7.4v or NiMh pack at the end of the day so it doesn't overspin.

If you can build a certain amount of overspin in and maintain it through the use of a battery with enough capacity so the voltage doesn't sag, you can actually gain the benefit of the pre cocking effect without requiring an expensive programmable Mosfet. I've done this with a 40k motor running on 7.4v, 18:1 gears and an M100 spring. At first the overspin annoyed me, but once I figured out what was going on and started using a bigger battery, now I get better trigger response in semi auto until the battery sags.

It's not static loads that kill gearboxes, it's shock and fatigue loadings. It doesn't do things like seals much good though.

Edited by Hangtight

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Sort of an AEG with Microswitches yeah...I can see that working. However proceed with a bit of caution cut to much or make a bad loop and you render that spring inoperative.

 

Not to mention since the op is using a 11.1V pack, I bet there is a bit of arcing that contributes to the overspin.

Edited by Guges Mk3

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Sort of an AEG with Microswitches yeah...I can see that working. However proceed with a bit of caution cut to much or make a bad loop and you render that spring inoperative.

 

Not to mention since the op is using a 11.1V pack, I bet there is a bit of arcing that contributes to the overspin.

Of course, we're talking 2-3 coils, depending on how much tension there is already. My CYMA MP5K had no resting tension on the trolley spring and had massive overspin, so I shortened the spring 3 or 4 coils for that one, it helped quite a bit. When there's already some resting tension I only cut 2 coils if necessary.

 

OP, if you have a mosfet installed then arcing won't be an issue.

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This is one of the oldest problems in airsoft ever since higher discharge batteries became common practice.

 

Basically the stock AEG electrical system is rendered obselete by any battery with an increased amperage output. Amps=/=Volts, so you can get this issue from using large type 9.6v batteries and 7.4 lipos, not just 11.1.

 

A mosfet transfers the electrical load from the trigger contacts to the unit. That's why you need one if you're using any lipo. If you have an 11.1 than you're opening pandoras box so to speak with the entire AEG gearbox, pushing it to run at levels not possible when it was designed.

 

What happens is the increased power makes your motor spin harder and the momentum built up from only a single shot is enough to carry the inertia through the entire system and cycle it again.

 

That being said this issue can be eliminated by using a heavier spring, or your problem will increase if you use a lighter spring.

 

that is why if you're overspinning your system needs a little assistance in the form of Active Braking. It stops the motor instantly when you release the trigger, creating a quicker shot and actually resetting the cycle of your gearbox so that it rests at the exact same point after each shot (that is what is considered 'cycle monitoring' and claimed only achievable with BTC fets/Electronic control units)

 

I've been building and running AB fets exclusively for nearly ten years now, short stroking seems to have been a phase because I used to have tons of the UA guys :pain: talking me because I elected to run AB fets instead. You may hear a rumor "AB kills your motor" what actually is happening is that the increased usage makes your brush commutators degrade faster which happens during normal use anyways. But a high performance build means more wear IMO and I'd rather replace $2 brushes than short stroke and try to perm mod any of my gearbox parts.

 

My $0.02

Edited by Sith

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Honestly in the 2 decades of Airsoft I have been in...I have only had over spin less than 5 times.

 

I currently run a near stock G&P with a SSR Mosfet and a 2S lipo with an 80A discharge potential and I don't over spin on this model, I have a 45K motor in it too. So...I don't think its the potential amps.

 

And also note. We hooked up an MG42 AEG as a gun emplacement (feed and fire) to a Motorcycle battery...and that thing did not have over spin either. But, not that you could tell with the ROF it had... :w00t2:

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Lol that mg42 on a motorcycle battery, bet that thing ran a good while too. Your setup draws very low amps. G&P is very efficient and well shimmed and your motor is drawing only what it needs. I doubt that GB draws more than 15A. Sustained auto fire might draw 20 on an 11.1. The 80c discharge is likely peak amps, there's a constant amp rating too that's probably about half of that. 65c constant is extremely high even for RC standards and would probably end up burning out your motor more than anything.

 

Another thing is overspin is an indicator of an unstable gearbox build, not a problem with the system or even something that can be expected to happen. If you're using a motor with strong magnets that alone can prevent overspinning.

Edited by Sith

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Don't assume...ask what is in my box and what I use.

My set-up draws roughly 18A under load. I actually have a device that shows what I draw under load. The G&P mechbox is not stock any more and its shimmed rather 'loose".

 

C is "only" a variable in the calculation to determine Discharge capability. Without mah you will "never" be able to calculate the Amp discharge capability. I have used both Ferrite (stock G&P), AMP and Tienly motors of which none of them has over spun my box.

 

And here is the interesting information. My battery is far excess of your estimation and scope of perceived "RC batteries" I run a LIHV (high output LIPO) Bolt 2S Made by Turnigy. Its 2400mah and the sustained C rating is 65C, yes this is a 150A+ pack. The burst rating is 100C, yes 240A. My motor has not burned up...it won't because as you said...it's "drawing what it needs"

 

Your deflecting from how potential amps causes over spin to a well made box drawing what it needs and that prevents over spin, yet the battery is very large.

The OP's over spin issue is not caused by the Potential DA in your first post.

 

We are all learning still, I am for sure. And we should only help by passing correct information.

 

Here is the pack info if your interested.

https://hobbyking.com/en_us/batteries/turnigy-bolt-lihv.html

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Guges is right, running an "over powered" battery, amperage wise, won't necessarily kill the motor. The thing is, if your li-po battery dumped every possible amp into the wiring, the wiring would literally melt. Even a dinky little airsoft li-po has a short circuit current that's enough to fry the motor in a second. The reason this doesn't happen has a very complicated explanation, but the short version is that it has to do with resistance. I use Gens Ace li-po's that can deliver several kilowatts, more than enough to fry the motor, but my motors hold up for years with these batteries.

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Okay, thank you for clarifying but what Guges said was confusing more than anything, I was the first to mention a motor draws the power it needs. What I was referring to was a possible scenario where a motor was pulling 65c continuously, and in that case it and the rest of the electrical system would be damaged as you said.

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A motor doesn't pull "65C", it pulls a certain amount of amps. I know from experience that the average motor brush in airsoft motors can't handle much more than 40 amps or so continuously before the brush lead burns off. If there's a scenario where the motor will pull every amp the battery can deliver, either motor or battery will fail regardless of battery performance. This is is why we have fuses in our AEG's and use batteries that can put out more current than the fuse rating. You do have a fuse in your AEG?

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Even a humble 15C lipo or a bog standard NiMh is capable of delivering an extraordinary amount of current if you simply short out the terminals.

The battery does not destroy the motor. The motor can only draw the current that it requires to do the job you're asking of it. If you put an exceeding high load on any electric motor it'll try and accelerate it up to its natural running speed which is dependent on the voltage applied. An electric motor generates its highest torque and hence draws the greatest current when it is stationary, or stalled. This is why we fit batteries with a high burst current so they can supply the high start up current needed by high torque motors pushing fast gears, in some cases exceeding 100A. If the motor remains stalled then it will continue to draw this current and wiring, motor brushes, trigger contacts or mosfets will be destroyed. A lesser battery will still supply enough current to destroy the wiring probably before it destroys itself.

 

Which is why we fit fuses...

 

Just thought of the perfect analogy...If the engine is the same, it doesn't matter what size fuel tank and fuel lines are fitted, it won't go any faster. But drop a match in the tank and you're going to regret it.

Edited by Hangtight

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We all started out as clueless noobs. The first ever internal modification I did to an AEG was to transplant the stock spring from my Cybergun (CYMA CM.028) into my TM MP5K to increase the muzzle velocity. Now the only real bottlenecks when upgrading my AEG's is how fast the mags can feed and how much stress the gearbox shell can handle. Live and learn as they say.

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