Over-Rotating

Discussion in 'Gun Building, Modifications & Repairs' started by M4Ever, Jul 22, 2012.

  1. M4Ever

    M4Ever New Member

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    San Antonio
    So my M4 has a beautifully shimmed gearbox and I run an 11.1v Lipo, and it's going so fast that my gears are "over-rotating" and bringing the piston back, at least halfway for the next shot, this is on semi automatic. It well sometimes be able to take two shots on semi. I take it this is because of the shimming and Lipo, which are good things, but the over-rotation is annoying. How do I get rid of it. I have been suggested to buy Mosfet, but I know nothing about it. Could I get a little information/advice on what is a good way to remedy this?
    Thanks
     
  2. Lefse

    Lefse Well-Known Member Supporting Member

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    One DIY mod to reduce overspin is to modify the cutoff cam on the sector gear with epoxy. You put on some epoxy on the side that hits the cutoff lever to make it engage it earlier. This will cut off power earlier in the cycle and reduce overspin.
     

  3. Uller

    Uller Well-Known Member

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    Topeka
    Any mosfet with active breaking will do.I had the same problem in a rifle I built until I installed one.I would seriously think about Nors idea before doing that.That would be a short term fix at best,as most epoxies dont bond well on metals.If you wish to explore a fix such as he suggests,I would suggest finding someone good with a tig welder,and performing the same fix by welding,or by brazing.
     
  4. Griffin

    Griffin Active Member Supporting Member

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    A higher-powered spring + short stroking will reduce (or in some cases, eliminate) over-spin.
     
  5. Robin-Hood

    Robin-Hood Active Member

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    Was gonna suggest the same as Griffin.
     
  6. M4Ever

    M4Ever New Member

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    San Antonio
    Ok guys, Thanks a ton for the help.

    @Nor, thanks for the idea, but I'm not sure how comfortable I would be doing that.

    I think I'm going to go with a Mosfet. The link you posted seems good, but i want to know if anyone has any advice as to a certain Mosfet (I guess I need it with the braking feature). Anyone have any suggestions or products I can compare this to?

    Sorry to be the guy who knows nothing, but I need to figure out what gauge my wires are in order to get the proper Mosfet. I have a DBoys M4A1 (yeah I know it's a DBoys, but I've put a lot of work into it). Is there a way I can tell, or do I just need to continue researching?

    Again, Thanks a ton for ya'lls help!!
     
  7. alex

    alex New Member

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    Atlanta
    the proper way to fix it is to use a heavier spring and short stroke it to meet your fps requirements. i use a dream army m130, SS -2 for 400 fps. you can use m120 ss -2 or 3 to get around 350 fps. this will also give you better trigger response and reduce PE with 11.1v high discharge.

    most stock wiring is around 18 awg. works fine for low amp loads (20rps), but needs to be upgraded to 16awg for 30rps.
     
  8. M4Ever

    M4Ever New Member

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    San Antonio
    I would rather not have to short stroke, thanks though. So again (newb Q) can I just go with an 18 gauge or does it have to be the same gauge as the rest? I am not familiar with wires. Thanks Alex!! And I take it i can use a Mosfet without having to short stroke and get a new spring? Thank you so much!
     
    Last edited: Jul 23, 2012
  9. spazzticsmurff

    spazzticsmurff Member

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    phoenix
    well since you dont want to seem to correct your problem the mechanical way and prefer to do it the electronic way. make sure you buy some extra motor brushes and possibly get ready to buy a new motor sooner than you would normaly.

    a few high quality fets that have active breaking that i would recomend are:
    http://extreme-fire.com/2011-SW-CHEETAH-2N.html
    http://extreme-fire.com/2011-SW-PANTHER.html
    the aws raptor (if you can find one for sale)
    the yet to be released btc chimera
    and there are a few others out there.

    active breaking causes faster wear on your motor brushes and has been said to cause your motor to heat up faster. i have actualy melted a motor when i was useing active breaking on a stock classic army high torque motor, it was an older motor with good brushes and springs, (old rc stuff). now i cant positivley confirm weather it was the active breaking or the 11.1v 30c lipo that killed the motor, but i have been useing the same batterys on other stock motors that i have and with out the active breaking i havent melted any other motors.

    edit: you dont have to use the same exact size wire but i wouldnt use anything lower than 18awg low resistance wire.
     
    Last edited: Jul 23, 2012
  10. alex

    alex New Member

    4,791
    9
    Atlanta
    your amp load determines the wire size. if your wires start getting warm, then increase the size. generally, 11.1v works more efficient with 16awg. using 18awg will drop a few rps.
     
  11. Lefse

    Lefse Well-Known Member Supporting Member

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    It's actually not my idea, heard about from a guy over at ASF. I would probably rather go with short-stroking myself, but overspin doesn't bother me much. My AUG has enough overspin to do a 2 round burst in semi hehe.