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Post by Tank on Apr 13, 2013 23:11:16 GMT -5
As far as M249s go, I'm completely in the dark on what to expect for its power requirements. I usually use an M4 and two 11.1V LiPOs at 1200mAh get me through a day of playing.
I just bought an A&K M249 back a few weeks ago and have spent a lot of time correcting all of the well known issues that plague these guns. I've finally reached the light at the end of the tunnel and now need to know what I needed to power this beast.
The stock battery, a 9.6V 1200mAh NiMH, I realize is likely complete junk but was only able to get me through less than half a box mag. This is an extreme estimate since I have fired it several times while working out feeding issues, without recharging the batteries, but I had about a third of a mag left today and barely got through it. Overall I'm estimating about a little less than half a box mag worth of firing on this charge. The firing that was done today was very heavy on the trigger, since I was trying to make sure the feeding issue was resolved.
My question is, what are all of you SAW gunners using to power your beasts, and how many mags do you get through with it? I'm assuming a standard box mag of around 2500 rounds to constitute a mag.
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Post by Ghast on Apr 14, 2013 3:15:51 GMT -5
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Post by X on Apr 14, 2013 8:51:00 GMT -5
So I was pondering this question last night and I ran some numbers in my head.
Say that our guns consume 20A of current. This is probably an overestimate, but it should be close. With a 2000 mAH battery you could hold the trigger down for 6 minutes. If you are shooting a leisurely 10 RPS, you would shoot 3,600 BBs in that amount of time. That's 1.8 BB/mAH. This coincides with what I've read that you can expect 1-2 BBs per mAH. The only problem with that estimate is that if you are shooting in short bursts you will get less BB/mAH because of the energy necessary to get the gearbox up to speed. I don't think there is a way to figure out how much current that is without using our current measuring equipment from work or actually testing it. Luckily we have a few games before NL4 to figure it out.
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Post by Priest (Immortal) on Apr 14, 2013 11:11:33 GMT -5
If I were you, I'd contact Casper. He has a wealth of knowledge when it comes to SAWs. He'd be your best bet to answer your question. He'll likely want to know what type of spring you have Installed and wiring, mosfet/low resistence/tomiya or deans to help you pick the right batteries and likely even toss you a few FYI's you might not have thought of.
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Krutch
New Member
To all those against us, good luck.
Posts: 499
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Post by Krutch on Apr 14, 2013 12:49:44 GMT -5
Not trying to thread jack, but did you fix the misfeeding? Had issues with mine since i got it.
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Post by Sniper Wolf on Apr 14, 2013 13:03:18 GMT -5
Ghast is absolutely right, a low power with a wicked high mah rating is the way to go. I know Rider's hobby shop in Flint has a cache of 5000+ mah batteries in 8.4 and 9.6 large type, and for a couple bucks they can chop shop whatever kind of connectors/ adaptors you need.
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Post by Zorak on Apr 14, 2013 13:20:15 GMT -5
I used a 3000mah nimh battery with my m249 and only once ever needed to change it during a game. That was at an early spring game where the lack of greenery meant that I was constantly blasting away at things.
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Post by Tank on Apr 14, 2013 14:51:17 GMT -5
If I were you, I'd contact Casper. He has a wealth of knowledge when it comes to SAWs. He'd be your best bet to answer your question. He'll likely want to know what type of spring you have Installed and wiring, mosfet/low resistence/tomiya or deans to help you pick the right batteries and likely even toss you a few FYI's you might not have thought of. I've been PM'ing back and forth with Casper for all of my build on this M249. I was just wanting to get some information about battery choice this weekend and I didn't know if he would be logged on at all this weekend. X based on your calculations, and the fact that I was doing a lot of bursts, while fixing the feeding issue, I'm guessing that I got about all I could expect from that cheap battery. The bursts would drain more, because of all the start up current drains. When I was heavy on the trigger, the battery wouldn't have the opportunity to "bounce back". Bottom line we will need some massive batteries to get our vehicle through Northern Light this year. Not trying to thread jack, but did you fix the misfeeding? Had issues with mine since i got it. I have gotten the M249 to the point where it dry fires only once every 2 or 3 seconds, possibly longer between dry fires. While working on it a little more last night, I discovered that the mods I made to the hop up chamber feeder hole didn't completely allow BBs to feed freely into it. I've now widened the hole a little more and BBs freely feed into the hop up chamber, with no force required. I've also changed out the feeder spring tube with a new spring that doesn't flare out on both ends. This prevents the BBs from double stacking and jamming up. Lastly, I sanded down some of the posts in the gravity feed in the mag. This makes it fit correctly and prevents double stacking in the gravity feed.
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Post by X on Apr 14, 2013 15:22:51 GMT -5
It's hard to say. As long as I can get a whole mag out of a battery that's good enough. Those lipos can charge in 12 minutes assuming the Hyperion charger can dish out the current.
Sent from my DROID RAZR using proboards
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Post by Tank on Apr 14, 2013 15:28:41 GMT -5
It's hard to say. As long as I can get a whole mag out of a battery that's good enough. Those lipos can charge in 12 minutes assuming the Hyperion charger can dish out the current. Sent from my DROID RAZR using proboards It can dish out the current. Can your power feed wiring provide enough supply? That is the question. Also, keep in mind we will be tearing through a mag in no time at, Northern Light. Edit: I just got done charging the battery that came with the gun. I only put 684mAh back into it. So this battery definitely sucks. I'm doing a discharge/charge cycle, on it right now to see what it can handle. At a 5A drain, which I only ever saw 4.2A being drawn (did I mention this battery sucks), I got 817mAh out of it. At a 2.4A charge rate, I was able to put 918mAh back into the pack. So I guessed the moral of this story is, cheap batteries, are cheap. At least I'm not so concerned about my shimming and motor height adjustment now. Now it is evident that the battery just doesn't have much to give.
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Post by X on Apr 14, 2013 20:27:31 GMT -5
According to this we should be good at 50A. I wired in a 30A fuse so we will have to keep under that or remove the fuse if we think that's safe. www.offroaders.com/tech/12-volt-wire-gauge-amps.htmWhats the capacity of that battery? Sounds like you are pushing the charge rate over 1C. Sent from my DROID RAZR using proboards
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Post by Tank on Apr 14, 2013 20:57:07 GMT -5
Yes I did push it over 1C. Any decent battery should easily handle the 2C rate I charged it at. It got warm to the touch, but no big deal.
Edit: We really should put an Ammeter in line with the charging setup, that way we will know if we are getting close to overdrawing.
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Post by specks159 on Apr 15, 2013 8:15:23 GMT -5
You can adjust your motor and gearset in order to improve efficiency. The higher torque your motor, the more efficient. For a maximum efficiency setup you want to get the highest torque motor you can find. A frankentorque is the popular choice. This is a general term used to describe a chaoli armature (stock dboys) fit in a neo magnet can. Chaoli armatures have something like 32 TPA. The drawback is that these are very slow, so now change gear ratios in order to achieve the rps you want from the gun.
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Post by Tank on Apr 15, 2013 8:26:59 GMT -5
You can adjust your motor and gearset in order to improve efficiency. The higher torque your motor, the more efficient. For a maximum efficiency setup you want to get the highest torque motor you can find. A frankentorque is the popular choice. This is a general term used to describe a chaoli armature (stock dboys) fit in a neo magnet can. Chaoli armatures have something like 32 TPA. The drawback is that these are very slow, so now change gear ratios in order to achieve the rps you want from the gun. I may look into changing out the motor, at a later date, but I already have a different one in mind. Casper has been walking me through the modification/upgrade process and already pointed me to a decent high torque motor. Thank you for the input though, I hadn't really thought of the inefficient motor hurting my battery performance. I'm not sure why I didn't think of it, but I didn't none-the-less.
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Bones
New Member
Hellfish! Whaaaaat.
Posts: 538
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Post by Bones on Apr 15, 2013 8:47:16 GMT -5
I have a 9.6 volt 5000mah battery that I used for my MK 43. If you are looking? I have one for you. Wired to Deans. They are Sub C cells thou.
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