greg Posted October 2, 2009 Report Share Posted October 2, 2009 Sorry to be such a catastrophically massive noob but... what's a mosfet? I'm sure someone will come along in a second & give a really serious tec type explanation, but as you are catastrophic newb. : BASICALLY: Tit's a small electronic (not mechanical) switch, which opens to allow the power from the battery to the motor. It uses the mechanical trigger switch as a signal switch, to trip & kind of sends the electricity direct, bypassing the contacts on the gun's trigger. This means the trigger switch's contacts don't get burned out by repetitive use, especially with higher voltage. Typically, faster trigger response & higher rates of fire are achieved than a like for like set up, that does not include a mosfet. Have a look back through this thread for more detailed descriptions, as I'm sure they are in there, somewhere. Greg. Link to post Share on other sites
CrazyApe Posted October 2, 2009 Report Share Posted October 2, 2009 thanks mate Link to post Share on other sites
reaper16 Posted October 2, 2009 Report Share Posted October 2, 2009 Infected, I cant wait to order one of your mosfets come Decmber, and finally get my CA working again... On a technical note, lets say my trigger contacts look like the surface of the moon (long story, 11.1v lipo + no mosfet...yeah I can vouch as to why you need those lil buggers) do I need to replace them to run a mosfet or will the current ones suffice? Since, the current going to the motor inst passing thought them anymore, I wouldnt think i needed to....... Link to post Share on other sites
crackisbad Posted October 2, 2009 Author Report Share Posted October 2, 2009 I would suggest trying to clean them first and see if that makes them any better (I did the same thing in a gun for a while and was able to just more or less wipe the contacts clean) EDIT: Brain Farted. Real information in later posts trumps the second half of post. Link to post Share on other sites
infected Posted October 2, 2009 Report Share Posted October 2, 2009 You don't need to replace them. I would suggest hitting them up with an eraser to clean the carbon off, then use a wire brush to clean them up a bit. Install your mosfet (one of mine naturally ) and you're good to go. Link to post Share on other sites
greg Posted October 2, 2009 Report Share Posted October 2, 2009 Infected, I cant wait to order one of your mosfets come Decmber, and finally get my CA working again... On a technical note, lets say my trigger contacts look like the surface of the moon (long story, 11.1v lipo + no mosfet...yeah I can vouch as to why you need those lil buggers) do I need to replace them to run a mosfet or will the current ones suffice? Since, the current going to the motor inst passing thought them anymore, I wouldnt think i needed to....... As long as the contacts, 'work', you WONT need to replace them. You are right, once a mosfet is installed, they are just making a comparitively low powered 'signal', the mosfet is sending the power propper. Greg. Link to post Share on other sites
teflon don Posted October 2, 2009 Report Share Posted October 2, 2009 I would never buy chips from ebay. There are pleanty of suppliers; MCM Electronics, Jameco, etc that have chips that will do the job with a respectable online shopping cart to KNOW for sure what you're getting. With ebay, you're likely to get junk. As for your question, I would suggest reading the 13 pages of information in this thread. There is more than enough research that you should not be asking if thats the mosfet you should be using. Here is the datasheet for the IC you asked about http://www.irf.com/product-info/datasheets/data/irf1404.pdf Your best bet is to compare it to the datasheets of the MOSFETs others have advertised using. i know that it should work i just wanted a second opinion just to make sure that i don't buy the wrong one and also because they cal it a transistor and not a mosfet i guess i will buy the mosfet on ebay the seller has a received good comments and al so i don't think that he sells junk Link to post Share on other sites
Vice Posted October 9, 2009 Report Share Posted October 9, 2009 Hello, I have just built a AB mosfet setup following Doubletap's rather good guide Clicky! But in the final parts of the instructions, something has confused me somewhat.. Here's the almost finished unit, now's the time to test it Note - you need to add another bit of signal wire from the other side of the trigger switch and join it to the motor+ red wire. Where you join it will be dictated by what gearbox it's going into Anyone able to shed light on this? I belive its refering to unsoldering the red wire in the trigger, and replacing with the fet switch wire? Or is there something I have missed? Cheers -v Link to post Share on other sites
Stealthbomber Posted October 16, 2009 Report Share Posted October 16, 2009 So, does anybody actually produce a mosfet that DOES use proper ACTIVE braking? That is, a circuit that sends a burst of reverse-polarity electricity through the motor to stop it spinning? I ask because it seems that every man and his dog is talking about "active-braking mosfets" and I've yet to see a design that actually does this. The standard N&P fet design certainly doesn't. Link to post Share on other sites
infected Posted October 16, 2009 Report Share Posted October 16, 2009 So, does anybody actually produce a mosfet that DOES use proper ACTIVE braking? That is, a circuit that sends a burst of reverse-polarity electricity through the motor to stop it spinning? I ask because it seems that every man and his dog is talking about "active-braking mosfets" and I've yet to see a design that actually does this. The standard N&P fet design certainly doesn't. You're right, and no I haven't. I've changed the marketing info on my mosfets to just say Braking (well, in most places I'm sure I've still got stuff out there that says "active"). I don't know of anyone that actually reverses the current through the motor. Thinking about it, is there an advantage to reversing the current? I'd think (and I can be wrong), that it would take marginally (maybe negligibly) longer to stop the movement. Link to post Share on other sites
Stealthbomber Posted October 16, 2009 Report Share Posted October 16, 2009 You're right, and no I haven't. I've changed the marketing info on my mosfets to just say Braking (well, in most places I'm sure I've still got stuff out there that says "active"). I don't know of anyone that actually reverses the current through the motor. Thinking about it, is there an advantage to reversing the current? I'd think (and I can be wrong), that it would take marginally (maybe negligibly) longer to stop the movement. That's very honest of you. Glad to see a bit of honesty prevailing. FWIW, the main use of proper "active" braking is in r/c cars. In that arena it's possible to program the transmitter to send a quick burst of reverse to the servo when the throttle is moved to the 0% position. This will, obviously, bring the car to a halt much quicker than if it just coasts to a halt at zero throttle. Obviously, this is a "software" solution to the issue and, unless we're building proper "fire computers" with microcontrollers built in we can't do this without several more components. TBH, I think passive braking is fine. Once you start getting into active braking you risk putting huge loads on the mechanical and electrical parts. Again, this isn't such a big deal with an r/c car because, ultimately, everything a car does goes through the tyres. If it's doing 30mph forwards and you shove a reverse current through the motor all that happens is the tyres lose traction and the car skids. Hello, I have just built a AB mosfet setup following Doubletap's rather good guide Clicky! But in the final parts of the instructions, something has confused me somewhat.. Anyone able to shed light on this? I belive its refering to unsoldering the red wire in the trigger, and replacing with the fet switch wire? Or is there something I have missed? Cheers -v I did a bit of a sketch showing how a complete mosfet circuit is layed out because I notice that most of the places with these guides on the internet seem to show a few things and then finish with something a bit vague or confusing. I've tried to do the sketch roughly how you would physically wire everything together to avoid confusion. Note that there's still a bit of latitude for creativity. There's nothing to stop you hooking the +ve wire from the trigger up to the +ve terminal of the motor, for example. I'd suggest running all the wires back to the mosfet and then fitting suitable connectors to them. This'll mean that you can unhook the trigger wires, motor wires and battery wires in a sensible way if you ever have to strip the gun down. *EDIT* Removed picture and replaced it with a PDF.... just for laughs, so I can see how many times it's downloaded. mosfet.pdf Link to post Share on other sites
Bersy Posted October 16, 2009 Report Share Posted October 16, 2009 Nice diagram Stealthbomber! makes it alot easier to see what goes where! I've been using micro deans on the trigger wires which makes it easier to disconnect the mosfet while taking the aeg apart! Link to post Share on other sites
Stealthbomber Posted October 16, 2009 Report Share Posted October 16, 2009 FWIW, my latest discovery is Servo extension leads off eBay. They cost peanuts. A servo extension lead will have a male connector on one end and a female connector on the other and be around 12" long. You can chop the lead in two about 3" from the female end then solder the short bit (with the female end) to the mosfet and the long bit (with the male end) to the trigger contacts. That'll give you a 9" long skinny wire to run back to the mosfet and a neat little connector to hook it up. Link to post Share on other sites
Vice Posted October 17, 2009 Report Share Posted October 17, 2009 Nice PDF What I've done so far is to copy DoubleTaps FET Then for the trigger/signal wire, I have attached a micro deans connector, and used a normal deans connector for the motor wires. Thus I can 'hotswap' FET units if I should ever kill one, also makes testing easier. After reading your PDF, it seems you can run two small wires to the trigger circuit, so in a V2 GB you would completely unsolder all the wires from the trigger, then attach two signal wires (thin) and then make a new red +'ve lead to the motor. How would you recommend 'tapping'/'splitting' the red wire so that it has a thin signal wire coming off? I guess you could do it at the same point it connects to the P-fet source pin.. Cheers -v Link to post Share on other sites
gzus11 Posted October 17, 2009 Report Share Posted October 17, 2009 take it off the +ve leg of the chip, and the other from the connected gate pins. the resistors can also be reduced to a single 1k across gate-source to limit the trigger current, and stop gate capacitance. you can pick the resistor size you wish, i=v/r 11/1000= 0.011Amps servo extension are good, you can also use jst plug/wire, to save having extra plastic connector, (reciever battery? Link to post Share on other sites
itech808 Posted October 21, 2009 Report Share Posted October 21, 2009 hi, about the MOSFET with Active Braking for AEG's (Short Type) and was wondering what rated fuse can i use, im running a 9.6v 4200 mah battery. thx =D Link to post Share on other sites
infected Posted October 21, 2009 Report Share Posted October 21, 2009 hi, about the MOSFET with Active Braking for AEG's (Short Type) and was wondering what rated fuse can i use, im running a 9.6v 4200 mah battery. thx =D What spring do you have installed? That will tell us more about what fuse your should have in there. For most setups I recommend a 15A, and sometimes for higher FPS setups a 20A. Link to post Share on other sites
itech808 Posted October 21, 2009 Report Share Posted October 21, 2009 What spring do you have installed? That will tell us more about what fuse your should have in there. For most setups I recommend a 15A, and sometimes for higher FPS setups a 20A. currently i have a Prometheus m190 with a systema magnum and prometheus max torque? so a 20A fuse will do? im asking these questions cause i put in a order for one from your site =D .. thx's Link to post Share on other sites
infected Posted October 21, 2009 Report Share Posted October 21, 2009 currently i have a Prometheus m190 with a systema magnum and prometheus max torque? so a 20A fuse will do? im asking these questions cause i put in a order for one from your site =D .. thx's Yeah, I saw the order before I saw your post. A 20A should be just fine given your spring and motor, just make sure your gearbox is shimmed correctly and there should be no worries. Link to post Share on other sites
itech808 Posted October 21, 2009 Report Share Posted October 21, 2009 Yeah, I saw the order before I saw your post. A 20A should be just fine given your spring and motor, just make sure your gearbox is shimmed correctly and there should be no worries. thx's .. Link to post Share on other sites
dephro Posted October 23, 2009 Report Share Posted October 23, 2009 I hope this is in the right topic I have installed a AB MOSFET (ordered from a german website) in my Tavor Gearbox - my problem is, when I close the gearbox the motor wont turn the gears anymore. The gears turn fine when i leave the piston out, but as soon as the motor has to compress the spring it wont move. I have opened the GB more than ten times now and I can't find anything I might have installed incorrectly. Could you guys point me in the right direction? Where could I have gone wrong? Link to post Share on other sites
chownsy Posted October 23, 2009 Report Share Posted October 23, 2009 I hope this is in the right topic I have installed a AB MOSFET (ordered from a german website) in my Tavor Gearbox - my problem is, when I close the gearbox the motor wont turn the gears anymore. The gears turn fine when i leave the piston out, but as soon as the motor has to compress the spring it wont move. I have opened the GB more than ten times now and I can't find anything I might have installed incorrectly. Could you guys point me in the right direction? Where could I have gone wrong? you got the polarity of the motor connectors right? and in the right way round? (i did it once where the motor was in backwards on my M4) Link to post Share on other sites
dephro Posted October 23, 2009 Report Share Posted October 23, 2009 you got the polarity of the motor connectors right? and in the right way round? (i did it once where the motor was in backwards on my M4) The motor is encased in the gearbox, so i never took it out. I'm pretty certain the polarity is right, but I am ready to doubt anything I did by now... I have thought about trying to switch polarity, but wouldn't that destroy the motor or the FET? The Tavor also has a microswitch trigger, but I don't suppose I could have messed up the polarity there? Link to post Share on other sites
infected Posted October 23, 2009 Report Share Posted October 23, 2009 Have you tried a different battery that is freshly charged? If your battery is staring to die, it will cause the MOSFET to do really weird things. Also, it might not be able to pull a load. Link to post Share on other sites
dephro Posted October 23, 2009 Report Share Posted October 23, 2009 Have you tried a different battery that is freshly charged? If your battery is staring to die, it will cause the MOSFET to do really weird things. Also, it might not be able to pull a load. I tried two of my lipos (7.4 1800mah 30c) one was half empty and the other one freshly charged - no difference... I still want to try the reversing the polarity thing but I don't want to ruin the FET/motor/battery in the process. So I was hoping that you could tell me if it is ok to try or if I'm at risk of blowing the whole thing up? Link to post Share on other sites
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