some quick electrical sanity checking

adolf hamster

adolf hamster

adolf hamster

Soldato
Joined
18 Oct 2012
Posts
8,382
ok, so i have a DC motor that's ordinarily powered by 4x aa batteries, however the device it's in has its own seperate power supply from a 11.1 lipo battery.

basically i want to replace the aa battery pack with a voltage divider and a supply from the main battery.

So i'm looking to approximately halve the input to the motor, supposedly "its ok" to take 11.1 directly, but given its a component that will be a massive pain to replace i'd rather not kill it prematurely.

So the plan is to switch main power to the motor then drop it with a potential divider. However i'm not sure how i should size it.

I have a bunch of 10k resistors, but i'm not sure if that'll drop the current capacity too much if i use 2 to make a potential divider. I dont know what current this motor takes, but i'll investigate tomorrow and see.

And hints on how i should be wiring/sizing this?
 
Its an airsoft gun with a seperate electrically wound mag.

The magazine motor is tiny in comparison to the main motor (that needs the lipo to spin it) but i'm currently trying to improve the longevity of the electrical system.

I've replaced the main switching element with a mosfet and the plan is to tap the power from the main motor directly to the magazine, it'll only wind when i'm firing which is exactly what i want.

I forgot i have an adjustable voltage supply so i'll run that at 6v and try to figure out the mag draw and report back. I'm guessing whatever wattage the motor takes is also what the potential divider needs to take?
 
ok, so the motor is drawing 0.22A with no load on it. if we want i can try loading the mag up and testing it while properly operating (the bb's come out a feed tube so i can just pop that back into the mag and create a loop)

basically this system only needs to function when the trigger is pressed and the main motor is firing, so whatever system it uses will either need to run direct from the main motor power in paralell or be switchable by an 11.1v signal.

mechanically this system doesn't have much load, all it does is life bb's from the mag into a feeding tube. although when the tube is full it'll just stall the motor. which seems to work ok given the default setup works fine.

i don't know exactly what the main motor draws, but i've heard estimates in the 16A range which seems beleivable.
 
AtaRo said:
What is the operating voltage of the motor? you say it is powered by 4 AA batteries, assuming the baterries are in series then it is about 6Volts.

Alkaline AA baterry is rated around 2800 mAh, if the motor actually can pull 16A then it is like shorting this batteries out.

It would be best to actually measure how much current the motor draws from the AA battery.
Click to expand...

the batteries are in series and it is 6v.

this small motor only draws 0.22A, it's the main motor that runs off the 11.1 lipo that draws 16A when in use.

what i want to do is be able to run the small 6v motor off the same 11.1v supply as the main motor, so the pair will drive at the same time. thus eliminating the need for a seperate battery pack for the small motor.

in terms of space if it needs a regulator there's plenty, as long as it's no bigger than a quad AA battery pack.
 
Tefal said:
How are you going to electrically connect it to the gun?

Contacts might become frustrating if they become lose or worn
Click to expand...

i'm thinking the main power comes in paralell from the mosfet, it came with connectors by default which are a bit of a pita to connect, it's easier to safe the gun by removing the battery than the magazine.
 
Tefal said:
I mean is the battery for the magazine in the magazine and seperat e electrically from the gun. And are you going to make a set of contacts to transfer power from gun to mag.

I'm guessing this is something like a imagine gun set up with a huge capacity may so you won't be changing it that often?

But if the connection isnt great the mag cutting out would get frustrating. Does the mag plug in as it were or jist have to exposed metal contacts that slide against each other

If it's for lightness the simplest solution may be replacing the 4xaa with a small Lipo paxk of thier own?
Click to expand...

it's an mg42, the mag is mahoosive and you can re-fill it without removing it from the gun. it only gets removed at the end of the game day.

in it's stock config there's a secondary microswitch on the trigger that switches the mag motor, and it has an external connection to join the 2 together.

thing is the secondary microswitch is very flimsy and the weak point in the system. seeing as i have the whole thing apart atm i figured it'd be the right time to eliminate it. plus by powering it off the main battery i won't need to worry about keeping 2 sets of batteries charged.

lightness isn't a problem- its already a heavy beast :P
 
AtaRo said:
You can try using this mp1584 step down converter, it is capable of 2A at 6 volts output.

RUl2ikY.jpg
Click to expand...

how quickly will that output properly from being turned on? this system will involve being turned on/off constantly when firing short bursts.
 
AtaRo said:
To removed the delay the converter can be wired in a way that it is always powered on when the airsoft is inoperation, then insert the on/off switch for the motor at the ouput of the converter in series with the motor.
A main power switch for the converter then can be installed in series at its input to put it, in its always on state.
Click to expand...

This is the thing, i'm trying to avoid using the second switch as its a weak point. Kinda hard to describe but basically the way its set up any over-zealous pressing of the trigger has the potential to kill the microswitch.
 
Tefal said:
I dont think he means use the second switch but run a second set of wires from the main trigger switch so that the dc-dc converter r is always live but not connected to the motor untill you pull the trigger and close the circuit.

Guessing trigger is linked to a much sturdier switch but the wiring for that might be buried In your gearboc
Click to expand...

yeah the main trigger is a much sturdier design, fortunately with the mosfet installed i have external access now to the trigger contact wires/main motor wires so running power from there won't be too big of an issue.

@lotus7 thanks for testing that out, sounds pretty decent, this thing runs at ~1200rpm but by default really short bursts doesn't give the motor enough time to spool and feed (the fix is just to fire a longer burst of 1-2 seconds) assuming it's ramp down is something similar it might be just the ticket.
 
well, converter arrived, looks like it'll do the job perfectly. have it wired up to the mag and tested working just fine. it's nice that if needs be i can up the power for a future where i do some tinkering and up the rof......

now all i need to do is get the reciever fixed and have the thing put back together.
 
necro time

so after some extensive mechanical surgery i've finally had the chance to give this thing a test in-situ.

unfortunately, it blew up, so i guess we're back to the drawing board.

to recap:

main battery is a 11.1v lipo

there's a single set of trigger contacts wired to a mosfet which switches power to the main motor

the second smaller motor is 6v and ~2A which i need powered at the same time as the main motor
 
Rroff said:
Did you heatsink the regulator? don't really have my head in the details here but if the current is high they definitely need it and not all have thermal shutdown, etc.
Click to expand...

fair point i did not, in fact the opposite i had to have it wrapped up because it's being tightly crammed into a metal body and i couldnt afford shorts.

thing is it didn't go pop in testing with the wrap on, so not sure it's a thermal issue.
 
You must log in or register to reply here.
Back
Top Bottom