i know its fairly bad forum etiquette to make a help request with a first forum post... so apologies about that. BUT i've been unable to find info about this anywhere else.
i'm building a couple of robots that are powered by 2 919D gear motors each. i'll be powering these with 12V and so will be needed to supply them with 2.85A. i have the motorshield but obviously its not cut out for these kind of motors. i got myself a couple of NJM2675D h-bridges as well, wired them up correctly (at least according to the data sheet, i think!) and got a pop and some smoke. not working - obviously. reading back on the datasheet seems to reveal that they are also underrated for these motors. :
i've been hunting around for either higher rated h-bridges OR another maybe transistor based driver but without any luck. i'm also a bit of an electronics dunce, despite dabbling with simple robotics for a few years, so i'm not even sure if i am using the correct terminology.
so, if anyone has any experience using these or similar motors from arduino, or can recommend a better h-bridge or other circuit, plus how best to teach myself to hook it up to arduino i'd be more than grateful.
well, its an option for sure. but i have 4 of these motors and the two robots and buying four ESCs is going to take me way over the budget which is already pretty much spent.
i was hoping there would be an h-bridge similar to the 2675D, or the L293 but with a higher current rating. or maybe a 'simple' circuit using any combination of transistors, mosfets and/or relays.
i've just been having a look at the LMD18200, but am yet to find conclusive proof that anyone has got one to work with arduino.
You can make your own H-bridge
use 4 logic level mosfets, something like IRL520 would do nicely:
Not quite - you also need a mosfet driver stage to forward bias the upper stages when switched on - you'll need 12+5 = 17V to drive the top stage mosfets into conduction - being logic level doesn't help at all
If you can get P-channel mosfets for the top stages they can be driven with a npn transistor (plus load-resistor) from logic levels. The p-channel mosfets must be 10 or 12V compatible. The lower stages can be logic-level N-channel still.
Also IRL520's aren't really powerful enough, you'll lose significant volts across them and they'll heat up. Get devices with Ron < 0.1 ohm. You'll need to make sure shoot-through can't happen (top and bottom same-side stages on simultaneously)
As a rule of thumb try to keep switching losses to a percent or two - here with two mosfets in series with the load at 3A, you want a total voltage drop of say 200mV tops, which actually means using 0.03 ohm devices or so - the IRL520 is 0.27 ohm, so two of them is 0.54 ohm, which at 3A is 1.6V drop, about 13% losses at 12V (and nearly 5W of heat to dissipate).
Stalled motors pull an order of magnitude more current than the nominal rating - this will be why you've blown things up, they may have been pulling 20A or so (or whatever the power supply can give). Design conservatively, make the semiconductors beefier than your fuse and then the fuse will be the only thing that fries.
@MarkT
He can well drive 4 mosfets from 4 pins, that should be no prob.
No need to complicate matters too much
It would simplyfy matters if he can parallell drive 2 FETs
=2 pins
It is only 2 loops, ground and power connected to the motor, are you sure that he can not power 2 mosfets from the same pin in parallel?
I think he is not asking for a motorbreaking thingy
interesting ideas guys, thanks. i think the best bet for me is to keep this as electronically simple as possible. maybe using a mosfet i don't know, in a circuit i'm making for the first time, and building my own voltage boosters to make it work is all a bit too much at the one time.
the 5A h-bridge tutorial from the wikipedia link looks good, but i can't open any of the files on my mac to make sense of the schematic. the guy also has this 4A h-bridge tutorial on his site http://www.ikalogic.com/shm_hb_l298.php which even though i can't open the files looks a little easier to recreate on veroboard or something. (although i'm a little unsure about how the LM7805 is wired in...).
anyone see any problems with this driver and my motors that i haven't seen myself?
