Here’s a 2 channel motor controller on the cheap ($12.98 US) that will work perfectly for you.
zagrosrobotics.com/index.asp?main.htm~main
But, don’t look at their robot kit’s, there awful, compared to Lynxmotion, that is… 
Richard
Um, H-bridges slowly switching a couple amperes are not difficult to piece together. H-bridges capable of PWM-ing 10 to 15 amperes or more at a few KHz are a different story. The shoot-through currents when your timing sucks combined with the all-over-the-place lead inductances of your hand wired prototype board have the potential to make very interesting pyrotechnic now-you-get-to-try-again moments. One you kill 1 FET (usually as a shorted lump), the one beneath it goes almost instantly, more often than not that will take out one of the FETs on the other side of the load, and then the one above it goes too. All you get to see of course is the flying bits of plastic shrapnel followed by that funny smelling smoke. 
Um… Thems only good for 800mA.
Sorry, the main page is the only URL… you need to navigate to the motor controller’s section. You are looking for Wirz #203 Dual Channel Low Current Motor Driver for $12.95 US
Richard
Ooopps… Hmmm this is reaaly strange as they include them in their 12V Max 96, 97, 99 Robotic platform kits. It says the standard 12V motor included in the kits draws 1.3amps and 20 inch/lbs torque. It doesn’t say if that’s free running or stall current, however. I can’t imagine it’s stall current. These have to be heavy duty motors for a base that specs 35lbs as a payload capacity.
Richard
heh, based on SN754410… good for 1A per channel, if you heat sink it.
Wow…
I go to school and in a few hours a neato topic blooms into three pages.
O.O
cough choke hack
Sorry, trying to stiffle laughter.
Really, though, I’m not laughing at you.
I’m laughing at myself, since I said exactly the same thing to myself when I started searching for tutorials on how to build a good speed controller.
If you’re looking for the cheap, easy answer, this is not it.
If you’re willing to get down and dirty and “waste” a lot of time reading .pdf documents it can be cheaply (monetarilly, that is) accomplished.
Here’s probably the best tutorial you can find for it (it’s a great Nutz and Volts article):
parallax.com/dl/docs/cols/nv … l/nv52.pdf
Allong with that, there’s the osmc yahoo group that’s very helpful.
Building your own speed controller definitely won’t be easy.
I’d not recommend it if you don’t enjoy soldering.
You’d better get real aquainted with reading and rereading .pdf documents about things you have no understanding of, too.
Oh… and a basic understanding of what resistors, capacitors, and combinations of the two do would definitely help (as well as being able to use their respective formulas, of course).
New things like charge pump capacitors and bootstrap supplies are explained pretty well in the tutorial, but it’s assumed that you already know the basics.
If you do things properly, electrically, you shouldn’t have the shoot-through and overheating problems that Eddie mentioned (which are real problems if not properly protected from!).
Right now, I’ve been spending the past few weeks trying to fully understand the osmc v2.2 design, so I can properly make my own speed controller.
Right now, it looks like the most cost-effective option for my usual overkill expectations will be to parallel 4 MOSFETs together in each of the four legs of the bridge.
This’ll yield a theoretical 300A that I can possibly draw from the controller (the FETs I’m using are both package and temperature limited to 75A, though they pretend to twice that by using sneaky footnotes to cover their butts).
I’ll be making one controller for each motor, so that’ll mean a total of 32 MOSFETs.
So far, it’s looking like the total expense for both will be around $120ish, which isn’t bad at all.
Choke
Anyway, as I say, I’ve been doing a bit of research and I found this:
What do you all think?
theChipmunk
Thats a “MOTOR DRIVER” like forward and reverse. Will that also allow you to turn your rover with tank style steering left to right?? It dosen’t specify.
you would need 4 of them, one fore each motor because they are rated only to 4 amps
While I don’t know what that so-called tank-style mixing actually does, I’m sure you could always do that in your microcontroller’s program.
You’ll need a microcontroller to PWM the H-bridge, anyway, so such extras such as that are probably only for convenience’s sake.
$120 for two 300A speed controllers is chump change.
In fact, I’m not sure if there’s any similar-rated speed controllers on the market for under $500!
I spend $55 per servo on my biped, so I can’t really complain.
If you’re wondering how much it’d cost you, it definitely wouldn’t be that expensive.
I’m using 4 times the normal amount of MOFSETS, which means I’m also using 4 times the normal amout of components.
You could make two 75A speed controllers for around $50.
But, again, you’d be spending quite a large amount of time just learning, not to mention building, testing, and debugging.
Before you jump on board the cheap boat, ask yourself if your time is worth the money that you’ll save and the electronics experience that you’ll earn.
IMO, it is.
But, then again, I’m not just following the OSMC design.
I’m going through and calculating the necessary values for the charge pump capacitors, figuring out how much air displacement the fan I’ll be using to cool the MOSFETs will need to be, evaluating the best value of HDEL and LDEL resistors to best limit shoot-through…
And the list goes on.
To me, learning all the little details is what’s most important.
Much more important than the time that I’ll spend doing it, and even more important than the money that I’ll be saving.
But that’s just my 12,000 cents.
Sounds like that’s the easy answer.
So the enigmatic question is:
Easy or cheap?
I am so confused… one second there are references to 300A h-bridges and the next there are links to 1 to 2A speed controllers. Where is the topic of this thread supposed to be going? Thanks.
Im with you Eddie, This isn’t making sense! I say, go with a regular motor controller that isn’t too expensive and that has the following functions: FORWARD/REVERSE and LEFT/RIGHT tank style steering. I am a Rover guy so I know that this is the easiest and best way to controll a rover robot and can be expanded on.
thx.
nick tank mixing refers to how you use 1 stick to control both sides of the “tank”, and unmixed is using 2 sticks to control the “tank” or watever it is, either its that, or its vise versa 
Yep, you nailed it, but its a little more than that too. Tank style steering is actually when one side of the rovers wheels (say left) spins in the opposite direction of the wheels on the right (going forward) which turns the rover left and vise versa to go right. This is controlled with a single stick on your controller which is the most comfortable I’ve ever felt. This catually allows you to use your 3 and 4 channel for something like a pan and tilt or a weapon if your into battle bots.
Um… well… the reference to the 300A controller does apply, at least in my head.
I’m just pointing out that you could build the two speed controllers you need for much cheaper than you can buy them, if you’re willing to DIY.
The MOSFETs I’m refering to are good for up to 75V and 75A, so they’re way overkill for what you’re doing.
If you so desire, you might save a few bucks by getting FETs that are down at around 10A or so.
Just throwing ideas out there…
Head explodes
Anyway…Nick, do you think you could point me in the direction of some 10A MOSFETs and I’ll try and take it from there…
BTW, ItalianGuy, an H-Bridge is supposed to do the forward, back, brake thing - that’s the whole point of H-Bridges!!!
I’m literally just looking for an H-Bridge that I can PWM. Nothing more - nothing fancy!
Thanks.
theChipmunk
I realized that, thought you might want more controll that all
DIY lets you make it as un-fancy as you wish.
Here’s a list of MOSFETs that pertain:
ec.irf.com/v6/en/US/adirect/ir?c … 4294851897
So, what does all those numbers mean?
Here’s the break-down, in order of most important to least important when selecting your FET:
Qg Typ = this you use to determines how much amps you’ll have to supply to turn the FET on, in a certain time period.
Just be sure to find one that’s as low as possible.
RDSon = this is the resistance when you’ve got the FET switched on.
It’s important to buy one with as low an RDS as you can find.
Because this list is a small selection that I picked out, you can chose to ignore the other numbers.
You may see that numbers such as ID @ 25C (which is the current that the FET can switch on and off when it’s cool).
Those numbers are lies, really.
When you’re actually using it, the MOSFET will be around 125C (well above boiling) even when it’s being cooled by the fan (you could use a heatsink, but fans are better).
So, I picked out FETs for you that’d be around 10A at their normal running temperature.
Also, I limited the list to the FETS which have a TO-220AB package.
Why?
Because it’s a pretty good package for cooling and fits into standard .1" prototype perfboards.
After you pick out a couple that look good, you can go check the prices at digikey.com, which carries most of them.
I wouldn’t recommend buying directly from IRF.com, since you’ll need a store like Digikey to get your other components from.
I’d also recommend you get one HIP4081A for each of your two H-bridges.
That’s the same MOSFET driver (a microcontroller isn’t “strong” enough to switch on and off these kinds of MOSFETs directly) that’s featured in the tutorial.
Whoa!
That’s one helluva post! Thanks, Nick!
Actually, I found this… Clicky.
I can use two (they’re only single channel) and they look as though they would do the job well for a good price.
What do you all think?
theChipmunk