I've searched a bit on google and have searched the forum here a bit for an applicable thread that isn't a year plus old and didn't really find anything that completely met my criteria so let me just pose the question to you all. I have built motor drivers that work great for my 6V DC motors using the L293D (Dual H-bridge) and I've gotten good results with them on my Arduino projects and my Raspberry Pi projects alike. Well, now that I am more comfortable with everything, I decided I want to build a much smaller robot.
I have a small RC tank on it's way in the mail, should be here this Friday that I want to tear down and turn into a robot. I will also test the motors to determine how much voltage and current they require to run and will also be looking at the voltage and current the pre-existing hardware is supplying. After that, all of the electronics are coming out and a tiny ATmega is going in, along with a rangefinder and a motor driver.
The motor driver is my main concern at this point. If these motors run at less than five or six volts, which they likely do due to their small size, what do I use to power them. I've found some different low voltage driver boards that are pre-made but I'm more interested in building my own. Can I still use an L293D to drive these motors and divide the voltage off on the output side? If anybody has some recommendation, schematics etc it would be greatly appreciated. My soldering iron is always at the ready.
I would like to know what battery is used to power the Arduino.
For the motors, you better use the battery voltage of the battery that comes with it. The L293D will not work for low voltage or high current motors. A mosfet driver will work. But you probably need low voltage mosfets. You might have to do some tests for the motors. What the normal current is, and what the stall current is, and so on.
I've seen people mention mosfet drivers before but only mentioned. It's not something I've worked with at all yet to be honest. I've found the A3901 Dual full bridge low voltage motor driver and it looks like it might fit the bill. Of course I will have to know the requirements of my motors as you mentioned to know for sure. The only thing that's got me leaning away from this one is it's a surface mount component. I'll keep searching for something through-hole as it will be easier for me to work with.
To power the Arduino, I'll probably use a 3.7v lithium polymer chemistry battery with a step-up circuit. I've got an off the shelf unit that will also recharge the battery that features a TPS6109 step-up and an MCP73831. It provides 5.2 volts at 500mAh which has worked well for other projects. It's basically a reverse-engineered cellphone charger. Because of the size of the chassis, I will probably have to avoid using AA batteries, though that would be my usual solution. I'll have to wait until I see it but I might be able to get away with using four or five AAA rechargeable batteries.
The RC tank I'll be tearing apart looks like it probably has a small LiPo in it already considering the pictures show that it's being charged from an umbilical coming out of the radio control. Best case scenario, I'll be able to re-purpose that battery to power the final project but I won't know for sure what all I'll be able to reuse until I actually have it in my hand this Friday.
The search continues for a low voltage, DC motor mosfet driver in a thru-hole package...
Just saw this mentioned in another thread though LV8548MC-AH and this might be the way to go. I'll let you know what kind of guts it has inside when it arrives though. It's a cheapie I found on Amazon so there's no telling what components it will have in it or if I will be able to identify them.
For low power you can use a BJT bridge, which have much less loss than
darlingtons, and a circuit like this:
Note the layout in this circuit is unusual as the legs of the 'H' cross over, but it does
make it clear that each input signal switches on current flow in one direction (you
must not activate them simultaneously or you have shoot-through and fry the transistors.
The resistors have to be chosen appropriate to the load current and transistors, which you
want to saturate at the load current levels.
Is there any chance the above circuit comes in any sort of integrated circuit package? As I mentioned, space is at a premium in this project so I'm trying to do it with as few parts as possible. I already know the battery and power circuitry are probably going to be the biggest space hogs.
The problem with the BJT bridge is that the resistor values matter and depend
on your load, so no one IC would be very general purpose. Also integrating power
NPN and PNP devices onto one die is at least as hard as doing this for MOSFETs
which perform better.
Darlington bridges are 3 or 4 decades old designs, completely obsolete in
the real world (but very handy as cheap and DIP packages)
I get what you're saying, but for the purpose of the project I am working on, the primary factors that matter are size and price. It needs to be small and I don't want to dump a lot of money into it. It doesn't need to be efficient really either as long as it will work for.. at least 30 minutes to an hour I would say.
As far as being obsolete, that word is not in my vocabulary. As long as it still does the job that it is built for, lets call it "Legacy technology". You're talking to a guy who still regularly tinkers with 8088 - 286 and 486 processor based hardware. It still does it's job and no smoke comes out
This is going to be a tiny robot that fits in the palm of your hand and navigates with one fixed position rangefinder. Realistically, it's a novelty item that I'm adding autonomy to. LV8548MC-AH is still currently at the top of my list of possible motor drivers.
It need not be elegant as long as it is functional.
Fits in the palm of your hand ? Then I would really like to know what voltages and currents are involved. It might even be possible to drive 4 transistors (and 4 base resistors) with 4 Arduino pins, to simulate a H-bridge.
8088 -286 and 486 processors ? You mean, you don't have a PDP-11 in your basement ?
That's an interesting Idea, I actually hadn't considered driving the motors directly from the Arduino pins. I'm guessing the running voltage is pretty low given the size of the thing. I'll have a better idea friday afternoon when the package arrives, assuming my local delivery guy does his job with the efficiency expected. After I mess around with it a little in it's as intended configuration I'll tear it apart and take some measurements. I don't have any fancy equipment but I have a multimeter, the cheap kind you pick up at a hardware store for a couple of dollars, but it does the trick and has been useful for years already. I should be able to at least measure voltage and current across the motors while running.
I suppose I could probably post a link to the particular item I bought in case anybody else is interested in building one. If I fail, also save them some time if not money. The dimensions are 5 x 9 x 4 centimeters, there's also a picture of it next to a soda can and sitting in somebody's hand.
After I get everything hacked together and doing decidedly robot things, I'm planning to remove the portion that makes it look like an antiquated killing machine and replace it with a plastic turtle shell. Not much is less menacing than a turtle and I feel it will make my robot more lovable
Functions according to the youtube movie : steering left and right; cannon left and right, sound effects; move forward and backward. That are 7 on/off signals.
Speed control for forward and backward ? I don't know, perhaps not.
Yes, connect it to 3.7V, measure the current while holding the motor (or the wheel) to make it stop or almost stop. The current for good quality motors might be 20 times the normal current. Perhaps you should use a seperate 3.7V power supply, because this 3.7 Lipo cell limits the current.
Cool, Karma to you sir for the advice. I've got a NiCd battery pack 9 cells rated at 1500 mAh each that I sourced from an old cordless hoover (Engineering fail) and a little buck converter. I'll try with that setup dialed back to 3.7v and see what kind of numbers I get. I've also got a variable voltage wall adapter that is brand new I could try out as well. I really hope this thing arrives friday! Amazon says it hasn't even shipped yet. Last night I also picked up a little step-up circuit that is supposed to take 1-5 volts in and convert it to USB power, I'm assuming that means 5.2v at ~500mAh but you never know. I know the IC that's on it so I can swap out some caps if I need more power. It might come in handy in the final build and it might not. It was $3 USD so maybe it will end up being a cell phone charger.
I've also completed a sketch for another of my robots that controls two 6v motors and has a rangefinder on a servo so it can actually look around before it decides which way to go. I posted that code in another thread I started, just wanted to mention it here as that robot will be this one's big brother. I just wanted to share it here to improve the audience to that thread in case anybody is looking for a similar sketch.. Basic rangefinder and servo sketch + Turtle 2.0
So the tank did arrive Friday after all and I was able to play with it for a few minutes. Unfortunately I have not yet been able to get any specifics as far as voltage, amperage and stall current. I ended up having a pretty busy weekend after all. Another thing I want to try and figure out is what kind of ICs the pre-existing circuitry is using to drive the motors. There are three very small 8-pin surface mounts and each one seems to be tied to it's own motor. Two on worm gears drive the vehicle and a third moves the turret side to side. They're all very small and covered in gear oil so I've been having some trouble even reading them but I will give it another shot. Maybe they are something I could use for my own low voltage motor driver.
I'll try to have more information in the next few days.
I think I may have found my solution at Pololu but I wanted to post here to get some opinions. It's a low voltage but also variable input voltage motor driver designed to handle a voltage range between 1.5 and 11 volts and features the Texas Instruments DRV8835 on a small shield designed to plug directly into an Arduino. I've only just started looking at it, but I'm sure this could be used with a Nano V3.
For a Nano, this 2MOTOR-4NANO Gravitech | Mouser motor shield is great. I think it has a L298, which can handle 2A.
Had a nasty time getting that link to work!
