Motor Controller

[Omar.M]

Hello,
Is this motor controller / H-bridge good enough to run the motors in the Tamiya Twin Motor Gearbox (70097)?

**broken link removed**

The parts are hard to get for me, so I'll have to pay a lot of shipping for just a few transistors etc. (Jameco seems to be the cheapest shipping to Canada).
So I was wondering, am I able to substitute any of the parts in the schematic from this shop:
**broken link removed**

From their ICs section, they have these two transistors:
**broken link removed**
**broken link removed**
I chose this shop, as it is the closest one in my town.

I was wondering: am I able to substitute the diagram with these? Or do I need to order online?

Thanks so much for your help, as I am pretty much stuck here,
Omar

 

[Hank Fletcher]

I did a quick search, but I couldn't find out how much current you need for the Tamiya. If you're looking for h-bridges, the SN754410 is the best amps/$ solution I've found yet. You get 36V and 2A (with proper cooling) out of one chip, with a minimum of external circuitry. And you can run mulitple chips in parallel if you want more current. Thought I'd mention it since I got mind from Counterparts in London, Ontario, for less than $5 each (and I picked them up, so shipping cost me nothing!). Don't know where you are, but if you're near Toronto there are plenty places you could go.

 

[Hank Fletcher]

Shoud have mentioned that it's not a standard stock item for Counterparts, but I ordered the h-bridges and they got them in something like two days. Great service.

 

[Omar.M]

Wow, that store sounds great. I am in Ottawa, Ontario. I can't exactly just walk there, you know?

I saw that chip, but all of the online sellers that sell that IC have shipping and handling rates so high-- that I am almost paying 15 dollars for one IC chip that costs 2 dollars!

So for that reason I am stuck making it, or finding stores around here that sell it. But I am not giving up hopes just yet-- maybe there is a cheap online seller available!

Would you happen to know any stores?

Btw, I only need about 4V-5V for the motor... 36V is an awful lot.
Omar

 

[Hank Fletcher]

There's gotta be a components store in Ottawa (check your yellow pages). There's no way you're going to save money if you're buying stuff from the Source. The place is a ripoff, and that's if they have what you need (which they invariably don't).

If you can't find the droids you're looking for, you could try www.robotshop.ca for mail order. They're a bit pricey, but at least they're domestic. My experience with Canada customs on international electronics orders is that they've said, "If in doubt, tax it." Also, I wouldn't rule out giving Counterparts a call - the cost on mailing a couple chips across the province has got to be, like, $2 tops. My experience for components from Counterparts has been that they'll get it if they don't have it, which means if the only way you can figure on getting something is by international order, get Counterparts to get it for you. Then you just pay the cost of shipping it from them (in London) to you, instead of internationally, and you don't have to pay customs. And even ordering stuff from Counterparts this way will be quicker (thanks to their customer service) than waiting for customs to do their job. Argh! That's so aggravating! I can't tell you how many times I've had something express mailed from the U.S. just to watch the tracking as my shipment sits in Canada customs for a week!

You can use whatever input voltage for SN754410 you like between something like 4.5V and 36V, I think. Check out the datasheet for it, it sounds like it'll be worth your time. They're really easy to use, or else I wouldn't be using them.

 

[Omar.M]

Wow. Thank you so much. Seriously, you may have saved me a lot of trouble!

So I give them a call, ask them if they carry the h-bridge IC. If so, ask them to ship it to me? How much did the IC cost you approx.?

Are they that flexible? And you're right. The Source is the biggest rip off ever. But when I need something fast, I go there. I'd rather pay 4 dollars extra than 10 dollars, you know (plus the wait)?

Thanks once again!
Omar

 

[Hank Fletcher]

Call them up and ask them for a price on the SN754410. They'll tell something like $5 or less for one, but that there's a price break if you want to buy 25 at once. Tell them you only want 3 (always buy one more than you need, in case your little brother eats one).

Omar, make sure you know how much current you need for the Tamiya motors. Low voltage hobby motors need a lot of current, and you'll never get more than 2A out of each h-bridge chip. I'm just saying it's better for you to know because it's more cost effective to only have to place one order (and pay mailing costs once). Research twice, order once.

After they've given you the details, tell them you're in Ottawa. I have no idea what they'll tell you, but it's worth a try. I'm pretty sure they'll give you a figure on what it'll cost to mail them to you, and if they don't, ask. If you think the price is too high, say thanks but you'll have to keep looking. If you like the deal, also say thanks, because you'll be going back there some day.

 

[Omar.M]

Thanks so much. I will try that on Monday, hopefully we'll get somewhere.
I checked the site, it seems the rating is as such for the motors:
• Voltage: 1.5-3V (1.5V Recommended) (4.5 V Max)
• Amperage: .66A

So this driver will be efficient? As well is it possible to pay by Paypal or something?

 

[Hank Fletcher]

Check the SN754410 datasheet. It's designed to operate with motor supply voltages of between 4.5V and 36V. What you could do is use a 4.5V or greater battery (or whatever power supply you're using, up to 36V), and then build a voltage divider on the outputs of the h-bridge to bring the voltage down to the safe operation voltage of your motors. That would only cost you a couple of resistors per output, or four resistors in total to get both directions out of one motor. You'll want resistors rated for power that can handle the maximum current from one h-bridge output, so order them from Counterparts when you order the h-bridges. Alternatively (and if you already have a lot of 1/4W resistors lying around, or you can justify buying a pack from the Source), you could run several 1/4W resistors in parallel for your voltage divider. What the heck, don't - just use one and watch ithe resistor fry! If it does, then next time use two. If they fry, next time use three. This isn't the most efficient way, but sometimes you can't beat trial and error.

You wouldn't have to do any of that if you're sending a PWM signal to the h-bridges, since you could just control the average voltage output that way, regardless of what the supply voltage is. A PWM signal on a 4.5V supply sounds like it would be the most efficient and ideal situation given the specs you claim for your motor.

The smarter alternative is to continue searching for a low voltage h-bridge IC. I'm sure there must be something like that out there. Find it (and tell me what it is!), and see if Counterparts can get it for you. Sorry, what I really should be telling you is that it might be most cost-effective to construct your own h-bridge from transistors, given your relatively low voltage and current requirement. Now that I know what kind of power you want, it's easier for me to put your original post in perspective. You were right to think you could do it with a few transistors, but the h-bridge you linked to is severe overkill for what you need. My suggestion of the SN754410 is overkill for what you need, and it's got only a fraction of the power of that beast!

I don't know if Counterparts use Paypal, but I'm guessing no since I think they do most of their business the old-fashioned way, i.e., in person. I know it's frustrating not having a credit card (I'm presuming that's why you're asking). How do I know? Because I'm 32 and I still have to borrow my girlfriend's, or mom's, or dad's! I just got turned down (again) for a credit card Friday, and here's the crazy thing: I make much more money than my girlfriend, mom, and dad! What's the lesson here, kids? Get a credit card while you're still young! I've never defaulted on a loan, or claimed bankruptcy. In fact, I'm a banker's dream: I make my payments, and I don't complain about the interest. I've paid down plenty of (student) debts, and I'm plugging away at the rest (which makes money for the banks), but the main reason I can't get a credit card? Because I never had one! They check your credit rating by, primarily, checking your history with credit cards, which after you reach a certain age becomes somewhat of a catch-22. BTW, student loans don't count - no matter how much you pay one off, in this country it doesn't mean squat to your credit rating.

Thankfully, any man and his dog can get a personal chequing account. Counterparts will probably take a personal cheque, although you might have to wait extra for them to cash the cheque. Check with them, they know better than I what they will and won't do. I still say you should look for a Counterparts equivalent in the Ottawa area, it'd save you a lot of hassle.

 

[Omar.M]

Shucks.

The credit card wont be a problem, but my father is a little hesitant when giving it out to me. I'm only 14, so I cannot yet get my own.

I wouldn't mind doing that, it would be better if I could just use a big enough resistor and not have to blow them. But it seems that this probably wont work. And I have tried finding shops around here, none of them are really carry anything good.

So I guess I have no more options?
Omar

 

[Omar.M]

Wait wait. I think I found one site that might work. There's really no information given but:
**broken link removed**

Any good?

 

[Hank Fletcher]

Check my last reply, and my comments there about using transistors. It looks like using three 2N3906s (as you originally suggested) in parallel for each direction is all you need (since you only need 1W for your motors), and seeing as the Source sells a pack of 15 for $4, then it's the best way to go. I bought a discounted RC car from the Source recently, and that's all they use for motor control.

What's your plan for how you want to control your motor/car/robot?

 

[Omar.M]

I don't want to use any PWM just yet. For my robot, I pretty much want to experiment with going forward, stopping, possibly going a different way.
But I say, if I am going to pay that much to make my own driver that might explode, why not pay a bit more for some working, premade ones?

I want a motor controller right now, but I was just thinking ahead if I ever get advanced with these motors-- I may decide to use PWM and such. Then it may be a problem?

I am very very sorry I did not read the past reply. The site I linked to you have 3 different types of transistors... source only sells NPN types that aren't exactly the same as the ones that I was told to use on the site...
does it matter? what about the TIP transistors?

 

[Hank Fletcher]

1W is not going to explode if it shorts. It might smell a bit funny, and if you're lucky, it might even smoke a little. So there's no danger in experimenting. How are you interfacing your robot? If you just want it to go forward and stop, why not just use a switch? You need a clear idea of what you want your robot to be able to do before you can start building it.

The reason why I started using the SN754410 was because it's dead easy to control its TTL inputs with the TTL from my computer's parallel port. There's not a lot of current from the parallel port by itself, but if you use those h-bridges you can have a lot of fun experimenting with controlling DC motors, relays, lights, etc., and you can control the timing and switching from whatever software you're using. This has its limits, but for starting out and prototyping, it's great fun.

 

[Omar.M]

Sorry I was not clear enough. Right now, I am building a line following robot. I am interfacing it with a PIC microcontroller. I bought a gearbox, wheels and a castor, as there are the basic robotics parts. So I can at any time work on what I want. The motor driver is important too, and so I was totally stuck.

I agree with the experimenting and such, I just wanted to make sure I had all of the 'features' with my self built things as I would have gotten with store bought.

So my question still remains... source only sells that one kind of transistor which is semi-close to what the website lists. What am I doing for the other transistors that that the author lists?

Will I still be able to, by the PIC, change directions and possibly have speed control for further on?
It seems I found that one site, so if I am totally in trouble I can always spend a few extra bucks and buy an IC. But it is a different IC.

Omar

 

[Omar.M]

BTW, Active seems to have NTE7043's as single motor drivers. They are the same voltage as the one you are speaking about-- but expensive are only for single driving.

EDIT: I am sorry. I forgot to edit the above post instead I created a second post . Please read above!

 

[Hank Fletcher]

I'm gonna go out on a limb here, because I'm brand new to PICs myself. Couldn't you use your PIC to do PWM with the SN754410 to get your 4.5V down to the ideal voltage level? Even if the PIC you have doesn't have a built-in PWM signal output, can't you just write a program that gets you the PWM you want out of one of the standard outputs (like one from portB on a 16F88, instead of using its designated PWM pin)?

I'm inclined at this point to say get the SN754410 and burn the hell out of those motors you have. You say they can take 4.5V max, so I say give it to them. You'll have the fastest robot on the block, and when you choose to upgrade to beef up your motors (or have to because you burnt the ones you have now out), you'll at least already have the h-bridge. Based on what you say you have already, all else you need is the SN754410 and some fancy programming to pulse the voltage down. I say go for it, order the SN754410 and try it out. I guarantee you'll definitely want to use it for something if you're not completely satisfied with it to run your motors.

 

[Omar.M]

The gearbox motors are pretty good, this gearbox is used a lot. So I don't exactly want to burn it out. I want to keep the burning to a minimum.

You suggested that making my own would be sufficient, is that out of the picture already? Should I still call and check with the Counterparts?

I can try to limit the driver voltage with resistors, I've got plenty of them to play around.

So is it Counterparts, Active or building my own?

 

[Hank Fletcher]

Get the SN754410 from Counterparts. After that, you've got everything you need (no extra resistors or anything), because you can just use PWM with your PIC for the proper voltage. It's the most clever solution that uses the least amount of parts, so it's win-win. I don't have a great understanding of PICs, but I'm very interested in working through this with you (BTW, what PIC are you using?). Plus, there are plenty of experts on PICs in the microcontroller area of this forum you can tap for advice, I'm absolutely sure of that. I really like the idea that the SN754410 will be there for you whenever you're ready to upgrade to a larger motor.

Here's a link to a tutorial explaining how to PWM with a 16F84.
**broken link removed**
It might be pretty deep for where you're (or I'm) at, but at least it'll give you faith that you can do it if you want it. Bear in mind that I'm talking about using the PWM to average the voltage to your motors, and consequently the speed at which they spin, as oppose to the tutorial which describes using PWM for servo positioning. But everything else still works out. Don't get confused, and remember you're using the PIC's PWM for speed control, but the h-bridge for motor on/off and direction. It can be, and is, done.

edit: Oh, snap! I just did a quick read through of that tutorial and he does in fact describe using PWM for DC motor speed control! And he even gives a little schematic with a suggested transistor...

 

[Omar.M]

I am using the 16F684. What if I fail to acquire the SN754410 IC?
I don't even mind using extra parts to limit it. I just don't want to damage my stuff. I don't exactly need to upgrade my motors, the gearbox is pretty powerful.