Motor Controller

[Hank Fletcher]

Omar,
Check the "questions about a line following robot" thread someone bumped recently in this forum, and the reply there by chan ying poh. You might find that reassuring.

 

[Omar.M]

I checked that, wow-- you were right on!
Anywho, changing the motors is out of the question. They were hard to find in Ottawa, but they work amazingly for the 15 dollars I bought them for. A lot of robots use them so I have no reason to try and improve them as they already fit my needs.

Building an H-Bridge seems out of question as you pointed out. But since we are thinking about voltage divider or pulsing with 555 timer, I have seen Spark Fun Electronics' tutorial on using the same gearbox with the same h-bridge you are recommending. Maybe I'll drop them an e-mail and ask how they can not burn the motors with such high voltage.

As for the 555 timer with any h-bridge-- how do you think it would work? Do you have some kind of schematic or code?

So if not in Ottawa, I guess I need to stick to online. What's going to be a good place online that has alright shipping, but won't burn a hole in my pocked with 20 dollar shipping charges?

Thanks a lot-- don't get me wrong, I appreciate it a lot that you are taking the time to help me,
Omar

 

[Omar.M]

Hmm, spark fun electronics says that the voltage range is 3-6V.
Question is, who is right? It seems on their forums most of the people are connecting the output directly to the motors without a problem...

https://www.sparkfun.com/commerce/product_info.php?products_id=319

On the site is says
"Can be controlled by L293DNE, SN754410, and other low-cost motor drivers"
:O

Omar

 

[Hank Fletcher]

Is this the gear motor you're using?
https://www.sparkfun.com/commerce/product_info.php?products_id=319#
I think it probably is, and if so, according to them it operates at 3 to 6V, which means you can just use the SN754410 (which is one of the chips they recommend for this, btw) with a 5V supply and hardly anything else. Check your information for your motors again, and always try to be 100% about understanding the specs of the equipment you're using, it'll save you a lot of frustration. 99% of technology engineering is reading comprehension, the other 1% is ingenuity.

According to sparkfun, the motor is fast, so I still like the idea of being able to manually adjust the speed with a 555. That way, after you've built your robot you won't be annoyed that it keeps zipping too far off the line it's trying to follow because the motor's driving it faster than your line sensor can keep up. The 555 won't require any programming. In fact, by using the 555 for PWM rather than your PIC you'll be significantly simplifying your PIC program while still having almost all the advantages of PWM.

You need to understand how a 555 works, it's the bread and butter of the electronics world, it's 8 pins of IC you'll be using until the day you're done electronics. Luckily they're inexpensive and readily available absolutely everywhere, including the Source. Pick one up today and start playing with it. With a 555, a couple resistors (and a couple pots) and capacitors, and an LED you can figure out all you need to know to PWM your motors. Tell me when you have this stuff and we'll go from there. Otherwise, you're wasting your time in electronics.

Since you don't know about the 555, and you're trying to conserve breadboard space, I'm guessing the PIC you mentioned is part of a BASIC Stamp microcontroller on a Board of Education, or something like that? If not, then I'm really surprised that you were able to figure out how to program a microcontroller before you learned what a 555 is. If you're using a BOE, or even if not, I really recommend picking up "Electronics for Dummies." There's no shame in it, I own a copy, it's well written, and it's an easy reference for basic electronics, the 555, and it even has an introductory chapter on microcontrollers. Sneak into Chapters and have a flip through it, at least.

 

[Hank Fletcher]

Forget about the L293DNE, it's obsolete and inferior to the SN754410 anyway.

Although I couldn't find any specs on the Tamiya motors, I did find this:
**broken link removed**
where a guy claims to have some experience with your motors, and that they will burn out at 5V. So you will have to PWM (which I think is what they conclude, including that the motors are only good to 3V or so), especially since the SN754410 drops hardly any voltage at all (which IMO is a good thing - more efficient, less heat, less unusable battery drain).

 

[blueroomelectronics]

Only problem with the SN754410 is you still need the diode clamps on a motor. I've used the L293D (D=Diode clamps) with the tamiya double gearbox and the 1.2V drop won't hurt those small motors. Just don't let it stall for too long, I'm using PTC fuses so a stall won't hurt the motors or the L293D.
**broken link removed**

 

[Omar.M]

I know what a 555 timer is. I just haven't found the need to use it so I never really got into it. I program PICs (from Microchip) with a JDM programmer. I don't use any development boards.

I might as well buy them online because I am going to be paying for shipping and such for the TI chips anyway. That was my reason for asking. I know for a fact Bill plays with these a lot (from his posts) so he's probably right. I can directly connect the chip to the motors without a problem! I'll order some anyways. (if I decide to buy online)

 

[Hank Fletcher]

Only problem with the is you still need the diode clamps on a motor.

Are you sure about needing diode clamps for the SN754410? I was under the impression that they were built-in on this IC, and that that was one of the major improvements over the L293D. I've never had any problems running DC motors without any extra diodes on the SN754410 .

 

[Hank Fletcher]

I know what a 555 timer is. I just haven't found the need to use it so I never really got into it. I program PICs...

That's surprising, from my perspective, because I'm only just getting started even thinking about a PIC programmer (maybe I can hit you up for some tips). It's probably a generational thing.

If you're cool with programming PICs then understanding a 555's not going to be much of a challenge, but you still might want to take the time to get your head around it. With the PIC you're using, it's got PWM so you could try to adapt the notes from the tutorial I linked earlier, which shouldn't be a stretch, and thus have PWM without using anymore breadboard space. [Whoops, I forgot that the 16F84 that the tutorial uses doesn't have PWM, so that might make it even easier for you since it's already on your mcu.]

That being said, if you PWM with the 555 I'd wager the ten minutes it will take you to build for the 555 will make it easier than trying to include the PWM routine in your robot's programming. Just my opinion, and like I said, I'm new to PICs myself so you might want to get an mcu expert's advice. If it was my first crack at it, I know I'd use the 555, because then I'd just have to write a tight little program that read the sensor and turned the motors on and off with a simple high/low to the h-bridge in response to the sensor reading.

 

[Hank Fletcher]

So, Omar, where did you get your JDM programmer and PIC, and what are using for compiling and burning software?

 

[Omar.M]

I guess you are right. I'll go pick some up then, but I still don't know where to buy the TI chip from. As well as POTS-- I haven't been able to find any around here (source is too much of a ripoff).

What Bill said-- apparently it is possible to run the motors with just a connection (so the motors can run at that voltage). What do you think? Go with Bill, or still stick with the PWM?

 

[Omar.M]

I got some samples from Microchip, so that is where I got the PICs. The JDM programmer I found on EBAY which was a part of someone's site. Actually, he's a fellow hobbyist himself. I'll give you the link from home.

For the software, I am using Great COw Basic compiler, and Crimson Editor for the code writing. It uses MPLAB to compile, btw (Great Cow Basic)

 

[Hank Fletcher]

What do you think? Go with Bill, or still stick with the PWM?

Sorry: Who's Bill, and what did he say (post a link to him if you've got one)?

blueroomelectronics is obviously much more an expert in this field than I am (despite my call on his view of the SN754410), and he's based in the Toronto area. Maybe he can tip you off to someplace in Toronto that'll let you mail order the SN754410, and some pots. I know for sure there's got to be a place in Toronto (or Montreal) that'll get you the chip, it's just a matter of finding out who they are. It's well worth the time to do the research finding the company you need, because if they can get you this thing you'll know that you finally found a place in Canada that can get you pretty much anything you could ever want for your robot. As for the pots, you just want some little trimmers like this:
**broken link removed**
and at $4 for a packet of 12, that's a deal that you won't be able to beat. You can solder some short lengths (oxymoron?) of 22 gauge wire to the pot to plug into your breadboard, and glue the back of the pot to the chassis of your robot. Keep an appropriate screwdriver for the pot on hand when you're running the robot in case you ever want to tweak the output to the motors.

Don't be bummed about having to wait to get your h-bridge, because there's plenty of design for your robot that you can get cracking on right away. $3.49 is pretty steep for a 555 timer, but I don't doubt that Active have some on hand or some other electronics place in Ottawa, so shop around, get one, and start experimenting with setting up a PWM so that you're good-to-go when the h-bridge arrives.

 

[Omar.M]

I'm sorry, Bill is blueroomelectronics.

Yeah, I guess finding the right shop in Canada would be good, chances are I wont any time soon.

I'll try to get some company around here to get it, but I am doubt they are willing to do it for a 10 dollar sale for some student. I think they'd be willing to do that if I was ordering like 100 or something.

If nothing works, Bill said that the L293D works well. Maybe I can ask them if they have that (Active).

Active does seem to have some Solarbotics stuff, and solarbotics seems to have nice drivers.
I'm not sure. There's so many possibilities, but they all seem to have a problem with them.


Omar

 

[Hank Fletcher]

There's so many possibilities, but they all seem to have a problem with them.

That's life, deal with it. Be thankful you have a choice of possibilities, choose one, and solve/realize it.

You could ask Bill where he got his L293D, just remember that if you're using that particular chip, you do have to have the clamp diodes he mentioned. Just one word of caution: didn't you say the motors draw 660mA of current (presumably their stall current)? Be sure of that spec, because if it's true it's slightly out of the specs of the L293D's 600mA limit. Most roboticists might not be aware (e.g. might not have any faults) with this because it is a relatively small margin, and that only excessive, purposeful stalling of the motor would be enough to damage the L293D. Even so, if I absolutely had to use the L293D on the Tamiya (and the spec for the motor is what you say it is) I'd run both h-bridges on the chip in parallel to be sure everything's kept within spec. To be quite honest, I just wouldn't go for the L293D and would hold out for the SN754410, but I think I said that already. Its greater compatibility with your application outweighs any greater hassles over the L293D you might have getting it.

 

[Omar.M]

True. I guess you have convinced me. I'll get the SN754410, get reassurance with Bill or some other people who might have used it with Tamiya Gear Box motors, and hopefully get it shipped. To be safe, I'll buy a 555 timer, as well as some resistors rater at 1W.

I contacted a few shops in Ottawa. They rudely responded and said no. So I guess I don't have the option of Ottawa, I contacted all of the stores that sell electronic components.

 

[Hank Fletcher]

So I guess I don't have the option of Ottawa, I contacted all of the stores that sell electronic components.

Ask Bill where he shops in T.O. He seems like a good sport.

 

[Omar.M]

I'll do that. Thanks for your help both of you, I'll surely keep you posted (and don't you worry-- my newbie questions are coming =P)!

Omar

 

[blueroomelectronics]

Are you sure about needing diode clamps for the SN754410? I was under the impression that they were built-in on this IC, and that that was one of the major improvements over the L293D. I've never had any problems running DC motors without any extra diodes on the SN754410 .

They have diodes in the schematic in the datasheet... But at the end of the datasheet they show external clamp diodes on a stepper motor.

This is the TI datasheet. If they have the clamp diodes then it's the better chip as it's still in production...

Creatron Inc on College has the L293D in stock for about $4 CDn.

 

[Omar.M]

For Bill, if I use the L293D, I can use it freely without any extra circuitry (except that fuse) and such straight from the PIC?

I really don't want to hurt the poor tamiya motors, they're my friends.