Struggling to power v.1 motor shield correctly

Hi there,

I have a question about powering a v.1 DK Electronics motor shield. At the moment I am currently using either two or four 3-6v motors and struggling to get a stable speed across all motors.

I have read the manual for the v.1 shield written by LadyAda and noticed she said not to bother using a 9v battery to power the shield as it would not be sufficient.

I have used a 9v battery to power 2 motors, so far with no problems--the motors spin fine, but when connecting the shield to a 12v supply, the motors behave erratically. I have noticed with 12v the speed needs to be kept under a certain level to control the voltage and have even used PWM with the delay function and cannot get a stable speed. One strange thing I noticed is that if I touch one of the motors or turn it on an angle, the motor slows right down and sometimes stops, almost like I’m changing the magnetic field or affecting the torque. Also (on the 12v supply) the motors slow down after about 10 seconds, sometimes coming to a halt. I can't seem to find a speed/voltage range that works correctly with 12 volts.

When I try and connect 4 motors with a 9v supply, not much happens. Two motors spin fast, one spins slow and the other is stalling. If I try and connect 4 motors to a 12v supply, the behaviour is just as erratic as if I had two connected. Really struggling to understand what's going on here.

(I am also powering the Arduino separately through USB connection, as advised)

Could anyone possibly advise me as to how to correctly use a 12v supply with a motor shield and where I may be going wrong? It generally seems the 12v is too much, but I was under the impression the voltage is regulated and the system could handle 24v or so. The bridge gets very hot very quickly, also. All I can think of is that I'm using the 'wrong' motors, but I presume there would be some way of getting them to work correctly.

To simplify: 2 motors is okay with 9v. 4 motors won't work with 9v. Nothing works correctly with 12v.

Thanks in advance!

PS. Sorry for the school boy questions, I’m genuinely stuck and cannot find the material to explain.

We can't help you as long as you persist in trying to use a PP3 9V smoke alarm battery.

This is totally unacceptable.

You should already know that you cannot use that battery . If you did not know before, you know now.

Come back when you have another power source that is adequate.

Could anyone possibly advise me as to how to correctly use a 12v supply with a motor shield and where I may be going wrong? It generally seems the 12v is too much, but I was under the impression the voltage is regulated and the system could handle 24v or so. The bridge gets very hot very quickly, also. All I can think of is that I'm using the 'wrong' motors, but I presume there would be some way of getting them to work correctly.

To simplify: 2 motors is okay with 9v. 4 motors won't work with 9v. Nothing works correctly with 12v.

You need to add an LM317 voltage regulator circuit or buy a variable power supply.

12V supply - you give no details, perhaps it doesnt have the current?

raschemmel:
We can't help you as long as you persist in trying to use a PP3 9V smoke alarm battery.

This is totally unacceptable.

You should already know that you cannot use that battery

Thanks for the animosity, really helps.

If you had have read what I wrote, you'd notice I already acknowledged that I can't use a 9v battery and was trying to use a 12v battery. I gave info about the 9v battery to explain the process I had gone through. I asked how to use a 12v supply, so not sure how you translated that into "persisting" to use a smoke alarm battery.

"you should already know that you cannot use that battery"

Did I not acknowledge this at the beginning of my post? Or do you PERSIST in being funny with people?

Don't answer that...answer is clear enough.

Next time a beginner asks for help, perhaps you should just refrain from talking, instead of being rude and talking to them like they are an idiot.

This is totally unacceptable.

You should already know that you cannot use that battery

Thanks for the animosity, really helps.

Animosity is a personal. My comment is technical. A 9V battery is totally unacceptable. That's simply a statement of fact, that I believe you have already agreed with. Let me put it another way. Knowing that a 9V battery won't work, what good does it do to tell us you tried to use one ? Wouldn't it make more sense to simply post a link of the vendor that sold you the motors or a link to the datasheet for the motors or something from which we can obtain the current rating of the motors (which you didn't include) ? If we know the current rating of the motors , we don't care how that relates to a 9V battery
You learned this from experience.

"Good decisions come from experience. Experience comes from making bad decisions"

You gained some experience . We need to know the current rating of the motors, which can be obtained from a datasheet or possibly a vendor link. The correct way to convey motor rating is post the specifications, not tell us how many of them will run off a 9V battery, but you probably know that by now.

Did I not acknowledge this at the beginning of my post?

Where ? I didn't see any statement in your original post indicating you realize that you shouldn't be using a 9V battery for motors. . I see you said it won't power 4 motors but you were ok with powering 2 motors. My statement was intended to convey that you should not be using a 9V battery for ANY motors, because the mAh rating is so low that it will run down very quickly. So no, it is not ok to use for 2 motors.

Could anyone possibly advise me as to how to correctly use a 12v supply with a motor shield and where I may be going wrong? It generally seems the 12v is too much, but I was under the impression the voltage is regulated and the system could handle 24vor so.The bridge gets very hot very quickly, also.

All I can think of is that I'm using the 'wrong' motors, but I presume there would be some way of getting them to work correctly.

It could also be because of the large difference between the P.S voltage and the rated motor voltage.
The bridge is not a regulator. It is a bridge. There is nothing regulating the voltage to the motors from the motor voltage input terminals. There is no voltage regulator between the motor input terminals and the motor terminals., so no, it is not regulated. I don't know where you got the impression it was since nothing in the document you linked would suggest that.

What exactly does this mean ? (why were you under that impression ?)

I was under the impression the voltage is regulated and the system could handle 24vor so

What's this ? :

You need to add an LM317 voltage regulator circuit or buy a variable power supply.

Next time a beginner asks for help, perhaps you should just refrain from talking, instead of being rude and talking to them like they are an idiot.

Where was I rude ?

Now let's get the technical details for why that isn't a good idea:

9V battery

There are two reasons why a smoke alarm battery won't power the motors. The newbie explanation is "it doesn't have enough power". The exact reason is the internal resistance is too high and the mAh rating is too low.

Do you have a DMM ?
Try measuring the motor current with the DMM

MarkT:
12V supply - you give no details, perhaps it doesnt have the current?

Hi MarkT, thanks for the reply.

Forgive me for my lack of understanding--I'm just starting out and struggling to get up to speed here.

I was under the impression that the current is relative to the load...didn't know there was any other details to give about the battery, all I know is that it is a 7ah and 12v lead-acid battery. The motors are 3-6v each but I'm struggling to find out their current draw or any other relative information such as you have suggested.

lewisReid:
the battery, all I know is that it is a 7ah and 12v lead-acid battery. The motors are 3-6v each...

12V source vs. 3V and/or 6V motors

Points from the v1 PDF (and not meaning to be a dick):

If you would like to have the Arduino powered off of USB and the motors powered off of a DC power supply, plug in the USB cable. Then connect the motor supply to the PWR_EXT block on
the shield. Do not place the jumper on the shield. This is a suggested method of powering your
motor project.

If you would like to have 2 separate DC power supplies for the Arduino and motors then plug in the
supply for the Arduino into the DC jack, and connect the motor supply to the PWR_EXT block.
Make sure the jumper is removed from the motor shield.

Either way, if you want to use the DC motor/Stepper system the motor shield LED should be
lit indicating good motor power.

The motors are 3-6v each but I'm struggling to find out their current draw o

Post a photo of the motors.

Runaway Pancake is tactifully suggesting you read this:

See "How to set up the Arduino + Shield for powering motors" (p19)

raschemmel:
Runaway Pancake is tactifully suggesting...

He listed the v1 PDF in his OP.
That's how I got the information.

Got it.

I must have missed that.

I’m not sure if I understand why you are referencing a document the OP linked. If he linked it I would think he read it.

raschemmel:
Got it.
I must have missed that.

I'm not sure if I understand why you are referencing a document the OP linked.
The fact that he linked it would suggest he read it, unless I'm expecting too much.
Is that a stretch ?

It's possible anyone might "miss" critical information.

My only interest is determining the baseline, getting the facts, finding the details of the situation.

Fair enough.

I tested a 6V motor with the DK Motor Shield and it was drawing about 750 mA with the bench Lab P.S. set to 6.0 V.

It wouldn't move with any voltage less than 6V.

The current peaked at about 780 mA.

P = 0.78A * 6V = 4.68 W (about 5W)

Sorry for the late reponse, I’ve been at work. Thank you for all of your replies and effort.

Where to start…

Firstly I’d like to acknowledge the help given here and point out its use for others who have similar problems - just as I have found help by typing in questions in my search engine and being directed to the forum here.

  1. Thanks for the info about 9v batteries, raschemmel, however I was not aware until reading this thread that AH’s played any role. I thought it was just a measure of capacity and how long the battery will run for.

  2. Thanks for the info about the voltage regulator system, raschemmel, I didn’t get a chance to reply but have used one this morning, with not much joy. I’m using an L7805CV 35/5v regulator and the speeds are stable across motors, however they slow down and stop after 30 seconds. (I’m currently using a 12v battery). I do not have any other regulator I can use right now. Perhaps I’ll order some of the ones you mentioned (LM317’s) when I have the money. Just to make it clear I am using the regulator circuit before the power pins on the shield…don’t tell me I put it in the wrong place?? And I need 4 circuits, one for each motor pin!!! Heck, I’ll try it anyway whilst I wait for a response. :o

  3. I was under the impression the shield was regulated as I had been suggested to use a shield for that reason by another member in a separate thread, when enquiring about voltage regulation for motors. Presumably I missunderstood the concept. Secondly, I was under the impression the “system” could handle 24v or so, after reading through the LadyAda V.1 manual. I won’t quote her but I thought she said the shield could power around 24v, maybe I was wrong or mistaken.

Thanks also for the info about the shield not being regulated, it took me a while to understand what you meant but I think I get it now. My simplistic thinking is probably due to nearly every single web page showing how to use a shield - simply plugging in great big motors of different sizes - plugging and playing. It all looks so simple, not one page has mentioned anything such as separate voltage regulation circuits. I get the feeling that all the popular posts online are written by people who understand SEO but have little knowledge of robotics and electronic engineering. Either that or I’m using some stupid motors that won’t even work properly with Arduino - which brings me to my next point.

  1. I genuinely would have given more info on the motors if I had it, I bought them from an eBay listing who’s only information was 3-6v, other than it’s speed which I thought was irrelevant, however it’s 18,000 RPM. As I had no info about them I could not look for a datasheet. Here’s the eBay listing:

http://www.ebay.co.uk/itm/15PCS-DC-3-6V-Mini-Miniature-DC-Motor-For-Remote-Control-Toy-Car-Robot-DIY-Parts-/262350437681?var=&hash=item3d154dfd31:m:mEokg3eZlontUyJULHGz_Dg

Sorry, I should have known to post that sooner…

5 & 6. I tried to acknowledge I couldn’t use 9v by showing my understanding from what I had read in the manual.

“I have read the manual for the v.1 shield written by LadyAda and noticed she said not to bother using a 9v battery to power the shield as it would not be sufficient.”

The information about me using 9v (although perhaps irrelevant) was to show my understanding, the route I had taken, so as to try and build a picture as best as possible, given that I do not fully understand all the info I need to convey to get an answer to my problem.

  1. Thanks - Runaway Pankake - I had read all of the info on the power section, along with every web page in the first 5 pages of results in Google, over and over and had not found anything that’s helped me. I thought it was lacking in information but it’s probably my understanding that’s lacking. I’ve disconnected the jumper pin from the board as suggested. It’s only 2 pins on the version I am using, no selection mode.

  2. I’ve tried taking a voltage and current reading from the motors whilst they are spinning (connected to the shield) however I’m not getting any readings – there really is not that much power available. Again, I’m currently using a 12v battery with a 35Vin/5Vout voltage regulator circuit with a diode and two 10uf 25v capacitors - as suggested by a post I had read. The regulator system works spinning 4 motors in paralell, just not with the shield.

I’m really sorry if I’m missing something or just being profoundly stupid. I’m working on it every day but do not have a tutor/teacher and struggling with the books I have - it’s a lot to take in, to do some very basic things.

All the help so far is much appreciated, any more suggestions would be great, if I’ve missed anything just ask away.

Lewis

There are two problems here
1-VOLTAGE: As I said in one of my posts, I ran a similar motor (though not the same type) and did not get any result until I increased the power supply voltage to 6V. This is because the L293 chips are not mosfets and they drop at least 1.5V across the transistors inside so you have to compensate by suppling more voltage so the motor will have enough after loosing 1.5V inside the chip.

2 CURRENT- my tests showed the motor draws about 750 mA each so 4 times that is 3A and the LM7805 maxes out at 1.5A with a super good heatsink (which I am fairly sure you aren't using).

I understand that you have no experience. There are two options.
1-option-A: we explain everything to you
2--option-B: we teach you how to learn what you need to know.

here is the information you need to know about the heatsink:

On page-2 of the LM7805 Intelligent Power and Sensing Technologies | onsemi, under
"Absolute Maximum Ratings" , it says

Thermal resistance junction to case [TO220] 5 degree C/W
Thermal resistance junction to air [TO220] 65 degree C/W

I'm not an expert on heatsink calculations but I believe that means with a heatsink the temp goes up 5 deg C per W and without a heatsink it goes up 65 deg C per W. You'll have to consult someone who knows this better than I but I tell you that in general it means it will overheat without a heatsink.
This might help.

That goes for the LM317 as well.
You might find this useful

If you had enough money to buy a 3A variable voltage , current controlled bench lab P.S. it would probably solve all your problems. An LM317 might work. Look for one of those regulator circuits on Google.

Basically , assuming that you have tested your motor shield with 12V with 12V motors using the "Motor Test" example in the library and verified that your motor shield is in fact ok and works with other motors at other voltages, then what you have to do is get at least 6V /3A connected to the motor shield motor power terminals, with the jumper removed and plug 12V into the external power connector on the motor shield to power the H-bridge chips 5V logic power off the onboard 5V regulator on the motor shield. If you do that you should be fine.

We really need you to tell us you have tested your motor shield and verified it works with other motors at other voltages. If you haven't done that or can't do that , then we are working in the dark because then we have a big unknown in the equation that impairs our ability to troubleshoot the issue for which you posted.

One problem I see right away is that if the motors draw about 700 mA, the L293s can only support up to about 300 mA per motor (1,2A total for 4 motors). It's possible that even with the right power supply you will not be able to drive all 4 motors from the shield. because it will overheat and eventually the chips will get damaged.

FYI,
It's not a mystery thr motors slow down and stop after 30 seconds. The LM7805 is overheating and going into thermal shutdown because ( ptobably) no heatsink.

You may find this tutorial about battery capacity by Afrotechmods useful.

And please try to stick to the technical subjects in the thread without sledging each other. You know who I am talking to here. :slight_smile:

Hi guys, sorry to bring up this old thread but i wish to say thanks to this thread that help solve my motor mystery problem. Especially Raschemmel, when you mention heatsink... that word strike a memory chord in my brain... the story is as followed... for 2 weeks i am having motor trouble... my bots will run for 30 s (or so) before it slow to a stop. After that it just refuse to move... after about a minute of letting it rest it move again and then it stop n refuse to move. First i thought its a motor problem and i tried a few motor i had,... still same result. Then i went out and bought a new smaller motor... still same problem so i figure its a broken adafruit motor shield... the same one that was discussed here... and i gave up... threw the towel... literally! Then as usual some part of tell me to fight back and wanting to solve this problem... i search the net... for a few days reading every thing about this motor shield. Then luck have me coming to here and read through every word... and Raschemmel mention heatsink... i remember i was burn once when i touch the L293D chip after the motor stop and was surprised how hot it was... so 'heatsink' gets me up the sofa and into my RC tool box... i dig out an old Alu metal beam with 6 screw holes from my other bot and some old RC ESC fan...

Off i went, using a thin doublesided tape, carefully taping the alu metal beam with holes on top of the L293D chip, and infront of the 6 hole alu metal beam, i slap the RC ESC fan on it, tightening it with transparent rubber band. Plug the RC ESC fan into Servo 1 plug of the motor shield.... insert the power jumper to the power pin using only one power source from arduino uno board... slap my plastic light weight 9v li-ion rechargable battery and power up my bot... and wow! It runs without stopping this time. The chip is not even hot as the high rpm fan blowing through the holes of the alu metal 'heatsink' does not even allow the chip to be hot!

Thanks again guys... and i hope my story will help someone in future coming here to look for a solutiom to this problem.

Glad someone was able to get something out of this thread.

HI,
Can you post a picture of your cooling arrangement please?

Thanks.. Tom.. :slight_smile:

Hi Tom, so sorry for the late reply. Below are the ‘homemade’ cooling system. The track vehicle is not much of looker anyway as it was intended to be an educational project for my nephew… something that we wanted to do together during the school holidays… bonding…

it consist of an alu beam with 4 holes through the front and back, sitting on top of the L293D chip with a thin layer of double sided tape. The inside of the alu beam are hollow and that makes it good for ventilation. I had secure a small fan blowing cool air constantly through the holes and side of the alu beam. The fan is then connected to the SERVO channel of the motor shield.

Hope this will be a good example of a fan asist heatsink.

Cheers!

IMG_0270.JPG

IMG_0269.JPG

Hi,
Very neat...

Thanks .. Tom.. :slight_smile: