L298N Motor Driver board smoking....

So I previously setup my Arduino Mega with this L298N Motor Driver board http://yourduino.com/sunshop2/index.php?l=product_detail&p=127. I used some 12v motors off of some kids/power wheels cars & they worked great. Now I want to upgrade my motors. So I got some 24v electric wheelchair motors, sim. to this: http://www.ebay.com/itm/Merit-power-chair-right-motor-gearbox-PC-MP3-R14-AR-/111135604269?pt=LH_DefaultDomain_0&hash=item19e032be2d

Even though the motor is 24v, if I connect it to a 12v battery, it seams to run fine (maybe at 1/2 speed). But when I connected it to my L298N Motor Driver board, the chip started to smoke & the motor was turning very slow, even though I had my speed pin set to 255. Can anyone tell me what I'm doing wrong? The L298N Motor Driver board says it can take up to 35v, but I'm only putting 12v through it, so I didn't think that would over heat it....

Thanks for any help, Barry

so what current do your new motors need ?

I'm not actually sure, there's no model number on the motor itself, so I'm not sure how to look it up. All it says is MP-3C Red, but that's the model number for the wheelchair not the motor. Is there another way to figure out what it needs?

Does the motor have a sticker on it that addresses the power rating or voltage. We can compute the current rating from power and voltage....for the purpose of learning.

For the purpose of using these motors in your project, you are definitely going to need a motor controller with more power. The one you bought in the link above is rated at 2A with a peak of 3A. Big 24V wheelchair motors are going to pull way more than 3A for startup current. So you may have smoked your board. Does it still run the other, smaller motors?

I'll have to check again when I get home if I can find more info on the power requirements. Yes, it still runs with the smaller motors connected. Can you suggest another motor controller? I found this one: http://www.robotshop.com/pololu-dual-motor-driver-shield-arduino-2.html 12A, 24V, would that work?

thx for the help, Barry

Barry, Pololu makes several boards...one of them will work. Let's figure out what your motors use for power consumption and then it will be easy to find the right controller.

A simple, but easy way to get us into the ballpark is to run the motor off your 12V battery with an ammeter in series and see what the steady state, no load current is.

Then with the motor held in a vice see if you can restrict it and watch the current spike to see the stall current. Just be careful here because these motors are likely to have a lot of torque.

Also take a cell phone snapshot of any data plate and post it here.

We'll get this sorted out.

12A, 24V, would that work?

That would work up about 12 amps. But until you determine the amps of your new motors, don't buy anything.

How many of the new motors are you running at the same time?

You may be able to reduce some peak power, by coding (when starting the motor, start slow, rather than "full speed ahead", for maybe 1 or 2 seconds.

Thx for the info guys. I'll get back to you tonight or tomorrow with more info.

I'd like to drive a total of 4 (maybe 5) motors, but they're spit into 2 sets. So 2 or 3 would always be going in the same direct & speed and the other 2 could be going a different direct & speed. So I'm thinking I only need a 2 channel controller, right?

Sounds like you need 4 (or 5) channels. I may not understand this question. But with that many how power motors all running, you will be using a lots of amps I bet. What are you building, or is that a secret?

What am I building…? That’s a good question.
No, it’s not really a secret, just a little odd & hard to explain.
I’m competing in a CANstruction competition. We build large sculptures out of canned food, they’re on display for a week, then donated to the local food bank. This year we’re building a 6’ Rubik’s cube where the top 2 levels will rotate.

Here’s a preview:

And attached is the layout of the system. The motors shown in the layout are out of date. My smaller inadequacy motors.

It’s going to have to rotate a lot of weight, maybe 1,500-1,800 lbs. So that’s why I want 3 motors on the lower level & 2 on the upper. But like you said start out slow… then I think it should have enough torque.

I was thinking since I only have 2 levels of rotation, that all the motors on that level could share a channel on the controller…
But I’m not sure if that works with the amp requirements or not…

Ok. Now I have more understanding. Thanks. With the size of motors, I don't think I would skimp to try to get more than one on a controler. If this display runs for hours, It will keep adding up heat from current draw. If you can, try to program in a little break from time to time, and add a fan to keep the air moving around the controllers.

Good luck with the construction. Any other questions, let us know. Jack

OK here is the only info on the motors…

From scooter website - SPECS!

up to 5mph
Range: up to 18 miles
Turning Radius: 21"
Ground Clearance: 3"
Motor: DC 24V, 180W
Controller: Dynamic Shark 60A/PG VR2 60A
Battery: 12V/U1(34AH) x 2pcs
Charger: 5A off-board
Gradient: 12°
Casters: 8" foam filled tires
Drive Wheels: 10" foam filled tires
Brakes: intelligent, regenerative, electromagnetic

Edit:
Here’s 60A x2 motor controller board at Pololu -

Thx much for the info. Wow, does it really need 60 amps? That seams pretty high...

OK here's a stupid question. If I cut down on the volts, does that mean I can cut down on the amps too? So could I do 12v & 30 amps?

If I connect my 12v, 12ah battery to the motor it seams to run fine.... Sorry for all the stupid questions, as you can tell I'm a noob.

I also have the wheelchair controller & joystick. Another thought is to use the Dynamic Shark controller as is & try to figure out what the joystick is sending to it & have the Arduino replicate that. But that sounds way over my head... :(

I think this is a cool project. They had one of these can sculpture contests in the Jacksonville airport last year and the moving displays were by far the coolest.

Here's a few suggestions to keep you moving forward.

  1. Don't try and reverse engineer the controller you have. If I or a lot of guys on this forum were tackling this project we would probably hack the existing controller. These sorts of hacks are one of the funniest things to do in this hobby...but for a beginner you need to start with components you have the data sheet on and start to understand how those data sheet values enable/restrict your design options.

  2. Do not put more than one motor on a channel, and you can build this with just two motors per level. These wheelchair motors are wotkhorses...two per level will be enough. This will keep your design more straightforward and easier to implement since it is the same on each level.

  3. Motor controllers allow you to change the speed of your motors, change their direction and in many cases they also include circuitry to monitor their current consumption and even calculate the number of rotations each has made via quadrature encoding. HOWEVER, it sounds like all you need to is turn your motors on and let them run at a constant speed while they spin their cube level. THEREFORE, you may not need a full blown motor controller and we can recommend some simpler (less expensive) circuitry.

  4. If you are going to go with the motor controller (so you can do cool things like spin the cube levels both directions, etc) then you will want to match the 60A controller they came with. My GUESS is that this is 60 amps max, meaning 30 amps per channel. This makes sense because the post above shows that the motors are 24V, 180W. The power formula is P=VI, where "I" is in Amps. Therefore, 180=24*I. So I is 7.5A. This is 7.5A steady state. The stall and/or startup current can peak at several times this rating so the original controller provides a peak of 30A per channel to allow cool, safe operation across the motors range. This is, of course, exactly the kind of high safety factor you would expect in a wheelchair. Setting grandmother on fire when she stalls out on a hill is not acceptable! But I would guess its equally unacceptable to set a display of food for the homeless on fire so you should set your design spec at 30A per channel and continue designing from there.

  5. Mechanical question: how are the motors engaging the cube level to spin it. In the drawing I saw where they were placed but did not see how they were mounted to spin the level.

Again, I think this is a cool project...read over the recent posts and fire your next round of questions and responses.

I'm working on building my own motor driver from the BTN7970. Maybe you could build something similar? Just another idea. Also, Trossen Robotics sells nice motor drivers.

http://forum.arduino.cc/index.php?topic=179561.0

http://www.trossenrobotics.com/

Best of luck!

Hi guys,
First thanks very very much for the replies. They’re very helpful & informative.
@zacstaples:
What where the moving displays they had at the airport? Last year I did a 7’ tall R2-D2 with a rotating head.

I haven’t seen any other moving can sculptures, but I’m sure they’re out there. He only rotated 90 deg. & the head was only around 200 lbs. so it was much easier then the cube this year.

  1. No I don’t think I’ll try to reverse engineer the controller. I know that’s over my head, but might be fun one of these days… :slight_smile:

  2. So you think 4 motors total? So, I’ll need a 4 channel control or 2x 2 channel controls…?

  3. Actually no I didn’t want them to spin consistently in the same direction. I’d like one level to spin 90 deg. then maybe wait 30-60 sec. then spin the other level maybe in the other direction. I was thinking of having it choose randomly which level to turn & which direction it’ll rotate, so it’s not a repeating pattern. I also think it should start out slow, then speed up, then slow down as it comes to a stop at the 90 deg. position. PID, I think it’s called…

  4. I’m so glad you think I should use 30A per channel. The 2x60A controllers seam to be a lot harder to find & a lot of money. It’s hard for me to justify spending $200 on something where the funds are supposed to be going to charity & it’ll only be on display for a week. I also e-mailed these guys: http://store.eurtonelectric.com/wheelchairscootermotorsmodel425500.aspx
    since they repair them & they said the motor was 5 amps (pretty close to your 7.5 amps)

  5. There will be what I call a “Rotation Ring”, basically a big circle all the way around inside the cube. Then the motors will spin against that ring. The ring is attached the the plywood below & the motor to the plywood above. It’s like a big turntable. In the first version, shown above, I just had a rubber wheel against the ring (this is how I did R2-D2). But I’m afraid the wheels won’t get enough traction with all this weight, so I want to try to do a geared system, cut on a CNC machine out of think plywood. See the new version attached below, with the correct sized motors & gears…
    I’ve already build a small prototype version:
    http://www.youtube.com/watch?v=iyvFpo_I1Mk
    Maybe this video will help show how the rotation is happening. This is of course with the small motors & no Arduino…
    Also, note at the end of the video, I can have both motors going in opposite directions to make the middle level spin & keep the top level stationary.
    So I have 3 rotation options: top only, bottom only, or top & bottom in opposite directions…

Hope that all makes since. I guess now I have to narrow down which controller to use…

Here’s another questions for ya.
I was planning on using these Slip Rings: http://www.ebay.com/itm/300Rpm-Capsule-Compact-Tiny-Slip-Ring-12-Circuits-12-5mm-2A-240V-Test-Equipment-/390591603081?pt=LH_DefaultDomain_0&hash=item5af112e189 so I can have the batteries at the bottom & pass the wires through the rotation plane. But now that I know I need the higher amps, I don’t think that will work anymore with these thin gauge wires… Maybe I can split the load & use 2 wires for positive & 2 for ground…? If that doesn’t work, I can always keep track of the rotation & be sure to always unwind it, but I was hopping to not have to do that… I was going to use a rotary encoder anyways, so that I can stop it at the 90 deg. faces…

@Drew,
Thanks for the suggestion, but I don’t have the skills to build my own…
This one looks interesting, since it can take 70A, but if I need 2 per motor, then I’d need 8 total & that’s almost as much as the 2x60A from Pololu:
http://www.ebay.co.uk/itm/BTS7970B-BTN7970B-power-motor-driver-Controller-module-70A-A2630-78M05-5V-25V-/300921027008?pt=Intercoms_Access_Controls&hash=item46104a79c0

thx,
Barry

How about this one: http://www.pololu.com/catalog/product/1494 But do I really need 2 of them?

Where did all my wonderful helpers from yesterday go...?