Let's Make Robots!

U7 got fried for some reason :(

I just got my Dagu 4 Channel Motor Controller, already a small part gave some smoke and one motor channel is not working anymore.

All four wheels were turning at the same time before the channel4 got fried.


  VCC to Arduino 5V

4 PWM on the motor controller to 4 PWMs on the Arduino uno.

All grounds on both  controllers where connected.

6*1.5V Alkaline AA to Vbat on the motor controller(connected after all the other connections).

After uploading a simple code with PWM set to 75, all wheels were turning until smoke came from U7 chip and i unplugged everything.

Repeated the same thing again, all 3 motors are still working, so why did U7 burn, i have no idea. 

Any ideas?

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If you are going to switch to a red back spider robot controller (please choose a shorter name for your next controller OddBot) in the future you might consider a different way to power the logic of your motor controller. The red back spider robot controller has a switch (on/off), when this switch is in the off position there is no 5V on the VCC pins. If you put that switch in the off position and your battery is connected to the motor controller power terminals you will have a nice smoking motor controller. If you use the 5V from the VCC pins on the spider controller for the logic you must always disconnect the battery from the power terminals FIRST before you turn the switch to the off position. This is not practical. Just imagine your rover driving around and something goes wrong, then you want to turn it off as fast as possible. Is not very practical to disconnect the battery, much easier to flip a switch.

Note: when an USB cable is connected to the red back spider robot controller there is always 5V on the VCC pins no matter what the position of the switch is.

I use a 2 cell Lipo battery to power my rover 5, battery gives 8,4V when fully charged. My Lipo battery is connected to a small pcb with screw terminals on, I use the plug from the battery to easily disconnect it. On the pcb I have a 5V regulator that provides voltage to the logic terminals of the motor controller. That way I'm sure there is always 5V on the logic of the motor controller when the battery is connected. I also put a green led on that 5V line so I have a visual confirmation that the battery is connected and the 5V regulator works.

All motor controllers are tested in the factory prior to shipment. The testing equipment only uses spring loaded contacts pressed against the back of the PCB so I doubt the quality of the connections is the problem. The inputs have pull down resistors so they cannot float.

Despite this there have been a handful of the controllers that have had a similar problem. I can only suggest that your motor power came on without the logic powered up. This often occurs when a different battery is used for the logic.



"This often occurs when a different battery is used for the logic."

The arduino was connected to the notebook and the logic on the controller was connected to the 5V pin on the arduino. Then, after uploading the program and checking everything, i connected the battery to the motor controler, so logic was 100% powered before the rest.

Anyway, i have no use of the 4 channels for now. Later i'll try to fix it when i upgrade to the arduino mega or spider... 

If you are sure you have made no mistakes then ask your supplier for a replacement under warantee.

I thought about that, but i decided to talk to my electronics department at the university, maybe they have some ideas. Might even have a chance of fixing it in the university lab.


there's not much on it but maby you can message robotfreak for more info

i sent him a message. 

Hi ziplague,

it looks like the same problem that happened to me. Unfortunately I don't know the cause for it. Only a vague suspicion: Maybe a loose logic power supply connector was the cause. I have used Jumper cables with round pins, that didn't give good contact. Now I use the srew terminals. No more problems so far. 

I used the screw terminals too. Weird. Any ideas as to how can i fix it, bypass it or replace the U7 chip?

Because I need only 2 out of 4 motor drivers I have no urgent intention to replace the defect one. Don't found the SP8M3 at my favorite distributors list, too. A replacement part could be the IRF7319. But in this case you should replace both half bridge ICs U7 and U8.

Replacement of the chip is not a big deal if you know how:

  • Use a cutter to cut off the pins of the defect IC.
  • Than remove the pins with the solder iron.
  • Than you can solder the new chip.
  • Hold it down with a pincette and solder one pin first.
  • If everything is in the right place continue with the other pins

Edit: I have some IRF7319 chips here, so I will try it by myself.