Let's Make Robots!

Servo killer

Ok, servo board works perfectly for my quadbot. However, I kill 3 servos(HS-485HB) in a day!!!

This servo board support 14 servos and I have connect them with external power - 7.4v lipo 2800mAh. The battery connected like this(the battery is 7.4 not 11.1v any more):

Here is what happening; When I do the coding I have USB connected and power off from battery. After coding I turn on the switch so servos has enough power to do the moves and USB still connected. It was fine for several attempts but after 5~6 times repeating the same procedure then I got my first servo not working, I replace it and I switched off the battery and did uploading and switch on, then I got 2nd servos burned right the way! No sparks or smoke but bad smells. Same procedure and 3rd servo burned. I have no idea why the servo burned so easily. Anyone have any ideas? I am assuming I probably can't have USB and battery on at same time, especially when the moment I repeating turn on the switch and have high current flows in that impact the servos??

Again, I have to say sorry for my bad English and writing skill. If this is not clearly explain what happened please let me know and I will try my best to explain again.

Thanks in advance for anyone could help me with this issue~~

P.S. Servo shield I am using now:



Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Use a measuring thingy on the servo power & signal, compare that with what the servos are rated at....

This should take they mystery out of it... 

You could add a pair of diodes in series instead of a voltage regulator. Diodes are said to cause a .6Vdc drop for each one in series. 6.2Vdc should be  a great deal safer than 7.4.

Hum... never use diodes before, could you tell me which model of diodes should I get?

And please correct me if I am wrong. This is what I have in mind how to wired them up:

[Battery+]_____>|_____[Servo Board+]___[Servo Board-]___|<____[Battery-]

LOL... Maybe I looks like a total idiot but hope you could understand what I mean and correct me.


Battery+ > diode1 > diode2 > servo pwr + Where each diode has the stripe pointing downstream
Check the spec sheet on those servos. Can they accept 7.4v? Or do they have a max voltage of 6? A better schematic of how its all wired might be helpful. Does the board have jumper settings for you to specify the voltage to the servo?

They have schematic here:


Yes, they do have 3 jumper but I can't quite read schematic and not sure if I should set these jumper in proper place. Now I am adding a 7806 to lower the power from battery. Hope it works.

Thanks Paul, you have helped me many times! 

Your welcome. I only hope I'm not sending you on wild goose chase. I like Birdmuns idea of using diodes instead of volt regulator since diode will have higher amp rating, whereas a typical VR might only allow 1amp and with multiple servos going at once you might blow that too. Unless you know what those 3 jumpers are doing I would leave them at factory setting. Actually, you must know what those 3 jumpers are doing because factor setting may not be what you want. The schematic you linked to is a PDF and I was able to zoom in and see it clearly but I don't understand what it's telling us. I quickly looked for a written spec sheet but didn't find it.

Sound like I need to grab a few diodes tomorrow. According to Birdmuns's plan what suggestion of Diodes and how to wire them up?

Ok...This is what I done for regulator:

I know, its so ugly and you can laugh at that :D

Of course if your going to use the diodes, you will remove the voltage regulator. For future reference, the screw hole on the VR is for a heat sink, like a piece of aluminum, because it will heat up and you want to pull the heat away from the VR.

LOL~ I know this one. Just want to have it steady on a spot.