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~~
Check the spec sheet on 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?
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.
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.
Your welcome. I only hope 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.
I can’t tell from the I can’t tell from the picture where you are attaching the output of VR to the board, but, I think you want to go into the screw mounts titled “servo power”. (you probably are doing that, I just can’t see it). Diodes are usually used to prevent current from flowing backward, ensuring the current only flows one way. They look like resistors, but usually one color, like black, with 1 stripe. This stripe is the output end. Usually they allow high voltage to pass thru. Like an LED, they consume some voltage in the process. So you wire a few of them in series to get the desired drop. I think the amount of drop depends on the voltage passing thru it. For instance, if the diode is a 50v diode, I think it will drop 1.6v if your circuit uses 50v. If your circuit is less than 50v, the drop will be less. Different diodes have different ratings. It’s another way of doing voltage regulation with less limitation on current. Goto radioshack.com and type in diodes and read about the different models.
Of course if your going to 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.
if you would like to reduce the voltage you should put in your mind the following:
1- if you are planing to use 78xx regulator. the input voltage must be at least 2.5V larger than the output voltage. if your supply is 7.2 then max output voltage is 7.2-2.5=4.7V. so if you used 7805 ,there will be no guaranty to get 5V. the second piont that you should know is that 78xx series max current 1.5A or only 1A for the 17J package.
2- the correct solution is to use diodes. each diode will have voltage drop about 0.7V. the type of diode you should use depends on the total current. if it is less than 1A you can use 1N4007. for larger currents up to 3A in average you can use 1N4508. the voltage drop across the diode will increase with current for example at 5A the drop will be around 1V.
3- i do not know what is exactly the driving circuit of this servo, i can not expect the cause of the burning.
please check that you may have some mechanical problems with the servos. if the load is too heavy the current may increase largely. this is mostly the reason for burning the electronic circuits.
I am using 4x Hitec HS-485HB and 8x Hitec HS-645MG. You may click into the link for spec. HS485HB is the one usually burned. Here is the schematics for servo board.
Sorry if I mistaken anything here since I have zero background in this field but just learn by doing with passion. Really appreciated for all of you great guys try to help me here.
Yep~ I think I am going to remove that regulator and have 2 diodes to reduce the voltage. To be honest why I am so confused to use 7.4 without reduce because my other Hexapod uses same battery without reduce power but still running with no servo destroyed. Perhaps the SSC32 board done some tricks? But from now on I will have this in mind to reduce the voltage for good.
Current Drain (6.0V): 9.1mA/idle and 450mA no load operating x8
and
Current Drain (6.0V): 8.8mA/idle and 180mA no load operating x4
I guess I will probably have 1Ax8 + 0.5Ax4 =10A when all servos operating with loads? If this is the case I might use bigger diodes or 1N5408 should be good to go?
if you are new to using servos there is a good tutorial about servos at Society of Robots (http://www.societyofrobots.com/actuators_servos.shtml). in design you should take the worst case. for servos there is no-load current and stall current. the stall current is the one that you should take care about. for your servos i could not find the exact stall currents, but it is good practical idea to consider stall current about 5 to 6 times the no-load current.so for :
the current that you calculated is the no-load current when all servos are on.usually there must be some load and not all servos are on at the same time. if you need them all ON together then you are talking about less than 2.5x8+ 0.75x4=23A.
That looks scary. So I wondering how hexapod or other multi servos robot manage such problem? by sequence? so 23A will never happen? Well, I gotta dig more information about this issue. Thank you for your information that really helps me to step further~
yes the servo motor have its driver and feedback circuit inside the case so it accepts pulses from the MCU. Usually one CPU can control up to 16 or even 32 servos. if looking at software the MCU will generate the required pulse for the first servo then the second servo, the third…and so on. so it is sequential operation. then expect only one servo running at instant (this is the common case), however the servo response may take some time to be settled so you may give the pulse to the second or third servo while the first is still rotating. it looks good from current point of view to put few ms delay between the servos pulses. this will be help full to decrease the max current especially if you put in your mind that the current response of the servo start from max decreasing to min with increasing time.
