Being stucked on a problem is never fun, and this is what’s going on right now. 

I had bought a fancy power supply thinking “This is The One” that will power the whole robot, but I guess I was wrong. You see since the beginning of this project I had been using a very small power supply DC6V3A I had laying around in my workshop. But by adding more and more servos to it, I came to realize it was not enough anymore to power up the 22 servos of InMoov. During the initialization, each servo seems to draw about 2 Amps. I guess I was just lucky with my small supply to already be able to run the arm and not fry it instantly.

So I got “The One” after searching quite a bit on the net, it seemed to have the amps I required and the 6V I needed for the servos I’m using. 
This thing was expensive, but it was sold by the same kind of shop that sales servos for hobbiest so I thought it must be compliant. I’m no electrician, I do all those things by guessing…

Okay, I received the Power supply, I was excited because I was going to finally get the whole robot to move. First thing I did was to test with a simple Arduino sketch with only one servo. It worked perfect!
Since I had the right arm connected to the Arduino Uno, I plugged it and ran the simple Arduino sketch again. Perfect!!

At that point I had to think of making a small pcb board to connect all my servos and my two Arduino board all to that single power supply.

Once again I ran a simple test with my two Aduino boards and only 8 servos attached. It went perfect again!
Boy, was I getting excited!
So I went straight forward and plugged every thing together, 22 servos, 2 Aduinos, 1 power supply. I had used only one side of the output of the power supply, instead of both, which can each deliver 20Amps and I think here lays my mistake.
I ran the simple sketch which is only moving all the servos from, let say, 0 to 30 position. Some of the servos were already at 0 position. Then they all had to move to their new positions, here started some strange behaviours. Some of the servos were jittering (shaking), and the movements of the robot became erratic.
I unplugged everything, rechecked all my connections, everything seemed okay.

At that point I thought, I must have plugged or touched something that did that strange acting, and decided to go on.

So excited I was , it was the time to get InMoov controlled through Myrobotlab.
Here starts the initialization, and I get this same kind of strange behaviour, all servos buzzing, erratical moves.
Then all of a sudden one of the arm starts to twist way further then what it is supposed to do!!
WOW! I unplugged everything…
I ran the same test again, but this time everything went off at once, no more power. The power supply is protected against short circuit, thermal heat, and overload drawing.
I checked all the connections one by one again, nothing was wrong.
What was the problem, so I restarted with my first initial test, 1 Arduino, 1 servo, simple sketch, it was not perfect at all anymore. It was acting totally erraticaly…! 
And since then of on.
There must be something damaged in the power supply, strangely if I use it with another device, like a little DC motor, it works normal.

So, end of the story, back in search on the net. I read on this page what I hadn’t found before about switching power supplies with servos.
Now, I have ordered three batteries with a small charger. They were very cheap when I passed my order, 8 euros per battery. I think that will do for now, I also had found some Lipo batteries but they are rather expensive.
I really would rather a power supply, because I just don’t want to have doubts about the power or wait for charging time. I need a DC 6V 44Amps or more, no swithching, with a 250V input.
Would be great if someone has an idea. Any suggestion is welcomed, please post in the comments.

In the meanwhile I have been designing and printing more parts for the head. I also redesigned the top of the front torso, the other was going too high in the middle, and it bothered me because it wasn’t taking a human shape structure.
The jaw has it’s own servo motor mounted and can be actionned. I still need to test the microphones in the ear circus amplifiers, but this is pure creating guessing. I have no idea if it’s going to help InMoov to hear better the voice commands. But hey, why not try something different since I can print and design what ever I want!

3D printed robot head inmoov
Robot head sideway without ear

3D printed robotic head inmoov
InMoov has ears and jaw attached

InMoov robot new neck and yes
Changements have been done on the torso structures of InMoov

Comments 25

  1. couldn’t you take a lesson from those delightful
    MC Hammer fans ? u know, the ones who
    shake your car windows at the stop light with
    those beautiful renditions of “back that ass up”.

    their speakers draw huge loads on their bass
    feed which is why they use VERY large capacitors
    on their audio outputs bass line. this keeps the Bass
    load from totally cancelling the Non-bass line out
    from simple low-current -availability while firing
    the bass speakers.

    now their Spike loads probably last longer than
    the inductive field loads drawn by 22 servo coils
    since a giant bass speaker will load the system
    for possibly 1 – 3 seconds at a time.

    ( I also like the idea of “Staggered switching”
    to spread out the spike over a longer time frame )

    why wouldn’t such a reservoir capacitor also work
    on the intermittent high loads of a large servo bank ?

    you might have to use an adequate Diode on the
    neg lead from the PS to make sure no bounce flows
    into the PS but that might also be a reasonable
    consideration ?

    regards !!! // Tom \\ ( AKA Ceolwynn )
    Dallas Maker Space ….

  2. oops… PS: !!!!

    REMEMBER !!! Electrons flow FROM
    a neg connection of a battery or PS.

    ( Very many people think the electrons
    come out of the positive terminals )

    HOLES flow from the Positive parts
    of a battery or PS.

    The traditional symbology of current
    flow on diagrams is actually drawn
    backwards from the way electrons flow
    in a system.

    the symbology is indicating
    “holes flow” not electron flow.

    many people have that backwards as
    most don’t realize that the Flow symbols
    created by ( I heard “the military” ? )
    are based on “Holes” NOT electrons.

    Holes flow from the Positive terminals

    Electrons flow from the Negative terminals.

    that is useful info when designing
    Current flow barriers using diodes in a
    complex system.

    sometimes you will ge better results when
    placing protection diodes right at the neg
    terminal of a battery or PS when you have
    a need to prevent Electron back pressure
    on your power source.

    // Tom \\
    Dallas Maker Space
    AKA: ceolwynn

    • Hi, How did I miss all your comments! Thanks for your help your very descriptive explanations! We don’t have those big hummers here but I get the picture! I will get a Diode frome ebay, as I’m sure it will make the difference. Any suggestions where to get a 6V44A power supply?

  3. Could you modify a PC power supply to work? Figure the 3.3 and 5 volt rail each put out around 25A, so one for each segment of the body or something? Plus they’re fairly cheap compared to something that’s going to put out at 44A for the whole thing.

    • Your suggestions is a good one. When I started looking for a power supply, I had found on the net this solutions of yours and since I had already a PC power supply laying around, I tried it. I followed a tutorial on the net, for to understand what cable to choose and what cable to remove. The first test I did with one servo did just fine, but later I plugged 10 of them, and the power supply just fried. At that point, I really don’t know what went wrong, I still have another good PC power supply in the workshop but I would need some good tuto to make sure of what I do is correct.
      Another thing is the 5V fom the PC supply, I really need 6V to get the best speed and torque out of my servos.
      Any help is welcomed.

  4. Hi There Gael. We are in the process of making functional Prosthetic for people who have lost there fingers for what ever reason. be it accidents etc. I am wondering if you are keen to lend a “hand” If so can you contact me @ Thank you. Rich

  5. Hi, I if I understand you correctly, you would like to borrow a printed hand for to work on your project. The problem is that I don’t have extra printed hand. The only two I have, are mounted on my robot. But you could contact a 3D printing service and get it printed for a reasonable price I think.

    • Hi, yes I will be posting the head and neck but I’m not finished with those parts. I still want to make a eye mechanism. Rodstock is an amazing cool printer for to build InMoov!

  6. Hi just saw your project. Very impressive!
    Regarding your power supply, you should use what we -electroengineers- are calling an industrial power supply. Just look in eBay for 6V 300W to have an example.
    Another tip: never combine power supplies by connecting their grounds, very dangerous, always use galvanic separation (relays, opto couplers). One big power supply could very expensive. Try to separate modules and power them individually.
    Computer PUs are not so good as most of them cannot handle the fact that draw all the power from only one rail. Computers use all the outlets and the power drain is more balanced; your project uses only one voltage, that’s why you probably fried the unit.

  7. Hi Patrick,
    Thanks for your comment, as you maybe noticed, I have decided to go on with batteries for now, since I got really good result for a very low and reasonable price. I did fry a Computer PU and didn’t try again, what you explain must certainly be the reason.

  8. Hello Gael!
    I am writing from Estonia. We are planning to make the inmoov robot as a university project. We have divided the hands, torso and head between teams, so we could get it done faster. Unfortunately, we from the head team cannot print anything since you have not uploaded the files yet. Would it be possible for you to send me the files to print? We would need the outer shell of the head and the neck part since we are not planning to move the mouth/eyes nor do we plan to use voice commands, but we would like to move the head, also attach a small camera into the eye.

  9. Gael, where yout see the tuto of de PC power supply? I am thinking in use it like the power supplies of the servos, but I dont find any good tutorial in the net. What other way you recommend me? The three batteries of 6V-12V?

    • Going for the batteries is a very low cost solution, which will be handy if InMoov ever gets autonomous. If you are building only a arm, one battery will be largely enough.

    • I am triying to make all the robot. I think 5 batteries maybe will be enought. What features must be the batteries? (V and Ah)

    • 3 batteries will be enough, you can find the link that shows the exact same battery I bought in this post, all words in green or grey are links.
      I used 6V12AH

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