Assembly of the “Finger Starter”

Here is the list of parts and the number of prints needed for 1 Finger Starter:

  • 1x FingerIndex
  • 1x FingerTester
  • 1x RobRing
  • 1x Servo-Pulley

This is going to be interesting!!
We are going to assemble a finger to a small servo for testing it with an Arduino board. The servo I used on the pictures is a digital HK15298 but you can use also a cheap analog MG995 or even cheaper if you find and if the size specifications are the same.
The Arduino board used here is a Arduino Uno. It is best to add an external power supply because even if these servos are small they draw too much current which will or might reboot your board.
At the end of this tuto, there is also a picture that illustrate how to simply connect your servo to the board.
REMEMBER: this connection set up can only power a single servo with low Amps drawing, if your board resets itself, or if the servo jitters, it means your servo is to high power consumption for the power pin. You will need an external power supply.

For connections and power supply you can see HERE. These connections drawing are mainly for the whole hand, but it is the same for one servo/finger or for five.

The pulling rods I use on this tuto is a fishing nylon, but it is not what works the best because it tends to stretch overtime. I recommand for InMoov, fishing braid 200LB. But for this test you can use anything you have at hand as long as it can pull and is thin enough to let the finger curl.

Now let see what we have printed and how we are going to do that.

Redrill the sides hinges holes with a 3mm drill.
The inside hinges holes should be redrilled with a 3.5mm drill.
So the inside hinges of the finger should also be done with a 3.5mm drill.
Note the finger parts have numbers printed for a easier assembly.
Depending on the material you have used to print there is different ways to glue the parts together.
If you have PLA prints, a two components epoxy glue is really good but you can also use Zap-A-Gap glue.
If you have printed in ABS, what works best, is Acetone but you can use epoxy, Zap-A-Gap glue.

Applying few drops of acetone will link disolve the parts together like it was printed in one piece. So take part 1 and part 2 and glue them together.

Glue together part 3 and 4.

Don’t glue yet parts 5 and 6

Take a piece of your 3mm filament, if you don’t have that you will need to get some screws of 3mm at your hardware shop.

Get it trimmed with a cutter knife.

Push it in the hole, assembling part 1/2 to 3/4 together.

Once it reaches the other side,

cut the filament with pliers.

Do the same trick with parts 3/4 to 5

Now we have a finger that should move freely.

Assemble the finger to the main part with the same technique.

You should have something like this. It should be able to freely fold to this angle.

Now lets see the servo. We are going to find an arbitrary zero point on the servo. Turn by hand the actuator to the maximum left, note until where it goes. Do the same to the left and note until where it went. These two points are the extremes positions of your servo, in the middle of these two points decide where is the arbitrary zero point. You can find that with your arduino board if you know how to do it, but this is a simple solution for now even though it isn’t precise.

Mount, Screw the “RobRing” on your servo, the two little holes should be on your extreme points.

Take a piece of rod of about 50cm long. Run your rod through one hole.

Make two knots at approximatly 25cm of your rod, like this. make them well tight.

Add another set of knots about a 1cm away from the first set.
On my picture I did only two knots like this, but they might run through the hole of “RobRing” and that shouldn’t happen. Adding a bunch of knots will help to avoid that.

Now run the other end of the rod through the second hole.

You should have something like this, with even more knots than me.

Time to fix the servo to the base.

Run the bottom rod through the parts like on the following pictures.

Just make sure not to invert your rod, it should always on the back of the finger.

Now run the second rod on the inside of the finger.

You should end up like this.

Check your servo is at his zero arbitrary point.

Curl a little bit the finger and make a few knots between the two wires.

When turning “RobRing” by hand you should be able to get the finger in this position. Finger totally stretched.

Now cut the rods.

Glue part 6 to 5. If you look close at part 6, there is a nail side, and I haven’t put the number on the nail for aesthetic reasons.

Try to move the finger by rotating “RobRing”, it should move freely without locking.

Insert the Arduino board and make a wire connection like this. Orange or yellow to pin3 on PWM. Red on +5V. Black or brown on Gnd (ground).

REMEMBER: this connection set up can only power a single servo with low Amps drawing, if your board resets itself, or if the servo jitters, it means your servo is to high power consumption for the power pin. You will need an external power supply. (see at the beginning of this tuto)

You can now upload this FingerStarter sketch to your Arduino to see it move. If you have never used Arduino before. Follow this link or use this introduction pdf.

You also can get to MyRobotLab and start learning about how to actuate the finger with a slider. Follow this tutorial to get started with Myrobotlab. Things have changed a bit since I wrote it but it helps to understand the basics.
Here is a script to voice control the FingerStarter with MyRobotLab:
If you have some muscle sensors or some ultra sound sensors you can try controlling the Finger Starter with them.

Comments 61

  1. Profile photo of Andy_Jun_Corea

    Hi, I’m trying to make starter kit. But “RobRing” is trouble.
    I can’t mount RobRing on my servo. Hole size is not match with servo gear.
    My servo is HK15298.
    I’ll try modify “RobRing”.

    Anyway your project is very interesting to me.
    I’ll make InMoov by myself.
    Thank you.

  2. Profile photo of Bill Langlais

    Hi, Thanks for the amazing work you have done! I have two Makerbot printers a replicator 2 and a Makerbot Replicator Gen 5. I have been very interested in Robotics and have purchased a bunch of Arduino stuff from Banggood and I bought my servos from Hobby King HK15298B.

    I have built the Finger starter kit and I am trying to hook it up with a Adruino Uno. First I tried your starter sketch with the latest Arduino. It compiles and I can upload it successfully but it does not execute. I then tried your My Robot Lab (using the latest version) and everything seems to go according to plan but the Arduino does not respond although I can see the voice commands are executing.

    I am new to Adruino and I am lost on what to do next. Any recommendations will be greatly apreciated

  3. Profile photo of Sam Clare

    I am planing on building an Inmoov starting with the finger to test but am having trouble printing the set of 6. Would it be possible for someone to split the file into six parts and upload a folder to thingiverse with each piece as its own STL file?

  4. Profile photo of quoc

    I have tried controlling my finger- starter by voice. I could make it opened or closed but i couldn’t hear any sounds from my computer like this ” did you said …” . I use MRL 1.0.119 , Chrome is my default browser . Can you help me please !!

  5. Profile photo of J Matthews

    Hello i am excited to join this fantastic project…i have one small contribution…when joining the finger joints I just used a piece of PLA (size doesn’t matter…so she said) and pushed it through about one quarter inch and used a soldering iron to melt the end resulted in kind of a rivet…then clipped the other end about one quarter inch and did the same…seems like a nice working finger

  6. Profile photo of Meow

    Hi, I’m currently trying to build this robot hand. But I actually started off with the finger starter kit first. I lost the file for RobRingV1, as I’m using generic servos and it woudn’t fit with the updated RobRingV2. Hence, was wondering if you still have the STL file for RobRingV1? :) Thanks so much! Please update me ASAP. It’s for one my projects.

      • Profile photo of Peter

        Hi Gael
        Thanks for your reply,
        I am installing it on an uno.
        I have followed the instructions. It uploads ok no errors but doesn’t run, I have also tried the voice control one as well, that tells me open hand but the servo doesn’t move, I sure I am doing something wrong but know what!!!

  7. Profile photo of Iain McCluskey

    Hi, this is an amazing project Gael.

    Id like to build my own InMoov, it seems an excellent base for learning more about robotics. With it being open source, am I able to adapt the files to develop my own look to it without copying it exactly, a female looking InMoov for example?.



  8. Profile photo of PIFOUINMOVE

    Hello Gaël,

    I’m very exited to start this project too, I downloaded yesterday all the stl of your website to be able to build my own Inmoov Robot. There is lots of technical interest, first is using my 3D Printer Solidoodle 3, second is using arduino, I bought a starter kit few month ago with lots of items , sensor, keyboard, screen but I never used it, this project has a very good documentation and it is a pleasure to learn it, third is to build a robot who looks like a human body, to many robots look like toys :-/ I think that this story will be fun ! :-)

    Congratulations for all the work you have done and for the work which is coming !

    PS : It’s cool that it was un français qui ai lance ce projet (je suis français aussi du 91 ^^)

      • Profile photo of Bernhard M

        Thanks – Gael

        I am unable to find 180 degree rotational servo supplied by HobbyKing HK15298 or HK15298B

        But I was able to find this. Will these specs work for the 180 degree rotational servo?

        Operating voltage range: 4.5v~6v
        Operating temperature range: -20°~60°
        Operating speed: 0.11sec/60° 4.8v – 0.10sec/60° 6v
        Torque: 4.8v – 6v
        Arm travel range: 180° ( 90°/one side pulse traveling 600usec)
        Idle current: 5mA at stopped
        Running current range: 50~150mA
        Locked rotor range: 600 mA
        Dead band width: ≤4usec
        Angle deviation center: <0.5°
        Size: 22.7×12×26.4mm
        Weight: 12.5g
        Bearing material: metal
        Gear material: metal
        Connector wire length: 21cm

        • Profile photo of Gael Langevin

          The servo you have selected have a very low torque power, only 2,2kg when the hk15298B does 21kg.
          I would recommend something stronger.
          Have a look in the Hardware and BOM list to see other possible servos:

          TGY-5521MDHV (24kg torque, should fit)
          JX PDI-6221MG(20-36kg torque, should fit)
          RS-550MGC-HV (11.2kg torque, should fit)
          HS-311 (3.5kg torque, should fit)
          XQ-S4020D (21.5kg torque, should fit)

          • Profile photo of Bernhard M

            Thanks – Gael

            I have begun printing the parts for the Inmoov robot. I am very excited to do this project. I don’t have much electrical experience, so this area is new to me.
            I started printing the parts starting from the head working my way downwards. Is this a good approach? I would then tackle the electronics. Perhaps you may have suggestions?
            Thanks Gael for all your help! This is an awesome project, I hope I am successful at completing the mission. I may overwhelm you with all my electrical questions, however I will make my part purchases thru the website to help support the mission. I’ve already helped with the purchase of a Inmoov t-shirt :) Will this project be easy for a non electrical person?

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