*Visit http://inmoov.fr/hand-and-forarm/ for the full official tutorial*
InMoov is a DIY mostly 3D printable humanoid robot controlled by Arduino microcontrollers that was originally designed as a prosthetic arm by French designer Gael Langevin in 2012. Since then it has turned into a personal project for Gael with him posting new improved pieces every couple of months with plans to add functional legs as it is currently being rolled around on wheels due to the major difficulties of making functional legs that can carry the weight of the all of the hardware in the rest of the body.
This will only be a simple guide on the processes when building an InMoov robotic hand which will include the total cost, the struggles throughout the project and how they were solved as well as some of the basic difficulties that other people have had with the project.
The process will be explained in 5 main sections including:
- 3D Printing the parts
- Assembling the parts
- Tensioning the fishing lines and final assembly
- Final Notes
Step 1: 3D Printing the Parts
All of the parts were printed at the ASMS Ideation Studio with Tiertime UP Printers using ABS but some parts were done on a more budget Wanhao i3 Plus.
Both of the printers used the same basic settings:
- 0.2mm layer height
- 30% infill
- Rafts (Not required for most printers)
- No supports
- Make sure to have all of the other settings put to those that have had the most success
Once each part is printed, it will have to be tidied up to ensure that all moving parts are not too rough and rub against each other. I would personally recommend printing the parts in order from top to bottom or bottom to top as this will allow for parts to be assembled while some are still printing. Another note would be to make sure to reprint some of the pieces if you can see immediate problems so that you don’t have to disassemble parts to replace the piece at a later date.
*Tips and tricks*
- Make sure to move the printed files into a labelled folder to make sure that pieces are not printed more than once
- Only some parts are shown in the images but use the checklist on inmoov.fr to make sure that you have them all printed (You won’t have to worry about quantities as the files are already correctly configured)
- Put the fingers in labelled plastic bags so they don’t get mixed up
Step 2: Assembling the Parts
Now that all of the parts are printed, you can now start assembling all of the pieces by brushing on Acetone for ABS or ZapAGap for PLA. Make sure to read the official tutorial for a detailed guide on which parts get glued together but most of them are pretty obvious and contain registration marks so that they can’t be assembled around the wrong way or in the wrong place. Once all of the parts of the forearm have been glued together or mounted according to the guide, the hand can start to be assembled using pegs and the fishing line can be run through the individual fingers.
Start off by removing only one finger from its bag so that it can’t be mixed with the others (Leave the fingertips in their bags as they will be glued on later). There are some small marks on two of the pieces which indicate what pieces go together and their correct orientation while the other pieces are simply glued together making sure that the straight edge is aligned on the same side. After this there should be only two pieces instead of the four that there were before and they can be put back in there bags and repeated for the remaining 3 fingers as the thumb is slightly different but has the same basic principle as the rest (Make sure to check with the official tutorial before gluing the pieces together permanently).
Once all of the fingers have been glued together the joints can start to be assembled using 3mm bolts or filament (Filament is recommended as it’s easier to work with). The inner joints must first be drilled out with a 3.2mm or 3.5mm drill bit as well as the outer joints with a 3mm drill bit. Cut off a small amount of filament and create a taper on the end to make it easier to insert into the joint. Once this is completed, insert the filament or bolt into the joint using pliers to help you and trim the excess off once it has been pushed all the way through. Repeat these steps for the remaining joints as well as for connecting the fingers to the palm.
Feeding the fishing line through the fingers is very easy as all that is required is to cut 10 lengths of braided fishing line and feed them through the top and bottom holes in the palm and all the way down the fingers where it is then tied off in a large knot to prevent it from going down the finger. During this step, the bolts can be pushed into the palm to allow the thumb, pinky and ring fingers to move inwards towards the palm. At this stage, you will also need to read this: http://inmoov.fr/dilemna-with-wristsmallv3-part/
*Tips and tricks*
- Use clamps when needed to make sure that the melted plastic solidifies in the right location
- Make sure to not put too much pressure on the fingers when drilling or inserting pins so that they don’t break
- Use filament from the larger side of the roll to make sure that it is as straight as possible
- Use gravity to help you when feeding the fishing line through the fingers
Step 3: Electronics
The whole of InMoov is controlled using an Arduino and M946R servo motors. The hand requires one motor for the wrist as well as one for each finger to pull on the fishing line. InMoov requires Gael’s own program called MyRobotLab which I couldn’t get working in the time limit that I had as it is meant to be easier to use than the official Arduino but requires more fiddling around to get installed and functioning. I have not heard many people say that they have not had very much success with using the program so it might have just been my experience or that the instructions just aren’t very clear.
The guide for using MyRobotLab can be found here: http://inmoov.fr/how-to-start-myrobotlab/
One of the images shows the servos attached to the bed out of the arm but it should be mounted into the arm first as the servos cover the two mounting holes.
Step 4: Tensioning the Fishing Lines and Final Assembly
I could not complete this step as I had didn’t manage to print all of the wrist pieces in time that would allow me to be able to pull the fishing lines through the arm to the servos. Once all of the pieces have been printed and assembled the guide linked below can be used to correctly tension the lines and the fingertips can be glued as well as screwing on the arm covers that hide the internal electronics.
Follow this guide for tensioning the lines: http://inmoov.fr/lining-and-tighting-the-tendons/
*Image from InMoov site*
Step 5: Final Notes
One element that I would also like to cover is the total price of all the electronics and the plastic required. Here are the amounts that I paid:
Arduino Mega: $44.95
6x MG946R servo motors: ~$45 (~7.90 each)
100m of 100lb braided fishing line: $3.89
800g Zortrax Z-ABS Filament: $40
Total price: ~133.84
- All prices are in AUD
- This doesn’t include the cost of a 3D printer if you don’t have one yet
- Prices will change depending on filament cost and amount of waste (Failed prints, rafts and supports when needed)
- Only about 250g of filament was used for the parts that I printed so you may need more depending on the amount of waste
- All prices will vary depending on country and current sales