11/12/2025 - Researched Current Robot Hand Designs

I looked into current designs that people have made. They all basically stem from a similar concept. The fingers have some sort of elastic string keeping them up, and then a servo connected to a tiny string pulls the finger down. Then, when the Servo stops turning, the fingers go back up. Most of the designs that I saw used the tiny blue micro servos; however, this probably won't provide much torque for the fingers. I am planning on using MG996R servos. The downside with this is that it's heavier, so the Robot Arm that it connects to needs to be able to support its weight. It will also need a bigger forearm to hide all the servos in. The main things to focus on that I saw are the joints between the parts of the finger. It needs to be smooth and have the least amount of friction possible.

These were some of the videos I watched to get an idea of current designs:
https://www.youtube.com/watch?v=sI3LLa0uKlI
This one actually uses smaller servos, and it seems like it has a decent amount of torque. The fingers also go all the way down to the palm, giving it a full range of motion. The motors are mounted right behind the fingers, and the electronics are hidden in the forearm.

https://www.youtube.com/watch?v=Fvg-v8FPcjg&t=663s

This is another design that I liked. He used a glove with flex sensors on it to control the hand. This is what I am planning on doing as well. The web UI that I make for the robot arm should also be able to control the hand, but using this glove, you can program certain repetitive functions since the servos have encoders built in. He also used the smaller servos. After looking at multiple designs, I decided these are the parts I will use and prioritize.

• Mini Servos to reduce weight
• A custom PCB that takes power from the 24V line on the PCB for the Robot Arm I am building. This way I don't need two power supplies. The bench power supply can supply both.
• The data lines from this PCB can connect to the PCB for the Robot Arm, or I can add an ESP to this hand as well.
• The elastic should be strong enough to pull the fingers all the way down so they touch the palm

Parts Brainstorming:

• PCB
• ESP32?
• 5 Servos
• Fishing Line
• Elastic Band
• 3D Printed Parts
• Some sort of touch sensors for the fingertips?
• Glove and Flex Sensors for motion programming and controlling the hand
• Total cost will probably be ~$50

11/17/2025 - Started CAD

Today I spent some time on the CAD of the hand. I made basic dimensions for now, and then I'll edit them later to be more accurate. I also changed my mind and am going to use MG996R servo motors instead after looking at some more designs. They have way more torque and will be able to pick up items. It will be heavier, and the motors will have to go into a longer forearm, but at least the hand will have enough torque to be useful.

This is the CAD so far:

I also started thinking about the PCB design. It will be powered by an ESP32 so that I can use ESP-NOW wireless communication between this robot hand, the robot arm I am building, and its controller. Using the same microcontroller makes it easy to connect all of them together wirelessly. My end goal is to make a UI that controls the arm and end effector together.

FYI: Made this journal over three days

11/19/2025 - Worked on CAD

I continued working on the CAD and finished the index finger. I'm still having issues where it's not able to bend all the way its supposed to. The tip of the finger should tough the palm but it's not so I need to work on that. Once I have the correct dimensions, I'll just copy it to the rest of the fingers so that shouldn't be that hard.

Future Steps:

My next steps are to do all the holes for the fishing line to go through to the tips of the fingers. I also need to make holes for the elastic in each finger which will probably be pretty complicated. After that, I'll make the PCB.

This is the current CAD:

11/20/2025 12 AM - Continued CAD

Today I worked on the CAD for the hand. I finished the second finger and started on the third finger on the left side. I also figured out and started the tunnels in the palm and fingers for the elastic and fishing line. I finished this for the index and middle finger. I also started the BOM.

This is the current CAD:

11/20/2025 10 PM - Finished first part of the CAD

Today I kept working on the CAD. I finished all the fingers and the proportions for them. They all seem to work well. Now I need to finish the tendon tunnels through the fingers and the palm for the fishing like and then I need to make the forearm. My plan for the forearm is a motor mount that all the motors mount to, and then that motor mount mounts into the forearm. The top half of the forearm will open up to be able to insert the motors inside, and then it will close using embedded magnets. I will also need some holes inside the forearm to tension the fishing line to keep it tight so that the motors have to rotate less to move the fingers.

This is how the current CAD looks:

After the CAD is done, I will start the PCB.

11/22/2025 1 AM - Continued CAD

I continued working on the CAD today. I finished all the tunnels in the wrist for the elastic and the fishing line that pulls the fingers. I also started working on the wrist. Here's how the current CAD looks. The plan for the wrist is to have the motors mount inside and then the top attaches on and closes the wrist using magnets since that's pretty simple to integrate.

11/22/2025 3 AM - Continued CAD

I refined the shape of the forearm to make it more of an oval shape and I also started adding the servo mounts inside it. I decided to just make the servo mounts attatched to the forearm to make it easier to assemble. I also decided to use heated inserts that I will put into the palm to add the forearm to the palm.

11/23/2025 - Finished CAD, Started PCB

I finished the CAD by adding the servo mounts and holes to tension the fishing line and keep it straight. I also added holes for the magnets so that the top of the forearm can magnet ontop after the project is completed to hide all the motors and electronics. I also started the PCB.

This is the current PCB:

This is the current CAD:

11/26/2025 - Finished PCB, BOM, Submitted Project

I finished the PCB and schematics. I added connectors for all the servos and the flex sensors. I also had to add resistors for each flex sensor since they need one to work. This is the finished PCB Schematic.

This is the finished PCB 3D view.

I added force sensors that will go on each of the finger tips so that I can tell the fingers when to stop, when enough force is on the object it's picking up. I added JST-XH connectors on the PCB for the force sensors as well as the flex sensors. The servos connect using 3-pin headers.

I also finished the GitHub and made a readme and firmware, and I finished the BOM and uploaded that as well. I sourced all the components from mainly Aliexpress and the flex sensors from Adafruit, since I couldn't really find good ones anywhere else. I also wrote a basic firmware and uploaded it to GitHub.

This is the GitHub:
https://github.com/parthdhingra27-maker/RobotHand

This is the finished BOM:
https://docs.google.com/spreadsheets/d/12Ga3T-jOdBLo3tYdAEF2mIIFh46kIetYSn9vqBXSKeI/edit?usp=sharing