Dontrell-SSFP

Dontrell Stephens Summer 2025

This week I:

This is a sample two-fingered tendon based system. I used it to model the fingers that I had created to see how their overall dimensions looked, weight, size, fragility, and grip strength. I found that the finger overall worked well with a few design improvements:
- 1. Instead of having two tiptoes going throughout the fingers as in gripper with black parts, I opted for a single zip tie to be routed from the base to halfway in the middle phalanges. and then the middle phlange has a one-to-two zip tie converter.
- 2. I increased the distance of the joint between the base and proximal phalange.
- 3. I slightly modified the dimensions of the gripper with white parts. The changes included changing the shell distance slightly, and size of extruded holes.
Currently, next steps involve adding a high friction material to the fingers and modeling the base of the fingers in Onshape.

This is what I currently have as base designs.

This week I:

I started CADing out the sketches that I drew.
- However, I was struggling a lot in the process, so I asked Stanley to help me out a little bit in the process.
  - I learned that with CADING, you should not just hop in without a solid idea of what your design should be. If you do just jump in, you will spend countless hours just struggling with no real progress being made.
Investigated ways to make the fingers as light weight as possible, currently the design is to have a shelled figure, and to include zipties inside of the figure instead of a silicone casting for hinges/joints

looked into FinRay designs.
- I was exploring gin different design choices (ex angled beams, less beams, more beams), can affect teh amount of grip and compliance you have you the FinRay.

This week I:

Brainstormed ideas with Stanley and Venny for research projects, and potential designs.
Finalized my research project:
- I decided to purse robotics in the agricultural field by designing an end effector to harvest avocados ( Avocado trees are normally 20 - ft tall)
Reviewed Literature on soft robotics grippers specifically tendon based grippers.
- This is the finger design I chose for the avocado gripper. I selected it because of its ability to conform to the shape of the avocado, allowing it to grasp the fruit securely without causing bruising
- Literature reviewed:
Made preliminary sketches for the avocado end effector:
- I opted for a two-finger, tendon-based design (both fingers will be controlled by the same tendon), with a camera positioned above them and a pair of scissors mounted on top. The concept is that when an avocado is identified, the system approaches it from one of the sides. The fingers—made of silicone rubber for both grip and conformity—then grasp the avocado. Inside the fingers, pressure plates will detect contact; once activated, they will trigger the scissors to move forward slightly and snip the stem of the avocado.

Attended the second Arduino workshop hosted by Mark.
- I learned how to recursively update the mean in code, and also assembled a pressured sensor- based circuit.
Reached out to farmers in California:
- I reached out to farmers in California by email and phone, asking about the methods they currently use and the challenges they face in harvesting avocados. I only received a response from one farmer, but I learned that it’s important to keep the stem attached to the avocado; otherwise, it will begin to rot more quickly.

Made preliminary cad designs for the avocado gripper
- Currently, I am designing the CAD model for the finger and the base/palm of the gripper. I initially struggled with implementing the finger, but I now have a working design. I will continue to improve it and complete the CAD for the rest of the end effector.
Assisted in lab cleanup

This week I:

Attended an Arudino workshop hosted by Mark, and learned how to create non-blocking code
Aided in data collection for ReachBot, collecting information about the correlation between measured length and the Encoder Wheel ticks
Worked in a group to code a ReachBot End effector to pick up a bottle, and move it to a different position
- We performed this task by having each of the effectors joints set to its center position, and then we inputted different values until we were able to reach specific milestones
Narrowed down potential research topics to Argicultural end effectors and braced Manipulation
Aided in data collection for the tree perching drone by taking pictures of various trees around campus
Learned about forward kinematics, inverse kinematics, and the Jacobian Matrix
Learned how to program Dynamixel Actuators, and create linear regression lines in python
Reviewed Literature and discussed how worked:
- I chose the Ocean One hand, and have linked a google doc with my summary below: https://docs.google.com/document/d/1TFQxP45_0eFDv-VxbaoTBhKyqKH0Gy6tWAAk6Z1p270/edit?usp=sharing

This week I:

designed tetrahelix in OnShape, however I went through the wrong process of deleting the frame so, I could not use fasteners to connect each individual triangle and instead used rotations
Learned about Dynamixel XL430-W250-T Actuators and how to control them using DYNMIXEL WIZARD

Assembled a ReachBot end effector
- In the process, I learned the importance of making sure designs have easy accessibility when it comes inserting fasteners
Reviewed Literature and discussed on various end effectors for harvesting Fruits, specifically for the Kiwi fruit: https://www.sciencedirect.com/science/article/pii/S153751101830638X
Attended the 2025 BDML Summer Kickoff! I had a great time meeting people in the lab, going hiking for the first time, and grilling!
Completed online and BDML lab specific safety trainings
Attained access to PRL
Learned about various projects at BDML, and discussed potential research directions

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Page last modified on July 25, 2025, at 11:25 am