Introduction: 3D Printed Table Tennis Robot
Hello! My name is Andrew and I attend Jefferson Forest High School in Virginia. I have always wanted to use more complex electronics so this is my first try with that. This is a 3D printed portable table tennis training robot with adjustable top-spin, backspin, and feed rate, all built for under $65. I love table tennis, also known as ping-pong and have always enjoyed playing with my siblings and recently, the rivalry has become quite intense. I built this to really up my game and be the most dominant player in the household. I used Autodesk Fusion 360 heavily in this project and enjoyed working on that program. Please note: The prototype pictured featured several issues that were fixed by removing material. All files and instructions for this Instructable are accurate to my knowledge and have been adjusted accordingly.
Picture generated with ChatGPT
Supplies
This build was made for under $65 at the time of writing. The supplies are as follows:
- 12V 30RPM Hobby Motor (I purchased 2 so I can add on to this later)
- 3 PWMs (Pulse Width Modulator - for controlling the speed of the motors)
- 2 12V 6000 RPM Motors
- 12V Rechargeable lithium ion Battery Pack
- Solid Hobby Wires (I didn't actually buy these, I just used some of my own. Any wires should work, I just find the solid wires easier to work with)
- 3D printer with large build plate (This was printed on my Flashforge Adventurer 5M)
- About 1 Kg of Filament
- 2 Rubber Bands
- Soldering iron (optional)
Step 1: Idea
I have recently enjoyed playing tennis and have a tennis ball launch machine. I have patterned this design around that setup. Most table tennis ball machines are very expensive, from what I saw, over $100 for one that has spin capabilities. I wanted to create the same idea but for much cheaper.
Picture courtesy of Spinshot Sports US
Step 2: Sketches
Before designing, it is important to get an idea of what you are going to design with appropriate dimensions. My design changed a lot over the course of the few months I have designed this so I have a lot of sketches.
Step 3: Design Motor Casing
The first step is to design the casing for the two 12V 6000 RPM motors so you are able to test their launch angle, power, and spin without specific motor control before fully assembling the machine.
Attachments
Step 4: Design the Flywheels
Before testing the motor set up, you also need to design the flywheels. These will provide enough torque to launch the ball at high speeds. Be sure to account for a rubber band that will sit on them to grip the ball.
Step 5: Motor Casing Tolerance Calibration
Before printing the whole motor casing, be sure to check the calibration of your printer to see if the flywheel shaft opening and the motor holders are a snug fit. This can be done by slicing the models and cutting them to the desired shape.
Step 6: Test the Launching System
Once all parts are printed, place the motor shaft in the flywheel and the motors in the openings on the motor holder. Using the battery and a few wires, connect the circuit to where the wheels are spinning opposite directions.
Step 7: Design the Bottom of the Case
After testing of the launching system is done, you can start working on designing the case that will hold the launch system in place. The battery will sit in the very back of the bottom of the case and the PWMs will sit in vertically in a row next to the battery as pictured.
Step 8: Design the Middle of the Case
The middle of the case will allow for the large motor holder to pivot and allow for different launch angles. The majority of the space will be used for that. There is also a PWM holder on the bottom of the middle of the case above the ones on the bottom of the case.
Step 9: Design the Motor Pivot and Pegs
The motor pivot and pegs are what will hold the motor holder in place and allow it to pivot. The bottom peg will go in a hole on the bottom of the bottom case, the top peg will go in its choice of a hole in the circular pattern on the side of the middle case.
Step 10: Design the Motor Holder and Ball Chute
The ball chute uses the path of the top flywheel to help propel it along. It will bring the ball from the ball feeder to the flywheels. The top and bottom of the motor holder will have holes for the pegs to sit in ensuring it is secure.
Step 11: Design the Top of the Case
The top of the case is responsible for holding the two gears that will allow for the ball feed mechanism to work. It also has an opening in the bottom for the balls to fall through and enter the chute.
Step 12: Design the Gears and Small Motor Holder
These gears work together to carry the ball from the ball holder to the chute. There is a motor situated under the white smaller gear that will be explained later.
Step 13: Design the Ball Holder
The ball holder sits on top of the completed case and slopes in slightly towards the opening so the balls can fall on their own into the larger gear.
Step 14: 3D Print the Casing
The casing consists of four parts- the Ball Holder, the Top, Middle, and and Bottom case. I had a lot of issues with warping while trying to print my case. Just make sure to check your printer often and address any issues that arise. The case bottom should be printed as is oriented with the bottom facing down. No supports should be needed. The case middle will need supports and should also be printed in the same orientation. The case top should be printed upside down so the gears rotate smoothly. You will probably need to use supports generously with this. The ball holder should be printed in the same orientation as the others.
Step 15: 3D Print the Gears
My original model had the gear holes too small, so I had to do a little work on the larger gear. This STL file has been adjusted to fix that problem. Make sure to print these gears with as little infill as you can so the motor isn't doing excess work to spin them.
Step 16: 3D Print the Pegs and Small Motor Holder
The pegs should be printed at a high infill so they are strong and the small motor holder should be printed in the orientation as pictured so the motor fits properly.
Step 17: 3D Print the Large Motor Holder and Chute
The large motor holder and chute should be printed in the orientation as pictured as well so the ball flows smoothly down the chute and the motor holder is strong. This can be printed with a high infill so the launcher is more stable.
Step 18: 3D Print the Flywheels
The flywheels should be printed at a low infill and should be as light as possible so they have more speed and torque. Add rubber bands around each one for grip.
Attachments
Step 19: Post Processing
As stated earlier, some of my models required a lot of material removal and therefore, I spent a lot of time post processing. The models have been updated so your post processing shouldn't be as long.
Step 20: Secure the Battery
Steps 20-25 show the correct assembly without electronics for the 3D printed table tennis robot. I have attached a video showing these steps in more detail. It is important to assemble this before using electronics to make sure everything fits properly and runs smoothly.
Step 21: Assemble the Large Motor Holder and Chute
As completed earlier, the motors go in the two large holes of the motor holder. This may require a little patience because the chute will be in the way so the motors will have to be placed carefully.
Step 22: Secure the PWMs
Two PWM's fit into the bottom of the case and one fits into the middle of the case. They should fit without any issues. The adjustable knobs fit through the holes in the case to be accessible from the outside.
Step 23: Secure the Large Motor Holder to the Case
Using the pegs, place the motor holder and chute into the lower case and secure it with a peg. Then place the middle case over the top of the motor holder and secure it with another peg.
Step 24: Assemble the Small Motor Holder
The small motor should fit into its case with the shaft facing up. If it is struggling to fit, take a blade and cut the opening out slightly. The gear should fit in the shaft of the motor.
Step 25: Assemble the Ball Feeder
Place the small motor holder in the hole in the corner of the top case, and place the large gear in the circle. This may be an appropriate time to test the ball feeder by wiring up the gear and seeing if the mechanism works correctly.
Step 26: Electronic Assembly 1
Steps 26-33 are for the electronic assembly. I created visual diagrams to help. This will require that the previous assembled robot is taken apart. Using the wires, place two 5" wires in the motor positive and negative of the bottom PWM by unscrewing the PWM, placing the wire in, and reassembling. This will be used to power the bottom flywheel.
Step 27: Electronic Assembly 2
Twist two 3" wires together with the positive and negative battery wires separately.
Step 28: Electronic Assembly 3
Attach the twisted positive wire to the positive power insert on the PWM and likewise for the negative wire.
Step 29: Electronic Assembly 4
Twist two more 3" wires to the negative and positive wires coming from the negative and positive power side of the first PWM.
Step 30: Electronic Assembly 5
Attach these newly twisted wires to the positive and negative power inserts on the middle PWM.
Step 31: Electronic Assembly 6
Attach two 8" wires to the positive and negative motor side of the second PWM. This will be used to power the top flywheel.
Step 32: Electronic Assembly 7
Attach the wires coming from the second PWM's power side to the positive and negative of the top PWM completing the power side of the circuit.
Step 33: Motor Attachment
Lastly, connect the remaining wires with the three motors. The bottom PWM should hook up to the bottom flywheel motor, the middle PWM should hook up to the top flywheel motor, and the top PWM should hood up to the small motor attached to the gear. If you are using non-solid wire, it may need to be soldered here. With solid wire, I was able to use plyers to clamp the wires in place.
Step 34: Test the Electronics
After reassembling the robot, it should be ready to go! There will likely be a few kinks so be prepared to work them out. I had a lot of trial and error and solved a lot of them at this step. I attached a video of a few of my tests.
Step 35: Play Testing
This is one of the videos of play testing that I have. Due to the warping, I had to adjust the case spacing for the flywheel to spin freely. That won't be a problem if the print doesn't warp. One of the issues was the opening on the case was too small, so I made a rugged cut to improve it. This has been smoothed out in the design.
Step 36: Conclusion
This was a great project! I enjoyed using Fusion 360 at a new complexity level for this design and enjoyed my first electronics project. I am no longer worried about table tennis matches with my brothers. When my brothers tried this robot, they were only able to return 1 of the 10 shots and they were amazed at the amount of speed and spin that it produced. I purchased an extra 30 RMP motor and have plans to either add oscillation or a mechanism to collect the balls after they are hit. I think we will have a lot of fun with this in the future!
Picture generated with ChatGPT :)
