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Homemade Table Tennis Robot - remix

by bbogdanmircea Dec 16, 2017
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Hello Bogdan,
Is this project still work in progress. Do you still have issues with the robot or is it running ok. I am thinking about building one myself. Any help would be great.

This is still a work in progress.
But most of the issues are fine tuning issues.
For a ready to go project, you can check the original project from instructables.
Most of the files are from that project, I just replaced the motors with cheaper ones, and the feeding mechanism with a stepper and a spiral.
So if you want to build mine, you will need to tinker with it.

Thanks for your fast reply.I am aware of the original project, but I don't like the costs. I also think the pistol mecaheninsm is to slow to be realy fun.
If a really wan't a complete robot I can better save the money and bying something on ebay or aliexpress for $400 (https://www.ebay.com/itm/Table-Tennis-Robot-Automatic-Ping-pong-Ball-Machine-Practice-Recycle-w-100-ball/401550860915?hash=item5d7e4be273:g:vyUAAOSwURlbHlZx)
So I am going to simplify this project to begin with and make it as cheap as possible. I will build one with a top feeder with a bucket, gravity wiil do its work. For now, I don't need horizontal, vertical and rotation movement. Oke this is a lot less functionality, but don't have to buy all the motors. For now I just want to train my backhand, because going fromp pips-out to pisp-in rubber. I already have a 3d printer, enough fillament, an arduino, psu, wiring, wood. So the investment I have to make is verry low, only a bit of time. If that is finished I would look at the feeding mechanism. I don't like to fill the bucket all the time, but I would like to work it without issues. I am not good in 3d moddeling, so I can't help you with that. But I will try, I only need some printed parts from you and a stepper motor as far as I understand.

I added one additional part for the side support of the stepper, the original part is too long, so the stepper is hanging ... with this additional parts it should be fixed and not cause again any wobble of the spiral .
This is still not a perfect solution, but it works for the moment .
Best solution would be to use a 8 mm threaded rod, a 608 bearing and make some printed parts so that the spiral is connected to the rod, rod is rotating inside the bearing and connected solidly to the motor shaft with a flex coupling maybe like for 3d printers .
Unfortunately no time to do this at this moment .

As I couldn't obtain nice results with the wheels that I bought from hobbyking, I decided to bite the bullet and get the same BaneBot wheels as the original projects .
They are definitely softer ! Repeatability is better but still I am not happy :(
In the last month I didn't do anything more, as I am a little dissapointed .
I will upload anyway the parts needed for the Banebot wheels and the Mabuchi motors .

After reassembling the head to the "body" I find some repeatability is lost, I think the cause is that I changed the distance between the wheels and the balls are not tight enough when making contact to the wheels, so many hits are very weak and going directly to the net .
Would be nice to find some nice solution to this, I don't know if the problem is that the screw holding the motors are too weak or if I need to make some king of fine adjustment for one motor support, maybe with some screw or something similar .
I will move the bottom wheel a little closer to see if this dissappears .
Due to the head being so heavy I didn't connect the vertical servo, so the vertical position of the head is fixed, I need to find some way to make a very strong connection between the vertical servo and the head, and also some kind of fail safe mechanism, because if the connection of the vertical servo breaks, then the whole head assembly will be destroyed .
Happened to me once, I was using a printed part to connect the vertical servo to the head, this part broke and the whole robot dropped, luckily nothing broke .

Hello, dc motors are still alive ? How does everything work after some workouts ?

DC motors are running only at maybe 50% of their max speed as I am currently feeding them with 8 V only and limiting also the PWM that I send to the ESCs ... these motors are monsters for these purpose I think .
I saw some decrease in repeatability after around 1 hour of testing, I think some screws are not tightened enough and there is some play in the bottom wheel which is deflecting when the ball is fed .
I took the throwing head out and will recheck all the screws .
Also need to find some combination of Top and Bottom speeds that are nice for training and save those as some kind of presets, like small Topspin, big Topspin, small Backspin, big Backspin as it is not really necessary to have so much precision when setting the speeds, but just to have some speed profiles presets .
But definitely I can recommend these motors, only disadvantage compared to the BLDCs is that they are really heavy, some DC motors that have half the size of these ones would be perfect I think ...

Thanks ! I added some additional parts for connecting the cardboard for collecting the balls .
Also the first link in the description is a link with a try of the recirculating system .

It's turning out great. I'm trying my hand at a simple Pvc single wheeled launcher.

I think it will work no problem also with a single wheel . Of course only topspin will be possible in this case .

I receive my prints from 3d hubs. Awesome design. I'll have to order new motors and wheels. My motor and wheels won't work.
Thanks again Dan !!

Ok that's great ! My name is Bogdan btw :P .
Now that I look again at the files list, I think some should be removed as they are doubled or not needed .
I will make a review and change the list again .
Unfortunately no time and motivation to do proper instructions, also interest is not so big it seems .

I'm surprised at the lack of interest. I'm not a programmer but love diy projects. Right now I'm am using AC to DC adapter with speed controller to run my motors. I also hacked a servo to run on the adapter as well. One day I'll try arduino but for now manual control of 2 motors and 1 servo is OK for me :) btw my name is Mario

Thanks again !

Ok, let me know if you have any problems or questions !
I am using arduino and I can control the robot from my phone over Bluetooth .
Unfortunately it is too cold in my garage to test the robot at this moment, and still I am struggling to make the net that catches the balls and recirculates them .

Hello Im using your motor mount with only one till I order two new ones. Its better than the pvc i was using !! I thought you might like to see the spiral toy I use to feed the balls :)

Which motor and wheel are you using ? The idea about using that spiral toy is really interesting ! Do you use gravitation to feed the balls ?
Maybe you could raise the pipe to horizontal more and move more in the back, if you use the same motor and wheel that I have it has plenty of power to launch the ball from the other side of the table . It looks to me that the reaction time when the ball is coming from the net is too short and no time to prepare and asses the trajectory .
Where are you located that you can stay outside and play ? Here in Germany is -2 degrees so no chance to do anything in the next 2 months probably . My robot is ready, also the recirculating net system is working . I will upload a video here too soon .

https://photos.app.goo.gl/GOgIWESgJvFg2eFe2 here is a link dunno if it works though

Hey Bogdan. I finally got all the parts . How do I keep the wheel from spinning freely on the axle?

Hello, I used the steel clips as a stopper on one side of the wheel .
To fix the wheel to the 4 mm axle I used some super glue that is put on the axle and the wheel .
Seems to be holding quite ok until now, just make sure it is nice and straight .

OK thanks dude !! I thought about super glue but wasn't sure :)

Hey Bogdan, I live in Florida :) the spiral is gravity to a pvc elbow underneath. Then a servo rotating small plastic wheel that feeds to your motor mount. I'm using a 1 1/2 inch foam wheel and a 6v 1200 rpm motor. I will order the same motors you suggested soon. I have the pipe angled down from the elbow or the balls get stuck at the end of the spiral. We shot over 200 balls without a jam .

Thanks. Will do.