I developed this 3D printed custom tank tread system for my robot. You can see it in action from the videos that I included.
The main purpose of this project is to develop stable, strong and reliable robotic tank tread. With this 3D printed part I can add 2 degrees of freedom to the tank tread as seen in the videos. Whole tank tread can turn 360 degrees around the connection point of the robot, so that you can make your robot walk with this system. Additionally by encapsulating the servo motor this system is minimizing the space that we will need.
Lets start with the part list:
1) Vex tank tread kit
2) M4 x 15mm hex head screws (4)
3) Tower Pro Servo motor and arms
4) M4 x 50mm philips head (2)
5) 2K ohm resistors (2) or 1K ohm resistors (4)
6) Aluminum pipe 80 mm long, 5mm diameter
7) 3.2 mm shaft 76 mm long
8) Self Locking retaining ring, 8mm outer diameter (4)
9) M3 x 25mm hex head and nuts (4)
10) 3D printer or 3D Hubs
Step 1: 3D Printing the Tread Holder (use PLA Not ABS)
Let us start by printing the main customized part.
You can find the .stl file attached to this step. In the pictures above you can see two different colors. White one is with abs orange one is with PLA. Since ABS is weaker than PLA, I switch my material into PLA.
You can use 3D Hubs ( https://www.3dhubs.com) for printing this part, depends on the place it is pretty fast. If you are willing to build a robotic platform with these tank treads, print 4 of them.
Warning: While you are printing select the infill density: 100% otherwise your part may breake :/
Step 2: Manipulating Servo Motor to Be 360 Degree Turnable
Manipulating Servo motor to be 360 degree turnable,
Lets start with turning a 180 degree servo motor into 360 degree servo motor. Tower pro servos have high torque and small space, which I like a lot.
Dissemble the servo motor as you see in the pictures. Leave only the dc motor inside the black servo box. Take the circuit out. We will connect this circuit with long cables later.
At this step use 2k ohm resistors to make the servo motor 360 degrees. For this process please follow this instructable: https://www.instructables.com/id/Convert-Towerpro-...
Step 3: Assembling Servo Into 3D Printed Part
As seen in the pictures,
Place the servo motor into our 3D printed part. (You may need to file the 3D printed part a little bit to fit your servo inside) Don't forget to take the cables out from the small hole provided in the 3D printed part
When you dissemble the servo motor keep the 4 long screws that you took from the servo motor and reattach them into 3D printed part to stabilize the servo into the part. Also use M4 x 15mm hex head screws (4) to stabilize the servo more into 3D printed part.
Warning: Expect 1 or 1.5 mm tolerance in your printed parts unless you are using very high quality 3D printer.
Step 4: Connecting Aluminum Cable Pipe
Connecting aluminum cable pipe,
Take 80 mm long, 5mm diameter aluminum pipe and insert into the 3D printed part. This will be our pipe for placing cables safely. I 3D print it before, but 3D printed part was too weak for this duty. It is better to keep this piece metal. Later place the servo cables from inside of the pipe.
Step 5: Connecting Middle Free Tires
Connecting middle free tires,
Take middle free tires from Vex tank tread kit and attach them into the 3D printed part. I didn't provide holes for this placement because it is up to you. Depending on your need you can place them wherever you want to place.
Use M4 x 50mm philips head (2) screws to place them.
Warning: When you are drilling the 3D printed part, be careful to not overheat your part. Otherwise it will melt and your hand drill will get stuck inside the part.
Step 6: Preparing Driving Gear and Attaching It Into the Servo Motor
Preparing driving gear and attaching it into the servo motor,
Take the driving gear from vex tank tread kit and drill for holes to place M3 x 25mm hex head and nuts (4) as seen in the picture.
Then take 4 way servo arm and extend the pre drilled holes according to your holes at the driving gear. Attach servo arm into driving gear and fasten the screws.
As a final step connect the driving gear with servo arm, into the servo motor by using the servo screw. See the pictures.
Step 7: Attaching Free Gear at the Other Edge
Attaching free gear at the other edge,
Take the same shaped gear, I called it free gear because we are not going to use any motor to make it turn directly.
Connect it into 76 mm long 3.2 mm shaft. Use 4 self locking retaining rings to stabilize it in the same alignment with other gears. See the pictures
Warning: be careful about the direction of self locking retaining rings. If you place them wrong it will be hard to take them out.
Step 8: Connecting Tread and Sealing Against Water
I also used these customized tank tread inside the water as well. Due to this fact, I sealed the holes for water resistivity with hot glue gun. See the pictures.
As a last step prepare your tread. I attach 35 piece tread into my system. Most probably it will be the same number in your system as well.
3D printed custom Vex Tank Tread System is now ready to use. Connect these two wires into the servo circuit and control the system by using Arduino.
In the next step, as a bonus I will provide you my motor info to turn these whole customized system around itself.
Step 9: Bonus
I used 2 rpm or 5 rpm 12V Electrical DC Worm Gear to make full cycle turn of the customized tread. Check out the video of the tank tread in action.
Here is the amazon link for that: https://www.amazon.com/Reversible-Worm-Gear-Motor...