I wanted to inspire people to use 3D printers to build real robots, so I built this car — I call it the Scout — to show off some of the 3D-printed robotics concepts I’ve been developing. First, the car isn’t a weakling. It can take repeated jumps and crashes with no damage. That’s important to show people that this works in the real world, not just on a workbench. If it does break, it’s easy to repair in minutes, thanks to its snap-together design. And the design is open source, so it can mature over time and inspire new variants. It uses a minimum of non-printed parts — only the tires, bearings, motors, batteries, and electronics — and it doesn’t even use screws, because they aren’t necessary and would only add complexity. (Plus, shunning screws makes it a harder problem, which I like!)
Ultimately, the 3D printed Scout is part of a broader robotics construction kit I am building. The wireless radio in the car and remote is my own design — a board called Flutter. Flutter runs Arduino code and has a built-in wireless radio with a 1-kilometer range. Since it runs Arduino, the car can be modified with lights, sensors, speakers, and more. I plan on adding an OLED display to my remote control to show me telemetry data on the car like speed, RPM, and battery level. Beyond the wireless boards, I hope to develop motor control and battery management boards for robots as well, so that one coherent open-source system can be used to build almost any robot.
Assembling the Scout car is easy, and only takes a few minutes. Printing the parts, however, is still a real commitment. Currently, it’s over 24 hours of print time, though I think it could be done in under 10 hours with a large-nozzle 3D print head like the E3D Volcano.
The STL file is attached here:
Print the parts
Most of the Scout’s parts can print on a 150mm × 150mm build surface, but the 2-part electronics housing is currently 156mm long. I recommend printing with PLA on a heated bed.
Download the parts and get printing. There are detailed instructions there, but basically, most parts can be 20%–30% infill, while gears, driveshafts, and steering pins should be 100% infill. Print the parts for the front end first, and note that the electronics bay and cover may need to be printed with a “brim” for extra adhesion.
Bill of Materials
R/C transmitter and receiver The new Flutter Vehicle Control Kit from Flutter Wireless has twice the range of standard R/C, and includes two Flutter Basic Boards, an Explorer Board, and a dual-joystick Remote Control Board with a lithium battery. You can also use standard R/C gear.
- Rubber band, thin
- Bearings, 12mm, 6001Z (6)
- Bearings, 8mm, 608 (2)
- Servomotor, metal gear, MG995
- Brushless motor, 1,000kV, D2830-11
- Propeller adapter, 3mm, collet type
- Electronic speed controller (ESC), 30A, with reverse I recommend HobbyKing #HK-30A.
- Bullet connectors, 3.5mm (3) or motor extension wires, for connecting ESC to motor
- Battery mating plug for your ESC
- Heat-shrink tubing
- Battery pack, lithium polymer (LiPo), 2S, 2,200mAh (1) roughly 104×34×17mm. I recommend HobbyKing’s Zippy Flightmax #Z22002S20C.
- Tires, foam rubber, 1:10 scale (4) 7006 type, 95mm diameter, 36mm wide
- Lithium battery charger/balancer such as Turnigy E3
Test the electronics
Solder connectors onto the ESC for the motor and the battery, and cover all connections with heat shrink tubing. Lithium batteries have a lot of power, and short circuits can be dangerous.
Follow the instructions that came with the Flutter kit (or your radio) to attach the servo and speed controller, and then power everything up and make sure it works.
Assemble the front end
The front end consists of 2 wheel assemblies and the center frame. Place the bearings and drive shaft into each bearing assembly and slide in the shaft cover.
Then for each wheel assembly slide on 2 hub plates and a tire, and secure them with the wheel shaft clip.
Next, take the servo (with the “horn” removed) and slide it into its cavity in the frame, first forward at a 45° angle and then down, so that the front of the servo locks underneath the lip in the front of the cavity.
Secure the servo by sliding a steering pin through the small hole in the frame member above the servo flange, and flip over the assembly.
Attach the 6-lobed servo horn to the servo, capturing the steering rack beneath it. If your servo didn’t come with a 6-lobed horn, a printable version is in the Github repository.
Attach the wheels
First, wrap the rubber band around the top steering towers, and attach the wheel assemblies using the short and long pins.
Then bring the front of the rubber band back over the steering towers.
The rubber band isn’t critical, but helps to keep the long steering pins from working their way out.
Power up the servo and make sure everything is centered. If the servo isn’t centered when powered on, just unscrew the servo horn and adjust the position until the steering is straight.
Assemble the rear end
The rear frame holds the motor and the drive shafts. Start by collecting the pieces needed for the small, middle drive shaft.
Install the gears on both ends of the shaft with the large gear on the longer end. Place one 608 bearing on the end of the shaft by the large gear, and the other 608 bearing in the frame. Guide the bearing on the shaft into its hole at an angle, then straighten out the shaft and place the short end into the opposite bearing.
Secure the shaft with the 8mm shaft clip, aligning the flat inside the clip with the small notch in the middle drive shaft.
Now you’ll assemble the rear driveshaft and install it into the frame. Take the large, rear driveshaft and install the rear-drive gear so that it mates with the rectangular section of the shaft, and then place 12mm bearings on both ends of the shaft. Lower the shaft into the frame so that the large rear gear mates with the small middle gear, and then slide the bearings into their recesses.
Snap the 12mm shaft clip onto the rear shaft.
Install the motor
Assemble the motor, small drive gear, and quadcopter propeller adapter as shown here.
These adapters were designed to turn only one direction, but our car spins the motor both directions, and the gear can loosen if it’s not tight enough.
So use the simple 3D printed wrench to hold the gear while tightening the adapter with pliers. It should be pretty tight, but be careful as these aluminum propeller adapters can break with heavy tightening.
Now slide the motor into its hole in the rear frame with the wires facing up, and then lock it in place with the motor lock wedge.
You should now have something that resembles a giant servo motor.
Final body assembly
Slide the front end assembly onto the large dovetail in the rear frame. Then slide the electronics bay over the top, with the motor wires feeding into the side hole.
Center the electronics bay over the rear frame, and drop in 2 short pins.
Install the electronics
If you sourced the recommended parts, they just drop into place. Remove the power switch from the ESC, feed it through the power switch hole, and then plug it back into the ESC.
Next, plug the motor leads into the ESC. There are 3 leads and they can be plugged into the ESC in any arrangement. If the motor spins backward, switch any 2 wires and you’ll be good.
Hook up the servo wire and the speed controller to the radio, and then plug in the battery and neatly stow all the wires.
Build the remote (optional)
Just plug the Flutter module and the battery into your Remote Control Board, and then snap it into the 3D printed controller housing.
If you’re using your own R/C gear you can skip this step.
Close it up and drive!
Snap on the lid and you should be ready to roll. Go outside and test Scout’s limits. Scout is fast and loves jumps. And if you break anything you can always print more parts!
Source: Taylor Alexander
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