The little Lego rover starts as a simple four-wheeled rover trying to climb on top of a book. Swap in a four-wheel-drive gearbox and grippy tires, and it clears the first obstacle. Add a few books to the stack causes the break-over angle to become an issue, so the rover gets an inverted-V chassis. As the obstacle height increases, batteries are moved around for better weight distribution, but the real improvement comes when an actuating middle joint is added, turning it into a wheeled inchworm. Clearing overhangs suspended beams, and gaps are all just a matter of finding the right technique.
Thanks to Lego’s modularity, all this is possible in an hour or two where a 3D printer and CAD might have stretched it into days. This robot does have the limitation of not being able to turn. Conventional car steering or Mecanum wheels are two options, but how would you do it?
The only electric components on this robot is a small geared DC motor and a LiPo battery. The motor drives a shaft fixed to a wheel on one side, while the opposite wheel is free-spinning. A third wheel is mounted perpendicular to the other two in the center of the robot, and is driven from the shaft by a bevel gear. The third wheel is lifted off the surface by a pair of conical wheels on a pivoting axle. When one of these conical wheels go over the edge of whatever surface it’s driving on, it lowers front and brings the third wheel into contact with the surface, spinning the robot around until both front wheels are back on the surface.
Mechanical alternatives for electronic systems are easily overlooked, but are often more reliable and rugged in hostile environments. NASA is looking at sending a rover to Venus, but with surface temperatures in excess of 450 °C and atmospheric pressure 92 times that of Earth, conventional electronics won’t survive. Earlier in the year NASA ran a design competition for a completely mechanical obstacle detection system for use on Venus.
What do you get when you stick 1738 MOSFETs together? If your answer was a ‘4-bit CPU’, you would be totally correct. Available as a product over at Marutsu as the ‘CPU1738’, it seems to target beginners to computer theory, with build instructions that explain how the CPU is built up from individual MOSFETs that are combined into logic gates.
While decidedly more compact in its SMD format than it would have been with pure through-hole parts, the use of countless small PCBs on top of the larger PCBs make for a pretty hefty package. Board after board build up the CPU, and the assembly continues with the addition of sensors, motors, and wheels. In the end, a robot emerges, albeit a somewhat wobbly-looking one.
Check out the video linked after the break, though before starting one up, note the 50,000 Yen (approximately $500) price tag for the CPU block alone. On the other hand, in addition to the 1738 MOSFETs, there are also 1070 LEDs, so you get what you pay for in blinkies.
With the Mars 2020 mission now past the halfway point between Earth and its destination, NASA’s Jet Propulsion Lab recently released a couple of stories about the 3D-printed parts that made it aboard the Perseverance rover. Tucked into its aeroshell and ready for its high-stakes ride to the Martian surface, Perseverance sports eleven separate parts that we created with additive manufacturing. It’s not the first time a spacecraft has flown with parts made with additive manufacturing technique, but it is the first time JPL has created a vehicle with so many printed parts.
To take a closer look at what 3D-printing for spaceflight-qualified components looks like, and to probe a little into the rationale for additive versus traditional subtractive manufacturing techniques, I reached out to JPL and was put in touch with Andre Pate, Additive Manufacturing Group Lead, and Michael Schein, lead engineer on one of the mission’s main scientific instruments. They both graciously gave me time to ask questions and geek out on all the cool stuff going on at JPL in terms of additive manufacturing, and to find out what the future holds for 3D-printing and spaceflight.
The robot is called the World Tour Robot, and the idea for it is to be small enough to ship to each new location around the world and be simple enough to be repaired easily. It is driven by two servo motors and controlled by a Raspberry Pi which also handles a small camera. Once at its location, it can connect to the internet and then be able to be controlled through a web interface. Locations are selected by application, and the robot is either handed off to the next person in the chain or put back in a box to be shipped.
Master of 3D printed robots, [James Bruton], plans to do some autonomous rover projects in the future, but first, he needed a modular rover platform. Everything is cooler with tank tracks, so he built a rover with flexible interlocking track sections.
The track sections are printed with flexible Ninjaflex filament. Each section has a tab designed to slot through two neighboring pieces. The ends of the tabs stick through on the inside of the track fit into slots on the drive wheel like gear teeth. This prevents the track from slipping under load. The Ninjaflex is almost too flexible, allowing the tracks to stretch and almost climb off the wheels, so [James] plans to experiment with some other materials in the future. The chassis consists of two 2020 T-slot extrusions, which allows convenient mounting of the wheel bogies and other components.
For initial driving tests [James] fitted two completely overpowered 1500 W brushless motors that he had on hand, which he plans to replace with smaller geared DC motors at a later stage.
A standard RC system is used for control, but it does not offer a simple way to control a skid steer vehicle. To solve this, [James] added an Arduino between the RC receiver and the motor ESC. It converts the PWM throttle and turn signal from the transmitter, and combines is into differential PWM outputs for the two ESCs.
For those wishing to explore robot autonomy, there’s no better way then to learn by doing. [Greg] was in that camp, and decided to build an autonomous rover to roam his house, and learned plenty along the way.
[Greg]’s aims with the project were to build a robot that was capable of navigating his home without external assistance. To do the job, a Raspberry Pi 3 was put in charge, and kitted out with a LIDAR for mapping. Pololu Roboclaw motor controllers are then used to allow the Raspberry Pi to drive the robot’s individual wheel motors, giving the four-wheeled bot skid steering capability.
[Greg] goes into immense detail on the project’s writeup, exploring the code and concepts behind its autonomous abilities. Creating a robot that can navigate using LIDAR is no easy task, but [Greg] does a great job of explaining how it all works, and why.