Robot Control Ties RC Receiver to Motor Controller

[Andrey Nechypurenko] has posted the second part of his robotics ground vehicle design guide. In his first post [Andrey] detailed the mechanical design decisions he faced. [Andrey] now begins covering the electrical components, starting with manual control using a standard radio control system. To accomplish this an RC system was used with an MD22 h-bridge driver and a picoUPS.

The MD22 is a neat motor control board which can take the PWM signals from the radio controller and use this to drive the DC motors. Optionally it can also use an I2C interface, giving a nice migration path to integrate with a microcontroller. Until that happens this can’t really be called a robot — its more of an RC vehicle. But the iterative design and build process he’s using is a good one!

The picoUPS provides on-board battery charging. Due to its UPS heritage it also allows the vehicle to be powered from an external supply, which has proved useful during development. Finally, a 5v regulator was required to supply the on-board digital logic. [Andrey] wanted a quick drop in solution with a budget large enough to allow for future expansion and went with the Pololu D15V35F5S3 which can supply 3.5 amps in a small and easy to use module.

After breadboarding the system [Andrey] fabricated a PCB to integrate all the components. The next step is to add sensors and and embedded computer to the platform.

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“Drones” Endanger Airborne Wildfire Fighting

usdaThere is no denying that personal drones are in the public eye these days. Unfortunately they tend to receive more negative press than positive. This past weekend, there were news reports of a wildfire in California. Efforts to fight the fire were hampered when no less than five drones were spotted flying in the area. Some reports even stated that two of the drones followed the firefighting aircraft as they returned to local airports. This is the fourth time this month firefighting planes have been grounded due to unmanned aircraft in the area. It’s not a new problem either, I’ve subscribed to a google alert on the word “Drone” for over a year now, and it is rare for a week to go by without a hobby drone flying somewhere they shouldn’t.

The waters are muddied by the fact that mass media loves a good drone story. Any pilotless vehicle is now a drone, much to the chagrin of radio control enthusiasts who were flying before the Wright brothers. In this case there were two fields relatively close to the action – Victor Valley R/C Park, about 10 miles away, and the Cajun Pass slope flying field, which overlooks the section of I-15 that burned. There are claims on the various R/C forums and subreddits that it may have been members from either of those groups who were mistaken as drones in the flight path. Realistically though, Victor Valley is too far away. Furthermore, anyone at the Cajun pass flying site would have been fearing for their own safety. Access requires a drive through 3 miles of dirt road just to reach the site. Not a place you’d want to be trapped by a wildfire for sure. Who or whatever was flying that day is apparently lying low for the moment – but the problem persists.

Rules and Regulations

In the USA, the FAA rules are (finally) relatively clear for recreational drone operations. The layman version can be found on the knowbeforeyoufly.org website, which was put together by the Academy of Model Aeronautics (AMA), The Association for Unmanned Vehicle Systems International (AUVSI), and other groups in partnership with the FAA.

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Amazingly Detailed Robotics Ground Vehicle Guide

[Andrey Nechypurenko] has put together an excellent design guide describing the development of his a20 grou1nd vehicle and is open sourcing all the schematics and source code.

20150627_180534One of [Andrey]’s previous designs used a Pololu tracked chassis. But this time he designed everything from scratch. In his first post on the a20, [Andrey] describes the mechanical design of the vehicle. In particular focusing on trade-offs between different drive systems, motor types, and approaches to chassis construction. He also covers the challenges of using open source design tools (FreeCAD), and other practical challenges he faced. His thorough documentation makes an invaluable reference for future hackers.

[Andrey] was eager to take the system for a spin so he quickly hacked a motor controller and radio receiver onto the platform (checkout the video below). The a20s final brain will be a Raspberry Pi, and we look forward to more posts from [Andrey] on the software and electronic control system.

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Simple Autonomy with an RC Boat

[Vlad] wrote in to tell us about his latest project—an RC boat that autonomously navigates between waypoints. Building an autonomous vehicle seems like a really complicated project, but [Vlad]’s build shows how you can make a simple waypoint-following vehicle without a background in autonomy and control systems. His design is inspired by the Scout autonomous vehicle that we’ve covered before.

[Vlad] started prototyping with an Arduino, a GPS module, and a digital compass. He wrote a quick sketch that uses the compass and GPS readings to control a servo that steers towards a waypoint. [Vlad] took his prototype outside and walked around to make sure that steering and navigation were working correctly before putting it in a boat. After a bit of tweaking, his controller steered correctly and advanced to the next waypoint after the GPS position was within 5 meters of its goal.

boatgifNext [Vlad] took to the water. His first attempt was a home-built airboat, which looked awesome but unfortunately didn’t work very well. Finally he ended up buying a $20 boat off of eBay and made a MOSFET-based motor controller to drive its dual thrusters. This design worked much better and after a bit of PID tuning, the boat was autonomously navigating between waypoints in the water. In the future [Vlad] plans to use the skills he learned on this project to make an autopilot for the 38-foot catamaran his dad is building (an awesome project by itself!). Watch the video after the break for more details and to see the boat in action.

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Tiny R/C P-51D Mustang Tips the Scales at 3 Grams

Commercial R/C aircraft have been getting smaller and smaller with each passing year. In the early 2000’s, a palm-sized plane or helicopter was the dream of many an R/C enthusiast. Today, you can pick them up for around $20 USD at the local mall. The smallest models however, are still built by an elite group of modelers. Weighing in at a mere 3 grams, [Martin Newell’s] P-51D mustang model certainly puts him into that group. While the P-51’s 11.6 cm wingspan may not make it the smallest plane in the world, its many functions make it incredible.

The Mustang is an 8 channel affair, with elevator, throttle, rudder, ailerons, flaps, navigation lights, working retracts, and flashing cannon lights. That’s Wright, we did say retracts, as in retractable landing gear on a 3 gram model.

All the Mustang’s flight surfaces feature fully proportional control. However, there are no closed loop servos involved. The flight surfaces use magnetic actuators, consisting of a tiny neodymium magnet surrounded by a coil of magnet wire. We’re not sure if the signals to these actuators is straight PWM or if [Martin] is varying the frequency, but the system works. The retracts use heat-sensitive Nitinol “muscle wire” along with a bellcrank system to make sure the landing gear is up and locked after takeoff, and comes down again before a landing.

We don’t have any in-flight video of the Mustang, but we do have footage of an even smaller 1.2 gram plane [Martin] has been flying lately. Click past the break to check it out!

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Extrinsic Motivation: Smart Antenna Tracker for R/C Aircraft

Long distance FPV (First Person View) flying can be a handful. Keeping a video feed alive generally requires a high gain directional antenna. Going directional creates the chore of keeping the antenna pointed at the aircraft. [Brandon’s] smart antenna tracker is designed to do all that automatically. What witchcraft is this, you ask? The answer is actually quite simple: Telemetry! Many flight control systems have an optional telemetry transmitter. [Brandon] is using the 3DRobotics APM or PixHawk systems, which use 3DR’s 915 MHz radios.

The airborne radio sends telemetry data, including aircraft latitude and longitude down to a ground station. Equipped with a receiver for this data and a GPS of its own, the smart antenna tracker knows the exact position, heading and velocity of the aircraft. Using a pan and tilt mount, the smart antenna tracker can then point the antenna directly at the airborne system. Since the FPV antenna is co-located on the pan tilt mount, it will also point at the aircraft and maintain a good video link.

One of the gotchas with a system like this is dealing with an aircraft that is flying directly overhead. The plane or rotorcraft can fly by faster than the antenna system can move. There are a few commercial systems out there that handle this by switching to a lower gain omnidirectional whip antenna when the aircraft is close in. This would be a great addition to [Brandon’s] design.

Droning On: Maiden Flights

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When we last left off, the Hackaday Drone Testbed was just a box of parts on workbench. Things have changed quite a bit since then! Let’s get straight to the build.

With the arms built and the speed controls soldered up, it was simply a matter of bolting the frame itself together. The HobbyKing frame is designed to fold, with nylon washers sliding on the fiberglass sheets. I don’t really need the folding feature, so I locked down the nylock nuts and they’ve stayed that way ever since. With the arms mounted, it was finally starting to look like a quadcopter.

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Using the correct screws, the motors easily screwed into the frames. I did have to do a bit of filing on each motor plate to get the motor’s screw pattern to fit. The speed controls didn’t have a specific mount, so I attached them to the sides of the arms with double-sided tape and used some zip ties to ensure nothing moved. In hindsight I should have mounted them on the top of the arms, as I’m planning to put LED light strips on the outside of edges of the quad. The LEDs will help with orientation and ensure a few UFO sightings during night flights.

Power distribution is a major issue with multicopters. Somehow you have to get the main battery power out to four speed controls, a flight controller, a voltage regulator, and any accessories. There are PCBs for this, which have worked for me in the past. For the Hackaday Testbed, I decided to go with a wiring harness. The harness really turned out to be more trouble than it was worth. I had to strip down the wires at the solder joint to add connections for the voltage regulator. The entire harness was a bit longer than necessary. There is plenty of room for the excess wire between the main body plates of the quad, but all that copper is excess weight the ‘bench’ doesn’t need to be carrying. The setup does work though. If I need to shed a bit of weight, I’ll switch over to a PCB.

Click past the break to read the rest of the story.

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