Electronic Design
How Multicore Chip Flies A Quadcopter

How Multicore Chip Flies A Quadcopter

Technology editor Bill Wong gets Hoverfly's Dr. Alfred D. Ducharme and Parallax's Ken Gracey to provide technical insights into their quad rotor UAV.

The ELEV-8 is a remote quadcopter (Fig. 1) from Parallax. If is available in kit form from Parallax (Fig. 2) and is priced at $599.

The ELEV-8 uses a guidance and control system from Hoverfly Technologies. I spoke with Al Ducharme, Ph.D., President and CEO of Hoverfly Technologies, and Ken Gracey, President of Parallax, about how the ELEV-8 works and how it came about.

 

Figure 1. The ELV-8 runs a multicore Parallax Propeller chip. It is designed to be a remote control (RC) quadcopter but programmers have full access to the Propeller chip.

 

As you can see, the kit does require some assembly. The HoverflySPORT guidance and control system comes assembled though so the quadcopter can be put with a soldering iron and regular tools.

 

Figure 2. The ELEV-8 kit includes everything except the RC controller and a battery.

 

The Parallax Propeller is an 8-core processor (see EiED Online >> Parallax Propeller) with a unique architecture. It is available in chip and board form for other applications like robotics.

 

Figure 3. The Propeller has eight identical cores called cogs. They share I/O and a central memory system. Each cog has only 2 Kbytes of RAM.

 

But onto the questions and answers.

Wong: Can you tell us a little about the ELEV-8.

Gracey: ELEV-8 is an aerial robotic platform, most widely known as a quadrotor, quadcopter or quadrocopter. The ELEV-8 is an entirely made-in-Rocklin product, constructed of several parts to provide field repair. The design is crash-ready in that the motor mounts could be swapped out, the landing gear replaced, etc. Underneath the chassis a customer could put a GoPro or Contour camera for aerial video. With a wireless video transmitter one could fly over first-person view using wireless video transmitters, displaying the ELEV-8's view on video goggles or a small display.

The parts are all acetal copolymer (Delrin), thin-walled aluminum tubing, and standard R/C electric hobby components. By changing the body and adding a few of the same parts in the core ELEV-8 kit, this can become a HEX, a Y-6, or an OCT version.

Wong: How did the ELEV-8 design come about?

Gracey: The design evolved on our forums, in front and with our customers. Several of our customers have programmed our Propeller controller to fly quadcopters. Several had worked with Hoverfly control systems so Parallax chose the Hoverfly Techologies SPORT to be the solution. The HoverCore technology evolved with a scientific approach and a qualified team. In flight it provides the stability and reliability we needed for ELEV-8 platform. Parallax provided some effort to gather the forum members and establish a mechanical design they can call their own. The airframe is totally open (Creative Commons 3.0) and customers have already built ELEV-8s out of acrylic, thin plywood and aluminum. The parts can be routed or laser-cut since they're all flat. The first 25 kits were bought by forum members and together we shook out the issues with the bill of materials, assembly process and flight setup. Forum members contributed back with anti-vibration standoffs, assembly videos, first-person view hardware suggestions, and airframe improvements.

Wong: What Hoverfly controller is used with the ELEV-8?

Ducharme: The HoverflySPORT is used with ELEV-8 currently and will eventually utilize the HoverflyOPEN.

 

Figure 4. The HoverflySPORT is available separately from Hoverfly Technologies.

 

Wong: What does the controller control?

Ducharme: The HoverflySPORT and HoverflyOPEN collects the user control inputs from a hobby receiver including Throttle, Aileron, Elevator, Rudder, and a Gain input. The HoverCore algorithm running on the Parallax Propeller fuses the user input with information from a 3-axis digital gyroscope. The HoverflySPORT and HoverflyOPEN then sends Pulse-Width-Modulated (PWM) signals to external brush-less motor Electronic Speed Controllers (ESC) driving between 4 and 8 brush-less motors. The HoverCore algorithms primary function is to make the aircraft stable in the air and then as a secondary function it uses the users control inputs to maneuver the aircraft. The aircraft behaves much like an air plane or helicopter where elevator changes the pitch of the aircraft and aileron controls the roll. The yaw of the aircraft is controlled by the rudder input. Yaw is maintained because of a balance in clockwise and counter-clockwise rotating propellers.

Wong: What features does the controller implement?

Ducharme: The HoverflySPORT and HoverflyOPEN both act to stabilize the aircraft and maintain user control rotational rates about each axis. A centered aileron, elevator, and rudder input means that the aircraft should maintain a zero rate of rotation about the roll, pitch, and yaw axis. The HoverflySPORT can also utilize an external ultrasonic sensor to automatically maintain the throttle so that a constant altitude is achieved.

Wong: Why did Hoverfly choose the Parallax Propeller for its controller?

Ducharme: There are several reasons that Hoverfly Technologies chose the Parallax Propeller. From a designers point of view, large active user community, inexpensive development tool cost, and numerous general input/output pins are all great reasons to choose the Propeller. From the development point of view, the simplicity of writing in Spin with the power of programming in assembly are very important. However, the most important aspect of the Propeller is the ability to easily incorporate parallel processing is above all other reasons.

Wong: Parallax Propeller has a unique multicore design. What challenges did you encounter in designing and implementing the controller software?

Ducharme: A multi-rotor aircraft presents a unique embedded systems challenge. The ability to monitor user inputs, while monitoring 3-axis of a digital gyroscope, while continuously updating the speed of multiple brushless motors is difficult with a single processor. On the HoverflySPORT and HoverflyOPEN the challenge is not as difficult as when adding other types of sensors such as accelerometers. As a development platform the HoverflyOPEN will benefit from multiple cores. Additional sensors can be accommodated without the need to simplify the main stability algorithm. On our other products such as the HoverflyPRO, which uses gyroscopes, accelerometers, barometers, and several other functions, having multiple cores is essential. We use two Propellers on the HoverflyPRO to accommodate the complex higher level functionality.

Wong: The ELEV-8 is designed as a remote control vehicle. Can it be made into an autonomous or semi-autonomous aircraft?

Gracey:  The ELEV-8 presently uses the HoverflySPORT which has only a MEMS gyroscope. With the Propeller controller between the receiver and electronic speed controllers, the gyro interface provides flight stability yet a very agile aerobatic R/C system. Hoverfly has also produced the Hoverfly OPEN board for Parallax. It is very similar to the SPORT except it has a prototype area. Customers may use the prototype to add an accelerometer, altimeter or other sensors. We are hopeful that the next manufacturing batch of ELEV-8 kits will ship with the OPEN board.

Wong: Is it possible to reprogram the controller?

Gracey: Hoverfly provides a setup program to download their tested firmware, check the sensors and radio connections, and access a flight log.

Wong: What other controllers does Hoverfly make?

Ducharme: Hoverfly Technologies currently manufactures the HoverflyPRO and HoverflyGPS, HoverflySPORT, HoverflyOPEN, HoverflyGIMBAL and have several new products on the way.

Wong: What kinds of systems can these controllers work with?

Ducharme: Our primary markets are professional aerial photography and cinematography, civil engineering, and surveillance.

Wong: What is the HoverflyGIMBAL?

Ducharme: The HoverflyPRO includes outputs to stabilize the Roll and Tilt of a mechanical camera mount. The HoverflyGIMBAL can stabilize roll, tilt, and pan on aerial gimbal.

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