Kansas City Maker Faire: Pi-Plates

As soon as he spied the Jolly Wrencher on my shirt, [Jerry Wasinger] beckoned me toward his booth at Kansas City Maker Faire. Honestly, though, I was already drawn in. [Jerry] had set up some interactive displays that demonstrate the virtues of his Pi-Plates—Raspberry Pi expansion boards that follow the HAT spec and are compatible with all flavors of Pi without following the HAT spec. Why not? Because it doesn’t allow for stacking the boards.

[Jerry] has developed three types of Pi-Plates to date. There’s a relay controller with seven slots, a data acquisition and controller combo board, and a motor controller that can handle two steppers or up to four DC motors. The main image shows the data acquisition board controlling a fan and some lights while it gathers distance sensor data and takes the temperature of the Faire.

The best part about these boards is that you can stack them and use up to eight of any one type. For the motor controller, that’s 16 steppers or 32 DC motors. But wait, there’s more: you can still stack up to eight each of the other two kinds of boards and put them in any order you want. That means you could run all those motors and simultaneously control several voltages or gather a lot of data points with a single Pi.

The Pi-Plates are available from [Jerry]’s site, both singly and in kits that include an acrylic base plate, a proto plate, and all the hardware and standoffs needed to stack everything together.

A Pi Robot Without a Hat

Daughter boards for microcontroller systems, whether they are shields, hats, feathers, capes, or whatever, are a convenient way to add sensors and controllers. Well, most of the time they are until challenges arise trying to stack multiple boards. Then you find the board you want to be mid-stack doesn’t have stackable headers, the top LCD board blocks the RF from a lower board, and extra headers are needed to provide clearance for the cabling to the servos, motors, and inputs. Then you find some boards try to use the pins for different purposes. Software gets into the act when support libraries want to use the same timer or other resources for different purposes. It can become a mess.

The alternative is to unstack the stack and use external boards. I took this approach in 2013 for a robotics competition. The computer on the robots was an ITX system which precluded using daughter boards, and USB ports were my interface of choice. I used a servo controller and two motor controllers from Pololu. They are still available and I’m using them on a rebuild, this time using the Raspberry Pi as the brain. USB isn’t the only option, though. A quick search found boards at Adafruit, Robotshop, and Sparkfun that use I2C.

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Reverse Engineering Hoverboard Motor Drive

The must-have toy of the moment last winter was the “Hoverboard”. We all probably secretly wished them to be the boards from the Back to the Future series of films made real, but the more achievable reality is a self-balancing scooter somewhat akin to a miniature Segway. It seemed every child wanted one, schools banned them, and there was a media frenzy over some of the cheaper models that lacked protection circuitry for their li-ion batteries and thus had a tendency for self-incineration.

[Drew Dibble] is interested in the Power Racing Series (PRS), in which toy electric cars are souped up for competition. Casting around for a source of cheap and relatively powerful motors he lit upon the self-balancing scooters, and waited on Craigslist for the inevitable cast-offs. His resulting purchase had two 350W brushless hub motors and all the associated circuit boards for motor control, gyroscope, and oddly a Bluetooth speaker. The motor control board received an unknown two-wire digital feed from the scooter’s control board, so he set to work investigating its protocol. His write-up of how he did it is an interesting primer in logic line detective work.

Hooking up his logic analyzer he was quickly able to rule out the possibility of the control signal being PWM because all signals followed the same timing. Both lines had data so he was able to rule out I2C, for in that case one line would carry a clock. He was therefore left with a serial line, and taking the 38 microsecond timing interval, he was able to calculate that it had a rather unusual bitrate of 26315 BPS. Each packet had a multiple of 9 bits so he either had 9-bit or 8-bit with parity, and trying all possible parity schemes resulted in parity errors. Therefore the boards used a highly unusual 9-bit non-standard bitrate serial port. Some experimentation led him to an Arduino library, and he was able to get some movement from his motors. Some clever timing detective work later and he could make them move at will, success!

All his code for the project is on GitHub, for his 9-bit SoftwareSerial library and a motor control sketch.

If you want a real Back to the Future hoverboard then you may have to wait a while longer. We have featured a replica made as an unrideable floating artwork though, and a working board that is more of a personal hovercraft.

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Adding Position Control To An Open Source Brushless Motor Driver

Brushless motors are everywhere now. From RC planes to CNC machines, if you need a lot of power to spin something really fast, you’re probably going to use a brushless motor. A brushless motor requires a motor controller, and for most of us, this means cheap Electronic Speed Controllers (ESC) from a warehouse in China. [Ben] had a better idea: build his own ESC. He’s been working on this project for a while, and he’s polishing the design to implement a very cool feature – position control.

We’ve seen [Ben]’s work on his custom, homebrew ESC before. It is, by any measure, a work of art. It’s capable of driving brushless and brushed motors with a powerful STM32F4 microcontroller running ChibiOS that’s able to communicate with other microcontrollers through I2C, UART, and CAN bus. If you want to build anything with a motor – from a CNC machine to an RC helicopter to an electric long board – this is the motor controller for you.

[Ben]’s latest update considers position encoders. Knowing how fast a motor is turning is very important to knowing how fast a wheel is turning, how much torque the motor is generating, and an awesome step in building the finest motor controller ever made.

Like the last update, [Ben] demonstrates the great control program written for this ESC. This GUI programs the microcontroller on the controller, with protection from high and low voltages and currents, high RPMs, duty cycle changes, and support for regenerative braking.

Thanks [Dudelbert] for sending this one in.

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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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Hackaday Prize Entry: DC Motor Controller

There are a lot of cheap Chinese CNC machines out there with okay mechanics and terrible electronics. The bearings aren’t complete crap, but the spindle of these CNC machines is a standalone PWM controller with a pot to control the speed. This means you can’t control the spindle speed with LinuxCNC or Mach3.

For his Hackaday Prize entry, [SUF] is building a DC motor controller for a Chinese spindle motor that doesn’t use any kind of encoder. The first part of that project is fairly easy; [SUF] has already built a high current driver. The second bit is a little it harder – because these spindles don’t have an encoder, [SUF] will have to read voltage spikes on the motor poles, giving him the RPM of the spindle. From there, it’s a bit of PID code to get this spindle running at a desired RPM and connecting it to a CNC control box.

So far, [SUF] has a second version of his board waiting for assembly. In the first version of the board, the switching time for the MOSFET was a little slow, but that’s all corrected in the current revision. It’s a great project to extend the capability of these cheap CNC machines, and perfect project for the Hackaday Prize.

The 2015 Hackaday Prize is sponsored by:

BLDC Controller With The Teensy 3.1

[Will] is on the electric vehicle team at Duke, and this year they’re trying to finally beat a high school team. This year they’re going all out with a monocoque carbon fiber body, and since [Will] is on the electronics team, he’s trying his best by building a new brushless DC motor controller.

Last year, a rule change required the Duke team to build a custom controller, and this time around they’re refining their earlier controller by making it smaller and putting a more beginner-friendly microcontroller on board. Last years used an STM32, but this time around they’re using a Teensy 3.1. The driver itself is a TI DRV8301, a somewhat magical 3 phase 2A gate driver.

The most efficient strategy of driving a motor is to pulse the throttle a little bit and coast the rest of the time. It’s the strategy most of the other teams in the competition use, but this driver is over-engineered by a large margin. [Will] put up a video of the motor controller in action, you can check that out below.

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