HobbyKing Cheetah: Building Running Robots from Hobby Motors

[Ben Katz] is building a running robot from hobby level brushless motors, all on his blog under the tag, “HobbyKing Cheetah.

One of the features of fancy modern industrial motor and controller sets is the ability for the motor to act as a mass-spring-damper. For example, let’s say you want a robot to hold an egg. You could have it move to the closed position, but tell the controller you only want to use so much force to do it. It will hold the egg as if there was a spring at its joint.

Another way you could use this is in the application of a robot leg. You tell the controller what kind of spring and shock absorber (damper) combination it is and it will behave as if those parts have been added to the mechanism. This is important if you want a mechanical leg to behave like a biological leg.

[Ben] had worked on a more formal project which used some very expensive geared motors to build a little running robot. It looks absolutely ridiculous, as you can see in the following video, but it gives an idea of where he’s going with this line of research. He wanted to see if he could replace all those giant geared motors with the cheap and ubiquitous high performance brushless DC motors for sale now. Especially given his experience with them.

So far he’s done a very impressive amount of work. He’s built a control board. He’s characterized different motors for the application.  He’s written a lot of cool software; he can even change the stiffness and damping settings on the fly. He has a single leg that can jump. It’s cool. He’s taking a hiatus from the project, but he’ll be right back at it soon. We’re excited for the updates!

Hackaday Prize Entry: Industrial Servo Control On The Cheap

[Oscar] wonders why hobby projects ignore all the powerful brushless motors available for far less than the equivalent stepper motors, especially with advanced techniques available to overcome their deficiencies.  He decided it must be because there is simply not a good, cheap, open source motor controller out there to drive them precisely. So, he made one.

Stepper motors are good for what they do, open-loop positioning along a grid, but as far as industrial motors go they’re really not the best technology available. Steppers win on the cost curve for being uncomplicated to manufacture and easy to control, but when it comes to higher-end automation it’s servo control all the way. The motors are more powerful and the closed-loop control can be more precise, but they require more control logic. [Oscar]’s board is designed to fill in this gap and take full advantage of this motor control technology.

The board can do some pretty impressive things for something with a price goal under $50 US dollars. It supports two motors at 24 volts with up to 150 amps peak current. It can take an encoder input for full closed loop control. It supports battery regeneration for braking. You can even augment a more modest power supply to allow for the occasional 1 KW peak movement with  the addition of a lithium battery. You can see the board showing off some of its features in the video after the break.

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Automating RC Motor Efficiency Testing

Small brushless motors and LiPo batteries are one of the most impressive bits of technology popularized in recent years. Just a few years ago, RC aircraft were powered by either anemic brushed motors or gas. Quadcopters were rare. Now, with brushless motors, flying has never been easier, building electric longboards is simple, and electric bicycles are common.

Of course, if you’re going to make anything fly with a brushless motor, you’ll probably want to know the efficiency of your motor and prop setup. That’s the idea behind [Michal]’s Automated RC Motor Efficiency Tester, his entry to the 2016 Hackaday Prize.

[Michal]’s project is not a dynamometer, the device you should use if you’re measuring the torque or power of a motor. That’s not really what you want if you’re testing brushless motors and prop configurations, anyway; similarly sized props can have very different thrust profiles. Instead of building a dyno for a brushless motor, [Michal] is simply testing the thrust of a motor and prop combination.

The device is very similar to a device sold at Hobby King, and includes a motor mount, microcontroller and display, and a force sensor to graph the thrust generated by a motor and prop. Data can be saved to an SD card, and the device can be connected to a computer for automatic generation of pretty graphs.

Brushless motors are finding a lot of uses in everything from RC planes and quadcopters, to robotics and personal transportation devices. You usually don’t get much of a data sheet with these motors, so any device that can test these motors will be very useful.

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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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Open Source ESC Developed for Longboard Commute

For electric and remote control vehicles – from quadcopters to electric longboards – the brains of the outfit is the Electronic Speed Controller (ESC). The ESC is just a device that drives a brushless motor in response to a servo signal, but in that simplicity is a lot of technology. For the last few months, [Ben] has been working on a completely open source ESC, and now he’s riding around on an electric longboard that’s powered by drivers created with his own hands.

esc-for-longboardThe ESC [Ben] made is built around the STM32F4, a powerful ARM microcontroller that’s able to do a lot of computation in a small package. The firmware is based on ChibiOS, and there’s a USB port for connection to a sensible desktop-bound UI for adjusting parameters.

While most hobby ESCs are essentially black boxes shipped from China, there is a significant number of high performance RC pilots that modify the firmware on these devices. While these new firmwares do increase the performance and response of off-the-shelf ESCs, building a new ESC from scratch opens up a lot of doors. [Ben]’s ESC can be controlled through I2C, a UART, or even a CAN bus, greatly opening up the potential for interesting electronic flying machines. Even for ground-based vehicles, this ESC supports regenerative braking, sensor-driven operation, and on-board odometry.

While this isn’t an ESC for tiny racing quadcopters (it’s complete overkill for that task) this is a very nice ESC for bigger ground-based electric vehicles and larger aerial camera platforms. It’s something that could even be used to drive a small CNC mill, and certainly one of the most interesting pieces of open source hardware we’ve seen in a long time.

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Kids Electric Mini Goes Brushless, pops wheelies

[ThatHpiGuy] had a problem. He wasn’t impressed with the performance from his kids’ electric-powered Mini. The 6 volt system was anemic at best, and was just begging for an upgrade. Pulling off the seat and checking the undercarriage, [ThatHpiGuy] realized the motor and gearbox were a perfect fit for the Turnigy 2300 Kv motor from his R/C short course truck. A couple of screws later, car-docuand he had the fastest ride-on toy on the block. Since this was a quick hack, [ThatHpiGuy] kept the truck’s R/C receiver, electronic speed control, and 2 cell LiPo power setup intact. The result is a cooperative system where he controls the throttle via R/C, and his kids control the steering.

That steering is still a bit of an issue though. Like many kid toys, the Mini only has one drive wheel, in this case the right rear. If [ThatHpiGuy] pours on the power a bit too quickly, the single wheel either spins or forces the car into a hard left turn. Aside from that, it looks like both [ThatHpiGuy] and his children are having a ball with this hack. The car will even pop a wheelie from a standing start! You’ve got to see it after the break.

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Take Your Samples for a Spin with the RWXBioFuge

We have a confession to make: we love centrifuges. We’ve used all shapes and sizes, for spinning bags of whole blood into separate components to extracting DNA, and everything in between. Unfortunately, these lab staples are too expensive for many DIY-biologists unless they buy them used or build them themselves. [Pieter van Boheemen] was inspired by other DIY centrifuges and decided to make his own, which he named the RWXBioFuge.

[Pieter] designed the RWXBioFuge using Sketchup, OpenSCAD, and InkScape. It features a Thermaltake SMART M850W ATX power supply, an R/C helicopter Electronic Speed Controller (ESC), and brushless outrunner motor. For user output it utilizes a 16×2 LCD character display with an I2C interface.The frame is laser-cut from 3mm MDF while the 3D-printed PLA rotor was designed with OpenSCAD.

An Arduino handles the processing side of things. [Pieter] used an Arduino Ethernet – allowing a web interface to control the centrifuge’s settings and operation from a distance. We can see this being useful in testing out the centrifuge for any rotor/motor balance issues, especially since [Pieter] states that it can be configured to run >10,000 rpm. We wouldn’t want to be in the room if pieces start flying off any centrifuge at that speed!  However, we feel that when everything’s said and done, you should have a centrifuge you can trust by your side when you’re at your lab bench.

While there are similarities to the Openfuge, the larger RWXBioFuge has rotor capacities of eight to twenty 1.5-2.0ml microcentrifuge tubes. Due to the power supply, it is not portable and a bit more expensive, but not incredibly so. There are some small touches about this centrifuge that we really like. The open lid detector is always a welcome safety feature. The “Short” button is very handy for quick 5-10 second spins.

A current version of the RWXBioFuge is being used at the Waag Society’s Open Wetlab. [Pieter’s] planned upgrades for the next version include a magnetic lid lock, different rotor sizes, an accelerometer to detect an improperly balanced rotor, and optimizing the power supply, ESC, and motor setup. You can never have enough centrifuges in a lab, and we are looking forward to seeing this project’s progress!

Check out a few more pictures of the RWXBioFuge after the break.

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