Procrastinatus

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Archive for the ‘Robotics’ Category

Using a car alternator as a ‘brushless’ motor

Posted by aonomus on September 18, 2009

So I’ve been tinkering with the idea of using a car alternator as a motor, and got it to work yesterday. Here is the result:

Posted in Electronics, Hacks, Robotics | Tagged: , | 1 Comment »

Parts: ST Micro’s VNH2SP30 and VNH3SP30 motor drivers

Posted by aonomus on July 27, 2009

So a new project that has come to mind is a remote controlled treadded vehicle such as a tank or crawler, and I started thinking about what motor drivers to use. Having had some good success with ST Micro before, I decided to take a look on their site first.

Having taken a look at their motor driver applications page showed old Multiwatt-11 packaged drivers or newer power-SSOP packaged drivers with less power than I’d like, however automotive grade electronics components typically have a few key features: good packaging/ease of mounting and cooling, power, reliability. The automotive page has a motor driver page as well which has shown the VNH2/3SP30 drivers (datasheet) to have voltage, current, and thermal protection on a thermally efficient die pattern (3 separate dies with direct connection to the bottom, PCB with thermal vias acts as the heatsink).

What is even more interesting is that you can run both sides of the H bridge in parallel, and use 2 separate IC’s to get even more power. The chip itself will withstand 30A, but only as long as it doesn’t overheat, which is limited by the board itself. The datasheet itself shows some example patterns of PCBs to connect the inputs and outputs while having more copper to cool the chip itself, however the chip would also benefit from a heatsink mounted above and maybe below (with a layer of conformal material). Pololu has actually done testing itself to show that continual current load can be in the 14-15A range, and Phidgets has simply derated their IC’s down to 15A maximum duty cycle.

I’ve noticed that a few devices such as the Phidgets high current motor driver and Pololu’s motor drivers use these chips, and in particular the Pololu website has a good comparison between the VNH2 and 3 series. While the chip itself is pricey ($15+ on Digikey, Mouser, etc) the form factor is useful since it lends itself to miniaturized robust robotics, despite the original automotive usage.

If any ST engineers read this, some suggestions for a product targeted towards robotics:

  • Non SMD format, thruhole preferrably
  • A SMD format that simply has the pins on the reverse side so that heatsinking can be done directly to a metal surface via clamping. (Note a insulating layer needs to be applied, such as the one used in your ISOTOP/SOT-227 packaged power-fets).

Update: I have discovered that at my Eagle install (5.4.0) has the MultiPowerSO-30 package and the VNH3 part already in the st-micro library, unfortunately the VNH2 with current sense and diagnostic are not present (had to make my own part).

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DIY Robot-boat at AUVSI’s Autonomous Surface Vehicle Competition 2009

Posted by aonomus on June 24, 2009

So the major project that I have been involved in recently was working on an autonomous surface vehicle (ASV) that was entered in AUVSI’s 2009 ASV competition. Given a small team (6 people, 2 builders), under $1000, and about 30 days we built what would be considered a feat of bodging and hacks based on extreme ingenuity and resourcefulness.

Note that of the four people in the photo above, it consists of (from left to right) a comp sci masters student on exchange, a political science student, a broadcast technician, and a chemistry/biology student.

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Posted in Arduino, Autonomous surface vehicle, Electronics, Projects, Robotics | Tagged: , | Leave a Comment »