Building and testing a Raspi Robot board

I have had a kit of parts for a RaspiRobot board in my "to do pile" for a while now. Today I had a bit of spare time so I followed the construction instructions and put it together.

Step one was to check I had the right bits. I opened the packet and laid the components out just like the helpful picture on the website. Mine were different! The official picture shows four 4-way headers, whereas the set I got had two 4-way and two 2-way. A bit further down the page is a list of components, and that did agree with what I had received. Shame about the picture, though.

RaspiRobot Parts

RaspiRobot Parts


Once I had sorted that out I began assembling the board, with the help of my "third hand". Soldering it was very straigtforward, and all the components fitted nicely into their allotted places.

RaspiRobot

After construction, I was keen to test it. First of all I plugged it in without any motors or power supplies connected and followed the "Getting Started" tutorial

Once I had installed the various python stuff it requires, I was able to switch the two LEDs on and off. The instructions for switching the motors and open-collector outputs had no effect, of course.

Next, I tried to drive a motor. This is, after all, what the board is supposed to be for - if all I wanted was to switch two LEDs on and off I could have done it much more simply! This, however was where I hit problems. So far I have not been able to get the board to actually drive a motor. From reading the comments on the RaspiRobot sparkfun page it seems likely that the problem is one of power.

My first attempt was to try using USB power from the Pi. Nothing. But I half expected that - motors can take a lot of power, so the board provides a separate power input to drive the motors and (via a regulator) the Raspberry Pi. The web site says anything from 7-12V will do, so I tried a spare 12V power adaptor which I had lying around and happened to have the right kind of plug. It tested OK with a voltmeter, but did not seem to have enough juice to power up the Pi. Still, it only claimed an output of 400mA, so I tried a bigger one. 500mA was enough to half-start the Raspberry Pi, but not enough to boot the OS. I was sure a 1A adapter would be enough, but this didn't work either. All that happened was the regulator on the RaspiRobot board got very hot.

RaspiRobot

I know the motor works, because connecting it directly to the power adapter makes it spin happily. The problem definitely seems to be in the power handling on the RaspiRobot board.

I'll shelve this for now, and see if I can find anything else to power this board another day.

5 Comments

  1. Did you manage to get the motor working – i get an error when i init the rr object as per the sample code that implies the pins are defined wrong in the library. Haven’t had time myself to look at this again for a while!

    Did you manage to fix it?

    Smudge

  2. Hi, I just got this board, and starting to solder it. But I found that the wholes are too small for my soldering iron and tin. So I just want to know what size tip and tin you use?

    • I have had my soldering iron for at least 30 years and still use the tip it came with, so I’m not really sure what size it is, it looks like it is about 2-3 mm across the tip, which is cylindrical with a slanted end. The iron is an Antex one something like: http://www.hobbytronics.co.uk/antex-soldering-iron-xs25 Generally I use 22 gauge flux-core leaded solder, as I find it easier than lead-free for general soldering tasks.

      I’m not sure what you mean about the holes being too small, though. As long as the component leads fit into their places, all you need to do is bring some solder and the tip of the iron up to the component lead and let the solder flow onto the joint.

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