Easy DC?

Well, six months after the fact, I believe I may have located the source of the pretty disastrous issues I had at the last Pi Wars. I actually managed to complete just three of the seven events so it was all a bit heartbreaking tbh.

I had severe issues using a PS3 controller and I fully believed that to be the issue and therefore have looked at moving away from this to another controller type for next time round. The Rock Candy PS3 controllers come highly recommended by Brian Corteil (aka @CannonFodder) who has used them to great effect, in fact winning – twice!

So, you may have seen FRED-209, my new Pi powered Nerf Tank. This uses same ZeroBorg motor controller and I had it linked to an original PS3 controller. I’ve tested extensively in the week and then this Saturday I took it to Cotswold Jam and bam… the controller fails. Niet… Zip… Diddly. Can’t get it to connect, then if it does it drops after a few seconds.

This is *identical* to the behaviour X-Bot exhibited at Pi Wars. So much discussion ensues as to the cause. I know of several other folks who also had issues with these controllers last time round. However, Brian C. lent me a Rock Candy one to test and this also showed exact same behaviour. The RC ones are 2.4ghz and the PS3 ones are Bluetooth so still wasn’t sure if it was radio interference of some kind. Another good guess was noisy DC motors causing problems.

But… I think we have a winner. This DC-DC converter board is a damn liar…

dcdc1

I recently recommended this type of thing having seen similar at Pi Wars last time. I now conclusively retract that recommendation! I used a similar board last time , without a read out, and I believe this suffers from the same issue.

Note the difference in alleged and actual voltage….

dcdc2

This difference is not enough to shut the Pi down, but it is enough to mean power hungry peripherals, say a bluetooth dongle for example, are just enough to make the power dip enough that the USB experiences issues and that kills the controller.

If this were the only problem then simply setting it higher to start off with would solve the problem. We did crank it up to 5.18v on the multimeter which may be getting a little hot for the Pi, but it then ran flawlessly for the rest of the day at Cotswold Jam with loads of people giving FRED-209 a good hammering.

I do though believe there is good reason to suspect that the setting on the board drifts over time. Whether this is vibration from the pot moving the micro screw that you use to set the output voltage or something else, it does seem to change. This is regardless of the state of the batteries being used.

So, I am now hunting for a DC-DC board that sticks out a guaranteed 5v that can be relied one. Core Robotics have one in the pipeline but it’s not available yet. I’d be interested to hear from other teams who used these or similar boards or PS3 controllers last time and also experienced issues.

T

Until next time….

3 thoughts on “Easy DC?

  1. I had similar problems with a potentiometer-controlled DC-DC power convertor for my Pololu Zuma; believe me it is not vibration/travel which is the cause of the problem, it’s the pot just generally being pants and not keeping its position. My multimeter showed it varied from 5v to 4.3v within the space of a few hours – the longer I left it, the further it drifted. I switched to a single-purpose (1-6v)->5v board with no pot (it only outputs 5v) and haven’t had any problems since. http://www.ebay.co.uk/itm/272238498671

  2. I was another one with this problem (right in the middle of pi noon!). I wish I could be convinced that this was the issue, but I’m not… or maybe partly. I have a nagging suspicion that the problem arose because of the sheer number of BT devices around… like you, this would always work fine at home, but “out in the wild” would have these failures. It might be due to fluctuations in the output, but we had a different voltage converter (OKI-78SR-5 switching voltage regulator), so I would worry that they all suffer from the same problems.

    1. I too was suspicious as I’d had a couple of dropouts whilst testing but it was again at a ‘public’ event where the problems seemed to get much worse. However, there were a multitude of other BT devices running at the jam – Brian with 2 or 3 bots and at least 5 or 6 other micro pi-noon all running on BT. Additionally, the fact that I had identical probs with a 2.4ghz wireless (non BT controller) I found exceedingly suspicious. Once I’d tweaked the power board settings however, the bot ran flawlessly all day on Saturday. It’s been suggested to me that any of the DC-DC converters with a variable output may well suffer from same problems. Am currently looking at a couple of ones that came recommended that have solid 5v output – these are apparently far superior.

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