Marty - The ball follower

Hi folks,

Yesterday, I tried to get Marty "Ball Follower" running. I followed the exact steps from:

Everything went fine at the beginning. Pi is running, Camera Image is there and even recognizes a white ball. The calibration also ran flawlessly, every motor could be controlled. Once i started running the python code under the point "Bringing it all together" in the article, Marty's servos went into strong jittering and they all moved in a specific ( in my case, the hips backwards, the knees both left) direction the whole time. I have now the problem, that my Raspberry Pi 3 B wont send commands out via its serial pins, the rick board won't load the battery ( no charging and no blue light). So i now have two defective Parts lying around.

Does anyone know, what my problem was? I just want to get the ball follower running. I tried the same thing with another Pi, another Image and another Marty. Same thing happened.

Second Question:

Can i use those batteries and charge it with the built in charger?

Thanks in advance Kind Regards AV


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4 Responses


Thank you for your help. With another battery and rick board everything goes fine now. Can you please let me know if you find any damaged hardware on the board / charging circuit? would be interesting.

11:52:38, 15th March 2018   |   Permalink   |   View Source
sandy STAFF

Hi all,

Sorry to hear about the issues. The behaviour sounds a bit like a power brown out, which can happen when a current spike (e.g. due to large motor loading) causes the battery voltage to drop below the level where the low voltage cutoff circuitry kicks in. The motors then turn off, battery voltage comes back up, and things can turn on again. The motors jerk slightly on power on, and if the battery voltage is a bit low, that can pull the voltage back to below where the low voltage protection circuit cuts things off again. The result is that Marty jitters as the servos continually get and lose power. This can usually be fixed by just charging, but it sounds like that isn't working for you.

The low voltage protection circuitry is needed as LiPo batteries can be damaged if you let them get too discharged. We're addressing the jittering problem for the future, and in the mean time we do try to have a soft cutoff (and a low voltage alarm) when the battery gets to a point where it might find that behaviour. Running from the pi, you are more likely to experience it as more power is being drawn from the battery - however, we've never had a situation where it's caused any damage to the control board or the Pi. It sounds a bit like the charger on your Rick has broken, and of course we'll get you a replacement out ASAP. Can I ask if it was plugged in to charge when it happened?

As for using other batteries - in the office we do sometimes use those 2000mAh hobbyking batteries, although I'm not allowed to recommend anybody else to do the same, as Marty's standard batteries have features like short circuit protection that you won't get with those batteries, and they haven't been tested with the charging circuit on Marty. In theory the charge management chip we use can charge most 2 cell lithium batteries, but you'd want to make sure you were also balance charging every so often.


19:06:35, 14th March 2018  *   |   Permalink   |   View Source

Hmm, i had the same jitter problem with and without charge.

regarding the batteries: i found the post and this was a 1500mah, exact same model as the one, which i posted, except other capacity.

07:00:46, 14th March 2018   |   Permalink   |   View Source

not sure if this will help, I have just managed to get the ball following working. I have had the jittery marty problem and putting it on charge has fixed it. I do not know about the 2000maH batteries but I have seen a link to some 1400maH batteries from hobby king that have been used elsewhere on the forum.

Sorry but I cant remember what topic the post is under.

20:38:32, 13th March 2018   |   Permalink   |   View Source