Postby spierce » Mon Apr 10, 2017 9:23 pm
Hi ScienceClass,
I apologize for the issues you're having with your new mePed. It's definitely entering a brown-out state where the voltage to the Arduino is dropping below its minimum voltage threshold, causing the Arduino to reset itself over and over. That's why the mePed is twitching over and over again. When the Arduino starts up, it commands all of the servos to move to their 90° or center position but once all of the servos start to move, they are drawing enough power to drop the supply voltage low enough to cause the brown-out.
A couple things I'd encourage you to try is to loosen all of the leg screws that are part of the pivot joints of the legs. If these screws and nuts are too tight and don't allow the legs to pivot and move freely, this will cause the servos to use extra amperage and cause the voltage to sink much more than in normal operation. These screw/nut combinations are item numbers 11 & 13 in step 4 of the assembly manual, 11 & 13 in step 8, and items 2 & 4 on step 15. You can loosen them quite a bit at first to make sure there is enough play and free movement to not over stress the servos. After you have verified whether this has fixed the issue, you can tighten these screws up a little bit to remove any excess play or slop in the legs.
The other thing I'd suggest doing if loosening the screws didn't help is to unplug all but one of the servos and then test the mePed. If the mePed functions properly, plug a second servo in and then re-test. Continue until all servos have been plugged back in. If you reach one servo that is causing the brown-out, unplug that one and continue plugging the rest of the servos in one at a time. It's rare for a servo to be bad (one or two out of a thousand) but it does still happen from time to time. If you are able to narrow it down to a bad servo, we'll replace it for you.
As for the commands repeating when pressing different buttons, fluorescent lights and direct sun light emit a lot of Infrared light and can cause interference. If the mePed sees IR signals coming in but can't clearly understand the command being sent, it will repeat the last good command that it understood. It's also helpful to point the IR Remote down at the IR Sensor to give it the best chance of understanding the commands you are sending.
A LiPo battery probably wouldn't be the best thing to hook up. Since we're bypassing the Arduino voltage regulator and powering the chip directly through one diode, our voltage threshold is pretty narrow. We did this to prevent having to use two power supplies on the mePed. The servos are good for 4.8-6.0VDC whereas the Arduino is good for about 4.5-5.5VDC. The diode drops the voltage from the battery pack from about 6VDC down to about 5.3VDC. If you used a 2 cell LiPo, the beginning voltage would be up to 8.4VDC and going through the diode would only drop it to about 7.7VDC. This would almost certainly fry the Arduino. Also, as mention earlier, the Servos are good for a max of 6VDC. Using a LiPo would put a full 8.4VDC to the Servos, damaging them as well. Using a single cell LiPo would only render about 4.2VDC which is below the operating threshold of both the Arduino and the Servos.
Please let me know if you are still having issues. We have literally hundreds of these little guys running around and after we removed one of the diodes from the circuit board back in October of last year, virtually all of our brown-out issues have stopped. This is what leads me to believe that it's either a bad servo drawing too many amps or the screws are too tight on your leg joints causing a high amp draw.
I hope this helps.
Thanks,
Scott Pierce
