Thursday, October 23, 2014

Robot Cart Progress -- It Drives!

First assembled prototype. Preliminary tests show that (a) it is capable of driving smoothly and (b) it doesn't draw too much current for the L298 motor driver. Spent yesterday evening hunting down flyback diodes at Sector and I even found two additional L298s, as well as a handful of extra large breadboard-compatible tactile switches (pictured left, in the background).

The Wixel code for the transmitter is done. Next up is integrating the PWM code to the receiver modules, and creating easy to use skeleton code for competition participants to come in and edit.

I still need to get additional batteries, a suitable USB camera with a good wide angle of view and OpenCV compatible drivers, and a few other parts. So far so good though.

Edit: Minor Setbacks
I bought these batteries from Adafruit and these batteries from Sparkfun. The Sparkfun batteries provide enough current to get the cart moving, but if it hits any obstacle and stalls, this triggers the overcurrent protection. Toggling the power on and off resets this protection. The Adafruit batteries can't even run the motors unloaded (wheels not in contact with the ground). They twitch, then die out (presumably, overcurrent protection). This is a shame, because I purchased them on the assumption that they would provide a maximum continuous 2C discharge rate, which they aren't, as far as I can tell. The datasheet seems to say that (bad formatting on it makes it hard to read).

In any case, Sparkfun's comment system and tendency to better document products on the page makes me feel a lot better about purchasing from them when they have the stock I want. Unfortunately neither battery will quite do for my needs, so I need to go back and rethink this.

Also, I wasn't able for whatever reason to get the wixel-pwm library by dpark83 working for me. It isn't particularly well commented which makes it difficult to use. I did find this simpler code, which works well enough for me to use instead.

Since the price for these robots is already quite high, I'm going to try and re-use some parts around Sector. Namely, a bin of old cheap lithium ion batteries without any protection circuits, and a bunch of scrapped prototypes for a battery board that has no documentation, but a ton of features (presumably). Or, in the interest of time, skip the reverse-engineering on the battery boards, and just triple check to make my circuits don't look too explode-y, and go protection-less. So far I haven't made any really serious mistakes with my wiring prototypes...

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