#robotics Logs

Apr 18 2013

05:00 Triffid_Hunter Jak_o_Shadows: brake and coast modes
05:01 Triffid_Hunter Jak_o_Shadows: there are many different ways to drive a motor, and a few of them require the ability to turn off both high and low side mosfets
05:02 Triffid_Hunter Jak_o_Shadows: also, if a high-side mosfet stays on for too long, the bootstrap capacitor runs low, so for things like braking it's preferable to use the low side mosfets which don't have that issue
05:03 Jak_o_Shadows so assuming that i'm running short a few pins on my chosen uC, i can easily just tie them to +12 V ?
05:04 Triffid_Hunter yep, then you lose ability to coast
05:04 Triffid_Hunter you'll have drag brake instead, and you need to pulse the other line every so often to keep the bootstrap cap topped up
05:05 Triffid_Hunter either that or hold one line low and PWM the other one, then switch when you change direction.. yeah that'll work
05:05 Triffid_Hunter my ESC is designed for maximum flexibility, that's why I have all the lines hooked up plus voltage monitoring everywhere, current sense and a signal filter on the servo input
05:05 Triffid_Hunter heh not just current sense but a hard overcurrent limit too
05:06 Triffid_Hunter most people don't realise that the atmega328 and higher have an analog comparator as well as the ADC
05:06 Jak_o_Shadows Oh well. I'll probably just end up doing that. I need 2 motor drivers, one servo/stepper, 3 ultrasonic sensors and 2 (possibly joined to 1) digital bump sensors
05:07 Triffid_Hunter servo is easier to drive than stepper, just need a timer output
05:08 Triffid_Hunter could even run from an interrupt if you've used all your timers
05:08 Jak_o_Shadows yes, probably a good idea
05:09 Triffid_Hunter you can trivially drive many servos from one timer actually
05:09 Triffid_Hunter just hook a 4017 to the timer output and switch the timeout for the next one in the compare interrupt
05:09 Jak_o_Shadows 4017 = switch register?
05:09 Triffid_Hunter nope it's a decade counter
05:09 Jak_o_Shadows wait, wrong termionology
05:12 Jak_o_Shadows Just checking, but a decade counter lets me multiplex outputs, while a shift register would let me multiplex inputs?
05:13 Triffid_Hunter no a decade counter just counts. the 4017 has 10 outputs, and sets the next one in sequence high when you pulse the input
05:13 Triffid_Hunter shift registers let you move data from serial to parallel and vice versa
05:13 Triffid_Hunter pro tip: hook your shift regs to the hardware SPI for extra speed :)
05:39 Jak_o_Shadows I think i want one PISO shift register.
05:40 Jak_o_Shadows to read the position of the steering motor
06:14 Triffid_Hunter Jak_o_Shadows: what, you're doing a soft-servo? why?
06:19 Jak_o_Shadows Because the steering linkage is already assembled. (I didn't build it, scavenged it)
06:19 Jak_o_Shadows I may be able to convert it to a servo, dunno
06:25 Triffid_Hunter Jak_o_Shadows: ah you're redoing an existing R/C? I did that for my first bot
06:26 Jak_o_Shadows Steering from an existing RC, motor from a drill.
06:26 Jak_o_Shadows Unwisely, I binned the control circuitry years ago
06:26 Triffid_Hunter trust me, chuck out the steering thing, put in a proper hobby servo. they use shit motors and shit gears and hope like hell that the servo saver gets it through the warranty period
06:26 Triffid_Hunter I binned the electronics from mine, they were shit anyway.. had gorram BJTs to drive the motor!
06:26 Triffid_Hunter and a 5w resistor to reduce reverse speed :/
06:27 Jak_o_Shadows Yeah, likewise with the BJT
06:27 Jak_o_Shadows 's
06:27 Jak_o_Shadows A servo would be simpler, especially with interfacing
06:31 Triffid_Hunter Jak_o_Shadows: MG996R is a really nice servo in the $10-15 pricerange fwiw
06:31 Triffid_Hunter wouldn't trust anything expensive to one but they sure are strong and I'm yet to break one.. I think Rifraf melted the mosfets on one from having it stalled too long
06:32 Triffid_Hunter and at that price there's no qualms hacking it up to fit
08:55 ocei3ko Any problems with putting an arduino through airport xray? would it get damaged?
09:03 ocei3ko_ Any answer? Got DCed
09:03 dunz0r ocei3ko_: I can't imagine it would.
09:04 ocei3ko_ Why not?
09:05 dunz0r ocei3ko_: Why would it? Xrays doesn't do damage to other electronics.
09:07 ocei3ko_ heh
09:14 rue_house if an arduino were run thru an airport xray machine it would probably blow up.
09:15 rue_house and you would be billed by the bomb squad that did it
09:15 dunz0r I like rue_houses answer better.
09:21 theBear laptops and vintage analogue electronic instruments don't mind airport xrays.. the people that watch the xrays tend to get a bit grumpy tho
09:22 ocei3ko_ Well I'm having a breadboard and arduino brought to me from another country. Assuming I dont have them bring wires too the xray shouldnt look too bad :P
09:23 rue_house stuff in packages goes all over the place all the time
09:23 rue_house the only problem occurs if the courier sits on the package during transport
09:23 theBear mm packages are ok, i was thinking the walkthru security checks
09:23 rue_house or dropkicks it
09:24 theBear i had a few minor problems over the years... coulda been much worse if i wasn't good at making friends with those kinda people
09:24 dunz0r My STM32VLDiscovery managed to survive the airport X-rays, so I think that ocei3ko_s Arduino will too.
09:24 rue_house ups often uses the dropkick method to get packages into the van
09:24 theBear heh
09:43 ocei3ko_ tom's site is down :/
09:47 ocei3ko_ hows this for a wall wart? http://www.watterott.com/en/Power-Supply-3-12V-1A