Got my motors running - at last!
Clemens
Posts: 236
Good (CET-) afternoon,
After trying to build my own shaft-encoders (http://www.geology.smu.edu/~dpa-www/robo/Encoder/pitt_html/encoders.html) for motors I found in broken DAT-backup devices without much success, I decided to take a shortcut and buy these:
http://www.shop.robotikhardware.de/shop/catalog/product_info.php?cPath=70&products_id=164
Not exactly cheap, but reading the encoders with "Quadrature_Encoder.spin" from the prop-tool-library works perfectly reliable (as far as I can tell by now).
I use the L293D to drive the motors:
So far, so good. - Here are my questions:
1.) When I turn the motor by hand with all current shut down, the green LED in the upper right corner lights up...·Is that acceptable or do·I have to put a diode between Vc and the L283D. If so, which diode would be appropriate?
I bought some "ZENER DIODES 1,3 WATT 36 V" (http://www.conrad.de/goto.php?artikel=180947). When I use them, the LED will light no more but they also lower the current so the motors don't operate at full speed. :-(
2.) When I start a programm that turns the motor in one direction and then rapidly changes direction the prop resets. Putting in the diode as described in 1.) doesn't change this behaviour. I can of course avoid such rapid changes by software, but I was wondering if there is an electronic measure I can take to make it failsafe. How is it done in those self-balancing robots like mydancebot, where motordirection has to change very fast?
3.) If I understand deSilva's post about Ohm's Law·correctly, (http://forums.parallax.com/showthread.php?p=687128) I should be ok powering my protoboard with 8 Rechargables (1.2V * 8 = 9.6V) or even with 12V coming from 8 Batteries, as long as the load is only my LCD-Display, an IR LED and the input pins of the L293d. Is this true?
I know that this is basic electronic knowledge, sorry to post these questions that have in variations all been asked before, but I want to avoid destroying my hardware and want to get my setup straight before soldering it·to a protoboard.
Thanks for any advice.
Clemens
Post Edited (Clemens) : 3/9/2008 2:54:23 PM GMT
After trying to build my own shaft-encoders (http://www.geology.smu.edu/~dpa-www/robo/Encoder/pitt_html/encoders.html) for motors I found in broken DAT-backup devices without much success, I decided to take a shortcut and buy these:
http://www.shop.robotikhardware.de/shop/catalog/product_info.php?cPath=70&products_id=164
Not exactly cheap, but reading the encoders with "Quadrature_Encoder.spin" from the prop-tool-library works perfectly reliable (as far as I can tell by now).
I use the L293D to drive the motors:
So far, so good. - Here are my questions:
1.) When I turn the motor by hand with all current shut down, the green LED in the upper right corner lights up...·Is that acceptable or do·I have to put a diode between Vc and the L283D. If so, which diode would be appropriate?
I bought some "ZENER DIODES 1,3 WATT 36 V" (http://www.conrad.de/goto.php?artikel=180947). When I use them, the LED will light no more but they also lower the current so the motors don't operate at full speed. :-(
2.) When I start a programm that turns the motor in one direction and then rapidly changes direction the prop resets. Putting in the diode as described in 1.) doesn't change this behaviour. I can of course avoid such rapid changes by software, but I was wondering if there is an electronic measure I can take to make it failsafe. How is it done in those self-balancing robots like mydancebot, where motordirection has to change very fast?
3.) If I understand deSilva's post about Ohm's Law·correctly, (http://forums.parallax.com/showthread.php?p=687128) I should be ok powering my protoboard with 8 Rechargables (1.2V * 8 = 9.6V) or even with 12V coming from 8 Batteries, as long as the load is only my LCD-Display, an IR LED and the input pins of the L293d. Is this true?
I know that this is basic electronic knowledge, sorry to post these questions that have in variations all been asked before, but I want to avoid destroying my hardware and want to get my setup straight before soldering it·to a protoboard.
Thanks for any advice.
Clemens
Post Edited (Clemens) : 3/9/2008 2:54:23 PM GMT
Comments
There is no electronic measure to make it failsafe, except to use a fairly hefty battery. The reason it is resetting is because it takes a fairly large amount of current to reverse the motor at full speed because of the rotational inertia it has to overcome from the weight of the gears, armature, and the gearbox that the motors appear to have. It draws so much current doing that, that the voltage sags below the 2.7v reset threshold of the brownout detector and the propeller resets. It is also probably not very good for the h-bridge chip either.
Hope I could help
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I am 1010, so be surprised!
I am not sure what happens in the upper right corner of your breadboartd!?
- You have an additional regulator on the PropStick...
- The L283 gets its power from where? 9,6 V pack?
- The "green LED" is directly connected to the 9,6 V?
(1) Turning the motor makes it a generator, the current will run up the L283 and into the 9,6 V rail...
A diode will avoid this... Schottky diodes have a quite low forward voltage 1N5818 is for 1A
(2) The reset is unexpected.. But I still wonder how you supply the stick....Adding a 1,000µF cap at the 3.3 V rail should help.
(3) What you say adds up to 60 mA.. But I think the bg lighting of the DOGM is someting that will add the same again! A standard regulator will work just with that (<1W) , but using a switching regulatator from 12 V would be perfect: The MC34063 is the most popular
www.nomad.ee/micros/mc34063a/index.shtml
A found another fabulous part at pollin.de the other day: LM2825N-3.3 which works without any additional parts...
Post Edited (deSilva) : 3/9/2008 4:54:51 PM GMT
I'm powering the L283D from 7.2V (6 Rechargables) right now because I did not dare to use the 9.6V pack. Yes, the green LED is between the power source and ground with a resistor.
I will get the diode and then I can start soldering and finish my first "real" project.
@tpw_man: Thanks for the reply, however the caps did the job (see above). I hope you're enjoying yourself among us old men... Good to see that a talented youngster is decreasing the average age here!