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Picaxe based robot driver


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Jtepper



Joined: 04 May 2009
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Picaxe based robot driver

After deciding to run our bot on 45v, to get the most out of our brushless weapon motor. We descovered that there is no motor driver, to drive the drive wheels, readily availiable to run on this voltage, so we made our own. Each motor is driven independantly by a 08M chip, each providing a pwm signal. The mosfets that we are using provide theoretical maximum outputs of 300A at 55v. Allthough the pcb tracks will most probably burn out before this current is reached, however it has been tested at 50v. Mostly made this post just to brag/ seek comments or questions

Post Tue Dec 22, 2009 10:42 pm 
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dyrodium
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Post a video of it working Razz then it counts. Laughing Sounds good though, nice work!
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Post Tue Dec 22, 2009 11:18 pm 
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Fish_in_a_Barrel



Joined: 30 Sep 2006
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http://www.robowars.org/wikka/EscHomeMade

especially: http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.html Razz

and there are many online calculators to determine the maximum heat rise for copper tracks.

For the fets you will either need to scope them to see the switching time/waveform or use the driver datasheet, which will determine switching losses. Then take the worst possible case and determine you heat sinking ability to give you how much current can flow before your fets go *pop*.

Also http://www.mcmanis.com/chuck/robotics/projects/esc2/hbridge_spiking.html may be worth a read since you are awfully close to the voltage limit of the fets.

Keep up the good work tho Smile
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Post Wed Dec 23, 2009 2:33 am 
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Knightrous
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No pictures, no schematics or PCB layouts?
Lol, what is this, one of those zero field free energy scams Laughing
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Post Wed Dec 23, 2009 4:00 am 
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Nick
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There are very few small motors that run @ 45V for wheel drive - what were you planning to use? Its usually easier to use a separate 3 or 4 cell Lipo pack and use regular 550 size motors. You could get away with a Scorpion XXL and drill motors or Banebots P60 gearboxes.

Post Wed Dec 23, 2009 7:10 am 
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Knightrous
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Looking at JTepper's build thread, in this photo it looks like some sort of wiper motor or electric window motor.

These picaxe controllers full h-bridge or relay reverse?
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Post Wed Dec 23, 2009 1:00 pm 
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NMO
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It couldn't be a full H bridge as the 08M only has 1 PWM output pin.

Post Wed Dec 23, 2009 6:10 pm 
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Valen
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with a large enough driver chip one PWM out is enough to drive a H bridge
otherwise a logic and gate is all you need if you are rolling your own drivers.
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Post Wed Dec 23, 2009 8:18 pm 
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seanet1310



Joined: 08 Nov 2006
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quote:
Originally posted by Knightrous:
Looking at JTepper's build thread, in this photo it looks like some sort of wiper motor or electric window motor.

These picaxe controllers full h-bridge or relay reverse?


could they be the bosh wormdrive mentioned on Fri Jul 24?
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Post Wed Dec 23, 2009 10:27 pm 
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Jtepper



Joined: 04 May 2009
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Yep they are the bosh worm drives, and they are 24v so they should overvolt pretty good to 50v, as they are very quiet and efficient at 24. Havnt got a scematic on the comp, did it by hand, but i will post some photos soon.

Yes using relay reverse in this version, but one of the relays has done somthing weird in testing today, (you can hear the relay switching but it doesnt connect the pins), so it might be time to try a h bridge version. Allthough i am just using gay 30A dpdt relays from jaycar (like $20 each too eeeekkkk). Does one know of some good relays i can replace them with?

Im using dual IRF1405N mosfets to drive each motor if anyone is interested. As for the overheating of the fets, im testing the controller in a chassis with 18v drill motors overvolted to 30v, and the fets are cold to the touch after 20mins of hard driving, with no heatsink currently installed, so i dont think overheating is an issue.

BTW i now see why so many ppl use gyros =)

Post Wed Dec 23, 2009 11:01 pm 
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Jtepper



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http://www.robowars.org/forum/album_pic.php?pic_id=1515
pcb overlay if anyone is interested

Post Wed Dec 23, 2009 11:08 pm 
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Fish_in_a_Barrel



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for the relays try either "anti-parallel" diodes or capacitors to eliminate excess arcing which tends to be the cause of death for most relays.
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Post Wed Dec 23, 2009 11:59 pm 
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Jtepper



Joined: 04 May 2009
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allready have antiparralel diodes on the relay coil and across the motors. Arcing shouldnt be a problem as there is actually no current flowing when the relays switch, i might reprogram the picaxes so that there is a longer moment of no current flow so the relay has time to switch. But i may have just got a dud relay, since i just spent the last 15mins slamming between full forward and full reverse in my test rig, with no apparent damage to the pcb or relays. Allso i soldered to the relays really badly and they got really hot, which is probably not great for them. Ill just replace the relay and do some more testing now i think.

Post Thu Dec 24, 2009 12:12 am 
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shreddy



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how big will the controller be once its finished?
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Post Thu Dec 24, 2009 11:58 am 
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