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Forum Index : EV's : Brushless electric motors

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larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 11:26am 14 Sep 2020
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I have a brushless motor taken from an old Cassette Tape Player.
It runs clockwise very well.  But, if I reverse the applied voltage, it runs anti clockwise but is erratic.  The speed varies in a cyclic manner.

I looked at a video on how to reverse these motors & it involves transposing 2 wires.  But my motor only has 2 wires.  In other words, the wires I need to transpose are not accessible unless I open the case - which I am reluctant to do in case I wreck it.
Any suggestions will be appreciated.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 3370
Posted: 04:58pm 14 Sep 2020
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If this is driving something through a pulley, can you just turn the motor around end for end?

What I mean by this is, some motors have a shaft at each end.
One end turns clockwise, the other anticlockwise.

If its directly driving something, I don't think you have any choice other than to get inside and try something desperate.
Cheers,  Tony.
 
NPHighview

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Joined: 02/09/2020
Location: United States
Posts: 13
Posted: 06:22pm 14 Sep 2020
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I don't know if you need to stick with your exact motor, but you might consider using a continuous rotation hobby servo (see https://www.pololu.com/category/143/continuous-rotation-servos), which you'd drive with a PWM output from the cmm2, Arduino, etc.  

A duty cycle below 50% makes the servo rotate in one direction (from very slow to maximum speed, depending on the actual PWM value).  A duty cycle above 50% makes the servo rotate in the other direction (again, from very slow to maximum speed).

Another advantage of the hobby servo alternative is the wide array of hardware (mounting brackets, wheels, levers, cams, etc.) already available for them, off the shelf, and also tons and tons of Thingiverse 3D printable or laser-cuttable stuff for them as well.

My son and I built a 2-lb. class battlebot ("Critter Crunch" competitions in the Midwest) using one continuous rotation servo for each of 4 wheels, driven by two SuperRooster PWM-controlled motor drivers powered by two small sealed lead-acid batteries (to provide +&- 12V).  This was extremely powerful, and we went undefeated until he got bored with it.
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 11:58pm 14 Sep 2020
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  Warpspeed said  If this is driving something through a pulley, can you just turn the motor around end for end?

What I mean by this is, some motors have a shaft at each end.
One end turns clockwise, the other anticlockwise.

If its directly driving something, I don't think you have any choice other than to get inside and try something desperate.

Thanks Tony.  However, I need to be able to reverse the motor electrically (i.e. by PIC control) when required.  So there is no point in turning the motor.

See the next reply I received.  I'll investigate his suggestions.
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 12:02am 15 Sep 2020
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  NPHighview said  I don't know if you need to stick with your exact motor, but you might consider using a continuous rotation hobby servo (see https://www.pololu.com/category/143/continuous-rotation-servos), which you'd drive with a PWM output from the cmm2, Arduino, etc.  

A duty cycle below 50% makes the servo rotate in one direction (from very slow to maximum speed, depending on the actual PWM value).  A duty cycle above 50% makes the servo rotate in the other direction (again, from very slow to maximum speed).

Another advantage of the hobby servo alternative is the wide array of hardware (mounting brackets, wheels, levers, cams, etc.) already available for them, off the shelf, and also tons and tons of Thingiverse 3D printable or laser-cuttable stuff for them as well.

My son and I built a 2-lb. class battlebot ("Critter Crunch" competitions in the Midwest) using one continuous rotation servo for each of 4 wheels, driven by two SuperRooster PWM-controlled motor drivers powered by two small sealed lead-acid batteries (to provide +&- 12V).  This was extremely powerful, and we went undefeated until he got bored with it.

Thanks NPHighview.  I'll investigate the types of motor you mentioned.  I'll do search for them in Australia.   It makes it easier now I have a starting point.  I'm not familiar with robots, etc.
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 08:04am 16 Sep 2020
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  NPHighview said  

My son and I built a 2-lb. class battlebot ("Critter Crunch" competitions in the Midwest) using one continuous rotation servo for each of 4 wheels, driven by two SuperRooster PWM-controlled motor drivers powered by two small sealed lead-acid batteries (to provide +&- 12V).  This was extremely powerful, and we went undefeated until he got bored with it.

I looked at the link you gave me but I'm confused by the description of the motor.

Quote

The FS90R continuous rotation servo converts standard RC servo position pulses into continuous rotation speed. The default rest point is 1.5 ms, but this can be adjusted by using a small screwdriver to turn the middle-point adjustment potentiometer. Pulse widths above the rest point result in counterclockwise rotation, with speed increasing as the pulse width increases; pulse widths below the rest point result in clockwise rotation, with speed increasing as the pulse width decrease.
--------------
I assume by "continuous rotation" they mean it will run continuously.  Which is presumably why your son was able to use them to drive the wheels.  But they mention a  
"default rest point is 1.5 ms, but this can be adjusted by using a small screwdriver to turn the middle-point adjustment potentiometer"
What does this mean?  i.e. why would wheels need a rest point?

Your assistance is appreciated.
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 11:27pm 20 Sep 2020
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Thanks Warpspeed & NPHighview
I decided to use a motor I extracted from an old Cassette Tape Player.  However, it would not run in reverse properly.  So I opened it and found it has an electronic speed control.  See the photo.  I was surprised that it was able to run in reverse at all given the speed control electronics.  But I don't have a circuit of it & did not waste time working it out.   So I cut the components off except for the trim pot & connected wires to the commutator tags.

So it now runs properly in both directions.

Motor EG-510AD-TA.zip.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 3370
Posted: 01:06am 21 Sep 2020
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Great effort Larny !
Cheers,  Tony.
 
NPHighview

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Joined: 02/09/2020
Location: United States
Posts: 13
Posted: 03:24am 21 Sep 2020
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larny - Sorry about not getting back to you sooner!  I didn't turn notifications on for the post (or your response) :-(

Typically these servos need to be "calibrated".  You set the PWM duty cycle to 50%, and adjust the trimpot so that the servo doesn't rotate either way.  Lower duty cycles make the servo turn in one direction / higher duty cycles make the servo turn in the other direction:

PWM Duty Cycle   Servo Speed
==============   =================
   0   (0%)      Full speed in one direction (call it "Forward")
  31 (~12%)      Three quarter speed Forward
  63  (25%)      Half speed Forward
  95 (~38%)      Quarter speed Forward
 127  (50%)      Stopped (at least, after calibration)
 159 (~62%)      Quarter speed in the other direction (call it "Reverse")
 191  (75%)      Half speed Reverse
 223 (~87%)      Three quarter speed Reverse
 255 (100%)      Full speed Reverse

Your conclusion regarding driving the wheels was correct!
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 05:04am 21 Sep 2020
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Thanks again HPHighview.
I did wonder why you did not answer the question.  I thought perhaps you were sick of my silly questions.

Your explanation above explains it very well.

So if ever I need to use one of these motors, I'll have a head start.

I hope you & yours are managing to avoid the virus.  We have been in lock down for several weeks now as Victoria had a resurgence of the virus.  But the number of cases are now thankfully decreasing.  So far, Australia has had about 27k cases & 824 deaths.  

All the best,  Len
 
Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 539
Posted: 11:09am 21 Sep 2020
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Don't even get me started on this China Flu insanity.
I am in Sydney and I am fed up  and over all stupid and worthless crap we have to go through here which would achieve nothing in stopping a diese.


I can only sympathise for what People in Vic are going through. The damage this lockdown crap must be doing on a personal and financial level will take years to really come out and those responsible will be long gone by then.

How this is allowed to happen in this country is beyond me. there are a lot of conspiracy theories and they get more creditable every day.
It's really been a complete write off of a year for everyone like no other.
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 329
Posted: 11:28am 21 Sep 2020
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I'm afraid I have to disagree.  Without the lock down, thousands of people would have died as has happened in several other countries.  For example, the US has had about 6.8 Million cases & 200k deaths so far.  Some countries have had a resurgence as they removed the restrictions too early.
It takes very little clear thinking to see the flaws in the conspiracy theories.  No government wants to destroy the economy.  They want to save lives.
 
Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 431
Posted: 09:10am 26 Sep 2020
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Interesting diversion of subject to something I had a good look into.

For some reason as soon as Mr Trump made comment about hydroxychloroquine, almost whole world made everything possible to discredit it.

To the point of probably speeding up death of people on ventilator in late stages of Covid, with toxic doses of hydroxychloroquine and no zinc, when this medicine works best in early stages of infection, with treatment recommended to start even before covid tests are back or even before covid tests are done.

Of course in sensible doses and with zinc.

Not to mention that Vitamin D3 and Vitamin C are a must to keep immune system at its best.

Similar problems had Mr Borody in Australia with Ivermectin treatment (medicine for parasites, re-purposed for this virus treatment).

Have a look at my other post:

https://www.thebackshed.com/forum/ViewTopic.php?FID=11&TID=12715

Sorry for further diversion from original topic.
George
 
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