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Old Oct 11, 2004, 09:20 PM
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Diy brushless esc

Hi,
I'm relatively new to rc, but i have an interest in electronics and am trying to build a brushless esc. I'm wondering if it would be possible to create a 1 speed sensored controller and then attaching a regular esc to the imput wires so that it would regulate the voltage, therefore regulating the speed. Any ideas?
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Old Oct 12, 2004, 08:53 AM
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a brushless controller regulates the speed of the brushless motor by controlling WHEN to turn on a particular set of coils, and when to turn it off.
regulating the voltage does not regulate the speed on a brushless motor.
it IS possible to use the controller board from, say a CDROM or floppy drive motor as a single-speed controller, but it is bigger and heavier than a standard brushless speed controller.
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Old Oct 12, 2004, 09:33 AM
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thanks for clearing that up,
im thinking of making a basic 1 speed controller using hal effect sensors and some transistors; so that the hal sensors dictate which transistors turn on, which dictates which set of coils is on. Do you know of any existing circuit diagrams for this purpose?
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Old Oct 12, 2004, 11:54 AM
"Simplify, then add lightness"
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When you use hall sensors to control a motor, you are just replacing the mechanical commutation on a brushed motor with more efficient electronic commutation, so changing the voltage to the motor will change the speed just like on a brushed motor. Here is a page that tells what you should need to design a sensored controller. http://www.allegromicro.com/techpub2/hurst/bldcmot.pdf
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Old Oct 12, 2004, 01:00 PM
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Thanks for the link. This should help me with my design. However, I'm on vacation right now, so I can't start building it right away. When I get back, I'll draw up some diagrams and make a trip to radio shack.
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Old Oct 31, 2004, 02:42 PM
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Heres my design so far. Please let me know if you have any comments or suggestions.
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Old Oct 31, 2004, 02:48 PM
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I know that my diagram's messy, but bear with me, I'm not that great at art
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Old Oct 31, 2004, 03:45 PM
Official Old Git!
Hampshire, UK
Joined Sep 2000
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Slowflyer90,

Sorry, I'm not sure what you are trying to achieve?

Problems like :-

a) where is the speed control input, in order to vary the motor speed?
b) Transistor aren't generally used - the suffer from too high an 'on' resistance - hence the reason for fets being used.
c) diodes generally take too high a voltage before the turn on, again a wasted voltage drop.
d) (haven't looked at the logic states etc)

Cheers,
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Old Nov 01, 2004, 04:25 PM
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Norman
First, this circuit is designed to be attached to a brushed speed controller to use it to sontrol the voltage. I'm not very clear on how fets work, so I didn't include them this time. I'll do some research and see if I can include them in the next diagram. As for the diodes, they are necessary for this circuit layout, but can be eliminated if I redo logic gates. I hadn't thought about voltage required to turn them on. I'll try to have a new circuit diagram drawn up soon.

By the way, I have ordered a motor from www.gobrushless.com and will post updates on how that turns out.

Thanks for the comments
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Old Nov 02, 2004, 08:34 PM
PDK
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Hi slowflyer90,

I had a similar thought a while ago. My plan was to use a servo drive output (the PWM signal that goes to the servo motor) like here ,for the PWM signal to the fets.

If you have not done so already download the An857 aplication note from microchip (An857) to get a better understanding of what is required. Look especially a the (I think pg 2) 'Sensor versus drive timing'. The coils are energised for 120 degrees then off for 60 then reversed for another120 and off again.

Have a look at my attempt. I have not done more than this as I have been to busy but it may work. Ic3d is the low voltage cutoff, Ic1 A, B, C are the P-fets while the Ic2 A, B, C are the corresponding N-fets. Also the PWM signal is on the Ic2.

The fets / transistors on your design will not work. The high side has to be p channel. N channel can only be used with a voltage boost system of some sort (ie. a driver).

Also I believe that the hall sensors on CD rom motors are linear devices not logic items.

Hope this is of some help,

Best regards
Phil
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Old Nov 05, 2004, 08:25 PM
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I have read the application note and see your point. However, would it be possible to use only P-fets and to use only positive voltages for the imputs?
I'm planning on posting another diagram when I have the time.
By the way, my motor from gobrushless came. I have wound phases 1 and 2 and am planning on winding phase 3 tonight.
I'll post pictures when I'm done.
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Old Nov 06, 2004, 07:15 PM
PDK
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Hi,

I am far from being an expert, but I don't see why not. The only limit is that p-fets are more expensive and usually have a higher on resistance than the n-fets so if they can be avoided do it!

I just thought I should point out that the high side fet (p) input will need to be switched from the the battery input voltage by a transistor or other fet like is shown by Kreature and Quax in the BLCD controller thread. I dont know exactly which page it is on but worth a look through them anyway.

Phil
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Old Nov 07, 2004, 09:20 PM
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Hi,
Thanks for the advise on the fets; I was unaware that the Pfets cost more. Saving money is always nice $-). I'll try and find the thread and check it out.

About the motor:
I finished winding it (22 turns) and it is now assembled on my kitchen table. I'll wire it with the wye connection, since it gives more torque and takes less amps. The motor will be mounted to the plane with a long brass tube attached to the back of the stator. I'm planning on cutting out a plywood disk that will fit around the brass tube to glue the Hall sensors onto.
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Old Nov 08, 2004, 08:48 PM
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Heres a pic of my motor:
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Old Nov 08, 2004, 08:49 PM
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The pics not great, but camera battery died, so its all I've got for the moment.
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