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Old Dec 07, 2003, 07:18 AM
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QLD, Australia
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Mike ,
I think we may need to look at this at the moment untill a lighter controller is developed at least it will get these small motors in the air without a great weight penalty.
Stewart
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Old Dec 07, 2003, 08:30 AM
It's a spiderweb of knit lines
Souderton Pa. USA
Joined Mar 2002
2,645 Posts
Stewart
I think you are right, this method does look like it will work. I will test the 6mm to see if it will trigger the Halls.
All the sensor motor controllers I have worked with always had a chip for some logic funtions but I'm not sure what they did or why, or even if we need them for our purpose. I don't think starting will be a problem. Step sequence maybe the reason for the chip, I'll have to sit down with it and go through each commutation of a rotation.
Mike
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Old Dec 07, 2003, 10:43 AM
"Simplify, then add lightness"
Raleigh,NC
Joined Nov 2000
2,701 Posts
Stewart,
The circuit you show should work, but it is only a half wave driver. It can only drive current thru the coil in one direction, so will deliver a lot less power to the motor. The normal brushless controller will have 2 mosfets per phase, one to pull high, and one to pull low. Using only one mosfet per phase would save weight, but you would probably loose more performance due to the power loss than you would gain with the weight loss. The new Phoenix 10 supposedly weighs only 2 grams. If you build a controller that weighs 1 gram, but you loose 2 grams of thrust, you haven't gained anything.

Jeff

PS The circuit you show is what is inside many of the small cheap brushless fans used in PC's.
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Old Dec 07, 2003, 11:08 AM
"Simplify, then add lightness"
Raleigh,NC
Joined Nov 2000
2,701 Posts
Mike,
To remove surface mount parts from a board, the easy way is with a heat gun. If you just want to remove one IC, then you can thread a fine enameled wire between the body and the pins on one side of the IC, then starting at one end, heat one pin at a time with a soldering iron, and pull on the wire so it slides under the pin and lifts it slightly.

Jeff
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Old Dec 07, 2003, 01:04 PM
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United States, VA, Clintwood
Joined Nov 2002
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Jeff
Thanks for the desoldering tip and info.
Mike
I use a plunger type solder sucker from Radio Shack.
I have removed chip sockets from video cards just by sliding a hobby knife in between the legs and board. There is usualy only enough solder on them that they pop right off. The method Jeff mentioned should work great as well. You can practice with old mother boards with the solder sucker try removing a 486 chip socket it will build up the muscles needed to use the solder sucker
for long periods of time. You might develop carpel tunnel from such activities though. When I was a kid I used to torch the back of electronic boards and most of the parts wold fall off. Some of them would end up burnt and the board would sometimes catch on fire. Maybe a torch with a big brass tip might be able to heat up the back side of the board so that parts will fall off but the heat may ruin the parts. Now I only use a 12watt iron and swipe some flux on the solder before removing it.

Billy
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Old Dec 07, 2003, 02:37 PM
It's a spiderweb of knit lines
Souderton Pa. USA
Joined Mar 2002
2,645 Posts
Thanks for the tips guys.
I made the board for the 5144 chip yesterday and will be soldering it soon. I'll let you know how it works.
Mike
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Old Dec 07, 2003, 04:40 PM
"Simplify, then add lightness"
Raleigh,NC
Joined Nov 2000
2,701 Posts
I also used a torch to remove components when I was young. Not a good idea, and I probably burned out a few brain cells doing it as I am sure burning epoxy fumes are toxic.

A solder sucker works great on thru hole parts, but will do nothing for surface mounted parts. If you are going to do it a lot, a cheap heat gun a good investment. With it you can strip a board of SMT components in a minute or two. Most of the small parts are so cheap it wouldn't be worth the trouble, but shipping and minimum order quantities make it so much more convenient just to strip them off old boards.

The heat gun also does a great job of shrinking heat shrink tubing.

Jeff
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Old Dec 07, 2003, 07:00 PM
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QLD, Australia
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Jeff,
wouldnt it be posiable to use 6 hall sensors and a fet bridge similar to a comercial controler to get the full phase drive ?
the hall sensors arent very big and neither are the fets to handle the current we need
Stewart
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Old Dec 07, 2003, 07:55 PM
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United States, CO, Longmont
Joined Jul 2001
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Why don't you guys just hack an existing brushless ESC and keep the micro but add smaller fets w/o drivers?

Q
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Old Dec 07, 2003, 08:31 PM
"Simplify, then add lightness"
Raleigh,NC
Joined Nov 2000
2,701 Posts
Stewart,
That would be possible, but getting even 3 hall devices aligned properly would be tough on these very small motors, 6 would be nearly impossible. With the mosfets driven directly from the hall devices, you have to control not only when the hall device is activated, but also how long it is activated, and the only control you have for a given hall device, is varying where it is positioned. Better to use some kind of controller, and sensorless is probably better. On a large diameter motor, it is easy to position the sensors. On a 6mm motor, if the sensor is off by 1mm the timing will be off by 10 degrees, even on a 2 pole motor. With more poles, it would be even worse.

Jeff
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Old Dec 11, 2003, 07:10 AM
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QLD, Australia
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I found a chip that maybe ok , its the Allegro A8904SLB, 1.4 Amp output 24 pin chip ,have a look and see what you guys think .
Stewart
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Old Dec 11, 2003, 09:25 AM
"Simplify, then add lightness"
Raleigh,NC
Joined Nov 2000
2,701 Posts
Stewart,
Again, the main problem with this chip is availability. None of the distributors listed on the allegro site stock this chip, and you would have to buy a quantity of them. Arrow has a budgetary price of $9.36 for 100-999 pieces.

Some other minor problems are that it needs a 5v supply, so would not work on a single lipoly without a booster, and would need a regulator for 2 lipoly. Since it is programmed thru a serial connection, you would need a microprocessor to interface it to the receiver. It also uses linear current control instead of PWM to control speed so some loss in efficiency.

It should work OK if you can get them.

Jeff
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Old Dec 11, 2003, 09:54 AM
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sw missouri
Joined Sep 2001
393 Posts
Small Brushless Experiment

Several years ago I did some experiments with parts I had laying around. Here was the result. I used a magnetic actuator coil and the magnet out of the actuator as it had a hole through it. This would swing a U-80 prop very nicely but not anywhere near enough power to fly an airplane. The coil was 100 ohms in resistance and I was using 4.8 volts, so the power was low.

The hall effect device I used had 2 outputs. One output went active when it saw a N pole and the other when it saw a S pole. This was used to drive the 4 transitor H bridge.

I could change the location of the HE device and that throttled the motor nicely.
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Last edited by bselman; Dec 11, 2003 at 09:57 AM.
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Old Dec 11, 2003, 09:57 AM
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Old Dec 11, 2003, 10:00 AM
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