Inexpensive DC brushless Motor Controller
Steve Joblin
Posts: 784
I've been searching for a cost effective brushless DC motor controller that can control a 24V 250W motor via PWM... The only ones I have found seem to be hundreds of dollars... does anyone know where I can find an inexpensive one, or does it make more sense to make it myself?
Comments
www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1523
The reason for the high prices is that they are complex and difficult to design, and the market is quite small.
Leon
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Amateur radio callsign: G1HSM
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Post Edited (Leon) : 7/1/2008 5:08:42 PM GMT
These units convert DC into 3 phase AC to power the brushless motor. You can use a PIC or an SX to create the 3 phase AC and then drive FETs to actally power the units.
The real dilemma for DIY is that you must either accept a larger board or design your own for minature applications, such as R/C airplanes.
Most of the expensive controllers do more than merely power the motor. They provide a low battery warning back to the person flying the plane so that it can be safely landed. And they also provide current limiting choices to protect the rather expensive battery packs from excessive discharge. Usually they have the ability to reconfigure to a variety of battery packs and motor sizes. It would take a bit of research if you want to include all that.
Since you are a radio amateur, you may have the knowhow and motivation to get all that engineering and programing done. The SX48 is a good chip to use as has two 16bit timers, higher speed than the PICs, and quite a bit more programing space. Guenther mentions how to synthesize a sine wave in his SXasm text. The same sine wave can be sampled at three different points to produce the 3 phases. I believe that the power output has to be a 'half H-bridge' to actually swing negative as well as positive. You will need three 'half H-bridge' modules.
If really don't want to build, I suggest you find a second hand controller from someone that wants to upgrade to something more powerful. Try you local R/C clubs.
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Post Edited (Kramer) : 7/2/2008 9:40:20 AM GMT
Have you looked at any of the brushless speed controlers for model airplanes?? Here is a $250.00 +300 Watt speed controler and motor combo. http://www3.towerhobbies.com/cgi-bin/WTI0001P?&I=LG5164&P=1.
Here is a $40.00 250 Watt brushless speed controller. http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXKSY4&P=ML.
Here is a $50.00 350 Watt. http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXKSY5&P=ML.
Go to www.towerhobbies.com and search "Brushless speed" or "Brushless controller".
I understand these controllers are standard servo pulse driven and not PWM like you had askes for.
I hope this helps.
SJW
Ron
Secondly, reversing a brushless DC motor and or modulating its speed are not usually considered because of the nature of the motor. There are brushless DC motors for CD player that include Hall effect sensors to retain one accurate speed, but I doubt that variable speed is realistic.
I really love the R/C Brushless electric airplane technology. They even have helicopters. But at the end of the day, one needs to invest quite a bit to be able to fly regularly. And if you don't have good weather where you live, you need larger planes and hefty power to overcome headwinds.
If one wants reversing motors, generally full H-bridges and conventional brushed DC motors are the way to go. And it is best to have a built-in gear box to reduce speed. Electric motors run smoothly at thousands of RPMs, while robot wheels are best at tens of RPMs.
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PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
Ron
I have an electric R/C plane, but it really requires have several sets of batteries to have a nice outing. Since each battery pack cost about $40, the 'fuel costs' are quite an initial investment.
It seems to me that brushless motors would be ideal for submersible ROVs because they could actually be submersed in water rather than having to isolated them in a housing. Generally a housing has to be pressurized to prevent water from seeping in around the turning shaft and shaft seals are both expensive and quite difficult to build for small diameter shafts.
One might pot the windings in epoxy to assure the insulation doesn't break down, especially in salt water. And I suppose that the immersion would provide sufficient cooling even though the coils are covered with epoxy.
Has anyone seen this done?
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PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
Post Edited (Kramer) : 7/4/2008 8:49:07 AM GMT
Ron