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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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I want to use a hobby BLDC motor to power a compact high speed
spindle to be used for engraving and the like. Mainly because they are so compact for the power and speed. I cannot find, for a price I can justify, a 24,000 to 40,000 RPM spindle that will fit in the space I want to put it. Looking at some hobby BLDC motors and then buying some to experiment with leads me to think that one of these motors may work. I have looked online for answers about these motors and maybe I'm just dense (good possibility) but I haven't been able to find exact answers. Maybe someone here can help. Motors are rated RPM/volt. This means maximum RPM per volt of course. If the motor is supplied with a higher voltage from a supply that limits the current to stay below the specs of the motor will higher RPM be possible? The ESCs (Electronic Speed Controller) are voltage and current rated. Could the output an ESC rated for a lower voltage and current be used to drive control power transistors in order to get around the lower voltage and/or current rating if a sensored motor is being used? I don't need to use a hobby ESC but they are plentiful and cheap. And all assembled. Which is most important. But I would be fine using some other BLDC motor driver in order to get the desired RPM that I want. I can do all the precision machining necessary to make the spindle that will hold the carbide cutting tools and to interface the motor with the spindle. I do not yet know enough about balancing in order to dynamically balance a motor which causes too much vibration from an out of balance condition but I think I can learn enough to do it. I am good with mechanical systems and have a pretty good intuitive feel for them. It's the electronics I'm not so good at. Thanks, Eric |
#2
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If you (spendy) source a servo-rated BLDC motor, it will tolerate all sorts of abuse, and may be loaded to a dead-stop without damage. And, if you are going to be doing this - purchase the correct speed control rated for the full shorted load of the motor. As there are no brushes, that is not the same as a short-circuit as it would be in a brush-type DC motor.
Peter Wieck Melrose Park, PA |
#3
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I have played around with these motors making drones from scratch. You can't just buy a motor and ESC connect them together and have it run. The input to the ECS is a pulse that varies in width for the desired speed of the motor. the direction of spin is controlled by how the 3 wires to the motor are connected (reverse any 2 and the motor spins in the opposite diredtion).. I have run these motors without the cpu controller that makes a drone fly but you need 2 things. A wireless control transmitter that usually has joy sticks to control the speed and direction of the drone (Usually $50 on up). A receiver that can be directly connected to the input side of the ESC to supply the appropriate pulse to the ESC (about $15). The ESC supplies the 5v back to the receiver so no extra power supply is needed other that the high current one used to power the ESC itself.
There are probably controllers that can be used with these BL motors directly but I have not researched these. Since the price of a wireless controller/receiver pair is so low I doubt that a dedicated controller would be worth the cost. If you were an electronics hobbyist you could build a controller that would supply the correct pulse to the ESC. Hope this helps. ....bob |
#4
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One more thing - an unbalanced motor spinning at 24,000 + rpm will destroy itself in short order. I suspect that the motor itself will be the least of your worries.
At the same time, is this engraving device for a pantograph, or similar, such that an off-the-shelf engraver would not be suitable? There are some pretty good ones out there. https://www.gesswein.com/p-2557-fore...Cs5 QQAvD_BwE That for the price will probably be competitive with your home-brew at the end of the process. Peter Wieck Melrose Park, PA |
#5
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On Mon, 7 May 2018 06:29:53 -0700 (PDT), wrote:
There are probably controllers that can be used with these BL motors directly but I have not researched these. Ebay shows 700 listings for such controllers: https://www.ebay.com/sch/i.html?_nkw=brushless+motor+speed+controller Most are for eBike and electric scooter speed controls but the smaller boards might be usable. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#6
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On Mon, 7 May 2018 06:51:25 -0700 (PDT), "
wrote: One more thing - an unbalanced motor spinning at 24,000 + rpm will destroy itself in short order. I suspect that the motor itself will be the least of your worries. At the same time, is this engraving device for a pantograph, or similar, such that an off-the-shelf engraver would not be suitable? There are some pretty good ones out there. https://www.gesswein.com/p-2557-fore...Cs5 QQAvD_BwE That for the price will probably be competitive with your home-brew at the end of the process. Peter Wieck Melrose Park, PA This engraving spindle is for use in a CNC mill. Ideally it will sit in the tool carousel along with the other 20 tools and be connected to power and cooling automatically. But I will probably need to manually plug in power and cooling connectors. I use different rotary tools for engraving and micromilling. The smallest engraving tools I use are .015" diameter at the tip. The smallest milling cutters I use are similar in size. The graver you linked to is a hammer type and is not the type of engraving I do. There are several ways to engrave and what my customers want requires rotary tools. I am really just doing shallow machining when I engrave, not any kind of artistic stuff. Letters, lines, numbers, that kind of thing. The top spindle speed of my main spindle is only 7,500 RPM. I do have a sub spindle that spins at 24,000 RPM but it is too big to fit in a CAT 40 tool and so is instead mounted in a clamp which in turn clamps around the main spindle housing. A kluge. I have some hobby BLDC motors but the ones with enough power for high feed rate cutting max out at 24,000 RPM and I really want 40,000 RPM. I have experimented with the motors spinning a tool at 24,000 RPM and surprisingly the things were pretty well balanced. But as I said they can't be fed along very fast. Eric |
#7
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That makes a lot more sense in terms of your request.
https://www.maxonmotorusa.com/maxon/...tent/ec-motors Gets you up to 120,000 rpm. I expect that they will be pretty well balanced as well. Peter Wieck Melrose Park, PA |
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