Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: davidhere40 on August 09, 2012, 09:40:34 AM
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I'm trying to create a brushless servo from scratch that is capable of industrial use because I'm unable to find what I need:
I need a continuous, multi-turn servo with position control and a magnetic encoder (anything except a pot is acceptable though). My price goal is around $120 or less. I've already sourced many of the parts and I'm confident this is feasible.
This is almost what I want: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=22612 (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=22612)
It has everything I want except continuous, multi-turn control.
S, here is the last part I could really use help on. I can't figure out what motor and controller combo is best! Must be brushless for long-life. I've gotten a couple of brushless motor combos to test out. But, I can't help but think these are not the right thing to use. The ones that futaba brushless motors and the hobbyking ones use are different. They are smaller.
So, any ideas on how to figure out what these other brushless servo manufacturers use for motors and controllers? I want to make sure I do this right.
Thanks,
Dave
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All you have to do is modify the servo for continuous rotation...
http://www.societyofrobots.com/actuators_modifyservo.shtml (http://www.societyofrobots.com/actuators_modifyservo.shtml)
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Hi,
[...] I've gotten a couple of brushless motor combos to test out. But, I can't help but think these are not the right thing to use. The ones that futaba brushless motors and the hobbyking ones use are different. They are smaller.
Just a guess, but I assume the ones you have are outrunners and I suspect that they use inrunners in servos.
However, you can get very small outrunners, but whichever, the smaller it is, the faster it will be and the harder you have to gear it.
The only economical feasible way of getting multiturn positioning is to reset to a known position at startup (and perhaps each nn timeunits, tests will tell) and then either count clicks up/down or, with an absolute 360° encoder count revolutions up/down (by index markings) plus the absolute position of the uncompleted turn (you can get absolute position multiturn resolvers, but you really won't like the price).
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wow. great idea. I can try to reset the servo. It's already able to rotate continuously, but only when the power is off... because the microcontroller inside of it prevents it from going any further. But, if I somehow reset it to center itself at its current position, I might be able to continue rotating. I'd add a second encoder on the outside to keep track of position on my own microcontroller.
I've been able to source absolute magnetic encoders for just $20. They come with the IC, PCB housing and a mounted magnet. The only thing missing is a plastic part to position and align the magnet. I'll also add a bearing for smooth rotation of the magnet. I can make the part with a 3D printer (can't live without that thing!)
If anyone else is interested, here are the encoders I got. The part number is AEAT-6012-A06
The website to buy it cheap at is avnetExpress.com Here is a direct link:
http://avnetexpress.avnet.com/store/em/EMController/Optoelectronics-Misc/Avago-Technologies/AEAT-6012-A06/_/R-5515966/A-5515966/An-0?action=part&catalogId=500201&langId=-1&storeId=500201&listIndex=-1&page=1&rank=0 (http://avnetexpress.avnet.com/store/em/EMController/Optoelectronics-Misc/Avago-Technologies/AEAT-6012-A06/_/R-5515966/A-5515966/An-0?action=part&catalogId=500201&langId=-1&storeId=500201&listIndex=-1&page=1&rank=0)
Someday I'm going to do a kickstarter campaign to make low-cost robotic parts that are industrial capable. like a $10 magnetic encoder. I could do it now if I had the money to order in bulk and have the plastic part manufactured in bulk. I'd just have to spend a little time testing and making the software for open source distribution. I also want to make $50 industrial-capable servos (for light weight jobs). It's really just 4 bearings, metal gears, a servo housing, brushless motor and controller, and a magnetic encoder. The rest can be done using a typical microcontroller like an arduino.