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Post by mattijs on Sept 4, 2014 13:45:13 GMT
Hi all, I've been wanting to make a motion platform for a while now...(i actually already built one when i was 10 or so...25 years ago...in LEGO technic ) It seems to me that the most DIY 6DOFs i see use x-sim, thanos board and really REALLY bulky motors and gearboxes. On the other hand, the amounts of power these motors are able to produce/Kg,cost are really small compared to RC brushless motors like: MOTOR (several of these motors in the 50 euro range can output 5kW peak and >1Kw continuous) Hall sensors can be added like so: youtube, brushless motor + hall sensorsCoupled with DIY controllers it seems for <100USD you can have 1DOF(without the gearbox) I don't think off the shelf ESC controllers are suited for 1ms update closed loop servo controller with the 1280USB as PID controller, but as i said...a DIY controller could be the ticket. Then there is the matter of the gearbox... A first stage (1:10 maybe??) could be handled by teeth and pully, readily available in the RC heli world. A last stage could be a worm gear. The worm gear drive...i'm not so sure how to obtain these cheaply...other than the wiper gearboxes so many of the 2DOF systems use. I have no idea how strong those worm drives are and if they can sustain that much power throughput. On the other hand...the gearboxes i see seem rather over engineered I might be entirely wrong though What do you guys think?
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Post by tronicgr on Sept 4, 2014 18:14:10 GMT
Hmm, these RC brushless motors might be strong but are efficient to run in very high RPM... You will need lots of reduction to convert the torque they provide to be usable for constant load application as we do in 6DOF platforms. The AC motors can provide lots of N-m for the limited RPM they run (1200-1800RPM) and there are gearbox that can fit on them to get exact the power and the rpm output speed you need. It will take lots of experimenting trying to get any usable result from these RC brushless motors. One way to use them would be in combination with cheap ball screw actuators, that normally would move slow with existing motors. Using those RC brushless motors (up to 20000RPM) with cheap actuators replacing their dc motors, would give enough speed to even reach the 400mm/s : www.pololu.com/category/103/concentric-ld-series-linear-actuatorsNow not sure how these actuator will hold together on these speeds or how much load will be able to take before break down... Thanos
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Post by mattijs on Sept 5, 2014 7:52:24 GMT
Hmm, these RC brushless motors might be strong but are efficient to run in very high RPM... You will need lots of reduction to convert the torque they provide to be usable for constant load application as we do in 6DOF platforms. The AC motors can provide lots of N-m for the limited RPM they run (1200-1800RPM) and there are gearbox that can fit on them to get exact the power and the rpm output speed you need. It will take lots of experimenting trying to get any usable result from these RC brushless motors. One way to use them would be in combination with cheap ball screw actuators, that normally would move slow with existing motors. Using those RC brushless motors (up to 20000RPM) with cheap actuators replacing their dc motors, would give enough speed to even reach the 400mm/s : www.pololu.com/category/103/concentric-ld-series-linear-actuatorsNow not sure how these actuator will hold together on these speeds or how much load will be able to take before break down... Thanos Yes indeed they run at high RPM..Is there a reason though they wouldn't have every bit of toraue at low RPM they have at high RPM IF you run them with sensors? I fly a lot of RC helis...they convert the high RPMs in ONE stage very efficiently to the main shaft spinning at 2000-3000RPM... So in just one stage...which uses readily available cheap but relatively high quality gears...these motors have the RPMs associated with the bigger AC motors but LOTS more wattage at their disposal. I can't figure out what else could be the problem apart from the following... Maybe it is the inertia keeping small outrunner motors like the one in the original post from being adequate for servo use because of the relatively low mass BUT very high RPM... I don't know... Like i said...i don't know much about this things and could very well be completely wrong...i just don't see where my logic fails.
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Post by mattijs on Sept 5, 2014 7:59:33 GMT
Hmm, these RC brushless motors might be strong but are efficient to run in very high RPM... You will need lots of reduction to convert the torque they provide to be usable for constant load application as we do in 6DOF platforms. The AC motors can provide lots of N-m for the limited RPM they run (1200-1800RPM) and there are gearbox that can fit on them to get exact the power and the rpm output speed you need. It will take lots of experimenting trying to get any usable result from these RC brushless motors. One way to use them would be in combination with cheap ball screw actuators, that normally would move slow with existing motors. Using those RC brushless motors (up to 20000RPM) with cheap actuators replacing their dc motors, would give enough speed to even reach the 400mm/s : www.pololu.com/category/103/concentric-ld-series-linear-actuatorsNow not sure how these actuator will hold together on these speeds or how much load will be able to take before break down... Thanos Your idea about the linear actuators is highly appreciated though! Might be worthwhile scouting ebay for some actuators...IF this works...it might make for a really clean installation. I do not know what the feedback mechanism (some of those are able to run closed loop) relies on....if it's wiper based, which it probably is, it won't be good for the loop and will surely make any differential component of the PID very...errr...exciting Might be worth using a costum homing procedure at startup with rotary encoders one of the gears for position afterwards
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