On Tue, Oct 11, 2022 at 10:06 PM gene heskett <ghesk...@shentel.net> wrote:
> On 10/11/22 19:51, Chris Albertson wrote: > > Here is a good table of mechanical properties of 3D printable materials. > > PLS actual comes out as very good, except for durability because of its > > typical failure mode, it breaks rather than deforms. > > > > https://www.simplify3d.com/support/materials-guide/properties-table/ > > > > I'll still repeat that good design is FAR more important than selecting > > some magic materials. A redesign can many times net a 10x or more > > improvement but swapping materials can only get an incremental increase. > > > > Going back to the question, If the goal is dimensional stability, the > best > > solid un-filled plastic is PLA, the stiffest is carbon-filled PLA but the > > carbon stuff is not as strong and dose not save weight. over plain PLA. > Which surprises me. > > > > If you want a "tough" plastic that does not shatter then you want > something > > flexible. But that was nt the question asked here. > True, but shatterproof because it its resilience make PETG a good deal > for the price. > Nylon or PC would be best but doesn't print that well in consumer printers. > > > > My walking robot is made from PLA and motors with hardened steel gears. > > The biggest design issue I'm having is the gears are wearing out too > soon. > > But large gears are over my budget > > > Metal gears are the only option in my case. I'm building a four-leg machine. Think of four robot-arms mounted to the underside of a box that is filled with computers and batteries. A goal is that the robot needs to be powerful enough to jump a half meter off the floor and land on its feet. Mine is 3D printed plastic with about 8% of the performance of the MIT Mini Cheetah. They are using what are basically Quadcopter drone motors that take up to 100 amps of peak power. Then a back drivable 6:1 reduction and full CNC structure. My goal is to do what they did but at 1/3 the cost with maybe a little sacrifice in power. Today I have about 8% of the power and 1/8th the cost. The video below shows the current state of the art in this space. https://youtu.be/xNeZWP5Mx9s Here is what I had working some months ago, obviously there is quite a gap. Filmed in slow motion, so I can see what is going on. The motors and drive reductions have to fit inside the available space. I have only a couple of cubic inches for the motor and reduction. https://youtu.be/eysH5BpcGs0 I'm actually thinking of using belts and motors where the outer housing spins. I could press-fit a toothed ring around the motor and make a timing pulley with a motor inside. The ring would need to be metal as it would get hot. A motor like below might work. See that in this kind of motor the shaft is welded to the housing and the entire motor housing spins. getfpv.com/brotherhobby-avenger-2806-5-motor-870kv-1300kv-1460kv-1700kv.html <https://www.getfpv.com/brotherhobby-avenger-2806-5-motor-870kv-1300kv-1460kv-1700kv.html> THese robots are not unlike machine tools. A leg is just a 3-axis arm driven with powerful servo motors. there is a encoder on each axis and a computer to control motion. The big difference is that to motion is not pre-programmed. But still it is just servo motors and closed loop motion control but with higher speed and lightweight. Much of the structure can be printed but high-stress part are turning out to need to be metal. Boston Dynamics pretty much "owns" this space but their base model sells for $70K and as fitted for "real work" with costom sensors and software sells for mabe $250K. I'm aiming for $1,500. Current prices in China are about $3,500 for bare hardware. My prototype cost about $500. One thing I've found that might be helpful in printing bigger stronger > gears, is grinding > a bigger flat on the motor shaft then printing the gear to be a hard > push fit on this bigger flat. > Don't need a metal hub with grub screws in the gear. My B axis on my > 6040 mill is a small 5/1 > worm drive from fleabay, has an 8mm to 11mm adapter I printed while > waiting for the metal > one from China. With a 3 phase, 3NM motor spinning it, the plastic piece > is still working several > hundred spinning hours hours later as I carve these vise screws. > > Take care & stay well Chris. > > Cheers, Gene Heskett. > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author, 1940) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/> > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
