On Sunday 21 April 2019 08:39:28 Leonardo Marsaglia wrote: > Thank you guys again for your support! > > Well, I'm now taking a look at the ServoBelt datasheets and it looks > more than promising. > > I guess I can make a belt reduction from the servo to the little > sprocket to gain torque. That was my original plan with the rack and > pinion but this seems to be much cheaper and easier. > > So basicly what they do is use to pieces of belt one slightly longer > than the other (to acommodate the sprocket and tensioners) and they > are engaged with each other and well tensioned at the ends. Is that > right? So the sprocket spins and makes the joint travel along the > axis. > > From what I've seen on their datasheet, the heavy system can handle up > to 500 Lbs of linear force so that's like 2200 N. I'm more than okey > with that. > > I'm worried about the streching of the belts under acceleration, do > you think I should use a special kind of timing belt? Like kevlar > belts to avoid stretching under accelerations from 0 speed or under > changes of direction? > kevlar belts are a given. Virtually zero stretch under tension in time periods of decades. Thats why we use phillystran (kevlar) ropes to steady 2000' television towers. We check those for tension by measuring the sag with a zeroed riflescope on the bottom to see where that zero is on a tower leg and record it when the tower is erected. If that "intercept" point moves in a decade, its probably because the hammerhead, a 30 to 60 cubic yards bar of concrete buried crossways 30 to 50 feet down that the rope is attached to for an anchor has shifted. And that generally takes an earthquake to move. > > > El dom., 21 abr. 2019 a las 0:40, Chris Albertson (< > > albertson.ch...@gmail.com>) escribió: > > Wow, 3 meters! Another way I've seen is to use a cable. There are > > pulleys at each end and the cable forms a loop. In the simplest > > design a motor powers on of the pulleys. The cable takes the price > > of a long timing belt. I've seen kevlar cord used for a cord and > > some steel cable also. In the better design there is a drum where > > the cable takes a few turns around and a spring to keep tension on > > the cable. The drum is powered. > > > > With a 3M long rack, I think keeping it clean will be an issue. > > Perhaps mount is on the bottom of the track so chips fall down and > > off of it. or use a continuous airblast > > > > With gears you will need to have a backlash budget tnad design for > > it. Or just use a larger motor that still has torque at the low end > > > > > > > > On Sat, Apr 20, 2019 at 2:03 PM Leonardo Marsaglia > > <ldmarsag...@gmail.com> > > > > wrote: > > > Thanks Andy and Chris for your quick response. > > > > > > I'll try to answer both messages into one because I lack the > > > quoting function here in gmail. > > > > > > I plan to reduce the servos of the Y axis about 10 to 1 at least. > > > I would love to use timing belts and pulleys but I preffer to > > > avoid all the > > > > trouble > > > > > of making the steps for the reduction. The servos I plan to use > > > are 750 W and 3000 RPM. > > > > > > About using a screw. The main problem is my Y axis is 3.5 meters > > > long and I'm not sure I can get ballscrews that long so easy from > > > China to > > > > Argentina > > > > > in a safe and cheap way (I don't even know if the Fedex or DHL > > > would ship me something that long). In case of using a screw that > > > long I guess is a must to have a rotating nut and that's not a > > > simple task too (at least > > > > not > > > > > as simple as the planetary reducer). So that's why I'm not > > > thinking about ballscrews although I would love to use them on all > > > axis. > > > > > > > > > > > > > > > > > > > > > > > > El sáb., 20 abr. 2019 a las 17:50, Chris Albertson (< > > > > > > albertson.ch...@gmail.com>) escribió: > > > > backlash is a big deal. Maybe not so much with wood routing as > > > > maybe > > > > you > > > > > > don't care about 0.1 mm error. But think about a how a > > > > backlash in the 10:1 reduction translated to linear motion. > > > > Every time the servo motor changes direction the cutter stops > > > > moving until the backlash in > > > > the > > > > > > system is taken up. I can not imagine a gear system that > > > > backlash. > > > > > > > > This is why most machine tools use ball screws. Chinese ball > > > > screws > > > > are > > > > > > now nearly cheap as dirt and have zero backlash and can be > > > > directly > > > > > > driven > > > > > > > with a motor with no reduction. > > > > https://www.ebay.com/itm/Ball-Screw-SFU1605 > > > > < > > > > https://www.ebay.com/itm/Ball-Screw-SFU1605-RM1605-End-Machined-BK-B > >F12-Ballscrew-Nut-Housing-Set/182984379186?hash=item2a9ab80b32:m:m0p8 > >OTgikJ4HQd-zu4XytTg > > > > > > I have some of these kind and as close as my dial indicator can > > > > measure > > > > > > the > > > > > > > scre/nut is "perfect". The balls are spring loaded so they > > > > bear on > > > > both > > > > > > sides of the screw so there is zero "play" For mettal > > > > working these screws are only "hobby grade" as they might have > > > > 0.03mm periodic error > > > > in > > > > > > the pitch but I can't measure 0.03 over a 1/2 meter distance. > > > > > > > > They also make some really nice Chinese linear ball bearing > > > > track as a > > > > > > kit > > > > > > > that makes building one of these things "plug and play" Hard > > > > to beat > > > > a > > > > > > full ball bearing linear motion setup for under $100. Here is > > > > one example. They come os bigger and smaller sizes > > > > https://www.ebay.com/itm/SFU1605-Ending-Machined-Ballscrew-Set-SBR16 > >-Linear-Rail-Kit-For-CNC- > > > > > > < > > > > https://www.ebay.com/itm/SFU1605-Ending-Machined-Ballscrew-Set-SBR16 > >-Linear-Rail-Kit-For-CNC-US-Stock/401566069770?var=&hash=item5d7f33f4 > >0a&enc=AQADAAADAFjVrDbVsZ8oH%2F8PNHtt9VX4%2Fw7FZcmMuqsX8uaFEduVZdN2xO > >9SlmphozVEOH7g7jX%2Bxew6Qceghk4QQfAx5sBCl3mvk4eHWuVUGaj8C5BkivfcPYRvo > >fBQwnqo2D6pzU%2BGUd3CvwVXAM1GCvgT5HKYTTJRaAeIZBdXqfWlMXTaon39bDBa3zC% > >2F1K9ZLnfOKqX05Hd3sFtOKZehDjsf0jFAfy7bTSEmDVD6AmIj6ajz1SzPHtc%2BnojN8 > >s5utpzO3078Jp6elV34r23RIuEGPXeqA%2By3BsRGYYbRCMxUNK7Td2il%2BzXdMr%2Be > >rE%2FeihOQd97OPlL94nECQyCWjqeVGtoxO232cboR1Wve0LY2A8zPL0z50lT0s9SeLuW > >3dajRLIHWtpgAzCKGxELJnOVNP9le4Jc%2FcbyRcoiJJv%2BGwcEgBY1vrr1dbjwhxAYn > >UJG43R4TRLGijViWapLTeb2Awsu1sDe2W5XmsXrIpqZ%2FwqZ%2BaPGBvQ72s1dSDJOAl > >RYgbqhBH%2F%2Fyr1dDEP47jY7CIzBtBCa%2BLIY3nrG49uIxuVA%2FdIYXzBneALLQgf > >3qNzOCTcTZJ%2B9mek7VnKpPd64lGwhjrGGem%2F28DybqcMFTeyb%2F9sue%2Bntf14Y > >CADI5p%2FBJlGfEgY2ISNKVHriCM%2Bkm4XDW%2F6L%2FptM%2BOXTnhjf42Rhr%2B1Jk > >d051YRz59z6A0dps9OkNBtAYq4kVrOR6LYMxMWryqdbtzIrV0RnjPeAheOW10TvnQ0kWi > >XCV9JrZv1Mw4jKCTVIBt2lwm25r%2BgAFIAErGwpUxwOFdoZ4Dg1v6iDMdbmbqeST70Iy > >5AG1ccQhl69XQvcHN2GTJ8b3qhCzLkLsglFBXTY7%2Bin2x4io6%2FV4vWLAr6sw9%2BB > >050TxvCZMd0a67R1ZdV4dCLxgFFdc%2BxyiZwmNYtXWOoY04tjWSJJGG9ptIWM1rCArFJ > >qn2kJc1Y1lKu9HjO6y1z4iz4N4HRY2%2B7rQwzoW%2BnmJoqmh%2Fa1c83xr0XP7XkA5j > >qL3Lwx3Gg%3D%3D&checksum=401566069770871222cfdded49168823fbf139903396 > > > > > > If you don't like ball screws then try long timing belts. They > > > > also > > > > are > > > > > > zero-backlash and come in any size you need at lower cost then > > > > gears > > > > > > > > > > > > On Sat, Apr 20, 2019 at 1:27 PM Leonardo Marsaglia < > > > > > > ldmarsag...@gmail.com> > > > > > > > wrote: > > > > > Hello to all again! > > > > > > > > > > I'm defining my router design after some months of inactivity. > > > > > I > > > > > > already > > > > > > > > defined my steel frame and purchased the iron to start > > > > > building it. > > > > The > > > > > > > idea is to use the router mainly for wood and melamine boards. > > > > > > > > Eventually I > > > > > > > > > may use it for aluminum but that's not the main purpose of the > > > > machine. > > > > > > > Since you guys have lots of experience I would like to ask for > > > > > advice > > > > > > to > > > > > > > > define two main concepts for my design: > > > > > > > > > > 1- Should I use helical or straight teeth racks and pinions? > > > > > > > > > > I plan to use some chinese rack and pinions (MOD 2 with 30 > > > > > teeth > > > > > > pinions > > > > > > > > rotating at a max speed of 200 RPM) for the obvious reason of > > > > > the > > > > > > budget. > > > > > > > > But I can get hardened and ground rack and pinions so I think > > > > > that > > > > > > sounds > > > > > > > > pretty good. Anyway, I think I should stick with the straight > > > > > rack > > > > and > > > > > > > pinion since it's the simpler solution and being hardened and > > > > > ground > > > > I > > > > > > > think they will behave pretty well but I would like to hear > > > > > your > > > > > > > > opinions. > > > > > > > > > 2- For the servo-to-pinion reduction: Planetary servo reducer > > > > > or worm > > > > > > and > > > > > > > > gear reducer with timing belt? > > > > > > > > > > I'm thinking about the worm and gear because I can machine > > > > > that in > > > > the > > > > > > shop > > > > > > > > > and reduce at least the apparent cost (I say apparent because > > > > > I still > > > > > > > > will > > > > > > > > > have to make more complex mounting plates for the servos and > > > > > > > > reductions..) > > > > > > > > > but also I'm tempted to buy something like this: > > > > https://www.aliexpress.com/store/product/high-Precision-Helical-plan > >etary-gear-reducer-5-arcmin-2-stage-ratio-15-1-to-100-1/1155094_32867 > >566227.html?spm=2114.12010612.8148356.28.1b5476fa9wYyAW > > > > > > > Do you think they are worth it? I have no experience with this > > > > > kind > > > > of > > > > > > > reducers but the seller has good reputation and sells Delta > > > > > servo > > > > > > motors > > > > > > > > wich I'm familiar with and work great. What do you think? > > > > > > > > > > In any case, I plan to mount encoders coupled directly to > > > > > each > > > > pinion > > > > > > so I > > > > > > > > > can always track the position of the pinions no matter the > > > > > backlash I > > > > > > > > have > > > > > > > > > in the reduction stage (but off course I want backlash to be > > > > > the > > > > > > minimum > > > > > > > > possible). > > > > > > > > > > Those are my concerns for now. Please tell what you think so I > > > > > can > > > > > > make a > > > > > > > > better choice. > > > > > > > > > > Thanks as always to all of you! > > > > > > > > > > Leonardo > > > > > > > > > > _______________________________________________ > > > > > 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 > > > > > > _______________________________________________ > > > 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 > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users
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) Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
