Cubix Posted January 11, 2011 Posted January 11, 2011 Hello everyone, I'm new to this forum because I need some help. I wanted to build a prmission of 2:15 using gears. I could not find a way to make it, so can you help me? It should be quite efficient, of course. If you know a way how to build it, could you please describe it for me? Thank you. Quote
Erik Leppen Posted January 11, 2011 Posted January 11, 2011 (edited) Lego has gears with 8, 12, 16, 20, 24, 36 and 40 teeth. Dividing out the common factor 4, this is 1, 2, 3, 4, 5, 6, 9, 10. The prime factors available are 2, 3 and 5. As both 2 and 15 consists only of those prime factors, this is doable with simple gear reductions only. 2:15 is 2 : (3 x 5) so it can be either 2:3 times 1:5 or 1:3 times 2:5. 2:3 is 8 to 12 or 16 to 24, the last one is most practical. 1:3 is 8 to 24 1:5 is 8 to 40 2:5 is 8 to 20 or 16 to 40, the last one is most practical. As the distance between the centers of two gears is 1/16 times the sum of their teeth, the distances between the holes in these four setups is a multiple of 1/2 stud each, so these can easily be secured with bricks with holes in a horizontal setup. Edit: what I mean with the last remark is this: Edited January 11, 2011 by Erik Leppen Quote
Zerobricks Posted January 11, 2011 Posted January 11, 2011 Use 12:20 to 8:24 to get 5 and another 8:24 to get 15. Than use 12:24 to get 2 and connect them both via a diff. Quote
DLuders Posted January 11, 2011 Posted January 11, 2011 (edited) "Sariel" (Paul Kmiec) posted his "Gear Ratio Calculator 2" on his excellent website. Read about it at http://sariel.pl/2010/04/gear-ratio-calculator-2-released/ ; the actual calculator is at http://sariel.pl/tools/ratios/ . One can place any type of "Driver Gear" and "Follower Gear" on a 6x6 hole grid, and there's a pictorial output and some data like: "The gear ratio is 1.8:1" "The speed is increased 1.8 times. The torque is decreased 1.8 times. The follower gear rotates 1.8 time per each revolution of the driver gear." Cool! Edited January 12, 2011 by DLuders Quote
Sariel Posted January 12, 2011 Posted January 12, 2011 (edited) 2:15 equals 1:7.5. You can achieve that easily using two pairs of gears: one with 1:3 ratio and another with 1:2.5 ratio (as 3 x 2.5 = 7.5). As Eric pointed our, the simplest possible combination is 8t gear > 24t gear in the first pair and 16t gear > 40t gear in the second pair. Edited January 12, 2011 by Sariel Quote
Cubix Posted January 12, 2011 Author Posted January 12, 2011 Thank you very much for the fast answers! Quote
teflon Posted January 12, 2011 Posted January 12, 2011 Use 12:20 to 8:24 to get 5 and another 8:24 to get 15. Than use 12:24 to get 2 and connect them both via a diff. Is this Lego Antikythera mechanism approach? Quote
allanp Posted January 12, 2011 Posted January 12, 2011 Is this Lego Antikythera mechanism approach? I believe it is yes. Quote
rgbrown Posted January 12, 2011 Posted January 12, 2011 Use 12:20 to 8:24 to get 5 and another 8:24 to get 15. Than use 12:24 to get 2 and connect them both via a diff. I don't think that works -- or maybe I'm misunderstanding what you're suggesting. If you connect 1/15 and 1/2 by a diff you get (1/15 + 1/2)/2 = 17/60. Conversely, if you connect 15 and 2 by a diff you get (15 + 2)/2 = 8.5 Is this Lego Antikythera mechanism approach? Sort of - using differentials lets you add, whereas regular gearing up and down only lets you multiply -- the output of a diff with inputs A and B is (A + B)/2. You can also subtract by negating (reversing direction) of one of the inputs, or by treating the differential casing as one of the inputs. This means with a bit of thought you can get any gear ratio you want, including ones that don't have 2,3,5 as prime factors. Quote
Zerobricks Posted January 13, 2011 Posted January 13, 2011 I don't think that works -- or maybe I'm misunderstanding what you're suggesting. If you connect 1/15 and 1/2 by a diff you get (1/15 + 1/2)/2 = 17/60. Conversely, if you connect 15 and 2 by a diff you get (15 + 2)/2 = 8.5 Sort of - using differentials lets you add, whereas regular gearing up and down only lets you multiply -- the output of a diff with inputs A and B is (A + B)/2. You can also subtract by negating (reversing direction) of one of the inputs, or by treating the differential casing as one of the inputs. This means with a bit of thought you can get any gear ratio you want, including ones that don't have 2,3,5 as prime factors. Yeah the other sone should be 24 to 12 Quote
rgbrown Posted January 13, 2011 Posted January 13, 2011 Yeah the other sone should be 24 to 12 It wasn't that - it's just that you don't want to join them with a diff Quote
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