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#31
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Re: Engaging Gears Perpendicular to Shaft Direction?
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(Though admittedly, small things like how much those shafts would deflect when they had a pneumatic on them were definitely calculated (.00045 inches)) To do so real quick: Maybe 250 in-lbs on that center gear, 1 in diameter, moment arm of a half inch off center... the pneumatic is about 3.4 inches away from the pivot point, at around a 15 degree angle, providing a max moment arm in the opposite direction of around 95 lbs * 3.4 inches with a 1.5 inch bore... There's also the force on the gears through the shaft centers, sin(20)*250 is around 85, times it's moment arm of 1.5.... So we've got around 70 in lbs to spare with the half inch. whew! Thanks for the reminder...Quote:
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I've already thought of some nice ideas about changing the sizes of the blue connecting sprockets to let them affect the gear ratio, and keep the gears a (larger to reduce load) constant size... but I'm certain this is not what you're proposing. If you could clarify, I'd truly appreciate it! Thanks, Matt |
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#32
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Re: Engaging Gears Perpendicular to Shaft Direction?
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I think he means to move gear to chain, rather then gear to gear. Have both final gears spinning, but rotate them to move the proper one into contact with the output chain. Puts all the meshing forces onto the chain. At least, that is what I understood him to be saying. Wetzel ~~~~~~~~~~~~~~~ Making and breaking chain with needlenose pliers is fun. I swear. |
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#33
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How's this kluggie cut up?
The idea is to move the gears closer together so that they are always turning with the input gear.
Then put an idler sprocket on the same shaft as the input shaft (now the shaft marked with the green cross). Then pivot the both output shafts on a lever that also pivots about the input shaft (it is outlined roughly in a T shape in the image attached). Then when you drive this link, you engage one sprocket or the other with the chain. (The sprockets are those round black circle things) You can have the air cylinder either be strong enough to take the load you are pulling on the chain -- in which case you sort of get a chain tensioner built in for free. Or you can add a drive link between the aircylinder and the sprocket pivoting gig - in this case, you can make the whole thing non-backdriveable and then tension in the chain cannot push the mechanism out of engagement (I like this solution better... ...but time is limited so I will have to discuss it another time if there is interest). The chain routing is shown for the mechanism in high gear (the thickish blue line). I hope this helps. Joe J. Last edited by Joe Johnson : 22-12-2003 at 14:35. |
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#34
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Re: How's this kluggie cut up?
That's BRILLIANT Dr. J !!
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#35
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Re: How's this kluggie cut up?
Can the chain &/or sprocket(s) take this type of abuse (shift on-the-fly ...) ?
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#36
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Re: How's this kluggie cut up?
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Shift on the fly may be a bit of a stretch, but I suppose that it wouldn't be too bad if you could figure a way to use #35 chain. Joe J. |
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#37
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Careful is an adjective not to be glossed over...
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You forgot the input torque of 250 in-lbs (or else you have to include the torque from the internal short chain -- which magically will work out to be the same 250 in-lbs). I see 4 torques to deal with In high gear with driving the input CCW, Tinput = 250 in-lbs Taircylinder = 95 lbs*3.4 in = 320 in-lbs TtoothNormal= -(250 in-lbs/.5 in)*.5 in = -250 in-lbs TtoothSep= ((250 in-lbs /.5) * sin(20deg) ) *1.5 in = 250 in-lbs This is okay because they sum to 470 in-lbs (and CCW is toward engagement). If you do the same thing only have the input torque switch to CW you will get Tinput = -250 Taircyliner= 320 TtoothNormal = +250 (the normal tooth load is trying to ENGAGE the mechanism in this case) TtoothSep = -250 Sum = 70 in-lbs Having done the summing carefully, I get the same answer as your "quick calculation", so what do I know? I suppose I will shut up now ;-) Joe J. |
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#38
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Re: Engaging Gears Perpendicular to Shaft Direction?
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Doing that would put waaaay more torque through this box than I would think is healthy. (I haven't run numbers on this). In order to function correctly, this thing would have to be as "early" in the gearbox as possible, to minimize torque on the shifter. Matt-- I'm very impressed with this design. This may be a step closer to the "rookie solution" to shifting the FIRST community could use so badly. (Sorry Andy )I'm very curious to see how it will work out for you guys. ![]() John |
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#39
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Re: Engaging Gears Perpendicular to Shaft Direction?
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National champion team 469 used the exact same(or at least very similar) shifting design in 2003 with two motors per side without any trouble, even though the shifter was very late in the transmission. |
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#40
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Re: Engaging Gears Perpendicular to Shaft Direction?
One change that can be easily made to the shifter to increase the speed change without using different gears could be making the output shaft always be the shaft that currently has the 1:1 ratio, and changing the blue sprocket to a 20 tooth if the other one is a 10 tooth, or something similar. This would give you a 3:1 reduction and then a 2:1 reduction giving you 6:1 and a 1:1. you could do less or more teeth to make the increase more or less dramatic. That way newer can be very competitive with just an atwood drive having maybe 6ft/s and then 1ft/s or whatever they would like.
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#41
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Re: Engaging Gears Perpendicular to Shaft Direction?
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Also... I'm almost 100% positive, "national champion team 469" used a shifter NOT like Matt's, but similar to 60-2002, or 116-2002 -- where the gears slide laterally. This system is able to handle much more torque than Matt's (in which applied torque would actually try to push the shifter out of gear). John |
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#42
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Re: Engaging Gears Perpendicular to Shaft Direction?
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Keep in mind, his design doesn't even use #25 chain. While the reductions possible using sprockets is somewhat limited, its still pretty wide. Using #35 chain, you can get as much as a 3:20 reduction, which is pretty good. If you needed any more than that you could just change the ratios inside the shifter or add another box with another reduction after. |
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#43
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![]() I've plugged some numbers into a Lewis bending equation spreadsheet I've made, and let me tell you, with the 1" gears, failure is VERY possible, depending on where you place it in the drive train. Using the initial configuration I had, the factor of safety was around 0.7... Quote:
Just some thoughts, Matt Last edited by Matt Adams : 23-12-2003 at 15:12. |
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#44
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Re: Engaging Gears Perpendicular to Shaft Direction?
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Any torque applied through THIS design, will cause the gears to try to disengage from each other. The only thing preventing this is the force of the pneumatic, holding the shafts together. In a Dog-style, Pin-Style, Mesh-Style... Shifter, the kind of shifters we see every day in this competition: The shafts are held rigidly. Therefore the applied torque CANNOT seperate the gears from meshing (unless it deflects the shaft, which is a discussion for another time). See the major differences? See why Matt's design would have MAJOR torque limitations that wouldn't apply to a "normal" shifter? I can guaruntee you haven't seen any design like this one in the FRC, so it is unfair of you to draw parallels between this box and another and make broad statements concerning it's capabilities. I love 469, they are a great team, their last 2 bots have been works of art, and their 2002 bot kicked my butt pretty hard. Great designs, in every part of their bots, including the shifter. But... that doesn't really apply here, now does it? Unless you understand all the principles involved, and the design itself... which you've shown some confusion about... perhaps you should limit the broad statements you make about it? John |
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#45
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Re: Engaging Gears Perpendicular to Shaft Direction?
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With the possibility of using multiple motors, you can still put this shifter as early in the transmission as you would with any other shifter. From my understandings Matt was trying to make a shifter for newer teams who do not have the machining capability that some of us have. No where has anyone said that the design was perfect, but you can always work in some additional support to the shifter to accomodate a more torquey drive to an extent. |
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