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#1
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Re: pic: Shaft Drive Bearing Blocks
Why cant you use chain instead of having a shaft all the way down your drive system?
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#2
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Re: pic: Shaft Drive Bearing Blocks
I believe(haven't actually calculated) that the shafting will end up weighing about the same as the chain required to drive a similar system.
Last year I got annoyed with tensioning chain. If I do it properly I won't have to worry about it breaking(though the same goes for a properly designed chain system). It is different. Its cool. Why not(seriously I would like to be critiqued. Though I probably don't have to ask on CD)? I just checked out the weight issue a little bit. #35 rollerchain is about .275 lbs/foot If you use 6 feet that is about 1.25 lbs the shafting in this system only weighs about .25 lbs If you went with #25 like a lot of teams the the chain is lighter I still havn't looked into sprockets vs miter gear weight Last edited by MAteo9944 : 30-12-2006 at 02:15. |
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#3
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Re: pic: Shaft Drive Bearing Blocks
I'm curious as to the advantages this method provides over more traditional chain drive systems, other than being really different and cool.
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#4
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Re: pic: Shaft Drive Bearing Blocks
I would not want to have to fix that thing...
Dropping a chain is one thing. Swapping out a whole shafting system might turn out to be another. |
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#5
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Re: pic: Shaft Drive Bearing Blocks
Quote:
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#6
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Re: pic: Shaft Drive Bearing Blocks
I know Team 1097 did something very similar to this in 2005. It took them almost the entire 6 weeks getting the base running perfectly, but it was one heck of a bot, they won the Davis Regional.
Even with the flexible shaft coupling your frame needs to be welded very straight, and should be sturdy enough not to bend. 1097 had everything very precisely machined and put together. Is the transmissions efficiency as good as a well tensioned/aligned chain drive? I take it there are several mitre gears, as well as shaft misalignments that all add up. |
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#7
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Re: pic: Shaft Drive Bearing Blocks
the only thing that scares me about this is those little bitty gears direct driving those moderately sized wheels., but what do I know Im not a meche. good luck on that drive system though
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#8
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Re: pic: Shaft Drive Bearing Blocks
It looks like you are machining your own wheels. If that's the case, why don't you just make a center wheel that is slightly bigger that the two outer ones. The speed of that wheel will be negligibly higher than the outer two, but it will allow you to have a standard pillow block in there, as opposed to the IGUS ones. This could make for a possibly more robust drive setup, as some teams had problems with those plastic IGUS bearings last year.
BEN |
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#9
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Re: pic: Shaft Drive Bearing Blocks
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As for the IGUS bearings, they should be fine. They are not under too much load from the miter gears. We are using conventional ball bearings where there are higher loads. |
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#10
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Re: pic: Shaft Drive Bearing Blocks
I always like the idea of a shaft drive. It can be quieter and requires less space and can be more reliable when put together well. I like the bearing support at the drive wheels. Some additional considerations: The drive pinion is ok, but should probably go to a larger gear, use the final gearing as a factor for the transmission. Also, you should consider incorporating a thrust bearing to absorb axial thrust. One other consideration. long shafts need more bearings for support. Have you looked into using a hollow shaft? There is always a certain amount of torque involved which a hollow shaft can absorb better without breaking. Or if you want to get really fancy you can use a quill shaft (you'll have to look it up). A quill shaft is essentially a shaft within a shaft that extends the effective length of a shaft. Length is good because that, too, increases torque flexion which reduces breakage.
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#11
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Re: pic: Shaft Drive Bearing Blocks
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I went with the solid shafts so that I could use shaft keys instead of set screws. I do like the idea of quill shafts. I will have to look into them. Hopefully one day soon I can get hold of an ME for long enough to go over all of the calculations for the strength of the system. As of now the design is still without the support of the calculations, so the sizes and types of components are subject to change. |
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#12
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Re: pic: Shaft Drive Bearing Blocks
Efficiency might be your worst nightmare with this system.
Chain & Belt Efficiency ~ 95% - 98% Spur Gears Efficiency ~ 95% - 98% Bevel Gears Efficiency ~ 90% - 95% Planetary Gears Efficiency ~ 80% - 90% Efficiencies multiply for every stage in your gearbox, so for your drive you have spur>planetary>bevel(x2) assuming that your gearboxes are that the top of efficiency you would be getting .98*.95*.90*.90= ~75.4% efficient at transferring torque. This also does not take into account the effects of torsion of your drive shaft on the efficiency. I like the idea and how different it is in application, but sometimes being innovative for no reasons can have adverse effects. That being said I would love to see this drive work, but I would be hesitant to build this for the competition season without building a prototype drive in the off season. |
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#13
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Re: pic: Shaft Drive Bearing Blocks
My team has also designed a similar system. There is one thing you may want to take into consideration. In our design we use spider couplings in the driveshaft to allow for slight misalignments in the bearing position. This was important for us because if the robot frame becomes bent slightly in any way it will bind the shaft. Ill post the drawings after our next meeting on Tuesday so you can see where they are located.
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#14
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Re: pic: Shaft Drive Bearing Blocks
Great design. but if the frame flexes chances are something is gonna skip or break. plus under the tremendous forces on that shaft i doubt the bearing blocks will stay in place. If its a flat game this year then it might work but even then the robots still take alot of beating.
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#15
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Re: pic: Shaft Drive Bearing Blocks
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On the keys/set screw thing, I suggest looking into using hex stock rather than round. I know that it will make the build phase harder, but I believe that the advantages gained will be well worth it. The hex gives you six corners to bear the load, and I would think that you could drill quite a bit out of the center without losing much strength. I know hex is used in John Deere hay balers for the main driving shaft, and I have never heard of there being problems with them (not there, at least). JH |
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