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  #41  
Old 04-28-2012, 09:02 PM
devinc devinc is offline
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

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Originally Posted by dontworryaboutit View Post
I'm assuming your output is a wheel.
Hold the wheel so it doesn't turn and run your contraption at different speeds. I'll bet you that at the lower speeds the motors will continue to turn even when the wheels are stalled, but at the higher speed it will stall the motors.

How are you getting 3 speeds? Do you use one output from one planetary and run that into a second planetary with 2 more motors?
it will stall if i hold the wheel but if i put power into the other set of motors it will flip the robot. I use 2 sets of motors and each set has 2 motors in it. High torque is run by chain and needs some power from the other set. I drive the second set much like a clutch in a car. The second speed is run by the gears and the chain is stalled and the third speed is run by both the chain and the gears. I dont know if that makes any sense but when I get back to school I will take some photos and a video and I will post it in here.
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  #42  
Old 04-29-2012, 11:55 AM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

I'm an idiot and still don't see how this works. Is there any resource out there that will "school" me in this type of transmission?
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  #43  
Old 04-29-2012, 01:02 PM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

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Originally Posted by snowpenguin View Post
I'm an idiot and still don't see how this works. Is there any resource out there that will "school" me in this type of transmission?
I didn't "see" it until I built one out of LEGOs... holding one in your hands makes it a lot clearer.

//Andrew

EDIT:
P.S. Just because you don't see it doesn't make you an idiot...
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  #44  
Old 04-29-2012, 01:25 PM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

Yeah I know, as soon as I see it I'm sure I'll understand totally... Maybe I'll try to build one this week, if I find some free time from our 20 motor dragster.
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  #45  
Old 04-29-2012, 02:24 PM
contagon contagon is offline
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

Ok, so this is looking pretty slick and completely doable. The only disadvantage to this I've seen is the inability to use mecanum wheels.

I'm thinking I'm getting the jist of how it works as well, although I'm with snowpenguin in the fact that I'm going to need to make one. My only question is how do you calculate the different gear ratios?
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  #46  
Old 04-29-2012, 02:29 PM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

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Originally Posted by contagon View Post
Ok, so this is looking pretty slick and completely doable. The only disadvantage to this I've seen is the inability to use mecanum wheels.

I'm thinking I'm getting the jist of how it works as well, although I'm with snowpenguin in the fact that I'm going to need to make one. My only question is how do you calculate the different gear ratios?

1. If you have an 8 motor drive, using 2 motors per wheel, then have a pneumatic lift, and 2 motors on the intake, it could work.

2. To find gear ratios, say you want a 1:7 gear ratio on your lift. So you basically have to find your gears, so you get a 12 tooth gear, which is on the motor axle, and then you get the biggest gear, an 84 tooth gear. To find the ratio basically you have to divide 84 by 12, and then you get 7. Also it means that the 84 tooth gear rotates once when the 12 tooth gear rotates 7 times
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  #47  
Old 04-29-2012, 02:55 PM
devinc devinc is offline
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

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Originally Posted by contagon View Post
Ok, so this is looking pretty slick and completely doable. The only disadvantage to this I've seen is the inability to use mecanum wheels.
You can use mechanum wheels with only 2 planetarys and a 4 motor drive...
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  #48  
Old 04-29-2012, 02:55 PM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

Or use an 8 motor drive, 2 motor lift, and pneumatic claw like we did :3 Though that's not nearly as good for sack attack.
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  #49  
Old 04-29-2012, 03:15 PM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

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Originally Posted by 3Dsnowpenguin View Post
I'm an idiot and still don't see how this works. Is there any resource out there that will "school" me in this type of transmission?
If you just search "planetary gear" on google you'll probably find something useful, but I'll try to explain how it works.

The gear shifting part is based on differentials. If you have seen vex differentials before this will be easier than if you haven't, but basically how they work is when you turn the housing, both of the output shafts will turn. However, if you hold one of the output shafts, then the other output shaft will continue to turn (at twice the speed). The way this works in the drive train is that you can use pneumatics to lock the arm output shaft, and the drive base will be the only thing turning. Or you can lock the drive base output shaft, and only the arm will move.

Now to the planetary gears.

The easiest way to explain these is to imagine a gear sandwiched vertically between two horizontal parallel rack gears (the flat gear-like things that you use to turn horizontal movement into linear movement), one above and one below the gear. Now imagine you have an axle through the gear and are holding the rack on top. If you move the gear and the top rack linearly at the same speed and in the same direction (so the gear doesn't turn), the lower rack will also move in that direction at the same speed. But here's the good part: if you move the top rack and the gear at the same speed but in differ ent directions, so that the gear is turning, the bottom rack will move in the same direction as the gear, but twice as quickly.

Now fold this sandwich of rack-gear-rack into a circle, with your lower rack towards the interior of the circle, and you have yourself a planetary gearset (you'll want to add some more gears (called the planets) around the circle so the center gear (called the sun gear) maintains spacing from the ring gear, the outer inside-out gear). The two inputs to this setup would be the top rack (the ring gear) and the gears (the planets).
So that's how their differentials and planetary gears work. Ask any more questions you have.
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  #50  
Old 04-29-2012, 03:17 PM
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Re: 4194B Drivetrain (Differential, Planetary, Pneumatics)

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Originally Posted by snowpenguin View Post
Or use an 8 motor drive, 2 motor lift, and pneumatic claw like we did :3 Though that's not nearly as good for sack attack.
An 8 motor drive might be the only possible drive base for teams that wish to pick up 30+ pounds of game objects.
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