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Offline ChrisYardTopic starter

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Gearing setup question
« on: September 16, 2010, 05:31:57 AM »
Hi all, sorry if this has been answered before.

I have a platform where may robot arm will be sitting.
The platform can rotate.  It has a gear on it that has 40 teeth. (this can NOT be changed).
What I would like to do is, have an encoder that will turn 360:1, yes to work out how many degrees the platform has moved.  Speed is not an issue here as long as it doesn't take all day to complete 1 turn.
What I need help with is the maths so the I can make the encoder turn 360 times.  The only fixed number is the 40 teeth on the plaform, the rest I haven't finished designing yet so is open to suggestions.

The encoder can not be mounted on the platform gear, so I can not just have the encoder with 360 division !! sorry, very limited space where the platform gear is.  so it would need a gear train to drive it at another location.

Thanks in advance
Chris
« Last Edit: September 16, 2010, 05:45:36 AM by ChrisYard »

Offline Alfa_Zulu

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Re: Gearing setup question
« Reply #1 on: September 16, 2010, 05:47:48 AM »
ok just summing up you want the gear attached to the encoder to rotate 360 times per 1 revolution of the main gear?

Offline Alfa_Zulu

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Re: Gearing setup question
« Reply #2 on: September 16, 2010, 05:58:19 AM »
ok sorry for a double post but i got bored of waiting for an answer lol,

if your trying to do what i asked ^^ then I believe this should work;

                             360°/Driver = Driven         
                             360°/40 = 9

now its been a while however i think this is correct and it sounds about right but don't take my word for it lol

Offline ChrisYardTopic starter

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Re: Gearing setup question
« Reply #3 on: September 16, 2010, 07:54:57 AM »
Thank you Alfa, yes you are correct, and sorry for the delay I had to do a proper job... god that always get in the way !!!!

The platform gear (40 tooth) is the final drive, then the encoder is attach to the final drive on the gear train and must turn 360 times per 1 rev of platform gear.

So you are saying that encoder gear will have 9 teeth on it ?? you think

Thanks Chris

Offline waltr

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Re: Gearing setup question
« Reply #4 on: September 16, 2010, 09:53:09 AM »
That gear ratio won't work.
A 9 tooth gear meshed to a 40 tooth gear will turn 4.444.... times for 1 revolution of the 40 tooth gear, 40/9 = 4.444.

You can not get 360 revolutions on a single secondary gear from a 40 tooth primary gear. However, what you could do is have multiple encoder 'ticks' on the secondary gear. If a 9 tooth gear had 81 'ticks' then you would get 360 encoder ticks for one revolution of the 40 tooth gear.

Or you can use multiple gears to increase the rotation rate to the desired 360 turns per.

Offline ChrisYardTopic starter

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Re: Gearing setup question
« Reply #5 on: September 16, 2010, 02:36:43 PM »
Thank you waltr.

I was hoping to have only one tick on the encoder, as I don't want the encoder to be to big.

I think I will have to use a multi gear train, just need to work out the gear teeth to make it right.

Is the a 'gear simulator' that you know of.  Of course free online version would be nice !!! :)

Offline Alfa_Zulu

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Re: Gearing setup question
« Reply #6 on: September 16, 2010, 05:56:26 PM »
See I told you I was probably wrong lol

Offline ChrisYardTopic starter

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Re: Gearing setup question
« Reply #7 on: September 17, 2010, 01:23:45 AM »
See I told you I was probably wrong lol

Ah never mind Alfa, at least you came up with a number I had NO idea what so ever.  I do the electronics never done a build before.  Didn't think it would be that hard.

I might have to just make some gears up and play about with them and see what I come up with

Chris

Offline waltr

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Re: Gearing setup question
« Reply #8 on: September 17, 2010, 07:42:56 AM »
Chris,
 Gearing is just simple ratios. If you have a old hobby servo open it an look at the gear train. Count the teeth on each gear and work out the ratios of each pair then the finial ratio. To get what you want you will need to have a gear train similar the what is in a servo but driven from the servo's output shaft instead of from the motor.

Offline Soeren

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Re: Gearing setup question
« Reply #9 on: September 23, 2010, 08:47:20 AM »
Hi,

The platform can rotate.  It has a gear on it that has 40 teeth. (this can NOT be changed).
What I would like to do is, have an encoder that will turn 360:1, yes to work out how many degrees the platform has moved.  Speed is not an issue here as long as it doesn't take all day to complete 1 turn.
What I need help with is the maths so the I can make the encoder turn 360 times.  The only fixed number is the 40 teeth on the plaform, the rest I haven't finished designing yet so is open to suggestions.
If you want a gear wheel rotating 360 times as fast as the end gear, this is one way to do it:
Dissolve the number 360 into integer divisors (I'm not sure of the right English term) by dividing with the least prime numbers that gives a division without a reminder.
360 /2 = 180, no remainder, so OK
180/2 = 90, still no remainder, so OK as well
90/2=45, OK
45/2 =22.5, it has got a remainder - so no go, try the next higher integer 3
45/3=15, OK
15/3=5, OK
5/3=1.67, no go, raise to next integer divider (5)
5/5=1, OK
Now you've reached one, gather all the good ones: 2x2x2x3x3x5 or more commonly expressed: 2^3x3^2x5

There's your gear ratios. you could perhaps find a set with a ratio of 4, 6, 8, 9 or so. As long as they can fit into the found ratios they can be used.

Remember, if you use a 10-tooth wheel on the 40-tooth wheel, you've got a ratio of 4 (2^2) in that alone and if you can find a "worm" to drive the 40-t, you will get a ratio of 40 (2^3x5) and need less gear wheels.


The encoder can not be mounted on the platform gear, so I can not just have the encoder with 360 division !! sorry, very limited space where the platform gear is.  so it would need a gear train to drive it at another location.
You could mount it on the wheel driving the 40-t. In that case you wouldn't need such a large total ratio. A disk with say 8 divisions (easy to draw) would lower the needed amount of gear wheels as well. Using a dual reader, you will get twice the ticks as there are divisions.


All that said, I really cannot imaging that you need a resolution of one entire revolution for each degree. The backlash and imprecision in the gear train alone gets you nowhere near the resolution that your method points towards and I don't believe you need a resolution of less than 0.3% even if using an entire rotation a tick.
Reality/sanity check: Most resistors you use is 5%. Do you think you can control or use a tolerance 18 times tighter (and don't get me started about the imprecision of a cheap motor).

If you describe what you are building, perhaps you could get some guesses to what's realistic.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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