Hi everyone, new to the forum, pretty new to mechanical engineering as well. Although what I'm about to ask for advice on is not directly related to CNC's I figure this forum would be where I could find the best advice. A lot of other places talk theory and don't get much done but here there's alot of great projects being accomplished. Anywho, I've done some preliminary research but admittidly as a chemist I'm a bit over my skiis here. Try and bear with me :). Sorry if it gets a bit wordy I like to try and explain what I am trying to do in likely too much detail.
So here's the goal. I want to be able to rotate a small load(by small I mean maybe 5-10 grams maximum) on a gear face or some similar rotating surface. I would like to achieve 0.01* angular resolution of this rotating "face". Torque and transmission of force is not a high concern here. The angular velocity will be quiet slow as a measurement will be taken per step handled by a microcontroller.
Here's what I am thinking,
I'm thinking I'll use a cheapy 0.9* step stepper motor. I am aware most of them have a 5% error but this will end up being very minimal as a 0.01* degrees already exceeds my needs(on purpose). Originally I wanted to use a worm gear drive train but quickly realized how expensive worm-gears and worms are! Especially with 50:1 gear ratios and such, then there's also back-lash. So I think I will settle on a timing belt pulley system with atleast one glider to ensure good tension on the drive. I ended up deriving the following equation:
A1 * R1/R2 = A2
Where A1 is the angle of the drive pulley(in this case the step of a stepper motor), R1 is the radius of the drive pulley, R2 is the radius of the pully I am spinning, and A2 is the angle that the pulley I am spinning will be rotated too. This is based on the fact that the arc-length of the drive pully must be the same as the arc-length of the pulley being 'driven'(sorry for lack of proper vernacular here).
From this I found that in order to get near the 0.01 degree resolution from a 0.9 degree step I will need my drive pulley to be 1/90th the size of the pulley being spun. https://sdp-si.com/ has tons of cheap polycarbonate timing pulleys with sizes that just won't provide that kind of ratio. I could get 0.1 resolution pretty easily it seems though. So I'm kind of stuck right there unfortunately. There has to be a more reasonable way. With a 7mm drive and a 125mm spun sheave I can get 0.05* which is pretty good but a little lower would be ideal.
My questions are as follows. How can I increase resolution without using a pulley that is a meter in radius? What kind of practical problems might I encounter along trying this out? Are there hollow rotors available or ways to mount timing pulleys to these?
So here's the goal. I want to be able to rotate a small load(by small I mean maybe 5-10 grams maximum) on a gear face or some similar rotating surface. I would like to achieve 0.01* angular resolution of this rotating "face". Torque and transmission of force is not a high concern here. The angular velocity will be quiet slow as a measurement will be taken per step handled by a microcontroller.
Here's what I am thinking,
I'm thinking I'll use a cheapy 0.9* step stepper motor. I am aware most of them have a 5% error but this will end up being very minimal as a 0.01* degrees already exceeds my needs(on purpose). Originally I wanted to use a worm gear drive train but quickly realized how expensive worm-gears and worms are! Especially with 50:1 gear ratios and such, then there's also back-lash. So I think I will settle on a timing belt pulley system with atleast one glider to ensure good tension on the drive. I ended up deriving the following equation:
A1 * R1/R2 = A2
Where A1 is the angle of the drive pulley(in this case the step of a stepper motor), R1 is the radius of the drive pulley, R2 is the radius of the pully I am spinning, and A2 is the angle that the pulley I am spinning will be rotated too. This is based on the fact that the arc-length of the drive pully must be the same as the arc-length of the pulley being 'driven'(sorry for lack of proper vernacular here).
From this I found that in order to get near the 0.01 degree resolution from a 0.9 degree step I will need my drive pulley to be 1/90th the size of the pulley being spun. https://sdp-si.com/ has tons of cheap polycarbonate timing pulleys with sizes that just won't provide that kind of ratio. I could get 0.1 resolution pretty easily it seems though. So I'm kind of stuck right there unfortunately. There has to be a more reasonable way. With a 7mm drive and a 125mm spun sheave I can get 0.05* which is pretty good but a little lower would be ideal.
My questions are as follows. How can I increase resolution without using a pulley that is a meter in radius? What kind of practical problems might I encounter along trying this out? Are there hollow rotors available or ways to mount timing pulleys to these?