mch62
18-05-2005, 10:58 AM
Just an update on my Observatory and EQ friction drive fork mount.
Some statistics for people interested in Friction Roller drives.
The drive system uses 2 servo motors with encoders running on large smooth drive discs.
No worm gears here just the frictional force of a drive roller against a disc as used in a lot of large observatory set ups.
The advantage is little or no PE and back lash and a lot cheaper than 12" plus low PE worm wheel gears sets.
The disadvantage , possible slippage and loss of positional orientation.
There is some PE and back lash due to reduction gearboxes but if there chosen carefully low PE is the result and also due to the primary reduction any gear box PE is reduced by that amount.
In a worm wheel set up you have the PE of the gear box as well as the worm wheel.
The over reduction for RA and DEC is 2212.5 : 1 with an encoder resolution of 4531200 .
This winds up about 3.5 ticks per arc sec resolution at a maximum slew speed of about 6 degrees /sec.
The primary roller reduction is 15:1 with a 660mm diameter SS rimmed steel disc for the RA and a SS rimmed ply disc for the DEC .
The DEC drive will be using a timing gear and belt on a ply disc and not a roller friction drive.
This set up is lighter on the fork for balance and the PE error of this is not as important for the DEC drive.
To ensure positional orientation if slippage occurs or the scope is moved manually as in drag and track mode , 2 extra shaft encoders are used to compare the motor encoders to the shafts.
The controller is Mel Bartels Servo drive system and can be adapted to just about any scope mount EQ design including ALT/Az and Dobs.
http://www.bbastrodesigns.com/NewProductAnnouncement.html
http://www.bbastrodesigns.com/#servoitemsforsale
I still have the fun part to do yet which is the mounting of the motors and there reducers and setting up all the parameters , but hope to be up and running within a month.
The observatory is self explanatory from the pics.
A simple roll off roof.
Question welcomed
Mark
Some statistics for people interested in Friction Roller drives.
The drive system uses 2 servo motors with encoders running on large smooth drive discs.
No worm gears here just the frictional force of a drive roller against a disc as used in a lot of large observatory set ups.
The advantage is little or no PE and back lash and a lot cheaper than 12" plus low PE worm wheel gears sets.
The disadvantage , possible slippage and loss of positional orientation.
There is some PE and back lash due to reduction gearboxes but if there chosen carefully low PE is the result and also due to the primary reduction any gear box PE is reduced by that amount.
In a worm wheel set up you have the PE of the gear box as well as the worm wheel.
The over reduction for RA and DEC is 2212.5 : 1 with an encoder resolution of 4531200 .
This winds up about 3.5 ticks per arc sec resolution at a maximum slew speed of about 6 degrees /sec.
The primary roller reduction is 15:1 with a 660mm diameter SS rimmed steel disc for the RA and a SS rimmed ply disc for the DEC .
The DEC drive will be using a timing gear and belt on a ply disc and not a roller friction drive.
This set up is lighter on the fork for balance and the PE error of this is not as important for the DEC drive.
To ensure positional orientation if slippage occurs or the scope is moved manually as in drag and track mode , 2 extra shaft encoders are used to compare the motor encoders to the shafts.
The controller is Mel Bartels Servo drive system and can be adapted to just about any scope mount EQ design including ALT/Az and Dobs.
http://www.bbastrodesigns.com/NewProductAnnouncement.html
http://www.bbastrodesigns.com/#servoitemsforsale
I still have the fun part to do yet which is the mounting of the motors and there reducers and setting up all the parameters , but hope to be up and running within a month.
The observatory is self explanatory from the pics.
A simple roll off roof.
Question welcomed
Mark