Equatorial Platform Info
Using a tangent drive (threaded rod) can or will cause some problem when passing the meridian.
Direct drive of one or more bearing should not have as much of a problem if there is no backlash in the drive. A dc motor or stepper (1/4 step) with a low backlash gear reducer or stepper with microstepping and direct drive should work.
See Equatorial Platform Dob Tracker Drive Design
The amount of force /power required to drive the scope is related to the amount of out of balance. If you don't mind some drive train slippage when manually moving the scope and you have a clutch in the drive train a direct drive may work with a small motor and small drive wheel.
The Astrosyn 17PY-Q202-03 400 step motor has 9 in oz of holding torque. Assuming 33% if that torque is a safety limit or 3 in oz. Using a 1" diam (0.5 radius drive) with a 10:1 reduction yield 60 in oz. Almost 4 lb of drive.
Reduction with flat belts: This has a very low drag
Look for Pulleys ->Flat belt.
A 6T19-152506 is 0.591" OD 3/16" bore $4.63 on motor
A 6T19-752508 is 2.953" OD 1/4 " bore $8.36 on counter shaft.
This gives 4.9966 :1
A 6R19-18025 7.09" belt $6.60
A 6R19-25025 9.84" belt $6.64
A 7Z56-BFM250N self align roller bear with flange 1/4" $7
A 7X 2-11608 1/4" Locking collar $4 carbon steel $4.60 Stainless
Minebea "Astrosyn" Type 17PY-Q202-03. Small precision bipolar stepper motor. 0.9 degrees/ step. 400 steps / revolution. 12.5 ohm coils. 1.66" x 1.66" x 0.92" body. 0.2" dia. x 0.4" long shaft. Four 2.25" leads w/ four pin socket connector, 0.1" spacing.
$6.75 + 6.00 S&H
15.00 Minimum order
5V, 0.4A, 12.5Ohms. 0.9°/step, 400 s/rev, 12.5 ohm coils, 9 oz. in. holding torque. NEMA17 size (1.65" sq. x 1.0" H. with 0.2" dia. x 0.4" long shaft). Four leads (*Y, R, *BK, OR) with four-pin socket connector. Minebea Astrosyn 17PY-Q202-03. Wt. 0.44 Lb. Large Quantity Available
23M003 $9.95 each
S&H from price
MFR: Shimano Kenshi DC VOLTS/PHASE: 5 AMPS/PHASE: 0.15 STEP ANGLE: 1.8
Degrees HOLDING TORQUE: 10 oz-in SHAFT SIZE: 3/16” dia. X ¼”
w/removable pulley NO. OF LEADS: 4 MOTOR SIZE: 1-5/8 sq. x 1-3/16”
FLANGE SIZE: 1-5/8” sq. CONDITION: New
53 oz-in DC Stepping Motor, Holding Torque
MFR: applied Motion
DC VOLTS/PHASE: 2.3
STEP ANGLE: 1.8 Degrees
HOLDING TORQUE: 53 oz-in
SHAFT SIZE: ¼ dia. X 1-3/16”
NO. OF LEADS: 6
MOTOR SIZE: 2-1/4 dia. X 2”
FLANGE SIZE: 2-1/4” sq.
CONDITION: Removed from equipment
16.67 RPM Geared Stepping Motor - Series SAS - Power input 8 Watts.
Winding resistance 36 Ohms.
Reduction 15, Step
Angle 0.500 degrees, Output Speed 16.67 RPM, Typical
Torque 200 p/s (Torque measured at nominal voltage with L/R drive) 52oz-in
2.2 - 4.2 RPM; 6 - 12 VDC MAXON Reversible Gearhead Motor
Maxon Motors #227135... Brushless DC Gearhead motor. At 12 VDC, 840 mA, 4.2 RPM, 6.8 in/lbs. stall torque. At 6 VDC, 600 mA, 2.2 RPM, 3 in/lbs. stall torque. Straight terminal tabs for wire connections. Shaft supported by sealed bearings. Shaft size 21/64"dia. x 3/4"L with flat. Gearbox size 1-1/4" dia. x 2-1/4"L. Motor size 1"dia. x 1-3/4"L. New. Motor normally retails at $165.00
Equatorial Platforms Commercial Aluminum Platform
Kit for platform
Pictures of various designs
Equatorial Platform With Direct Drive Stepper Motor and Auto Rewind
Wooden platform with worm drive on taped Aluminum sector
Big Dob with dual angled sectors.
Good pictures with one south cylinder and north conic bearing
Equatorial Platform Dob Tracker Drive Design
Bigfoot Shows clutch for quick manual drive reset
Analog stepper driver PCB layout
Micro stepping IC
Source for metal
Aluminum plate and tubing supply
HOW TO ALIGN YOUR EQUATORIAL PLATFORM