Gravity Assisted Tensioning System (GATS) - For V-Core 4 and 3.1

Gravity Assisted Tensioning System (GATS)

A streamlined method for precise belt tensioning on the RatRig V-Core 4 and V-Core 3.1 (with front tensioner upgrades).

Overview:

The GATS simplifies belt tensioning using hanging weights to apply constant, equal tension on both belts simultaneously. The system includes two brackets that temporarily attach to the front frame, and weights (e.g., buckets with water bottles and/or soda cans) provide the pulling force. A printed adapter connects the tensioner bolt to a length of 9mm 2GT belt, while the main bracket redirects the pull horizontally via an idler pulley.

Key Features:

• Constant Tension: Ensures both belts balance automatically for optimal synchronization.
• Easy Length Verification: Measure the extension of tensioner pulleys to confirm equal belt lengths.
• Repeatable Process: Reset the same tension quickly and accurately.
• Time-Saving: Achieve precise results without tedious manual tuning.

Compatibility:

Designed for the V-Core 4 (Hybrid, CoreXY, or IDEX) and compatible with the V-Core 3.1 if upgraded with similar front tensioners.

Recommended Procedure (CoreXY & Hybrid):

1. Prepare: Loosen belts and ensure the X and Y rails are aligned and square.
2. Detach Hybrid Belts: Disconnect the hybrid belts from the X rail to prevent interference with tension equalization. If you wish to generate isolated belt tension graphs for the CoreXY system, also disconnect the hybrid motors.
3. Setup: Attach the printed brackets to the frame, replace the tensioner bolts with longer bolts, and connect the weighted belts to the adapters. Adjust the bracket height so the weighted belt is horizontally aligned with the tensioner bolts, ensuring the pulling force is perfectly inline with the bolts.
4. Add Weight: Place equal weights in both buckets, allowing tension to distribute evenly.
5. Measure Belt Lengths: Use calipers to measure the protruding length of the tensioner pulleys. Adjust the belt loops until both sides are of exact, identical length.
6. Secure with Care: Gently tighten the grub screws to avoid disturbing the set tension.
7. Reinstall the original tensioner bolts and snug them up to secure the tensioner position.
   Then repeat the process for the top/hybrid belts using the same weight. (see update 28.01.2024)

Motor Synchronization:
When stepper motors are energized, they lock to the nearest/easiest-to-reach full-step position. Since the Hybrid and CoreXY motion systems are interconnected, I recommend synchronizing the motor pulleys after tensioning for optimal alignment:

Position the Toolhead:
Manually move the toolhead to the center of the bed and activate the debug macro button: Set Center Cinematics Position.

Loosen Motor Pulleys:
Loosen the grub screws on both Hybrid/Y motor pulleys so they can freely rotate on the motor shafts.

Command a Y Movement:
Issue a command to move the Y-axis 1mm forward and then 1mm back. This ensures all four steppers actively hold their initial powered positions.

Tighten Grub Screws:
Retighten the grub screws on the Hybrid/Y motor pulleys, taking care to avoid any rotational offset.

• If the grub screw does not align perfectly with the motor shaft flat, it can be tricky. Personally, I rotate the pulleys so the grub screws do not bite into the flat side of the shaft at all, tightening them securely(very hard) on the round surface instead.
• Alternatively, consider using radially clamping motor pulleys, which are ideal for avoiding such issues.

Results and comments:

I have tested a few "higher than normal" 3+ Kg tension/weights. All tests still provided better belt tension graphs and Input Shaper (IS) graphs compared to my previous manual tuning attempts. I have recently received feedback from other users to expect even better result with more normal/lower tension. But since he optimal tension might be size and type dependant i dont know yet. I will update this page with more findings later. Until then i advise you to start low weights 1-1.5Kg and increment up from there. Don't go super tight if you have unsupported motor shafts (no bearing on the shaft ends).  

While I did not observe any issues with these tension levels, it is important to note that excessive belt tension can increase strain on motors and and bearings and may potentially introduce printing artifacts and reduction in available acceleration. 

Printing Tips:

• Print two sets of each file.
• PLA works fine; print the small adapter solid for strength.

Hardware Needed:

• 2x 9mm timing belts (weighted belt)
• 2x Idler pulley stacks with bearings
• 2x 1mm washers (bearing spacers)
• 2x M5 bolts (bearing pulleys)
• 2x M6x12 bolts with T-nuts (frame mounting)
• 2x M3x14 bolts with hex nuts (belt clamp adapter)
• 2x M4x25mm or longer bolts (temporary tension bolt replacement for VC4 tensioners)
• 2x M5x40mm or longer bolts (temporary tension bolt replacement for Funssor type tensioners

Update (28.01.2024):
Recommended procedure  has been updated with info about hybrid motors and motor synchronization.
A custom parallel block has been added to the design files. Please print 2x.

Purpose:

• Acts as Y travel stops for the initial squaring of the gantry.
• Ensures the gantry can be held perpendicular at a distance from pulleys when “wiggling” the toolhead before locking in the final tension.
• The blocks are designed to match the height of the X/Y joiners. This allows you to rest the detached Y/Hybrid blocks on the parallel blocks while setting the Y/Hybrid belt tension, so they can be tensioned unaffected by friction losses in the coreXY system.

Update 2 (28.01.2024):
I received feedback that VC4 tensioners use M4 bolts as opposed to the M5 used on Funssor tensioners, i have therefore uploaded separate belt clips to fit the two types
also uploaded .step files for all parts as well.