Touch Path Driving With Sabertooth

Yes - for Touch Path + Sabertooth, the most reliable setup is usually:

Recommended approach

1) Use Hardware UART instead of Software Serial

For timed path driving like Touch Path, hardware UART is strongly preferred. Software serial can be more sensitive to timing jitter because Touch Path is issuing timed movement changes back-to-back.

On an EZB v4, configure the Sabertooth Movement Panel to use a hardware UART if available, and match the Sabertooth baud exactly.

Sabertooth docs:

• Sabertooth Movement Panel

2) Make sure the Sabertooth dip switches match the baud and mode

For Simplified Serial, verify the Sabertooth 2x12 DIP switches are set for:

• Simplified Serial
• Correct baud rate matching ARC

If ARC is set to 9600, the Sabertooth must be set to 9600.
If you’re not sure, I’d recommend testing at the Sabertooth’s recommended Simplified Serial baud for your model and keeping ARC matched to that.

3) Keep Touch Path speeds conservative

Touch Path is timed movement, not encoder-based movement. That means the robot is never truly "measuring" whether it made the turn correctly - it’s only estimating based on time.

For a rover like Roli, try:

• Movement Speed: 35-50
• Turning Speed: 25-40

Your 60/40 is not crazy, but if the rover is overshooting or under-turning, reduce both and re-test.

Touch Path overview:

• Touch Path Skill

4) Calibrate in this order

A good workflow is:

1. Confirm Sabertooth manual driving works
   You already did this - great.

2. Test Touch Path with one very short line

   • Forward only
   • Then a simple right turn only
   • Then an L-shape

3. Tune turning first If the rover turns too little, increase turning speed slightly. If it turns too much, reduce turning speed.

4. Tune forward second If it travels too far on straight segments, reduce movement speed.

5) Expect some drift with Touch Path

Even when everything is configured correctly, Touch Path will never be as consistent as encoder-based navigation because:

• battery voltage changes motor speed
• floor surface affects traction
• rover weight and wheel slip change turn distance
• timed movement is approximate by design

So occasional slight mismatch is normal.

About the "dropped" commands

What you described - forward works, then turn hesitates or the last forward is ignored - usually points to one of these:

• Software serial timing instability
• baud mismatch
• movement timing being too aggressive
• the rover is still completing a prior motion when the next command arrives
• turn duration is too short for that chassis

Since hardware UART improved consistency for you, that’s a strong clue that timing reliability is the issue, not the Sabertooth hardware itself.

What I would try next

Best test settings

Try this setup:

• Sabertooth Movement Panel: Hardware UART
• Baud: whatever your Sabertooth DIP switches are set to
• Touch Path Movement Speed: 40
• Touch Path Turning Speed: 30

Then test:

• straight line
• 90 turn
• L-shape
• square path

If it still under-turns, raise turning speed in steps of 5.

Wiring checklist

For the Sabertooth 2x12 in Simplified Serial:

• Sabertooth S1 UART TX from EZB
• GND common between EZB and Sabertooth
• Battery directly to Sabertooth power terminals
• No motor power from the EZB

If you use hardware UART, make sure you’re on the correct UART port in ARC’s Sabertooth configuration.

ARC note

If you want more reliable path following than Touch Path, ARC can do better with sensor feedback such as:

• encoders
• IMU heading correction
• distance sensing
• navigation messaging / autonomous logic

Touch Path is great for demo-style timed driving, but for a rover you’ll usually get better consistency by adding feedback. If needed, I can help you build a simple JavaScript-based path driver in ARC that uses timed turns plus a heading sensor for better repeatability.

If you want, I can help you with either of these next steps:

1. Exact Sabertooth UART wiring/settings for Roli, or
2. A Touch Path calibration table for your rover speeds and turn times.