ArloBot will not drive in a straight line when using the default driveGeometry values

[TCIII]

@chrisl8,

I found that ArloBot would veer off to the left when it should go straight when using 2D Nav Goal with Rviz.

So I ran ~/catkin_ws/src/ArloBot/scripts/PropellerSerialTest.sh and used cut and try (instead of the "[Borenstein, J., & Feng, L. (1995). UMBmark: A benchmark test for measuring odometry errors in mobile robots"] method) to adjust the wheelSymmetryError and the distancePerCount until ArloBot would go straight for 1 meter. I converged on the correct values farily quickly though I found that adjustments in the distancePerCount affected the wheelSymmetryError and vice versa. Here is what I found: wheelSymmetryError IS: 1.0, S/B: 0.79

distancePerCount IS: 0.00338, S/B: 0.00350

In the driveGeometry tuning guide you state that the wheelSymmetryError "accounts for a difference in left/right wheel diameter." I have accurately measured both of the six inch diameter wheels and when inflated to the same pressure, they both are the same diameter. The only thing that I can think of that is causing ArloBot to veer off to the left of a straight line, when wheelSymmetryError is set to 1.0, is that the right hand motor is turning faster than the left hand motor for the same drive voltage?

Comments?

Regards, TCIII

[TCIII]

https://github.com/chrisl8/ArloBot/issues/198#issuecomment-1080167112

[TCIII]

@chrisl8,

Thanks for the response and detailed guidance. 1) Both tires are inflated to the same pressure: 12 pounds atmospheric. 2) Both tires measure the same diameter. 3) There is no observable slip between the tires and driving surface. 4) There is approximately 1/2 inch of wheel circumference slop in the drive train between the motor and the wheel on both sides of the chassis. According to Parallax technical support this is expected and acceptable. 5) During the Rviz 2D Nav Goal the drawn path was initially straight ahead and ArloBot slowly veered to the left (began to turn slowly left CCW) instead of moving straight ahead as per the drawn path. 6) The slow drift to the left was observed when running ArloBot in a straight line for one meter using the maneuver function in ~/catkin_ws/src/ArloBot/scripts/PropellerSerialTest.sh with the default values for wheelSymmetryError and the distancePerCount. Changing to the wheelSymmetryError and the distancePerCount values I published in my post above corrected the slow drift to the left and kept ArloBot moving straight ahead for one meter.

When using the default wheelSymmetryError and the distancePerCount values ArloBot overshot the commanded angle of rotation both during CW and CCW operation. When I use my wheelSymmetryError and the distancePerCount values the ArloBot rotation to the commanded angle is virtually spot on during CW and CCW operation.

I will have to make a disclaimer here: My Arlo robot chassis uses the Eddie chassis and the Eddie motor/ wheels, but is using the Arlo encoder and wheel disks. The distance between the center of the Eddie chassis wheels is within a 0.01 meter of the default trackWidth so I have left it at the default value of 0.403 meter.

Comments?

Regards, TCIII

[TCIII]

https://github.com/chrisl8/ArloBot/issues/198#issuecomment-1080850767

[TCIII]

@chrisl8,

Are you using the Arlo Motor/Wheel Assemblies or the Eddie Motor Wheel Assemblies?

Mine are the original Eddie Motor/Wheel Assemblies.

Parallax Tech Supports says that the Arlo Motor/Wheel Assemblies can fit on the Eddie Robot Base (might have to possibly do a little clearance cutting of the Delrin chassis) and have significantly less gear train backlash which would be a real plus.

Comments?

TCIII

[chrisl8]

I am using the Arlo Motor/Wheel Assemblies.

[TCIII]

@chrisl8,

I purchased one of the remaining pairs of the Arlo Motor/Wheel assembly and it arrived on Saturday.

I quickly assembled the Motor/Wheel Assemblies on Sunday morning and installed them on my ArloBot, which was equipped with the original Eddie Motor/Wheel Assemblies, but had been converted to the ArloBot Encoders, this afternoon which was no mean trick especially when removing the battery plate with the batteries still on it.

After reassembling ArloBot I used the ~/catkin_ws/src/ArloBot/scripts/PropellerSerialTest.sh maneuver function to test the Arlo Motor/Wheel assemblies after I had set the distancePerCount: and wheelSymmetryError: values back to their default values.

The Arlo Motor Wheel Assemblies performed to expectations without the startup clunk of the Eddied Motor/Wheel Assemblies due to the 1/2 inch of wheel circumference slop inherent in the Eddie gear train. They are very quite and were almost spot on when performing the 1 meter travel test.

Definitely a worthwhile upgrade to my ArloBot chassis irrespective of the cost.

Now to try out making a map.

TCIII

[TCIII]

@chrisl8,

I am closing this issue since I was able to resolve the maneuvering issue by replacing the original Eddie Motor/Wheel assemblies with the Arlo Motor/Wheel assemblies.

Regards, TCIII