Hi,
I am building the URDF for the FastBot robot and I am stuck on two things related to the base plate geometry and wheel axle positioning. Would appreciate some help!
Background:
The FastBot has a two-part base plate:
- Larger plate (front, houses caster wheel): 78mm in X, 120mm in Y, 3mm thick
- Smaller plate (rear, houses drive wheels): 72mm in X, 92mm in Y, 3mm thick
I am using the convention: X=forward, Y=left, Z=up.
Question 1: What do the ±0.070 markings represent in the top view?
In the reference CAD top view image, there are orange bounding box annotations showing ±0.070 in the X direction. However:
- The larger plate is 78mm in X
- The smaller plate is 72mm in X
- Combined length = 150mm
None of these cleanly explain where ±0.070 comes from. My best guess is that the origin (0,0) is not at the junction of the two plates, and ±0.070 represents the front and rear ends of the combined plate — but that would make total length 140mm which doesn’t match 150mm either.
Is there an overlap between the two plates that I am missing?
Question 2: Confirming the wheel axle X position
From the side view image, the motor shaft annotation shows the axle is 0.011m from the rear end of the motor+support block. The motor+support block is 75mm long in X, with its center at x = -0.015mfrom origin, giving:
- Rear edge of motor block = -0.015 - 0.0375 = -0.0525m
- Axle position = -0.0525 + 0.011 = -0.0415m
The drive wheels have a 32.5mm radius. Is x = -0.0415m the correct position for the wheel joint origin in the URDF.
Alternatively, do the STL files of the wheel already have the position offset we need for the wheel?
Any help or clarification would be greatly appreciated!
Best,
Ninad Mehta