While I am waiting on my components, thought I would do the math to figure out how fast the bot would travel carrying 50 gallons of water (400 lbs) in a reservoir.

Wheel size: 6 inches diameter.

Wheel size sprocket:3 inches OD.

Motor size sprocket:2 inches OD.

Reduction ratio: 1.5 to 1

Target water weight: 400 lbs (50 gallons)

Torque rating of the (50rpm) motor = 8ft-lbs.

Torque to drive the wheel: 8 ft-lbs x 1.5 = 12 ft-lbs.

Convert units from ft-lbs to in-lbs: 12 ft-lbs x 12 = 144 in-lbs.

Convert to force: 144 in-lbs / 3 in = 48 force lbs

48 lbs force: traction of one wheel

Maximum traction for two wheels: 48 lbs force x 2 = 96 lbs force

96 lbs force = 427 N (Newton)

6 in = 0.152 meter

400 lbs = 181 kg.

427 N = 181 kg x a and a = 2.36 m/sec^2

50rpm / 1.5 = 33.3rpm = 0.556 rev/second

0.556 rev/second x 6 in x Pi = 10.5 inch/second = 0.267 m/s (final speed).

2.36 m/sec^2 = (0.267 m/s - 0 m/s) /0.11 s

Conclusion:

400 lbs robot should be able to move from static to 10.5 inch/second in just 0.11 second.

** Probably slower because I didn’t account for debris / rubble on the ground, uneven surface, etc … also, climbing a slope may create issues as well.

Of course, 50 gallons is the end goal. For the initial build the reservoir will contain only 35 gallons of water ( 280 lbs )