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Aarhus-University-MPE / ArcticRover

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Insufficient motor torque #5

Open grinsted opened 2 years ago

grinsted commented 2 years ago

ArcticRover firmware version

No response

Area(s) with issue?

Hardware Issue

Steps to reproduce

Wrap wheels in snowmobile belt (to ensure good traction). Drive into soft snow, where the wheels sink in by 5-10cm.

✔️ Expected Behavior

That the wheels keep turning even if traction is good and the wheels have sunk in a little into the snow.

❌ Actual Behavior

Motors stalled. (insufficient torque).

grinsted commented 2 years ago

It is unclear if this is because the motors are underperforming or if they are underdimensioned.

MadsR commented 2 years ago

Using the motor torque (60Nm) and the new wheel diameter (~50cm), each motor is able to lift 22 kg, for a total of 44 kg. The total weight of the rover is approximately 170 kg, meaning it would need >85 kg to be able to lift the front of the rover vertically.

The torque needed to lift its own weight vertically would be approximately 120 Nm, resulting in a power to weight ratio of 1.41 Nm/kg (currently 0.71 Nm/kg). Comparing this to a model 3 Tesla, which has 0.37 Nm/kg. Or (quick google search) a 2 stroke snowmobile 200 kg / 135 Nm = 0.68 Nm/kg.

I don't think this is a matter of increasing torque, but reducing the sinking.