# Motor vs weight

I hope someone can help me out with please. Revolving platform on rollers. weight 800kg. Add car that parks on top . Weight 2000kg Total weight 2800kg to be rotated. 6x dc motors pushing against the edge of the platform.making it rotate. motor code TTOEC070240-S2 MOTOR SPECS 24V 0.07 NM 3000rpm 100watt GEARBOX MNRV025 60-1 RATIO

100mm rubber wheels attached to gearbox. The wheels push against the platform edge to make it rotate. Final speed out of gearbox is 50rpm Platform is 4.4m diameter

Everything works well with current setup but, the gearboxes overheat. Cannot take the 3000rpm input. My question is, If I supplied 12v instead of 24v power to the motors, I would be reducing the motor speed to 1500rpm. Which is acceptable to the gearboxes. But I have to change the gearbox ratio to 30-1 so as to keep the final rpm at 50 rpm. Will there be enough power to push the 2800kg mass?

Thanks in advance

## 1 Answer

The weight is not really relevant, it is the rolling friction. In steady state the motor torque $$\tau_m$$ is equal to the friction torque $$\tau_f$$ which is related to angular velocity $$\omega$$ by

$$\tau_f = B \omega$$

where $$B$$ is the friction coefficient (which will be proportional to weight). The power required is

$$P = \tau_f \omega = B \omega^2$$

so if you halve the input voltage you will need to double the current to provide the same amount of power, ie. to rotate the turntable at the same speed. This is likely to move the pain from the gearboxes to the motors. Perhaps add more motors at the original gear ratios so that everything is a bit less stressed -- your components will last longer.