Power to Weight Ratio

One very important consideration when talking about any kind of battery operated device is how much power is being generated by the batteries versus how much the device weighs. In our case, we don’t have a firm figure on weight of the robot but we can still learn some important figures from other devices.

From a quick Google, we can learn that the batteries for the Tesla Model S weigh 1,200 pounds and generate 85 kWh of energy. Scaling down i.e. estimating a 40 pound robot and dividing by the 1,200 pounds of the Tesla and multiplying times the 85 kWh of power generated equals 2.8 kWh of power roughly.

To give a perspective: Electricity is usually measured in kilowatt-hours (kWh). One kWh represents the amount of energy needed by a 1000-Watt device such as a clothes-iron or a microwave oven to operate for one hour. Leaving a 100-watt light bulb on for 10 hours consumes 1 kilowatt (kWh) of energy.

I would like the robot to be able to run for one hour before recharging so we’re somewhere in the neighborhood, but not quite there. We need to be very aware of weight in order to maximize battery life. Materials and distribution of weight/batteries will have a significant impact on this.

My plan is to use a wireless charging pad for the robot. When low, the robot will be smart enough to go lay down on the mat to recharge. Based on other devices, it will take 3-4 times the hours of use to recharge meaning 1 hour of use will require 3-4 hours of recharging. I will see if there is an opportunity to reduce that.

Hope that was interesting. I’ll be back with as we move this forward. Did I miss something? Get it wrong? Let me know. I don’t claim to be an engineer or roboticist.

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