Motor control and torque

Quite a few questions I’d like answered for an at home project:
I would like some advice on motor components and the partnering pieces to run with wheels and an Arduino. My first query is to do with 2 normal or gear motors that would be connected to wheels directly (without axle due to shape of design). The wheels need to move (at most) a walking speed and carry around 5kgs along carpet. I would like a stepper motor that has a torque of 20Nm - to rotate up to a 80 degree angle, could you please guide me on what motors would be preferable?
In order to control these 3 motors I’d like to purchase a motor drive shield but I’m unsure of which one would be appropriate, at any one point it will either be the 2 normal motors running together or the stepper motor running on its own, could you also please advise me on this?
I friend of mine suggested a micro controller however I’m using an Arduino Uno and the motor drive shield - is it necessary?
What sort of power source would be required to run these motors, that wouldn’t require the device to be plugged into a wall?

Thanks for all you contributions

An Arduino Uno contains a microcontroller, so you’re all set there. Unless your friend had some other reason, like available code space.

A motor drive shield is certainly helpful for where you want an Arduino Uno to drive motors.

Power source would be a battery, which will contribute to the weight of the vehicle. The size of the battery would depend on the time of movement. Small battery for something that has to move for a few seconds, or a large battery for something that has to do it all day. Lightest batteries are lithium polymer.

Here’s a design sequence;

  • work out the time of movement you need,
  • choose a chassis and motor set that will do what you need; 5kg at 6km/h,
  • based on the current and voltage of the motors, calculate the power,
  • based on the time of movement and the power, choose a battery that holds that much power for that much time,
  • based on the current and voltage of the motors, select a motor drive shield, or make your own.

You may need to go through the design sequence a few times Hope that helps.

Thank you for the guidance on the microcontroller and motor drive shield. Do you know if lithium polymer batteries are rechargeable - I was looking at heavy duty lithium ion batteries such as the ones used in cordless drills, would be this be acceptable?

Also do you know any specifics on the motor strengths?

Yes, lithium polymer batteries are rechargeable; they are used in phones, tablets, and laptops. They must have a special charging circuit though, because doing it wrong starts a fire. A lithium ion battery can be a lithium polymer battery too. I would not use the ones on cordless drills because I wouldn’t know their safe charging method, and the cordless drill manufacturers tend to keep that knowledge secret. You can find some lithium batteries on Little Bird Electronics.

No, I don’t know any specifics on the motor strengths. It isn’t something I’ve got into for a while. I would start by looking at a chassis with motors included rather than selecting motors themselves.

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