This is my first large project as an electrical engineering student and I'm working with DC motors for the very first time.

I'm working on designing an unmanned ground vehicle that will weigh approximately 1200 pounds maximum.

I'm having trouble determining the power rating and type of DC motor and electric drive-train to use. Each wheel must have independent motor.

I Cannot use Lithium Ion type batteries.

It must also be durable and rugged.

I've looked at the in-hub type DC motors but I am having trouble determine what size each motor must be, and how to control the speed of each of the in-hub motors.

Any suggestions on how to calculate motor size and ratings, control mechanisms.


closed as too broad by Trevor_G, Brian Carlton, Chris Stratton, Voltage Spike, Enric Blanco Jun 14 '17 at 8:40

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Way too wide a question. This is also really more of a mechanical engineering question to figure out what shaft speeds and torques you need. Once you know that you can look for a motor that matches, or find your best bet and have the spanner guys rethink their end. However, even in the mechanical engineering forum this question is probably still too broad. \$\endgroup\$ – Trevor_G Jun 13 '17 at 21:22
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    \$\begingroup\$ "cannot use Lithium Ion type batteries" is really limiting; you'll end up with much of the weight being lead-acid batteries. \$\endgroup\$ – pjc50 Jun 13 '17 at 21:32
  • \$\begingroup\$ A word about in-hub motors. They are unadviseable as they add unsuspended mass. For a light, slow vehicle it doesn't matter but as soon you add suspended weight and drive a bit faster, you really want to have the unsuspended mass as light as possible. \$\endgroup\$ – Janka Jun 13 '17 at 21:45
  • \$\begingroup\$ The client for the project does not approve the use of Lithium Ion batteries due to volatility and the fact it will have to be shipped commercially, possibly via plane. \$\endgroup\$ – egcfsu.13 Jun 13 '17 at 22:02
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    \$\begingroup\$ "1200 pounds". Go metric, man. Use SI units. It eliminates most of the conversion factors. \$\endgroup\$ – Transistor Jun 13 '17 at 22:06

When sizing things, think physics and energy. The motor converts electricity So find out the max torque load at a given speed and then convert that to energy. The wheel will not turn if you put more torque on the motor than the stall torque is rated for.

f you can find an efficiency number on the datasheet then use that to help determine how much electrical power you need.

Remember when sizing physical systems for design requirements, if you can't find a value exactly (like torque on a wheel) then estimate it. Add margin to make the difference with cost in consideration. (So if you think your only going to put 50Nm of force on the wheel, then get a motor with a stall torque of 60Nm.

Here is more info on sizing motors.

  • \$\begingroup\$ This is very helpful! I'm not so good at the mechanical side of things, but I'm working on that. \$\endgroup\$ – egcfsu.13 Jun 13 '17 at 22:03

You should start by making the Power and energy budgets. I will try to simplify as much as possible and generalize.

1-Power= Torque X speed

The torque depends on the weight and acceleration required .

The speed is based on motor RPM , gear ratio and wheel diameter .

Now you can decide the Power rating of the motor . After this start selecting the preferred motor type between brush-less (HUB motor for example) or brushed (wheel chair motor for example)

2-Energy= Power X time

How much does the robot have to operate and in which conditions , on-road or off-road , slopes ,etc... This is required to size your battery

This tool does all the required for you :Roboshop Drive motor Sizing


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