DC Brushless Motor For Electric Rover

Question

I'm an industrial designer, and am working on building a small electronic rover,

however I've been doing some research and I feel a little bit lost in terms of what motor is best for me,

The device consist on a 4wd electric vehicle, (a dc brushless motor on each wheel)

Wheel diameter: 7cm

Weight carried: 100kg (mass 980N)

Top speed: 20km/h (results in about 2000rpm)

Acceleration: 0.4m/ss (value may vary)

After doing some research I plugged numbers in equations and figured out the following:

Total torque: 40N

Torque in each motor: 0.350Nm

Power required by each motor: 73 watts

Now, this means I need a dc motor which gives me 2000rpm and a 0.350Nm torque As I have little experience with these motors, I can't seem to find any that match these settings,

The question is: Am I looking for something feasible by a dc brushless motor?

Follow-up question: What Voltage/Amperage values am I to expect from a motor of these characteristics?

Answer 1

This is a bit off-the-cuff mathematically just to see if things stack-up: -

Your mass is 100 kg and your top speed is 20 kmph (5.56 m/s).

You want to accelerate at 0.4 m/\$s^2\$ - this means it'll take about 14 seconds to get to full speed.

The energy attained by 100 kg at 5.56 m/s is \$\dfrac{mV^2}{2}\$ = 1546 J and this equates to a power during acceleration of \$\dfrac{1546}{14}\$ = 110 watts or about 28 watts per motor.

Am I looking for something feasible by a dc brushless motor?

It definitely sounds feasible - I don't see why you shouldn't find a brushless motor like this but it'll be easier to find a brushed one for sure.

What Voltage/Amperage values am I to expect from a motor of these characteristics?

I think you can be looking at 80% efficiency so each motor will consume about 35 watts. 4 x 12V, 3A full-load rated motor should work but maybe I'd play conservative and go for something like 50 watts: -

I know these aren't cheap but it was virtually the first hit when I searched for "50W brushless motor". There should be plenty that are a bit cheaper.

Try this too - maxon are the supplier.

Answer 2

This is definitely in the realm of possibilities, you just need to know where to look. I would google "fractional horsepower brushless DC motor" and you'll get multiple manufacturers.

As far as voltage/current, typical voltages for this size motor would be 12, 24, and sometimes 48 V. And Andy aka is correct in his assumption of about 80% efficiency for a motor this size. That is a pretty typical value. Assuming 73 W output power, this would give you currents of 7.6 A, 3.8 A, and 1.9 A for 12 V, 24 V, and 48 V, respectively. If you assume 90% efficient control, you are looking at currents closer to 8.4 A, 4.2 A, and 2.1 A, respectively.