I'm making an electric wheelchair . I want to lift a total weight of 100kg on it with a max speed of 4mph. So help me choose appropriate motors(dc geared , stepper, or .....) and batteries (12 or 24 V) for the project. I plan to use two motors driving the back wheels.

My calculations so far:

F=ma + uN = 100x 0.5 +0.04x980 = 90 N approx I used an acceleration of 0.5 max, u=0.04 maximum for the roughest surface possible; I calculated the normal force N using N=mg.

Radius of my tire is 0.15 m.
power = force x velocity(max) = 90 x 4 = 360W
torque= force x radius = 90 x 0.15= 13.5 Nm or take 15 Nm (max).

What should be the current requirements because torque is directly proportional to current and speed to voltage. high rpm decreases the torque...

  • 2
    \$\begingroup\$ "4 mps" is quite quick for a wheelchair. \$\endgroup\$ – Andy aka Oct 28 '15 at 11:14
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    \$\begingroup\$ So far so good, you're doing OK. The next step is to understand the voltage/speed/torque/current relationships in motors, and look at some actual motor specs. You will also need gearing (or toothed belt drive) between motor and wheels, allowing you to match high speed low torque motors to your low speed high torque needs. \$\endgroup\$ – Brian Drummond Oct 28 '15 at 11:17
  • \$\begingroup\$ You might also think about if the wheelchair can climb ramps if that is needed. \$\endgroup\$ – 0x6d64 Oct 28 '15 at 11:24
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    \$\begingroup\$ Rather than worry about current per se, I notice you have already computed power at 360W, stick with that. Allow a 50% efficney for motors of that size, so you need 720 electrical watts. If 12v motors, then a current of 60A is needed, for 24v motors you would need only 30A. Generally, higher voltage and lower current makes for easier wiring, devices etc. 42v is an emergeing standard for hybrid cars, so there will be lots of nice new silicon designed around that voltage, though 24v is likely to be the highest voltage motor you'll find easily in that power. \$\endgroup\$ – Neil_UK Oct 28 '15 at 11:47
  • \$\begingroup\$ sorry it's 4 mps. Thank you for your support, everybody and ANDY AKA, m taking 15 kph max speed for my wheelchair which is almost equivalent to 4 mps. I hope it's gonna work. \$\endgroup\$ – Deepak Lodhi Oct 28 '15 at 13:33

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