### Author Topic: Electric WheelChair project Help ! Urgent  (Read 4419 times)

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#### andrwo2

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##### Electric WheelChair project Help ! Urgent
« on: February 21, 2012, 04:50:10 AM »
Hello guys ,

I'm doing a solar panel powered electric wheelchair ,

I Will have a weight of total 100 kg (  person + motors + wheels + batteries + panel )

I will use 2 identical motors to power the 2  back wheels of  20 cm of diameter  each

I need you to help me to know the specifications  of the motor i should buy  , ( torque , power , rpm )

I have no idea to relate the weight to the torque and power i need !!  knowing that the ideal speed of an electric wheelchair  is  3 to  5  mph

Waiting for your help   , thank you guys

#### newInRobotics

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##### Re: Electric WheelChair project Help ! Urgent
« Reply #1 on: February 21, 2012, 05:29:45 AM »
Hi there,

knowing that the ideal speed of an electric wheelchair  is  3 to  5  mph
1. If You use wheels with diameter of 20 cm, then circumference of the wheel = ~62.8 cm
2. Required speed is 5m/h, which equals to 13411.2 cm/min
2. All of the above gives us that motor RPM should be 13411.2/62.8 = ~213.6 RPM

I need you to help me to know the specifications  of the motor i should buy  [...]
If max weight carried is equal to 100kg and wheel radius is 10cm then torque required must be no less than 100/10 = 10 kg-cm. Two motors must be able to deliver at least half of that torque at 213.6 RPM in order to meet requirements.

What voltage are You planning to use to drive motors?
« Last Edit: February 21, 2012, 05:34:25 AM by newInRobotics »
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

#### andrwo2

• Jr. Member
• Posts: 7
##### Re: Electric WheelChair project Help ! Urgent
« Reply #2 on: February 22, 2012, 02:30:41 AM »
12 or 24 volt

#### newInRobotics

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##### Re: Electric WheelChair project Help ! Urgent
« Reply #3 on: February 22, 2012, 03:10:27 AM »
12 or 24 volt
So which one? 12V or 24V?
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

#### andrwo2

• Jr. Member
• Posts: 7
##### Re: Electric WheelChair project Help ! Urgent
« Reply #4 on: February 22, 2012, 04:35:02 AM »
it depends on which i find in market but i want 12 V !  but  can i ask a question !

what formulas did you use to calculate the torque  ?

F = m * a  ( a ? is this the acceleration of gravity 9.8 or the acceleration i use to reach the max speed )

T of one motor  = F/2 * R (   R = 10 cm )

is that right ?

V =  pi * diamter * w ( in rps )  (  * 60 ) to get it in RPM ?

#### andrwo2

• Jr. Member
• Posts: 7
##### Re: Electric WheelChair project Help ! Urgent
« Reply #5 on: February 22, 2012, 04:57:28 AM »
through my formulas :  F = 100 * 1.5 =  150 N

Torque ( per wheel ) =  150 /2   * 0.1 = 7.5 N.M   WHICH IS EQUAL   76  Kg. cm

is that wrong ? and why ?

#### newInRobotics

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##### Re: Electric WheelChair project Help ! Urgent
« Reply #6 on: February 22, 2012, 05:07:17 AM »
My first post in this thread outlines formulas used quite well

torqueToMoveVehicle = vehicleWeight / wheelRadius;

circumference  = radius * pi;

rpm = desiredSpeed / circumference;
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

#### andrwo2

• Jr. Member
• Posts: 7
##### Re: Electric WheelChair project Help ! Urgent
« Reply #7 on: February 22, 2012, 05:11:07 AM »
so i shall not use these equations ?
http://www.societyofrobots.com/mechanics_dynamics.shtml

im really confused and i can't get the exact information

sorry

#### newInRobotics

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##### Re: Electric WheelChair project Help ! Urgent
« Reply #8 on: February 22, 2012, 06:00:04 AM »
so i shall not use these equations ?
http://www.societyofrobots.com/mechanics_dynamics.shtml

im really confused and i can't get the exact information

sorry
These equations use You shall

Desired values one must know if equation result correct must be

What is desired acceleration (in how many seconds do You want Your vehicle to reach 5mph)?

Example: If You want 5mph to be reached in 3 seconds, then desired acceleration is 5mph/3 = ~2.45ft/s^2 = ~0.75m/s^2;
Now, force required to achieve that (on flat ground) = 100kg * 0.75m/s^2 = 75N (Newtons);
Torque required (leaving friction out) to achieve the goal = 75N * 10cm = 750N-cm = ~76.5kgf-cm

Before You did not specify what acceleration You need, hence 10kgf-cm is overall torque required to move object from the spot.
« Last Edit: February 22, 2012, 06:04:09 AM by newInRobotics »
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

#### Soeren

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##### Re: Electric WheelChair project Help ! Urgent
« Reply #9 on: February 23, 2012, 07:40:44 PM »
Hi,

I'm doing a solar panel powered electric wheelchair ,

I Will have a weight of total 100 kg (  person + motors + wheels + batteries + panel )
Did you consider just how little power you can get from even the largest panels you can fit?
You might wanna use a battery and let the panels add however much (or little) they can.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?