No one can answer that question sensibly - the capacitor size depends on the H bridge design, the size of the motor, the precise nature of the power supply, the length of the wires etc etc.
You are way out of your depth here - you need to learn a lot more about circuit design than you seem to know to design your own motor control stuff or alternatively find a ready made design that does what you want.
There are companies that sell ready made motor controllers with instructions and support but they are not at Arduino type prices.
If you post a circuit (schematic) of your design so far it might be possible to advise about component values. (You need to put all the component values and types that you do know on the diagram and ideally explain how you got there.)
When using PWM to drive H-Bridge type power amplifiers, use 1,000uF per ampere of motor current. For example, if you use a 12V 10A DC motors, each of their H-Bridge supplies should use 10,000uF 25V capacitors, connected as close as possible to the H-Bridge.
1. Read an analog 2-axis joystick with the Arduino analog input ports. The magnitude and direction of the X-axis input of the joystick should output a differential PWM output to the left and right DC motor H-Bridge amplifiers which is applied to the PWM duty-cycle worked out in point 2 below.
2. The Y-axis input of the joystick should control the duty-cycle of the PWM, i.e. the speed of the wheelchair.
3. There should be an Emergency Stop switch, easily accessible by the user of the wheelchair.
4 Steering will be effected by using caster wheels in front and differential drive to left and right motors ( Point 1 above)
5. You may also want to examine raising and lowering the chair with an up/down selector, to empower the wheelchair user in raising him/her to the height of upright bipedal people.
Before you actually allow a differently abled person to use the wheelchair, you will need to examine safety features like over-riding the system if it begins to misbehave due to faulty input from the joystick. Please ensure you use a WDT (watch dog timer) system to check that your processor has not locked up with a certain output.
It's good to have some rough estimates, but can you give a bit of background on this estimation? Do you know where this figure (10,000uF) comes from? Also, can you give a guideline for the ripple current needed in these capacitors?
Victor, I design and build DC servo drives. The figure of 1000uF per Ampere is derived from years of practice across over a thousand servo drives... Do remember, the capacitor is to be placed at the input to the H-Bridge, never at the output...
OK, cool. Just wondered whether there's a theoretical background for your experience. Not that I don't trust you, more that I'd like to know whether I could have done some back-of-the-napkin calculation to get to the same result.
Look up how to read a potentiometer via the analog port. A joystick has two potentiometers - one for X and the other for Y axis. The Arduino's 10-bit ADC will give you 0-1023 values between 0V and Aref (usually 5V). Obviously, whatever maximum and minimum values you get for X and Y axes, the centre-point of the joystick will be approximately at the middle of the two extrema. To get a feedback of the two extrema and the centre-point value, read the values and print them to the serial monitor with a serial.print command. Please look up how to use that... make use of the copious examples accompanying the IDE...
