Is it possible to input two PWM signals into an Arduino and use one as output

I wish to build a four wheel drive wheelchair, two existing motors and add a third motor on the rear axle.
My knowledge of electronics is nil. My concept was to find a way of “ listening “ to the signals
to the existing motors , select the signal for the faster turning motor and re transmit that signal to run the third motor.( the two motors control the steering hence varying speeds , axle needs to match the faster turning of these motors)
My understanding is this should be possible via an Arduino or similar and a dc motor controller that can handle 24v and 10amps continuously .
Is this possible, all help will be much appreciated.
Tony

"My concept was to find a way of " listening " to the signals
to the existing motors ,"

All depends on WHAT those signals are? Do you know?

Paul

Paul , sorry I should have said they are PWM Signals to the motors(, 24v 10amp).

Amk1:
Paul , sorry I should have said they are PWM Signals to the motors(, 24v 10amp).

Then they are not "signals". They are actually POWERING the motors

You may be able to use voltage dividing resistors to lower the voltage to something an Arduino is able to use, if one side of the PWM is at ground level.

In any case, the Arduino cannot ever create a 24 volt PWM power train to power the motors. There is much more that would have to be designed.

Paul

Thank you Paul
As you recognise my electronic knowledge is nil.
I had appreciated that the Arduino would not be able to drive a motor and that some interface will be required , but again I am ignorant on what and how.
Is the concept feasible? If so help on how to build a system is my problem.

Feasible, of course, but clearly a lot of work.

How much time and resources do you have?

Do you have an Arduino? Have you worked through basic exercises with it?

You said

Amk1:
I wish to build a four wheel drive wheelchair

so what have you done so far?


And it occurs to me to wonder how a “four wheel drive wheelchair” could have “a third motor on the rear axle”?

…select the signal for the faster turning motor and re transmit that signal to run the third motor…

This logic isn’t right. I take it you turn the two front wheels at different speeds to steer the wheelchair. That’s fine so far, different speeds is how many types of vehicles steer. However the rear wheels will not be turning at the same rate as the fastest front wheel.

Here is a diagram:

The blue T represents your chair before a sharp left turn, and the red T is the chair in the middle of the turn.

The right front wheel is the fastest wheel. Note that the rear wheels do not quite travel as far as the right front wheel, thus they are not turning as fast. More importantly, note that the rear wheels (like the front wheels) do not turn at the same speed, in order to turn the same angle.

So you will either need independent motors on the rear wheels or a differential gear that can spin the two rear wheels at different speeds.

Paul,
Re time I am retired so in theory have time available.
No I don’t have an Arduino , trying to explore the way forward before buying kit, which may prove unusable.re single rear motor this drives a transaxle with differential, ie as with road cars etc.

Thank you Chris, you are correct if the rear axle doesn’t have a differential thus allowing the rear wheel to turn at different speeds.
My concept is a system which takes the speed of the fastest front wheel and turns the rear transaxle at the same speed. The differential then adjusting the rear wheels to match the speed required for the turning circle.

So your proposal is puzzling.

It would seem that your first statement should have been: "I wish to modify a two wheel drive wheelchair to four wheel drive".

Four wheel drive is not in itself about control of wheel speed, but in providing thrust to all four wheels. And thrust is more-or-less proportional to the PWM power being applied. There is no obvious advantage of matching the rear wheel speed to the speed that the front wheels are turning at a given moment, but you may want the rear wheels to supplement the driving thrust.

ChrisTenone has indicated a certain geometry. This also presumes the rear wheels caster, in which case a differential will be a singular engineering problem.

As I indicated, the problem quickly becomes much more complex. If you did need to arrange powering of the rear wheels, you would obviously integrate this directly into the control system, not as an add-on. You have a lot more design work to do before you become concerned about PWM signals! :astonished:

Thank you Paul,
I am clearly displaying my electronic ignorance and greatly appreciate all the input.
Re rear wheels and caster, I have the front wheels turning in the same manner as a car, with the track arms at the correct Ackerman angle and the rear axle with a differential.
Re the thrust , thank you, you are correct that I wish to supplement the drive with power to the rear axle. Our adult granddaughter loves the beach, and currently her wheelchair cannot cross the soft sand to gain access. The existing front casters dig in. And going in reverse whilst better is still very difficult.
Electronics , due to my ignorance had thought it easier to add onto the current controls, joy stick and existing “ control box” on the chair. Am I trying the impossible, or most difficult route?

Millie is unable to drive any form of wheelchair, joystick is at the rear so that parents etc control.

Quote: " Millie is unable to drive any form of wheelchair, joystick is at the rear so that parents etc control.".

Obvious lack of research on your part. There are lots of wheel chairs available to traverse any type of surface. Go research the VA offerings for disabled veterans.

Paul

Wow, yeah. I wish you had told us the purpose first off. Merely mking the rear wheels drive wheels will not insure that the chair will be able to roll on sand. The most important part of traversing sand (or mud or vegitation, etc.) is weight distribution. You will get best results with large balloon tires. 4 wheel drive will help, but with skinny wheelchair tires, they will always dig into sand. You want wheels that will ‘float’ on top, so the part that contacts the ground needs to be large.

I turned this one up in the first page of a search for “all terrain wheelchair”:

Look at that! It’s made from PVC pipe, and could be a good diy project. They even sell the wheels separately.

Thank you Chris,
We were aware of the need for wide wheels and by coincidence had seen the chair you display, but trying to make a driven chair ,Millie is an adult and power makes parents and careers life easier. When at school one teacher refused to push her chair, even on paved paths- claimed too difficult!
The other usual challenge is cost, specialised chairs are thousands of pounds.Millie’s father is an engineer so making is not a challenge and much cheaper.

Amk1:
...The other usual challenge is cost, specialised chairs are thousands of pounds.Millie’s father is an engineer so making is not a challenge and much cheaper.

Precisely why I suggested DIY. A plastic beach chair could easily be made, motorized and automated. I have seen chairs that utilize all sorts of alternative controls, such as head movement, and even breath control, or as you are thinking, control from the push handle area.

ChrisTenone:
Look at that! It's made from PVC pipe, and could be a good diy project. They even sell the wheels separately.

But not powered, so not particularly relevant here.

Amk1:
Re rear wheels and caster, I have the front wheels turning in the same manner as a car, with the track arms at the correct Ackerman angle and the rear axle with a differential.

So you are not using differential steering then? You have a "steering wheel" or joystick.

You need to describe this in more detail.

I am not sure. Is this any actual construction, or purely notional? If the former, let's have some pictures.

This is a concept at the moment, though we do have motors axle and original electric wheelchair electrical components. Control will be via a joystick, carer will control chair.
As with life there are conflicting aspects to take into account. Need to cross soft ground, therefore wider wheels but chair still must fit into the car ( converted to accept wheelchair , ramp lowered floor ,winch, hold down straps etc)
. Seat must recline and securely hold Millie when she has a fit and becomes floppy and immobile. Ideally seat to rise and move forward to assist her into and out of the chair.
We believe we can find reasonable solutions to all these aspects.
Our challenge is how to control the electronics , power drive is necessary, access to beaches in Cornwall are all via slipways, area is also hilly.

Paul,
Thank you for the input.

Unfamiliar with the system of loading files, hopefully rough sketch attached?

Second attempt at loading sketch

Paul__B:
But not powered, so not particularly relevant here.
...

Obviously there are no electrical parts in the chassis. Amk1 would need to build all that AND engineer a way to couple the wheels to the motors (a shaft or belt drive). Fat tires are the key to rolling on sand. Starting with Arduino controlled joystick steering is an XYish solution. It does use an Arduino, so it's relevant here, but it's unlikely to lead to a chair that can maneuver on sand.

Chris . We already have transaxle( which includes a differential) and motor units for each of the wheels which steer. No need for drive shafts , chains etc. Chassis construction is not a challenge, electronics is a huge hurdle for us.
All your inputs are relevant and helpful
Hopefully my sketch file is visible?