4 DOF en Smart For Two (real) HELP ME!!! please!!!

THIS is my project:

Is a Smart For two real car, My intention is to change the stock shock absorbers (all 4) for pneumatic pistons. I am new to this, I do not have any experience in setting up simulators, I studied electronics, I have worked as an electrician, and I have knowledge in computer programming, I also know how to solder iron. I need your help to start and finish this project "with dignity." Thank you very much, I hope for your help!
I live in Girona (Spain).

I'm already in contact with him via private messages, and he's been a great help. I'll try not to repeat the same questions on the forum and will use the search function instead. Thank you very much.

Hello,
I have seen several options, and I think the most logical would be to make a 2 DOF, but with 4 motors (or 4 actuators), one on each wheel, only doing the ROLL and PITCH movement.
The 4 wheels are going to touch the ground and move, I want to change the original suspension of the car, for the 4 actuators, I have no idea how to start, or what type of motors to use, the car does not have an engine, I am going to disassemble the entire mechanical part, to remove weight, even so, it can weigh quite a bit... Any suggestions on where to start? High power electric motors? or pneumatic??

Pneumatic cylinders are an easy way to move heavy things but they are difficult to control if you need a defined position other then the ends of the stroke. You'd need proportional/analogue valves that are very expensive and then it's still difficult to control as you can control only force (pressure) but not position (volume) directly.
With hydraulics it would be better because the fluid is incompressible making position control easier but it would get even more expensive and you'd need a very powerful pump (I estimate at least 15kW).

So my suggestion is to use pneumatic cylinders in the center to support at least part of the weight so that the electrical motors at the 4 wheels need less power.

If you really want only 2DOF you could also mount the whole car on a universal joint in the middle to support the full weight. But with 4 actuators you'd get the 3rd DOF for free so why not use it.

Thanks for your response. I want all four wheels to remain on the ground, and I'd like to be able to push the car to move it. Without the engine, I estimate the body and seats will weigh around 200-300 kg. Add one or two people, and we're looking at a maximum total weight of 500 kg. I'm planning to use electric motors controlled by a variable frequency drive. What power output should these motors have?
For the pneumatic system, a fully realistic simulation isn't necessary. Minimal vehicle movement would suffice. I've considered using air bags at the rear and linear actuators at the front. These would be controlled by solenoid valves, which in turn are driven by a relay board connected to an Arduino. Would this be a more practical and cost-effective solution?

The problem with simple solenoid valves is that you can only turn them fully open or closed. To avoid hitting the end stops to agressively gas flow has to be throttled to the average desired speed. But that also means a delayed reaction to the commanded motion from the sim software. The car will jump several 10..20m AFTER hitting a bump which will result in a quite unrealistic feeling.

That is totally OK if you just play a pre-recorded movie on the screen in front of the car. In this screnario you can program the Arduino to control the valves with a bit look ahead. They did something like this in the Hollywood Universal Studios, I was there several years ago and it was fun. But if the car driver has control over the steering wheel there is no way of predicting his actions and the required motion.

Don't get me wrong. Some sort of "pneumatic roller coaster" can still be fun. I just like to avoid that you're disappointed if the simulation is not very realistic.

What do you mean with "air bags"? Maybe you mean something like this? Those rubber cyclinders can provide quite high forces with minimum space required. If you take them from an old truck from the scrap yard they are far less expensive.

So I'll discard pneumatics and hydraulics... it doesn't need to be very realistic, but I don't want much delay. You're right that the most dangerous thing about pneumatics and hydraulics is the shocks in the tubes... I hadn't thought of that.
So the only solution is to use high-power motors with gearboxes, or high-power linear actuators... that's going to be too expensive for me, I think I'm going to discard the project.

Sorry, I didn't mean to discourage you. I just think a good plan saves you from having to build it twice...

So I think with some pneumatic support (gas springs or rubber bag cyclinders) in the middle 3 or 4 electric motors with 0.75 to 1kW should be sufficient. With some limitation of stroke even half the power might do. But the cheap wheelchair or windscreen wiper motors are definitely too small to move the car chassis with two passengers.

No, no, not at all. I appreciate your comments. The stock car has 2 front shock absorbers, and in the back, it has 2 more shock absorbers and 2 springs. The car's weight is basically in the back... maybe changing the shock absorbers for electric motors and leaving the springs in the back, or making them shorter... it could work...