Rc car steering

Hello guys,
As a kid i always loved rc car (only had one :frowning: ) and this christmas i want to give one to my kid, but i don't want to buy one, i'll build it with arduino.
At this point i'm researching, and learning.

I plan to use a servo for the front weels to steer (i just learned that the inclination angle is not the same, so i must this in consideration when building the chassis)

For movement i plan to use one single motor for the back weels, and here is where i'm stuck to understand how steering will work.
I saw some articles on differential weels, but this seems rather complex.

Can you guys share some thoughs?

A normal 2-wheel drive RC car only steers the front wheels. The back wheels just need to drive the car and don't have anything to do with the steering. Just like full size rear wheel drive cars.

Steve

Except that on a full size rear wheel drive car, the differential slows down the inside wheel. And while that doesn't "do" any steering, the lack of certainly "affects" the car's desire to turn.

My brother-in-law has been a serious Mecanno (Meccano?) user for 70-odd years and once built a radio controlled truck about 2m long. (Muggins here is the only one in the family who had a photo, and lost it....)

It had full Ackerman steering to turn the inner steering wheel a bit tighter and a differential. Not to mention a 2-speed automatic gearbox and a centrifugal clutch.

So between now and Christmas, you could study the Mecanno sites to see how to build such mechanisms.

(Prime mover had a motor cycle battery under the bonnet. It was too heavy to get up his drive, but went down and into the road at a hell of a pace. The semi was attached on a proper working 5th wheel.)

When a car turns a corner the outside wheels need to travel farther than the inside wheels. The purpose of the differential is to allow that to happen while both wheels remain powered. Without that the rear wheels will want to travel in a straight line and will be fighting against the steered wheels with greater tyre wear on all wheels.

The presence or absence of ackerman steering is unlikely to matter on a model car. The behaviour of wheels and the surface for a model car are not the scaled-down equivalent of a real car.

And the need for ackerman steering it is not a simple issue on a full sized car either because the sharing of the turning force between the two steered wheels depends on the angles of the tyres relative to the direction of travel. The outer wheel generally does more work (because there is more load on it) and that requires the slip angle to be greater than on the inner wheel.

The ackerman angle is in the horizontal plane. "Inclination angle" usually means in the vertical plane. Car suspensions have inclination partly to provide some castoring action and partly to ensure that the wheel remains as nearly vertical as possible when the suspension is compressed - as, for example, when the car rolls while cornering. I would not worry about the niceties of suspension geometry in a model car.

...R

But the fact remains that most RC cars have simple steering and no differential. Some do have a little basic sort-of-Ackermann built in but many don't. Yes they skid a bit but that's not exactly a problem when when you don;t need to drive on rally tight courses with precision. And you'll probably have far more power than you need.

A more important question is if the RC car is planned to have any suspension. If not it's more like a go-kart than a full-size car and most of the niceties like Ackermann, castor and camber go out the window.

Of course the OP can make it really complicated if that's what they want but it's not at all necessary.

Steve

How old is the child? If 12 or older, buy a kit and let them build on their own. The reason for buying the kit is so you know everything is included and they don't get frustrated when they have to buy more parts.

If you are building this for a younger child then, based on your basic questions, you should buy the kit and assemble it yourself. Let them help paint it.

There are a lot of kits available. I would try to buy one which has some optional modules available. Start with building the basic R/C car and add the line-follower module so you can make it follow a line autonomously. Then add the bumper module so it can run around bumping into walls and furniture.

I have had ready to run rc cars, kits I've built myself, as well as a fully scratch built chassis rock crawler RC i built a few years back.

I would recommend if starting out, and you want to have fun building it, you do what Morgan S suggested and get a pre-made kit. This will teach you all you need to know about RC cars before you scratch build your own.

Also, others have mentions diff vs no diff. Diff is better for on-road race cars or off-road shortcourse / monster trucks with handling/turning.

However, I changed the diff on my drift car to a spool (locked diff). This helps with starting the drift as the rear wheels start slipping simultaneously.

I also have solid axles with locked diffs on my rock crawler. This is so as it crawls over obstacles and one wheel is off the ground, it does not stay put spinning the lifted wheel. Instead the power still goes to the wheel on the ground for much better traction.

Do you need a diff? Though usually its better with one,short answer is no.

wow, you guys just blow my mind ( :slight_smile: :slight_smile: :slight_smile: ), thanks for sharing
ok, i was loosing myself (trying to run before i walk), but i'm back on track again.
i'll keep it simple, so i can understand the basics. i'll keep the differential out (for now), and search for a pre-made kit.
my kid is 3, so you're correct, we don't need anything fancy :frowning: (i mean he doesn't need anything fancy).
i'll research about the Ackermann steering.
thanks again guys