How to build a steerable remote-controlled vehicle with just 1 motor?

Question

In WeDo 2.0 set there is only 1 motor, which can be remotely switched on and off by using the iPad app (by writing a Scratch program).

Also motor rotating direction can be toggled remotely.

As an inexperienced LEGO builder I wonder if it is possible to build a remote-controlled vehicle out of 280 WeDo 2.0 pieces, which would be steered by changing the motor rotation direction.

I am thinking of having 2 wheels with wide tires in front the vehicle, connected to the motor.

And having a single caster wheel with narrow tire at the back of the vehicle, not connected to the motor.

The caster wheel would roll straight, when the vehicle drives forwards.

But when driving backwards, it would snap to a certain angle.

UPDATE 3:

Found a picture for such a caster wheel in the LEGO Technic Idea Book by Mr. Yoshihito Isogawa:

UPDATE:

I have followed Aaganrmu's suggestion (thank you) and have tried to build a simple vehicle using ratchet instead of caster wheel:

https://www.youtube.com/watch?v=uqYQ79SdBpY

Unfortunately, it doesn't work well. There is too much friction - on the axles of all 3 wheels and on the rubber band.

I wonder if experienced LEGO builders can propose a better vehicle out of WeDo 2.0 parts than mine:

And I feel that my Scratch program can be improved too, since it is not very responsive to user input (when touching the 4 green arrows):

UPDATE 2: Got a nice suggestion at Eurobricks forum:

(video authored by Mr. Yoshihito Isogawa again).

UPDATE 4:

Here a good WeDo 2.0 model with steering:

https://www.youtube.com/watch?v=Q9sd4MxW4YY

Answer 1

This can be done without a caster wheel as well:

Start out with a three wheeled vehicle, with two wheels in the front and one smaller wheel with less traction than the front wheels in the back. All wheels need to be fixed.

One of the front wheels is attached to the motor. This might need to have some gearing to get an appropriate speed.
The other front wheel is unpowered but can only rotate forward by adding a ratchet:

The back wheel is unpowered.

Driving forward the vehicle will more or less move straight, guided by the rear wheel.
Driving backwards the ratchet will engage, stopping one wheel. The vehicle will now turn.

Answer 2

In WeDo 2.0 app "LEGO® Education WeDo 2.0" there is a complete project 12. Steer that is exactly about that

When it drives forward it goes in straight line, when it drives backward it then turns to one side.

There is full build instruction in the app.

I've also added distance sensor and made it fully autonomous - whenever it sees obstacle it goes back, turns, changes direction and continuous driving

Answer 3

I designed some WeDo 2.0 models that can drive and steer using just one motor. This one uses a system of gears to alternately drive the left or right wheel of a differential drive robot, depending on the turning direction of the motor. You can find the complete building and programming instructions here: https://robotics.benedettelli.com/lego-wedo2-zigzag/

Another idea is making a steering vehicle similar to the one shown in the WeDo App, and involves directly driving a pair of wheels, and having two steering wheels that act as a caster with limited swinging movement. That way, when the motor pushes the vehicle forward, the steering wheels are forced to stay straight and the vehicle goes straight; when the motor drives the vehicle backwards, the steering wheels will be free to rotate a bit, and the vehicle will steer. You can find the complete building and programming instructions here: https://robotics.benedettelli.com/lego-wedo2-car/

Answer 4

One motor and a caster wheel will give you two degrees of movement but will not be steerable. If you can build a differential, then drive two wheels with the motor.

If you have limited gears, then drive one wheel, have an idler wheel and a caster or simple skid arrangement.

You can get more interesting behaviour by having a bumpbot, that simply reverses the motor when it detects an obstacle.

See the Wikipedia article on casters, but there is a strong relationship between wheel diameter and how high the caster should be. And the surface area of the wheel and the mass of the load drive the how easy and fast things swivel. It's an interesting engineering trade-off, and I've never been able to make a perfect caster, even with lots of Technics parts. I now have reasonable respect for those people who design the casters into the everyday things we use without considering how difficult these trade-offs can be. (As in, it isn't an intractable problem, but the problem domain is extremely sensitive to small changes.)

Start with a skid first, and an easy, smooth surface to see if you get the basic behaviour you want.

Finally, you may get more interesting behaviour by ramping or stuttering motor direction and speed a little on obstacle sense. This is a cheap way to introduce some more randomness into the system.

Even more finally, you might want to get your hands on some LEGO Ball Casters, which I didn't know existed until this very moment.