4WD chassis not turning properly

[Leonti]

Hi!

I've built a rover using 4WD chassis but it has a problem with turning.
Going back and forth is working properly but turning is very weak and on some surfaces it's not working at all.

I've connected both right and left wheels so when I want to turn I make left wheels go to one direction and right wheels to opposite direction. It should behave like a tank.

I guess that the problem is in friction but why is this happening? Is it because the wheels are so close together?
I saw videos with similar types of chassis and they are working properly.

Here are images of my chassis:



What are my options?

Thanks,
Leonti

 

[Nigel Goodwin]

'skid' steering like this relies on the tyres sliding on the ground, if friction is too high that's not going to happen.

 

[Leonti]

If I move wheels more apart, so they form a square, will it significantly decrease the friction or should I try another solution? Caster wheel?

 

[Nigel Goodwin]

If I move wheels more apart, so they form a square, will it significantly decrease the friction or should I try another solution? Caster wheel?

A caster wheel makes it a lot more controllable.

 

[alec_t]

A short, wide vehicle will skid-steer more easily than a long, narrow vehicle.

 

[JimB]

I guess that the problem is in friction but why is this happening? Is it because the wheels are so close together?
I saw videos with similar types of chassis and they are working properly.

I have a "gut feeling" that the best overall compromise is for the wheels to be at the corners of a square, athough I have no mathematics or experience to back that up.

Having said that, whatever the wheel layout, you need more power in the driving motors to make the wheels skid on the road surface.

JimB

 

[Leonti]

Just added second regulator, so my motors can run with different voltage (before they used 5v as the brains of the device) and added more juice (7.5v) - it solved the issue!
Didn't expect for change to be so noticeable but now it turns on any surface.

Thanks for the help!
Leonti