Four Wheel Drive Questions

[ChrisKazoo]

Hey Guys

I am redesigning Loki to be four wheel drive with four drill motors.

I'm not too sure about what things I should be considering. I remember the Razer team saying that Razer was quite manoeuvrable because the wheels were equally spaced from each other. Should the wheel base be as large as possible?

Planning to make wheels using Ellis' videos.

Also what is/is there a difference between four wheel drive tank steering and skid style steering?

Thanks

[Ellis]

There is no difference, believe they're just two ways of saying the same thing.

As for wheel layout, being big enough to be stable, but small enough to not make the robot massive/weigh a load, is the balance. I seem to aim for about 30cm square, measuring to the ground contact point for each wheel. No idea if there is an optimum, but T2 feels stable whilst not being crazy massive, at 32x30. Current designs have T3 at about 28x27 (in both cases wider than longer by a fraction).

Razer was a special case, in that its rear wheels were designed to grip less than the front ones (actually think they were omniwheels but, details), so its turning "axis" was around the beak. This made the awesome control it had in battle possible. You can achieve this sort of thing by having either different wheel materials front and back, or in T2's case, the weight distribution means it favours the front wheels a little and it tends to slide the back.

Using drills, expect to have reliability issues, but with the right tweaking you can make them work. Also driving style plays a part, I drive T2 like a *cough* pleb, so the gearboxes get a real thundering. I intend to make a few more YouTube videos on what we've found works for making drills more reliable.

[Gaseraki]

Im not a mechanical engineer so my research is mostly from practice and theories rather than solid knowledge but:

I usually aim to have the space between the wheels on 4wd at least square or a tad wider. If a robot is too long I find the wheels fight against itself to turn.

[ChrisKazoo]

cool thanks guys, the design I made last night had a wheel base of 32 x 32 so looks like I was on the right tracks

Looking forward to more videos from you Ellis, they've already helped me a lot

and hopefully you won't be able to push me around so easily next time Marco

[Eventorizon]

To my knowledge, tank and skid steering are not the same, but they are very similar.

Tank steering is the vehicle turns about the centre of the points of contact. This doesn't matter if you use tank tracks, 4 wheels, 6 or what ever.

Skid steering the robot spins about a point that is not the centre. Typically this is done by using 4 wheels where the front 2 grip and the back two skid or slide. Razer was easy to steer as it pivoted about the centre of its front two wheels, right under the weapon tip, thanks too its back wheels being omniwheels and allowing it to slide side ways.

(I hope that makes sense)

[typhoon_driver]

They're the same thing

[grant_ploughbot]

As Alex said, 4wd is your standard 4 grippy wheels turning around its center point for most traction. Skid steer tends to use either slippy wheels on the back or omni wheels to give good pushing ability forward but turn around its front wheels making it easier to keep your weapon at your enemy.