Steering (Bump and Play)

[PorkyMonster]

Not sure if anyone has had something similar, but here goes...

In creating my models I observed two issues with steering:

(1) Lego's pinion and rack steering mechanism allows for the turning of pinion by a mere 1/4 to 1/2 turn each direction (unless you use a long track, which may not fit in most models), and when connected to a steering wheel, some gearing down may be needed for more realistic 'feel' (i.e. u turn more on steering wheel for that 1/4 to 1/2 turn of the pinion gear). This gearing down worsens the play involved.

(2) Bump steer - in push-along vehicles, you have to hold on to the steering wheel at all times, or else the wheels will veer left or right happily when you just push your vehicle freely. While there are ways to incorporate "return-to-center' behavior, these won't solve problem (1), and will add more load to the servo (if connected).

So I thought of one way to solve these two problems at the same time - placing a worm gear in between, as below (worm gear in red):

(lxf)

So, from the rack and pinion, there's the worm gear, followed by 3 sets of 24:8 gears - axle from the first set can go to the steering wheel, while the axle from the 3rd set goes to the servo.

I believe it is possible to make the structure more compact, and I'll do that when I get down to creating my next model .

Any thoughts?

Edited December 28, 2016 by PorkyMonster

[BusterHaus]

I'm not sure if this will work out like you hope.  The 2L worm gear has quite a bit of slack and floats on the axle, you will need a few half bushes on each side to lock it in place.

I have also never seen the servo be forced out of center in a steering application. Do you experience this often?  

[PorkyMonster]

50 minutes ago, BusterHaus said:

I'm not sure if this will work out like you hope.  The 2L worm gear has quite a bit of slack and floats on the axle, you will need a few half bushes on each side to lock it in place.

I have also never seen the servo be forced out of center in a steering application. Do you experience this often?  

Yes, will need a few half bushes to lock the worm gear in place. I think that can be achieved.

No, servo is unlikely to be forced out of center. However, in scenarios where a servo is not engaged (e.g. if I choose to play in manual mode), the steering wheel can get forced out of center easily.

[Didumos69]

This could actually work. You do need to secure the worm gear properly and you will get a lot of slack, as @BusterHaus already pointed out.

Instead of using a worm gear you could also play with friction to reduce bump steer, for instance by using to hold the pinion. This approach was also used in the Go-Kart Creator set (31030, LXF in this post) - in a gear / gear rack setup - and manual steering still worked pleasantly. When you gear down, the servo should be able to overcome the extra friction. You might even try to apply the friction to an intermediate axle closer to the steering wheel.

Edited December 28, 2016 by Didumos69

[PorkyMonster]

50 minutes ago, Didumos69 said:

Instead of using a worm gear you could also play with friction to reduce bump steer, for instance by using to hold the pinion. This approach was also used in the Go-Kart Creator set (31030, LXF in this post) - in a gear / gear rack setup - and manual steering still worked pleasantly. When you gear down, the servo should be able to overcome the extra friction. You might even try to apply the friction to an intermediate axle closer to the steering wheel.

Yes, I've tried the friction solution before. First of all it's not foolproof (even more so as the model gets larger ), secondly, while it does 'shield' the steering wheel from the effects of hitting bumps (note that this does not necessarily mean that the tyres won't deflect and continue down a new path), it does not help in terms of steering 'responsiveness' (especially after gearing down from steering-to-tyre) - when you rotate steering wheel by 5 degrees, for instance, I hope to see slight tyre rotation as well, however small that might be.