Tuesday, September 1, 2009

TBs TechTips 26 - Return-to-center steering

As many other topics, this one has been in my to-post list, just for too long...

Today I decided it must go because I'm also preparing a post for the next weekend, where something very similar was used. So it wouldn't make any sense to post it afterwards...

It is a simple and clever idea, although not an obvious usage for its core part (x928cx1, hockey slap shot springs), on how to implement a compact automatic return-to-center steering mechanism.

A brilliant application, found at LUGNET and Brickshelf. Where else it could be?... ;)
It was presented by Ian Power (chase2K) at LUGNET, already in March 2008.

As it seems, the idea was attempted more than once before, but only the new PF M-motors offer low enough resistance when getting no power applied, to let axle rotate back to the center position.

But just because, hardly the TECHNIC builders leave a problem with one single solution, lets see a different method by Mrutek, featured at one video from Sariel.

Return-to-center steering function is here achieved with a rubber band layout, added over a Sariel's mini pendular steered suspension.
This requires however some tunning of rubber band strength and steering motor gear ratio, to the vehicles weight, used tires type and floor friction.

Edit 1:
In the sequence of Jetro's comment, I've decided to add here Sheppo's return-to-center solution as well, which I hadn't seen before.
Not so compact as Ian's solution, bas working as good as it seems.

More photos from Sheppo's BS folder.
Still wonder how these elastics have the strength, to force the axle rotating back to the central position. Must give it a try.

Edit 2:
Suddenly it looks like everybody has also his own solution for this problem...
Below a new one that Jacob's left to us, on this post's comments.
Would anyone like to come with a smaller and fewer parts version of it?...

You may also find the mechanism proofing to work, on this video.

Edit 3:
A late finding originated by a comment from Peer Kreuger (Mahjqa), shown us the "hockey spring" part being used for return-to-center steering purposes already back in 2005 [1].

In the image above we can clearly see the mentioned return-to-center mechanism, underneath this Vayamenda Industries F1 Racer, by Peer.
You may also find additional images from this model at Peer's BS folder and MOCpages account.

Last Update: 2009.Sep.10 13:09 GMT


Ian said...

I check this blog every day for cool ideas, and today was shocked and amazed to find my own idea posted!

Thanks for the cred :)

And keep up with the blog - I love it!!


(aka Ian Power)

sunsky said...

Hi, Chase

I saw your idea on BrickShelf in March this year, and applied the mechanism on a couple of my cars. Thank you for excellent idea.
Recently, I am trying to implement clutch gear together with return-to-center mechanism. :)

Thank you AVCampos and Conchas
for valuable informations.

TechnicBRICKs said...

You are welcome. Thank you too!

;D ;)

JAMS said...

can someone make a video of this mechanism? I'd like to see how quickly the wheels turn, as I want to know how much this spring mechanism slows down the motorrrr

TechnicBRICKs said...

Something to show, the next weekend.

Meanwhile have some other very interesting posts to prepare...
A bit more patience. ;)

Anonymous said...

Very nice. I have several of those spring mechanisms and didn't know any other way to use them.

Anonymous said...

I found Ians idea on bs months ago and used it in many cars. JAMS, it doesn't really slow it down.
So some things I found out
-don't use a XL motor it destroyed one of this parts in 2 seconds, same with gearing it down before the spring-part.
-a cluth gear can be used, but also after the spring-part-thingy, or the motor will just turn freely without moving the steering.

Jetro said...

I much prefer Sheepo's solution:


TechnicBRICKs said...

Oh, I haven't seen that one before.

Can you summarize on Sheepo's solution advantages.

I may add it to the post, once I find sometime available later.

Jetro said...

There are several advantages. For starters, Sheepo's solution uses more common parts. Also, the friction that the spring part in the first solution provides is very high and as a consequence requires a lot of effort from the motor whereas Sheepo's solution has less friction. You can regulate the necessary force by adjusting the rubber bands (or using different ones) which means you can adapt it to the motor you use and the direction system you have.

JAMS said...

The one pitfall i can see from return to center steering mechanisms:

the inability to add gear reduction to slow the turn speed.

I mean, the more reduction you add before the spring/elastic, the more work the mechanism has to do to move all those gears, and the torque, so thats pretty impossible.

I also cant conceptualize adding gears after the mechanism, because then it has to actuate a whole lot more to turn the wheels.

I'm sure if you added the gear reduction inbetween the motor and the spring mechanism, you could get away with using 3 or 4 of those slapshot spring things in a row to give you the torque needed to center the wheels, AND rotate the motor at the same time.


Anonymous said...

Great post. I've seen these ideas floating around, but it's nice to see them in one place. I remember seeing Sheepo's design and coming up with my own variation. I just rebuilt it, albeit a bit more compactly.

The rubber band (it is a single small white one) does a fine job of pulling the axle back to center. Note that it can be modified for a longer travel (in that case, I should have also switched to a longer band). Here's a movie to prove it works.



Carlos Ribeiro said...

Interesting and clever ideas ,Thanks for bring to us different ideas. Great Post

Jetro said...


Can you confirm if your construction still works properly with the added friction of the steering linkage and, more importantly, the tyres?

MagerValp said...

I implemented return to center steering with two rubber bands and a 40 tooth technic gear, youtube video here: http://www.youtube.com/watch?v=kSUfN7KjpE8

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