Whats the best way to do multi axle steering?

[aminnich]

Hey guys,

I think i finally have an idea of what i want to build, but it will probably change by tomorrow. :laugh: Anyway, i want to incorporate twin steering in the front and a rear steerable axle. But i'm not sure how I want to go about doing this. I will use a servo for steering, so i guess another question is, can the servo handle 3 axles.

Any ideas of how this could be done most efficiently would be great. Thanks guys!!

[Zerobricks]

What axles are we talking about? Solid, independent suspension? Also what kind of weight and steering system? Pivot point distances, steering angles, etc...

[aminnich]

The model is going to have solid suspension. As for the steering system, im not sure what is it called, but the one that is used in 99% of LEGO sets. I hope that helps

[bonox]

i think you're talking about rack and pinion.

Either way, you'll find it about impossible to have multiple servo motors linked at different rates to different axles. Most sove this mechanically with different gear ratio's and or mechanical offsets of the steering rack from the wheel pivots on each axle to keep the steering arcs at suitable radii with respect to the other axles. ie one steering shaft controlled by your servo, with axle steering angles controlled by gearing or offsets.

As for 'can the servo handle it', you're down to tyres, surface, vehicle weight etc - too much to estimate with no further data.

edit: speeling

for factory examples, look at the 8454, 8053, 8421 etc

Edited September 4, 2015 by bonox

[D3K]

There are basically three ways (at least that I can think of) to achieve this.

1. Different steering arm lenghts (as seen in the 42009) This is probably the easiest with today's parts

2. Have different gear ratios between the gears and the racks, by gearing up/down one or more of the gears driving the racks. This will have more play/backlash due to the extra axle and gears necessary.

3. Different gear ratios by using different sized gears on the racks. This is easier with the old, studded steering racks.

[aminnich]

Ok, so for what i recall, the normal steer arm length is three. But if i want to make the steering not as sharp, then the length goes to 4+, right??

As for the number of axles, right now im thinking 5 (3 steering, 2 drive) so the weight will be distributed well.

[bonox]

Correct. Steering arm length is what I called offsetting the rack from the wheel pivot axis.

It's not so much total weight as weight per (steering) axle, plus the friction of the tyre on the ground plus friction in the steering assembly and axle/gear runs that will determine whether your chosen motor will be capable.

If you had a continuous motor, you can gear down a lot - like gerger did with his Grove 6400 - but with the servo you're more limited, so you need relatively light steering or accept the smaller stering angle that will come from gearing it down a bit. You could find that your design will work on a hard floor but not carpet for example.

Edited September 4, 2015 by bonox

[Kiwi_Builder]

Yes that's correct. I'm interested to see what it is that you're making.

[aminnich]

ok, i am going to use similar turning radius as the 42009 crane. Im going to try using one servo for all 3 axles, but if that is too strenuous, then ill add another servo for the rear axle.

Kiwi builder, Im planning on sharing WIP posts for this build. I usually dont share my creations just because they never get finished. So hopefully i have the time to complete it thanks for your support

[aminnich]

Did anyone here build the ultimate 42009?? if so, can u tell me when motor was used for steering??? i think this will give me a better idea for what i should do.

[LennyRhys]

In my opinion, the best way to do steering is not to use the servo motor. I really don't like it... at all!

[aminnich]

What do you suggest in place of the servo motor?

[Jelmer]

If your creation is fairly long you might need to add a second servo. I have a model with a wheelbase around 100 studs and when you steer with a single servo the torsion in the central steering axle prevents te rear axle from turning. Only axles close to the servo will steer depending on the weight and friction on the remaining wheels.

[LennyRhys]

What do you suggest in place of the servo motor?

I'm using an L motor with clutch gear in the gear train and it works perfectly. You could also use a pulley and elastic band for the same effect.

I find the servo useless for steering because it is so limited - you have only one steering angle either side of centre, which gets pretty boring if you have an RC vehicle. I also have the train remote and I find that it doesn't really help... I much prefer using either an L or M motor which allows proportional steering, and it also adds the challenge of getting the wheels straight again! :)

[aminnich]

i am just going to have to experiment with the weight distribution of the steerable axles. There is no way of telling how it will work without trying it .

I'm using an L motor with clutch gear in the gear train and it works perfectly. You could also use a pulley and elastic band for the same effect.

I find the servo useless for steering because it is so limited - you have only one steering angle either side of centre, which gets pretty boring if you have an RC vehicle. I also have the train remote and I find that it doesn't really help... I much prefer using either an L or M motor which allows proportional steering, and it also adds the challenge of getting the wheels straight again! :)

I find that using a servo is better because of that true return to center part of it. To get a larger turning radius, i just change the output gearing so that the vehicle turns sharper

[aminnich]

this is a super quick make up of a super simple chassis, mine will be just like this, but not as quickly made.

[Zerobricks]

Use setup as it is for first axle, use 1 stud longer steering rims for secind axle and 2 stud longer steering arms for rear axle.

Oh and your wheel are misplaced, they should be in non-moving parts of axle, not the steering rack part.

[aminnich]

I know, i just through all of that together. Thanks though

[bonox]

I find the servo useless for steering because it is so limited - you have only one steering angle either side of centre, which gets pretty boring if you have an RC vehicle.

it's got seven positions using the train remote and quite a few more options if you use an sbrick instead.

[aminnich]

What do you guys think of this....

Edited September 5, 2015 by aminnich

[Beck]

The vehicle that you're trying build is either 4x2 or 4x4 tractor unit with a crane on a trailer. Your truck that you have is a 5x2x3 meaning 5 total sets of wheels, 2 driven, and three steered on one chassis. Solid suspension basically means none right? Or is just another way of saying live axle? Anyways. If you want the truck to have any type of off road capability dont use the servo, but if the truck is a roadgoing vehicle then you should be fine.

[aminnich]

I was just searching for a cool something to build. I'm going to modify that to the number of axles and such I want. Also I is going to go an on road vehicle and have no suspension

[D3K]

So you're building a five axle mobile crane then?

[aminnich]

I think it is going to be a 5 axle truck and a 6 axle trailer, with a crane in the trailer

Edited September 5, 2015 by aminnich

[LennyRhys]

it's got seven positions using the train remote and quite a few more options if you use an sbrick instead.

Exactly - you need a specialized remote or accessory to make the servo motor worthwhile, and even then it's not great . Either an M or L motor works perfectly with some gearing and a standard PF remote. The servo motor has other uses, but IMO steering is its weakest application. I have the train remote and still wouldn't dream of using a servo for steering. The only reason I've not sold my servo yet is because I might need it for something else...or at the very least it could be used for a purely "fun" RC vehicle where proportional steering is not required.

Edited September 5, 2015 by LennyRhys2