[HELP] Steering and Suspension on RWD 1:10 PF Car

[Saberwing40k]

I've got a solution, but I haven't built it out yet. I have to warn you, it uses the 42000 rear hubs, so if you don't have those, it's kind of worthless.

[Hrafn]

I've got a solution, but I haven't built it out yet. I have to warn you, it uses the 42000 rear hubs, so if you don't have those, it's kind of worthless.

I'm curious to see it, since I do have those hubs but haven't been able to find a solution with them that's narrow enough.

[Saberwing40k]

Here ya go, I have built this out, and it is very strong.

And yes, it does fit the 21 stud wide requirement:

I'm leaving the spring mounting and stuff to you. I have tested this without springs, and it works very well.

The LXF: http://www.brickshelf.com/gallery/saberwing2/Ideas/rearaxel.lxf

Also, I'm wondering why you aren't using a servo motor for steering on a rally car. For high speed vehicles, it is better for the steering to be self centering.

[Hrafn]

Thanks, I appreciate it! I'll give it a go, though I'm worried about the bevel gears. I'm going to be running 2 buggy motors through this.

EDIT: This works superbly. It's exactly what I was looking for, and the bevel gears have no trouble with two stalled buggy motors. Thank you so much! When I posted my request for help, I figured I might get some pointers and general advice, and maybe an example or two to look at. I didn't think anyone would solve my exact problem and give me an .lxf file to boot!

Also, I'm wondering why you aren't using a servo motor for steering on a rally car. For high speed vehicles, it is better for the steering to be self centering.

I haven't decided whether I'll use the servo or an M-motor (geared down) for steering yet. Initial tests suggested to me that the servo lag is so long that (with my poor RC driving skills) I'm likely to crash a lot. Implementing return-to-center with an M-motor is easy, if need be. I'm also toying with the idea of variable ratio steering but I don't know if it will be useful or worth the extra complication and space.

Edited February 11, 2014 by Hrafn

[nicjasno]

This is genius.

[MrNumbskull13]

Let us know how you decide to do your steering please! I only have an M motor and I want to make a trophy truck, I was thinking of doing RTC steering but it's a bit laggy with the speed remote...

[unimog123]

Here ya go, I have built this out, and it is very strong.

And yes, it does fit the 21 stud wide requirement:

I'm leaving the spring mounting and stuff to you. I have tested this without springs, and it works very well.

The LXF: http://www.brickshel...as/rearaxel.lxf

Also, I'm wondering why you aren't using a servo motor for steering on a rally car. For high speed vehicles, it is better for the steering to be self centering.

This is a great solution! I could have used this so many times in my previous creations and I can't believe how simple and efficient it is. Also I would post it on the Axle Thread here:

http://www.eurobricks.com/forum/index.php?showtopic=92099

Edited February 11, 2014 by unimog123

[Hrafn]

Time for an update! Any suggestions or advice would be welcomed.

For the rear axle, I'm using Saberwing's design. It works well, with two caveats. First, after a few crash tests (running into walls), one of the bevel gears fell out when the 2L axle it was on slipped into the CV joint. I had been careful to use an old 2L axle (with no notches) in hopes of avoiding this, but I guess it's just an inherently weak connection. Second, the vehicle moved a LOT more slowly than when I tested the same motors on a somewhat lighter and much simpler dummy chassis, so I think I'm losing a lot of power to friction in the rear axle.

For the front axle, I abandoned caster angle but kept the short-long-arm suspension, kingpin inclination, and pseudo-Ackerman steering. Including caster just made things too complicated. The kingpin inclination is 18 degrees, which is not as steep as earlier designs, but because the lower ball joint is tucked inside the wheel, the scrub radius ends up being near zero.

The front axle still needs some work - I haven't fully integrated the steering motor, figured out the shock mounting locations, or gotten the ground clearance quite right (it's currently much higher than the 2.5 studs or so the rest of the vehicle has).

I've been using 2 RC buggy motors to power this, directly coupled and with no gearing from the fast output on the motors. Unfortunately the motors are not delivering the kind of performance I was hoping for, or that tests of a simple chassis led me to expect. I suspect I've got a lot of frictional losses. Also, I'm now seeing the overload protection on the 9V battery box kick in after the motors stall half a dozen times or so; with the simple chassis that didn't happen. I'm very reluctant to use the RC receiver / battery / steering unit, since it takes a huge amount of room, so I'll keep working to see if I can improve the drivetrain

[unimog123]

Nice progress! It stinks with the buggy motors, all the friction in the drivetrain makes them practically useless. I had a similar problem a year ago with a little buggy I made with 1 buggy motor and the double wishbones were in the steepest position possible, putting loads of pressure on the CV joints. Because of this I could only drive it for about 5-10 seconds before the friction became too great, it even etched away at the CV joint permanently.

Anyway I think the use of those small 12 tooth gears in between the diff and wheel is the cause of friction because of the relatively loose connection the 2L axle. I don't know how to fix such a problem at the moment, but don't give up.

[timslegos]

Why dont you try gearing down the motor more? Harnessing the power of the buggy motor is truly a challenge!

tim

[Hrafn]

Nice progress! It stinks with the buggy motors, all the friction in the drivetrain makes them practically useless. I had a similar problem a year ago with a little buggy I made with 1 buggy motor and the double wishbones were in the steepest position possible, putting loads of pressure on the CV joints. Because of this I could only drive it for about 5-10 seconds before the friction became too great, it even etched away at the CV joint permanently.

Anyway I think the use of those small 12 tooth gears in between the diff and wheel is the cause of friction because of the relatively loose connection the 2L axle. I don't know how to fix such a problem at the moment, but don't give up.

Right now I'm looking at loosening my scale standards and going with the usual 23-stud-wide double-wishbone setup. It's only 1 stud wider on each side and it has a LOT less friction.

Why dont you try gearing down the motor more? Harnessing the power of the buggy motor is truly a challenge!

tim

I have tried that, but the friction in the axles still dissipates power, no matter how the motor is geared. The differential probably drains some power, too, but I'm reluctant to give that up in the name of more power since I also want maneuverability.

[unimog123]

Well I suppose that could work, but make sure you don't put any pressure on the CV joint because you'll have the same problem I had.

[Teo LEGO Technic]

Another solution to stop the wobbling in the steering would be to have longer steering arms at the wheel, and the extra mechanical advantage would allow for more precision.

It would however become necessary to have the steering rack move more to have as much steering as it does now.

[Hrafn]

Well I suppose that could work, but make sure you don't put any pressure on the CV joint because you'll have the same problem I had.

The rear suspension will have limited travel, so I don't think it'll be an issue. I know what you mean, though - I've had those bind and pop out, or grind against other parts, when the suspension moved too much.

Another solution to stop the wobbling in the steering would be to have longer steering arms at the wheel, and the extra mechanical advantage would allow for more precision.

It would however become necessary to have the steering rack move more to have as much steering as it does now.

The new steering setup doesn't wobble at all. I thought about having longer steering arms, but then to get Ackerman steering the arms also need to come 'in' more - which means the steering rack is placed further back, is even shorter, and (as you point out) has to move a lot more. The other thing is that with kingpin inclination, the end of the steering arm moves up and down as the wheel steers. The longer the steering arm, the more this is an issue. The current setup is a pretty good compromise, in my opinion, between all the various considerations (size, travel, steering lock, Ackerman, kingpin tilting, etc.)

[Hrafn]

Time for a quick update.

The rear axle has been largely solved by using a modified version of the rear axle from Thirdwigg's 8081 MOD. The "floating differential" allows for fully independent, driven suspension in 21 (or, in his model, 19) studs' width.

The front suspension is nearing completion. I've successfully incorporated

- kingpin inclination to give near-zero scrub radius

- caster

- short long arm suspension to give increasingly negative camber as the body moves down

- Ackerman steering

Here is the current hub:

And here, stripped of all the supporting structure and the steering motor, is the general setup of the front axle, showing the basic geometry:

Stripped down like this, the maximum steering lock is about 45 degrees for the inside wheel (30 for the outside wheel):

The angles look a bit off in this photo because of perspective caused by the camera; slight positive camber on the inside wheel; and the fact that the suspension is not depressed the way it will be once the vehicle adds some weight on the springs.

So far, so good. The 7L steering rack will probably have to go, though - its 4L stretch of teeth doesn't allow for enough travel to get to the full steering lock. Instead the inside wheel ends up stopping at about 30 degrees, which isn't nearly as much as I want. I'm also still working on making sure that the steering links don't collide with anything during suspension travel, and that the steering rack is secured in a track so it doesn't wobble. The latter two goals keep conflicting but I'm sure there's a good solution out there.

[unimog123]

Nice setup. Since the chassis is almost done, do you have any ideas as to a specific rally car you are going to model?

[MrNumbskull13]

Yes, this is a very nice set up! :) the only thing I would change is the angle of the springs, point them in, instead of out.

[0RBlT]

Hello!

Tell me please, I watch as you incrementally construct Front Axle car, and all I can not understand what you are trying to achieve? Realistic convergence collapse?

Here's how a little bit can be seen in this picture!

http://www.google.com.ua/imgres?start=465&sa=X&espvd=210&es_sm=93&biw=1366&bih=620&tbm=isch&tbnid=EErkX624RJ8cMM%3A&imgrefurl=http%3A%2F%2Fvipavto.com.ua%2Findex.php%3Fpage%3Dorder%26id%3D362&docid=xHH39PtjG8vSLM&imgurl=http%3A%2F%2Fvipavto.com.ua%2Fimages%2Fphoto%2Fmercedes-benz_s550_221_amg_1.jpg&w=640&h=426&ei=CI4RU6jHAYzs4wSX74GgDA&zoom=1&ved=0CPkBEIQcMFA4kAM&iact=rc&dur=1063&page=25&ndsp=20

[Hrafn]

Nice setup. Since the chassis is almost done, do you have any ideas as to a specific rally car you are going to model?

Thanks! Yes, I do - but I'm not planning on revealing which until I've gotten a bit further, especially with some of the bodywork.

Yes, this is a very nice set up! :) the only thing I would change is the angle of the springs, point them in, instead of out.

Thanks! That's a good point, they should be angled inward. I haven't decided on the final configuration of the springs because I'm not sure how much weight will be on the front wheels and therefore how stiff the suspension should be.

Hello!

Tell me please, I watch as you incrementally construct Front Axle car, and all I can not understand what you are trying to achieve? Realistic convergence collapse?

Here's how a little bit can be seen in this picture!

http://www.google.co...page=25&ndsp=20

I'm not sure I understand your question (or why you included that link) - could you explain? What I'm trying to do is twofold. First, I want the vehicle I'm building to have good handling, and the geometry of the front suspension and steering will factor into that. Second, I'm using this project as a way to learn about suspension in general.

[unimog123]

I can't wait for the surprise bodywork.

[Hrafn]

I can't wait for the surprise bodywork.

Given how slowly I work, I'm afraid you're going to have to!

[Thirdwigg]

I was thinking about suggesting my "floating differential" idea, but then I kept reading. I am glad you like it, and I hope it works well for this set up. I have been pleased with the way it functions.

[Hrafn]

I was thinking about suggesting my "floating differential" idea, but then I kept reading. I am glad you like it, and I hope it works well for this set up. I have been pleased with the way it functions.

It does seem to work very well indeed - thanks for sharing it! I'll have to see how it works when the vehicle is finished and there's more weight on it, but so far it seems quite robust and I really appreciate how little friction there is in the drivetrain.

[0RBlT]

I'm not sure I understand your question (or why you included that link) - could you explain? What I'm trying to do is twofold. First, I want the vehicle I'm building to have good handling, and the geometry of the front suspension and steering will factor into that. Second, I'm using this project as a way to learn about suspension in general.

As for the proper control of the car that's described below

Camber - is the angle between the plane in which the wheel rotates and the vertical. Negative value - internal focus upper side wheels. Positive value - external focus. If you change the car roll camber changes. A negative value is bad for the stability of the car when cornering. The right to be considered a value of zero camber, which contributes to less wear on tires.

Kaster ( castor ) - the angle between the vertical and the projection axis of rotation of the wheel to the longitudinal plane of the vehicle. Responsible for self-regulation of steering wheels due to the speed of movement. In some cases, changing the factory default leads to a more stable straight-ahead position .

Convergence - the angle between the plane in which the wheel rotates and the direction of movement of the car , in other words - the difference of the distances between the rear and front edges of the wheels. Has the most significant impact on service life of tires.

Persuaded to check toe-out as possible by special diagnostic procedures , and independently :

worsened control over handling car ;

excessive noise from the tires during fast driving ;

when driving on a flat straight car noticeably moves away , etc.

As for my question, I would like to understand what you are trying to implement this in LEGO?

I can see how you go step by step to this realization, but what can be seen in your pictures do not correspond to reality, the reality must be the collapse, and you also get the opposite wheels collapsing.

Although I could be wrong, because the picture is not all clearly visible, perhaps a distortion of reality!

[Hrafn]

As for my question, I would like to understand what you are trying to implement this in LEGO?

I can see how you go step by step to this realization, but what can be seen in your pictures do not correspond to reality, the reality must be the collapse, and you also get the opposite wheels collapsing.

Although I could be wrong, because the picture is not all clearly visible, perhaps a distortion of reality!

Thanks for the further detail, but I'm still not entirely sure what you mean. The current setup results in no toe in or out, though I may add some toe in later since the inherent slack in Lego means the wheels experience a bit of toe out when moving forward. When the control arms are horizontal there is no camber; as the wheels move up relative to the body, the camber becomes negative, which is what I want in a corner. There is some caster angle at all times. When the wheels turn to maximum steering lock, the wheel on the inside of the turn does experience some positive camber due to the kingpin inclination, but it's fairly slight and seems to be an acceptable feature in real vehicles.

I realize the photos are not very good - my intention was just to show that I am (slowly) making some progress. I hope to take better photos as I make more progress. Right now it's definitely hard to tell from the photos what all the angles actually are. I think a big part of that is that I'm taking close-in photos of a small object, which results in distortions of the angles due to perspective.