I've been trying to build a 1:10, rear-wheel-drive rally car and am running into a number of problems. Right now the issues are with the front suspension and steering. I had hoped to have

1) short long arms suspension (for progressive camber with suspension travel)

2) some caster angle (to help with bump steer)

3) Ackerman steering (or close to it); here I'm using a three-piece tie rod

[EDIT: adding a bit of longitudinal reinforcement fixed a lot of this, but I'd still like to hear what people think of the setup and if they have any suggestions]

However, I'm having three two problems:

1) SLA suspension plus caster leads to terrible toe-in and -out with suspension travel

2) The tie rods are behind the wheels, and there is way too much play in the system (and some toe-out when moving forward). Some of this I know is due to my not having fully reinforced the steering rack assembly, but I'm not sure more reinforcement will totally fix it. Basically, the two-stud-wide rack assembly wiggles forward and backward a lot when you push on the wheels.

3) With aligned and equal-length wishbones, I get near-Ackerman performance; with this setup I no longer seem to.

The wheelbase is 30 studs, and the current (tentative) design is below.

Top (with the motor towards the front of the vehicle)

Bottom (note that the 6L arms are offset .5 studs from the top arms):

Any advice would be much appreciated. Or if you can think of other people's MOCs I should look at for inspiration, let me know. Thank you!

Edited February 5, 201411 yr by Hrafn

I think it would help if you watched the LPE power show suspension tutorials on YouTube. Sadly I can't really help you because I'm not very good with suspension myself. :(

I think it would help if you watched the LPE power show suspension tutorials on YouTube. Sadly I can't really help you because I'm not very good with suspension myself. :(

Thanks. It looks like a big part of my problem is the gear rack location, which forces the tie rods to be angled.

Yeah, I found his tutorials quite helpful. I'm wondering if you really need such a complex setup in such a relatively small car, like for example with Sheepo's Mustang he made complex wheel hubs himself to achieve these complex angles and geometries, but his model was huge! For yours I don't know if you need all those angles and stuff, it might just be better off making it a bit more simple, but robust!

Tried something like this... I did this in studfull and its a bit messy I intend to test it studless 100% one day but haven't got round to it....

Edited February 5, 201411 yr by Rockbrick

Thats quite a unique front suspension

Look at the suspension on this trophy truck. I'm sure it could be adapted for SLA. The trophy truck suspension also has kingpin inclination, which moves the steering pivot closer to the center of the wheel. http://mocpages.com/moc.php/372342

Edited February 5, 201411 yr by Technyk32231

Yeah, I found his tutorials quite helpful. I'm wondering if you really need such a complex setup in such a relatively small car, like for example with Sheepo's Mustang he made complex wheel hubs himself to achieve these complex angles and geometries, but his model was huge! For yours I don't know if you need all those angles and stuff, it might just be better off making it a bit more simple, but robust!

I realize it might be overkill, but I'm hoping to have this car be very maneuverable at the high speeds I expect its 2 RC motors to propel it at. My hope is that some of these variables (camber, caster, etc.) will help with maneuverability.

Interesting! I hadn't really seen trailing arms done for front axles before. The vehicle I'm modeling has double wishbones so I wanted to stick with that.

Look at the suspension on this trophy truck. I'm sure it could be adapted for SLA. The trophy truck suspension also has kingpin inclination, which moves the steering pivot closer to the center of the wheel. http://mocpages.com/moc.php/372342

Thanks, I hadn't seen that one. I may have to go with custom hubs to get kingpin inclination. That particular hub decreases ground clearance by 1 stud over using the hubs I have now, but it could probably be adapted to improve ground clearance for my application.

The tie rods MUST NOT be angled like that. :)

Thanks. It looks like a big part of my problem is the gear rack location, which forces the tie rods to be angled.

It's quite easy to do. You have no driving in this axle, no extra thing. So you have place for getting closer at least two studs the steering rack to the wheels. The 7L Lightbluishgray liftarms is unnecessary. It's pretty hard to write how to do it better, but I can't make a picture only for this. One thing is certain: with those functions, you can make the tie rods with much smaller angle and the gear rack closer to the center of the axle. One modification is doable right now: you can switch the 7L gear rack and the 3L perpendicular connectors. They should be inversely placed, the gear rack can be more further than those 3L pieces, because they have the connection points to the rods. The gear rack can be even "20 studs" away from the axle, the placing of the connection points are important only.

Of course, the length of the tie rods are important for the correct wheel angle, try to experiment with connector pieces to the gear rack to get the correct setup.

The white 24t gear is also unnecessary (directly connected to the steering axle). It helps to increase the play in the steering system. You should place it after the M motor's 8t gear.

Edited February 5, 201411 yr by Mbmc

Mbmc, Nicjasno - thanks! I'll try getting rid of the 5x9 frame (or turning it 90 degrees and using one on each side, or using some other structural solution including maybe dogbone frames) so that I can get the rack properly aligned with the towballs on the hubs. One issue with using these hubs and tilting them for caster angle is that the optimum location for the rack is no longer an integer number of half-studs from anything else, which is another reason to try custom hubs where I can set all the relevant dimensions independently.

Which is more important for steering: a kingpin inclination that puts the steering centerpoint near or under the tire, or some amount of caster angle? I'm having trouble achieving both with custom hubs without sacrificing performance in other areas.

For the moment I've put together a few hubs with kingpin inclination but no caster; the second one allows the wheel to be steered around a point under the tire.

The second one was inspired by Piterx's use of . I haven't added a steering link attachment point yet.

EDIT: here's an improved version that keeps the lower arm from hitting the hub as you steer, and adds caster angle. The downside is that I get some negative camber at extreme steering angles.

Edited February 6, 201411 yr by Hrafn

Your kingpin is too large. No wonder you have problems. If the upper and lower balljoints are in adjacent stud holes, its steep enough. Now you have one whole stud between them.

Your kingpin is too large. No wonder you have problems. If the upper and lower balljoints are in adjacent stud holes, its steep enough. Now you have one whole stud between them.

Thanks! Moving the top towball 1 stud closer to the wheel greatly reduced the camber issue, even when I then added a bit of caster.

Edited February 6, 201411 yr by Hrafn

Too angled. See the red liftarm. The light bluish grey suspension arm needs to be connected to it with the last pin. Which means that the upper balljoint needs to get 1 stud closer to the wheel.

How does this look? I don't know if the steering offset will turn out to be correct for Ackerman (or near-Ackerman) steering, and any caster angle will have to be created by offsetting the a-arms relative to each other. Otherwise I'm pretty happy with it; with 62.4 x 20 tires the turning point is under the tire, though not centered.

Has anyone ever made suspension with caster using the small A arms? I'm trying to right now and my only issue is that when the suspension is compressed I get a toe out effect :(

[edit] I don't have any fancy suspension parts so I'm going to sit back and see how your project goes. :)

Edited February 7, 201411 yr by MrNumbskull13

If it's 'caster' you are talking about, a much easier solution would be to have a tilted subframe. This allows for simpler/stronger suspension while still including the angle.

If it's 'caster' you are talking about, a much easier solution would be to have a tilted subframe. This allows for simpler/stronger suspension while still including the angle.

I may do that myself. Just offsetting the a-arms causes them to experience torsional loads, which then requires me to reinforce them. Also, offsetting the arms by 1/2 stud makes adding a shock absorber a bit awkward.

OK, the front suspension is coming along nicely (with caster, kingpin inclination giving minimal scrub, Ackerman steering, SLA suspension to improve camber in cornering). Now I'm having an issue with the rear suspension, which needs to be 21 studs wide (including the 62.4x20 tires), be driven, have a differential, and be a double-wishbone setup. The width rules out using 2 CV joints per side, so I was using 1 CV and 1 u-joint, custom hubs, and 5L liftarms as wishbones. The problem is that the wheels aren't held on robustly. If I put the u-joint near the wheel, the axle that the wheel is on tends to slip out of the u-joint, making the wheel fall off. If instead I use the CV joint near the wheel, and attach the wheel to the last 1L of the CV axle, the wheel tends to slip off the CV axle.

Does anyone know of an existing solution to this problem? Widening the axle to 23 studs is not really an option if I am going to keep things scaled properly.

Thanks!

Oh, and could an administrator change the title of this topic to something like [WIP][MOC] 1:10 RWD Rally Car? Thanks again!

This discussion is worthless without pics :)

Use a 5,5L axle, which cant slip out :)

This discussion is worthless without pics :)

In the top version, the wheel tends to fall right off the CV axle. In the bottom one, the axle pulls out of the 3L u-joint.

Use a 5,5L axle, which cant slip out :)

Hm. This works, but leaves 2L+ of axle sticking out from the side of the wheel, which looks bad. I wish the tan 4L axles with smooth center section had a stop in the middle.

#2 with 5.5 axles with stop will solve it.

I would go with 5.5L axles on #2...

Axles sticking out is better than a wheel falling off :P