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Mechbuilds

[Help] Crawler suspension.

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Posted (edited)

I'm currently constructing a crawler and after building @filsawgood's Rancher chassis, i was interested in building a better crawler. 
After doing tests on the chassis, i found out that the suspension needs to be a tad softer for extreme angles.. 

Then i stumbled on @Madoca 1977's Jeep Wrangler. I don't know what this suspension is called but i like it. 
I'd like to build a similar chassis, just 2 studs wider and a little bit longer.. 

I like the fact that the linkage allows the axle to twist like that and achieve better and higher angles. 
What i'd like to do is add springs to it so the chassis would have up and down suspension while twisting as much as possible.. 
Also i'd like to get as much as steering angle as possible. 

All this while having beefy enough front and rear axles that they don't flex or bend due to the weight of the model. 
I really want this crawler to hug rocks when it climbs. 

I do have a steering servo now. Should i use motor steering instead to achieve better steering angles and more control? 
I also don't like the weight of the model resting on a single axle, that's why i use wheel hub assemblies as much as possible. 

Edited by Mechbuilds

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I only have built one crawler so not sure how good my advise is but it seems like I was trying to do similar at the time based on Unimog style.

I was very determined to get soft suspension that mimicked real vehicles (where the body stays almost still and only the wheel moves going over bumps) and also large amounts of flexibility between front and rear axles and have the shocks in a somewhat realistic position and I spent a long, long...long! time stuffing around with just the placement of the springs and the spring types (hard,soft etc) compared to the weight of the vehicle and of course re designing the axles and chassis every step of the way to suit spring placements.

so from my experience one needs to build a chassis then build axles to suit but also be ready to modify everything until your happy with the ride. I don’t think there is a do this or that advise?

that one of madoca you listed is pretty insane flex angles but not sure it would work that well with a springs setup? That is the springs may dampen the twist factor?

640x502.jpg

This was an early version but shows the travel capabilities I ended up with and ease of access to the chassis to change spring  locations.

so all I can contribute is ‘build, change, experiment’  :wall:

Edited by MangaNOID

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Currently i have a setup which is basically @filsawgood's modified rancher axles attached to the modified suzuki jimny chassis. It works surprisingly well as an offroad chassis. (it's soft by normal lego standards but for me, i still would like a stud or two more flex.) It has enough flex to raise the front tire on top of the lego technic 6AA battery box while having all 3 other tires on the ground. (And by battery box, i mean that the orange knob is pointing upwards. That kind of flex.) Also the turning angle with the steering servo is awful. I can only fit one turning axle so 4 wheel turning is not an option. 

This is my front axle:
TqK2epll.png

The 3 links and the 2 springs are connected to the chassis. The steering servo BARELY has enough room to fit between the two springs. 
If anybody knows how to add more cowbell to the steering, i'd appreciate it. I'm also willing to swap the servo to an M motor for better steering control when crawling. 
(I mean that the whole front axle can be redesigned completely, but the links and shocks need to remain in the same position.) 

This is going to be a trial truck that can crawl a little.   

Edited by Mechbuilds

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You should check out some of PunkTacoNYC's crawlers, here on these forums. They have excellent suspension characteristics and he would probably be glad to help you out. 

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Here is my frame:

cLEHlmEl.png

The rear axle is complete, the motor and gearbox are all complete. I just didn't bother adding it to the LDD. 
But yeah, that's how the links are connected and the driveshaft comes from the middle.

The springs can be placed wider by removing the 9 long beams and they can be moved 1 stud forward or back.  

I need a front axle that can fit here.. I already used the @filsawgood's rancher front axle but replaced the 92908's with 11950 instead. 
The distance between tire to tire needs to be 11 studs (if the tyre is outward or 13 studs if the tyre is inward.) I'm using 86652 wheels with 32019 tires. 

Can somebody help me make a front axle that has better steering? The front axle i copied from the rancher only turns by one stud. So turning radius is horrible. 

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The tops of those springs can only move in 1 direction relative to the upper frame; I think it needs to be able to move in two?

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1 hour ago, pleegwat said:

The tops of those springs can only move in 1 direction relative to the upper frame; I think it needs to be able to move in two?

It does work for the axle i posted earlier.  Lots of sideways flex and a little bit of up and down flex. 

Only problem i have with the previous axle i've shown was the terrible turning radius. 

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I just can't figure out what kind of front axle to do so i get better steering.. For now, it seems that i have to either settle with rear wheel drive good steering or 4 wheel drive but bad steering.. I might do a completely different front axle all together with less flex than the rear if i can just get more steering angle so the thing can actually turn without going back and fourth 6 times to turn 90 degrees. 

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Here's an .LXF of the whole moc currently: Rear axle + chassis

If anybody can figure out an front axle that has okay steering angle and at least close to the flex that the rear axle has then please help if you can! 
I really want to finish this moc and offroad it. 
 

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