PDA

View Full Version : Cantilever on buggies?



Interstate
12-08-2003, 10:01 PM
First off, I don't own a buggy so don't criticise me too much.

I always see buggies with giant shock towers up front and in the rear. I do understand that buggies require a lot of suspention travel to soak up the bumps, but why not make a lay-down shock design to increade aerodynamics, if not all four corners, but just the front. It would appear as if some components could be re-located to make room, or some clever engineering to make this work. Has this been done before, or what?

adam lancia
12-08-2003, 10:13 PM
it has been done. tenth technologies did it with their predator 4wd electric buggy back in 96 i think. it was also one of the first high performance electric buggies to use a shaft drive system very similar to the TC3's. i think the problem was that it didn't like the rough tracks too much because it's suspension travel was compromised by the design.

adam

InspGadgt
12-08-2003, 10:52 PM
The problem with cantilever suspension setups is the angle of the push rods. The angle of the push rod determines how much leverage the arm gets on the shock. If it's too laid down then the arm gets more leverage on the rod then the rod gets on the arm. This results in a very soft suspension even with stiff springs. The same reason applies as to why you don't see very many cars these days with front shocks that are laid down. A shock or push rod's best angle is close to perpendicular with the ground. hence the tall front shock towers which allow the shock to stand up more.

SteveK
12-08-2003, 11:31 PM
Mounting the shocks in the middle of the suspension arms takes the place of the cantilevers. If you look at old Clod designs, they would put the shocks right over the center of the axle. This makes the springs too stiff for the chassis weight, and gives too little travel. Then cantilevers were added to extend the travel and soften the relative spring rate.

Then the real monster truckers copied the off-road guys and put the shocks in the middle of the suspension links, which gives the same effect as a cantilever but without the extra moving parts.

Any more moving parts just add weight and more mechanical things to maintain and repair. The current system works pretty well, and is about as simple as you can get.

Schumacher also tried the cantilevered shocks on their 2WD buggy in the late 80's. They just did the fronts, that I can remember. I think part of the problem with those buggies, as well as the Tenth Technology ones, is that they were designed for smoother, more 'natural' off-road tracks: Americans like rougher tracks with big jumps (Or at least they DID, these were pre-blue groove days). I don't think it was just the cantilever design, more the overall design of the cars, but the cantilevers didn't help matters.

Grant Tokumi
12-10-2003, 01:22 AM
Just for kicks, I tried to fool around with a different shock position while trying to maintain the same push rod geometry. Came up with this front shock schematic. Top schematic is typical setup today. Below is more of a laydown shock geometry.

http://rcarchive.com/pics/shock.gif

As you can see, it has the same amount of moving parts in the suspension. Shock tower won't be necessary anymore, but arm becomes more bulky with the 90 degree added arm. It does create its own problems such as shocks crossing, and arms conflicting when both are compressed. Major things that need to be addressed, but maybe the pic may stir up some "clever engineering" ideas rather than simply accepting the current standard as "the best".

Perhaps having the arms point forward instead of sideways would aid in a laydown shock geometry because shocks can lay flat in a front to back direction instead of left to right. That would be much like how the old Tamiya Frog rear geometry was setup.

Losi Stealth
12-10-2003, 07:37 AM
What ever happened to trailing suspension arms, I have a neighbor who showed me his old RC10, and he had a trailing arm conversion on it.

SteveK
12-10-2003, 10:49 AM
No matter what the numbers and theoretical tests tell you, simplicity and cost will always win out.

The traling-arm rear suspensions fell victim to some of the same problems as cantilevers: There are more moving parts to build, maintain, and replace. The Losi 5-link suspension had 20 pivot balls to install and keep clean. Other systems using a single swing-arm, like the A&L and Andy's kits, didn't easily allow for camber and toe adjustments.

And while they gave great traction, as tires and suspension tuning got better and better, you could get better traction all around and get the more aggressive handling afforded by 'H' or 'A' arm rear suspension setups (Losi called their first setup H-arm because the arms looked like an H, not like an A like on other vehicles).

InspGadgt
12-10-2003, 03:17 PM
Grant your pushrods may be the same length but the geometry is different. The 2nd drawing has them more laid down then the first. The trick is to get them more upright so they can be more effective.

Grant Tokumi
12-11-2003, 12:25 AM
They are actually very close in geometry as far as shock angle is concerned. And when copy pasting the yellow angle label from 1 to 2, I found that 2 is actually a little closer to perpendicular than 1 is. :cool:
http://www.rcarchive.com/pics/shock2.gif

InspGadgt
12-11-2003, 05:28 AM
Not really....your measuring your angle from 2 different locations. The angle needs to be measured from the same place on where it attaches to the arm. In the first one your measuring the angle relative to perpendicular to the arm but in the second your measuring relative to parllel to the arm.

Another thing to consider too is how far out the push rod mounts on the arm. In your 2nd drawing the mount point is closer to the inner hinge pin. With it like that the arm will have even more leverage over the shock so now it's doubly soft from the angle and the pivot location.

379
12-11-2003, 12:26 PM
why not just put 2 shocks at the top of the bulkhead thingie and integrate it into the a-arms

Grant Tokumi
12-12-2003, 03:14 AM
A shock or push rod's best angle is close to perpendicular with the ground.

In a standard arm, yes, its almost perpendicular to the ground, but its not applicable in "all" cases. The 2nd drawing is a perfect example where the shock is mounted to a vertical arm, and then the best angle becomes parallel to the ground.

I can't think of a way to explain it better.... The only thing I can think of is to imagine the shock still connected to the arm end, but not connected to the chassis, and then clamp the chassis to the table. Then lift one a-arm with one hand, and push on the shock with your other hand to keep the arm from moving (to imitate what a shock does). In the 1st drawing, the best direction to push on the shock to keep the arm from moving is "down" or perpendicular to the ground. But in 2nd drawing, the best direction to push on the shock to keep the arm from moving is parallel to the ground.

Anyways ..... :)

InspGadgt
12-12-2003, 05:00 PM
Oh I see what your getting at now...I thought you were talking about a cantilever at the top there but what it is is a arm with a 90 degree bend in it with the shock or push rod mounted at the top of the arm instead of at the bottom. Delta had a front end similar to that on a 1/12th scale except it used a mono shock between the two vertical sections of the arm. I think the main reason companies stopped using such a setup was because of arm flex in the materials at that time. Mounting the shock out on the horizontal arm reduces a lot of the effect of the flex on the suspension. But with today's materials being much stiffer perhaps it is time to look at this type of suspension once again.