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Post by fatherchuck53 on May 23, 2018 12:15:21 GMT -5
It appears to me that most builders are setting up their pushrod front suspension with the dampers and springs mounted high on the chassis. I would think that instead of mounting a pushrod off the lower A arm, mount a pull rod off the top A arm and mount the damper/ spring low on the frame outboard the A arm pivot points might be a better choice.
1. Drop that mass of weight to a lower point, lowering the cg .
2. By using a pull rod instead of a pushrod and lighter rod would be able to be used reducing overall sprung weight and vehicle weight.
3. Pivot point actuating arm would be lower, again lower cg.
4. Increase usable space for legroom, instruments, and possible decrease of cd .
Anybody have thoughts?
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Post by Liteway on May 23, 2018 12:52:48 GMT -5
If you are talking about an an open wheel vehicle here,and I understand you correctly, this would result in putting the spring/shock back out into the airstream which negates the clean look and low drag afforded by inboard mounting, so it depends on what you are trying to achieve.
(Later edit) Do I have the picture right, coilovers positioned outboard the bodywork, but laid over horizontally? End edit.
As a practical matter, for a home builder, it is probably best to go with conventional lower A-arm direct mounted coilovers and save the weight,friction, packaging disadvantages of all bellcrank type springing.
I have to admit I did it as much for the "cool" factor as anything else.
Puzzling to me is the design of the P-6 Scorpion, where the designer went to the trouble to incorporate linkage spring/shocks and then mounted all the dirty bits above the smooth bodywork.
I think I recall seeing the config you are describing on a 70's era Lotus formula 1 car while visiting the Barber museum in Birmingham. I took pics but cannot find them nor can I recall which model Lotus it was. If it was good enough for Colin, it must have merit.
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Post by eclipse on May 24, 2018 3:20:01 GMT -5
In my limited experience, the defining factor seems to be the influence of the definition of the roll centre height and the corresponding arrangement of control arms. If you wish to prioritise a low roll centre then, generally speaking, the control arms need to be angled down (when considered from outbound to inbound). This means that you inherently have a higher mechanical efficiency with a pushrod (that will be able to convert vertical wheel displacement into linear pushrod motion, with only a ~small amount of angular displacement at the pushrod spherical bearing) than with a pullrod (which will see a higher proportion of angular displacement at the pushrod spherical bearing). To a certain extend you can design a bellcrank to accomodate this, so I guess it's "horses for courses". In 'proper' high performance vehicles such as this Empire Wraith, it's the influence of aero that rules above all else. Check out his control arm angles and the cavernous space under the nose!  -Rob |
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Post by fatherchuck53 on May 25, 2018 10:20:35 GMT -5
Yes liteway you are thinking correctly. Damper/ spring laid horizontal along inboard pivot point of lower a arm. The standard damper directly to lower a arm is simplest and efficient. The cool factor is very important to home building.
As to being in the airstream, laid along the length of the body with the a arms , brakes, wheels you all ready have a large amount of turbulence. A small bubble fairing on the body would negate this or even better a lower wing blended into the a arm damper. But I agree with you. If I was to go to the work and designing of such a system, I would mount it out in the open for everyone to see how hi performance it is.
Eclipse, I don’t follow the reasoning of the control arm angles have to do with the mounting of the damper high centered on chassis vs lower outboard, or punch rod vs pull rod actuator. I don’t mean to criticize your thinking, I believe we are thinking of 2 different scenariors.
Hi performance 4 wheelers have a lot of different parameters to work then 3 wheeled. Maintaining the cg as low as possible is more critical on a tadpole.
I believe main factors influencing trike building; safety, weight, easy of construction, and cool factor. Not to exclude the most important one. Convincing the spouse of how little it cost.
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Post by DaveJ98092 on May 25, 2018 15:31:05 GMT -5
<<<<SNIP>>>> Not to exclude the most important one. Convincing the spouse of how little it costs. OH boy, if SWMBO ever reads this, your done.  |
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Post by eclipse on May 27, 2018 12:57:36 GMT -5
@op - it's quite possible (probable?) that I'm incorrect. The outboard positioning of the spring dampers certainly helps resolve the mechanical efficiency issue that I was trying to explain, but when comparing like-for-like scenarios if the spring dampers are inbound of the main chassis structure then I believe that my concern remains valid.
In the design that I'm working through at the moment I'm looking at the feasibility of a pullrod system for all of the benefits that you cited. In my instance, though, the trailing lower control arm attachment points would be prohibitive to positioning the spring dampers outbound, and I suspect that this would also be the case for the majority of similar SLA double-wishbone designs?
-Rob
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