derf
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| posted on 31/3/04 at 05:15 AM |
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Would this pushrod work?
I am not sure if the pushrod will work because it is below the upper A arm? I am using a yamaha R1 rear shock. I plan to add the rear upright
(pictured) and I will have to brace the 2 uprights alot more than they are.
Image deleted by owner
[Edited on 31/3/04 by derf]
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JoelP
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| posted on 31/3/04 at 08:17 AM |
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my only comments would be that it would have a lot of leverage on it being so low, so the bar its all attached to would need strengthening, plus the
pivot thing would have to be adjusted to compensate for the leverage (change in apparent spring rate).
aside from that, not too much of a problem.
is the piccy to scale?
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Digger Barnes
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| posted on 31/3/04 at 08:36 AM |
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mmm the more different ideas I see the better.
I am currently doing the design for my own bike shocked locost.
Yep as jeol said it will work, but because of the strength of the spring on the shock (2-3 times that of a locost shock) you will put one hell of a
load on that mounting point if you design the linkage correctly.
Just out of interest what raito of lengths about the pivot point are you thinking of using on the linkage to deal with the high spring stiffness and
the low amount of travel available on the shock?
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pbura
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| posted on 31/3/04 at 09:40 AM |
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Derf,
The front lower ball joint on the RX-7 doesn't normally take much of a load, so I am planning a pullrod instead, like this from Steve
Graber's car:
 
Rescued attachment BalaFrnt.jpg
Pete
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britishtrident
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| posted on 31/3/04 at 10:30 AM |
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Way too much bending stress on the chassis members. Loads should be fed into spaceframes only at nodes (where tubes join), otherwise you put
bending loads on the chassis tubes. -- every spaceframe breaks this rule but you can get away with provided the loads aren't too high, the
book chassis spring mountings are marginal in this respect.
Get it wrong and the chassis will flex more than the suspension unit moves, Racing cars with pushrod and pull rod suspension (and spaceframe chassis)
tend to use complex spaceframes made up of short tubes with a lot of triangulation. If you take a look at the way the type of chassis used in Formula
Ford and other similar formulas evolved you will see what I mean.
Also its diificult to judge from a 3d drawing but the angles of the rocker lever just don't look right.
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britishtrident
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| posted on 31/3/04 at 10:33 AM |
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quote:
Originally posted by pbura
Derf,
The front lower ball joint on the RX-7 doesn't normally take much of a load, so I am planning a pullrod instead, like this from Steve
Graber's car:
Looks good --- if it was in the UK i couldn't imagine getting it through our SVA test for road use.
[Edited on 31/3/04 by britishtrident]
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DaveFJ
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| posted on 31/3/04 at 11:19 AM |
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there was a recent thread about the angle at which dampers could be fitted. If I remember correctly you had to use a special kind if you wanted to
mount them horizontally like you have.......
Dave
"In Support of Help the Heroes" - Always
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Bob C
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| posted on 31/3/04 at 11:54 AM |
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I think the bike shocks are designed to run horizontal. Your design looks reasonable from the "loads near nodes" viewpoint. If you make
the bellcrank right you can compensate for the spring rate reduction under bump that you get with the standard setup - should be good!
Bob C
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JoelP
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| posted on 31/3/04 at 12:47 PM |
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quote:
Originally posted by britishtrident
Looks good --- if it was in the UK i couldn't imagine getting it through our SVA test for road use.
which bit is in doubt? the pull rod? i really like the simplicity of the lower arm, looks well light yet still adequate.
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derf
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| posted on 31/3/04 at 01:36 PM |
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No not at all to scale, actually that is a 5 minute drawing in MSpaint. The pivot point as it is shown would be at full compression. I have been
talking to Mr Grabber himself, mainly to find out the ratio of the bellcrank (2:1) which was my guess. That should give me a spring rate of about
250lbs. Those would all be 1"x1" 16gauge steel tube, and definatly some cross bracing in there.
I wanted to try to keep it as simple as possible, but I am not sure I wanted to bring the pushrod over the top rail.
I do want to use the rx7 spindles, but really would like to use a solid rear and keep the same bolt patern up front too. I am looking in the local
junk yards for a matching set of front spindles with brakes, and solid rear axle. I am trying to stay away from IRS or dedion as I( am super scared of
my lack of good ability to measure stuff straight (last year I built a go kart that was 2" off center line but looked straight and had all 4
wheels off eachother by at least 5 degrees) because of this fact a solid rear with adjustable trailing arms in my ideal rear end. This would be my
ideal front end.
I believe that this design would be very beneficial to anyone who wants to build a shorter chassis as the suspension is very adjustable, cheap, and I
dont see it interfering with any other parts of the car.
To help strengthen the "nodes" I was planing on using some of my 1/4" plate steel and cut out a T and weld that over the joint,
maybee use a triangle plate in the corner for strength, it is also possible for me to cross brace with 1" sq or 3/4" sq tube.
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JoelP
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| posted on 31/3/04 at 01:39 PM |
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steves design has a nice rising rate doesnt it. you could probably remove the spring completely and still not hit the ground! it would be swinging off
the pivot piece!
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britishtrident
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| posted on 31/3/04 at 02:17 PM |
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Cross bracing lots of it rather than add fillets. The other thing you will have to be very careful with is the crank geometry, it would be very easy
to end up with a falling rate suspension rather than rising rate.
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britishtrident
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| posted on 31/3/04 at 02:21 PM |
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quote:
Originally posted by JoelP
quote:
Originally posted by britishtrident
Looks good --- if it was in the UK i couldn't imagine getting it through our SVA test for road use.
which bit is in doubt? the pull rod? i really like the simplicity of the lower arm, looks well light yet still adequate.
I
n the UK we have to wrap anything that looks the least bit mechanical in cotton wool least a pedestrian decides to entangle his or her self with the
oily bits.
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derf
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| posted on 31/3/04 at 03:11 PM |
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I have the NJ DMV requiremnt booklet for kit cars, and a locost wpuld fall into this category. The closest thing to having to hide any mechanical
stuff is that the front bumper would have to be designed to so as to avoid a pedestrian from being killed, the exaust must be designed so as to keep a
pedestrian from being burned. Kinda kills my idea on how I wanted to do the exaust.
The prowler front bumper is legal so I am going to copy that until I pass the initial inspection. I havnt figured what I am going to do with the
exaust yet, I am hopeing exaust wrap works.
I have seen photos of other sevens that are NJ legal without a bumper though or any kind of exaust wrap on them.
These are some of the better suspension ics I am looking at, I am looking for better pics of pushrod designs to mimic.
[Edited on 31/3/04 by derf]
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mranlet
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| posted on 31/3/04 at 05:48 PM |
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Derf - looks like you've got a lot of positive camber there, you'll have to fix that.....
at 45* the damper is only 30% efficient - your car would have some really crappy geometry.
-MR
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derf
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| posted on 31/3/04 at 06:20 PM |
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Positive camber? I havnt even put thought into the spindles yet. If you are refering to the photo of the prowler, It's not mine, and the car has
sucky handling (IMHO)
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sgraber
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| posted on 31/3/04 at 07:25 PM |
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quote:
Originally posted by JoelP
steves design has a nice rising rate doesnt it. you could probably remove the spring completely and still not hit the ground! it would be swinging off
the pivot piece!
Am I too late join to this party?
In a completely non-scientific way I can tell you how well the rising rate works on my car. If jump on the front end as hard as I can (I weigh 220 big
American pounds - But I'm 6'-4" so I'm not a FAT American so don't get on my case!) I can get the suspension within
1" of bottoming the lower rail on the ground. With the assistance of another 220Lb person jumping on the car at the same time, we can just get
the frame to just touch the ground. And we had to jump HARD! That's 440Lbs jumping to move the suspension 5", 220 Lbs jumping to move it
4".
Regarding my design: It is untested in real life driving conditions. Sure a couple of times around the neighborhood at 70MPH proves that it works, But
that is in no way an indication that it works well. So I'm prepared to hate how it works. Of course, I'm hoping that it'll be
great.
Fred, regarding your drawing. How about move the bellcrank to the outside face (instead of around the back), move it up to the top rail, angle it
downward more. You can attach the bellcrank to a bracket welded to the top rail in double shear. I'll post a little piccy in a few minutes.
Graber
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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derf
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| posted on 31/3/04 at 08:40 PM |
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Like this?
Image deleted by owner
I dont quite think I am understanding what you say, but this is what I got...
The whole reason I wanted to open up the area that would be where the inboard suspension sits is to hopefully move my radiator into that area, which
will open the area up for me to put a battery in. Plus I kinda like the idea of having the springs out in the open and I want the one piece hood to be
as rigid as possible.
[Edited on 31/3/04 by derf]
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sgraber
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| posted on 31/3/04 at 11:52 PM |
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I'm sorry Derf, for my terrible explanation. What I meant is this, (I know it's a crappy image, but you should get the idea.
Racecars use the pushrod-bellcrank design quite a bit. The bellcrank is an interesting shape, with both the input and the output on the same side of
the crank. (Not a traditional triangle)
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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andkilde
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| posted on 1/4/04 at 03:13 AM |
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Hey Derf
Were you the one bidding up the price of R1 bits on me a few weeks back? I had to pay nearly $100 for four of them, sheesh
Anyhow, these guys
http://www.pohlsprings.com/
apparently wind custom coils to your specifications for about $20 US apiece.
I'm basing my bellcrank lengths on my desired suspension travel, then calculating appropriate spring rates using the formulas for "Wheel
Frequency" in Staniforth's book.
Cheers, Ted
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derf
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| posted on 1/4/04 at 01:22 PM |
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Yeh that was prolly me, (Ebay id= Focusfred) I only bought 2 but in a few weeks I'm gonna start to look for another 2.
The pic of the race car isnt exactly clear, I'm gonna blow it up to get a better look in a few.
I tried to blow it up, couldnt see too good. This is what i understood though, a quasi-torsion bar design.
Image deleted by owner
[Edited on 1/4/04 by derf]
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pbura
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| posted on 1/4/04 at 02:44 PM |
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quote:
Originally posted by andkilde
Hey Derf
Were you the one bidding up the price of R1 bits on me a few weeks back? I had to pay nearly $100 for four of them, sheesh
Patience is everything in buying these things. I was in a bit of a hurry and spent about $100 for a set of 2002 R6 shocks, which aren't quite
as pretty as the R1 shocks, then watched in horror as a nice one went with no bids. Could have had it for $1!
One consolation is that these shocks are over $500 apiece, new.
Pete
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derf
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| posted on 1/4/04 at 02:53 PM |
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Yeh I wont say I was in a hurry, I bid on like 7 or 8 different shocks, with a max price of $32 US, I won some lost most, Wasnt in a hurry, but I set
my max suspension price for all 4 as $150 (with shipping), and I should finish all 4 within that price. Although one guy that I won one from and
explained what I was using them for offered to sell me a set of 4 for $240 plus shipping (including the one for $32) he said that at the price I won
it wasnt worth it for him to sell them any cheaper. I really want to win the remaining rear shocks from him just to wee him off. I made a counter
offer for 150 plus shipping and he turned it down, his loss.
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derf
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| posted on 1/4/04 at 03:11 PM |
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I found this...
I am gonna drop them an email and ask for some details of their design.
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JoelP
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| posted on 1/4/04 at 04:08 PM |
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Image deleted by owner
because length AB is (appears anyway) to be shorter than length CB, you would have an increase in the relative/effective spring rate in this case.
This compensates for the very low angle of the pushrod, whereby say an inch of wheel rise would only compress the spring maybe 8mm. this would
compensate for the fact that the bike spring is so much more powerful/harder than the desired rate.
A result of this is that the mounting points for the pivot are under a tremendous load, and must be well thought out. Goes without saying i suppose
but they might experience 4 times the force of regular shocker pickup points.
all figures are approximations so criticism/modification will be tolerated, this once.
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