Direct Acting Spring Damper

[ritwikdas18]

Also Z , I have 2 last year's springs from KAZ with spring rate of 27.2 N/mm .Given that I require only around ~32mm of travel on spring , I can cut those in about half or as much as required to get me to ~51 N/mm . Infact I think better would be to cut it to give me around ~45 since I can always increase stiffness with spacers but cannot decrease it. So perhaps I would not have to search for motorbike springs.

[JT A.]

edit: Having watched all of the afternoon session of Endurance at FSAE-M this year, the GFR car was incredibly fast. Did DASD's cause this? No, they have been fast for years now. Did DASD's make them slower? It sure didn't look like it on track. Good job to the GFR team, your car was very well put together. As mentioned by the Kansas adviser in your paddock, I wonder how many teams show up with DASD's next year, because you guys showed they are not holding a car back... We only showed that it was feasible. GFR showed the real speed potential.

I think the lesson to learn from GFR's performance with pushrods vs DASD is that any time spent debating pro's and con's & desiging different suspension layouts is wasted time that should've been spent improving your aero and drivers.

If you've never built a car before, sure, go with DASD because it will get you driving sooner and developing wings sooner.
If you've already built a car with bellcranks, it will probably take you more time & effort to redesign your car for DASD. Just copy over your previous suspension design and get to work on your wings & drivers.

[Z]

Ritwik,

... I have 2 last year's springs from KAZ with spring rate of 27.2 N/mm .Given that I require only around ~32mm of travel on spring , I can cut those in about half or as much as required to get me to ~51 N/mm...

Yes, but...

IF you cut them in half, then you must also,
1. Make some spacers to fill the missing gap, so the total length of spring+spacer is as required. Spacers can be steel, aluminium, or even plastic.
2. Learn how to do "closed and ground ends". This involves cutting the spring so that you have almost one full coil extra, using oxy-torch to heat a small section of the wire to red-hot about 80% of a full coil from the end, bending that last coil to "close" the end, then grinding that last coil so the end is "square".

Probably an easier way to begin with is to keep the original springs at full length. Then insert spacers between the coils, as per the Cincinnati picture. You can make these spacers out of any plastic such as nylon, HDPE, etc, or any hardish rubber. I would try making them as many little roughly ~1.5 cm cubical blocks with "grooves" on opposite faces, with radius of groove same as of spring-wire. Then push the blocks between the coils so that the coils sit firmly in the grooves and prevent the spacers from falling out.

Fill the gaps between half the coils on the original spring, and you double the spring-rate. Or adjust the number of "blocked out coils" for any other rate you want. When you eventually settle on a good spring-rate, you can get custom springs made that have just the right number of "working coils", for a neater and (very slightly) lighter job overall. But maybe leave that for next year...

Z

[P^squared]

DASD Connector.jpg
Hey, everyone. The thing about the connectors between the dampers and length extensions is that the damper needs to fit fairly well in the connector, or else any compliance there will lead to bending loads.
Also the other end could be threaded to allow adjusting the right height on the go by rotating the extension tube.
Any suggestions about the connector design ?
I hope the pic gets uploaded

[ritwikdas18]

P squared , I have planned the same. The connector would simply be a threaded rod right?
and it must be attached to the shaft of the damper after removing the eyelet which is held tight with Loctite in my case .The shaft should not be damaged while doing so.Also since the eyelet is threaded the same thread is to be copied in the rod after removing it.

Could anyone (Z??) give a list of do's and dont's if I missed anything because we are doing it for the first time?

[P^squared]

The MTB dampers we have don't have eyelets(similar to female rodends ??) which could be screwed out.
Instead I plan on manufacturing a bolt-on connector, which would bolt onto the damper,at the opposite end of the reservoir, where a bellcrank would originally. Then the inner walls of the connector would be tasked with keeping it in place.
elka_stage5_shock.jpg The dampers are similar in design, albeit shorter in length.

[Z]

Could anyone (Z??) give a list of do's and dont's if I missed anything...

Ritwik,

Refer to:
http://www.kaztechnologies.com/wp-co...cal-Manual.pdf

Pages 2 and 3 have a Parts List and drawing, with
part #25 = the damper-rod, called "Shaft" and possibly with 3/8"UNC(?)-male-thread, and
part #28 = the female-threaded-lower-rod-end, called the "Eyelet".

At the bottom of page 4 are instructions for removing "Eyelet" from "Shaft". This requires special shaft-clamp-tool "TL-78SC", which I assume is just some soft jaws (eg. aluminium blocks with V-notches to grip the shaft?). At worst, use a hot-air-gun to heat the Eyelet and soften the Loctite...

The Spring-Damper-Extension can be made something like this "ascii drawing" below (with bottom/wheel-end of damper at the left, and "<" or ">" indicating direction of male>female thread...).

(Eyelet<3/8")<-(3/8"<steel-hexbar-with-male-thrds>12mm)->(12mm-locknut)(12mm>alum-female-thrds<3/8")<-(3/8"<Shaft.....)

So the "Extension" fits between the Eyelet and Shaft. The Extension is made of two main parts:
A steel-piece, machined from ~16 mm hex-bar, with male threads at each end, and is Loctite-fitted to the Eyelet (shown at left above).
An aluminium-piece, machined from ~30 mm round-bar, with female threads at each end, and is Loctite-fitted to the Shaft (at right above). This part must also be machined at its "top/right" end to carry the Spring-Retainer (#26).

The steel-piece then screws into the aluminium-piece via a 12 mm thread (x 1.5 mm pitch), which should overlap about 50 mm, and is locked with the 12 mm nut. This 12 mm threaded section is where you do "ride-height-adjustment". Only a single right-hand thread is needed here because the damper-shaft can rotate freely in the damper-body (some adjusters need LH and RH threaded sections). The other two threaded joints (ie. 3/8" to Eyelet and Shaft) should be "semi-permanent-Loctited-joints", done similarly to a steel-stud into aluminium.

Hope that makes sense.
~~~o0o~~~

P^squared,

Because you have a damper-adjuster-screw at the bottom of the rod (from what I can see in the Elka image) you probably have to do something like your CAD image, or better yet like Cincinnati's extension piece.

https://www.facebook.com/bearcatmoto...type=1&theater

Note how C's extension has one bolt through the ball-joint-hole, and a SECOND bolt closer to the spring, with this second bolt CLAMPING the C-shaped extension hard around the damper. This is a preferable way of doing it because it eliminates any sloppiness. Alternatively, you can use grub-screws to eliminate slop between the extension and damper.

Also note how Cincinnati use shim-spacers to adjust overall SD length, and thus adjust ride-height. I would be inclined to use the threaded adjustment described above, but either way would work.

Z