John Stranahan

iTrader: (27)

Very nice.

Here is the countersink bit that you and I need or its metric equivalent. It will also improve the position accuracy of drilled holes by not flexing or walking if used first. At Mcmaster.com
Step-Saver Double-End Carbide Countersink Carbide, 1/4" Dia, 82 Deg Angle, 2" O'all Length
In stock at $33.23 Each

Quante

iTrader: (6)

Lol, do you have any idea how long I searched for the correct countersink bit without finding any I could use on a mill!!
Gotta get me one of these shortly.

Quante

iTrader: (6)

Day 2 of cutting CFK and Delrin.
Everything falls together nicely as you can see in the pictures.
The rearsuspension works very well as far as you can feel it by hand.

I'll be cutting the CRC front suspension plates tomorro so I can at least mount a Front end on it

John Stranahan

iTrader: (27)

Super nice. Here are those same two pics doctored a bit.
Notice that at the moment you have almost parallel links to the back pod. This puts the instant center near infinity and the line from the tire at the ground; antisquat, to 0%. Moving the front of the lower links up and the back of the upper link up raises the instant center and improves the antisquat. I realize you are not to the adjustment phase yet, but thought I would mention this early on. Another thing is the Panhard bar mounts. Are they fixed. If so you are adding spring rate, it may be assymetrical to one side of the pod.
John

Quante

iTrader: (6)

I honestly didnt know the antisquat setting, thx for telling me, this will definately be an important tuning help.
I dont really understand what you mean if the panhard bar mounts are fixed, I'll take a picture of them tomorrow. I can change their height with shims so fixed is a big word.
I've drawn up how the front end will be for testing.
I'm attaching a pic for the front end and the panhardbar, but they're from my CAD prog, no Live pictures

John Stranahan

iTrader: (27)

The Panhard bar ends I see in the schematic are good. They have pivot balls. I was unable to see this detail in the live shot. By fixed I meant I could see no pivots on the end of the Panhard Bar. Very nice progress.

Antisquat. The center of gravity of our cars is about 3/4 inch from the ground. Get the two sets of links (to the rear pod)to aim to this point; the upper tilted down as it goes forward a bit. The lower tilted up quite a bit in front. This would be a good starting point for antisquat and improves the forward bite out of corners.

John

Quante

iTrader: (6)

Finally finished, and with great results!!
I finalized my own front-end which also uses Tamiya TRF shocks now, I gotta check how much space I have left when I check with the body, I now need to use too hard a spring to get the suspension hard enough. Getting a 3rd position to mount the shock to the wishbone would be a solution.

Quickly went out for a test drive outside on the driveway and wow, I'm impressed! Its incredibly uneven and slippery (wintertime ) but the car would let me get a good start without spinning out. Then some quick zig-zags (some 10-ish), it was very eager to turn but the rear was stable as hell, no spinouts nor did it ever seem to wanting to spin.

Things to do a slight redesign on:
The rear bellcranks wobble a bit (I only use 1 bearing!), I should think about how to improve this.
Gotta think about designing stabi's on the front, to be able to tune in turn stifness and stifness over bumps.

Oh, I can see it will be a good outdoor season for me this year

Here's the final/ latest pictures.

Pro ten Holland

iTrader: (1)

Cool!
I can't wait to see it run!

John Stranahan

iTrader: (27)

Very Nice. Can't wait for a track report. I see the Panhard bar now with pivoting rod ends. I mistook a light area of a previous pic for the Panhard bar although it was not installed. I wonder if you can find bearings with less play. Bocabearings.com has written specs and quite a variety. Traxxas uses a similar bellcrank setup on a couple of their large RC cars.

Here is a thought load a thrust bearing on top of your caged radial ball bearing. Similar to what some guys use on the rear diff. Support the inner cage of the radial ball bearing near the fixed end of your shaft. Have the thrust bearing bear on the outer cage of the radial ball bearing with an adjusting nut. This will remove the play while still allowing free motion and a narrow thickness for the assembly.

Pic is Quante's front end cropped
John

xprainman

Quante:
Concerning the issue of finding hard enough springs at the front, you might want to try using Corally springs from the former old type of front ends. These are not used anymore on the current cars as they have the Asso-type front end, except for the European version of the SP12X. This car still has the large springs, although as far as I know these are slightly shorter than the even older springs used on e.g. SP12M or C10X and all the former Corally cars.

I don´t know whether they will fit with Tamiya TRF dampers but the Hatzenbach by Achim Schulz uses dampers from the RC18T in combination with Corally front springs, since this car has the same problem of to soft springs when using bell cranks.

Corally part numbers:

SP12X
75564 - extra soft
75567 - soft
75565 - medium
75568 - hard
75566 - extra hard

SP12M etc.
75571 - extra soft
75572 - soft
75573 - medium
75574 - hard
75576 - extra hard

Regards,
Daniel

John Stranahan

iTrader: (27)

There is an extra stiff set of center springs for pan cars at Windtunnel (Wolfe). Never too late to change to RC18T shocks. It will cut an ounce or more off the weight of the car using the smaller shock.

Hatzenbach
It was requested that I discuss this novel design by private message a while ago. This link to the assembly manual is really needed to tell the story of the back end.

http://www.moosi-masters.de/forum/files/hatzenbach_a12_manual_978.pdf

The front end is much modified since this assembly manual was published. See XPrainman's link up above.
The back end is a multilink design. Two side links prevent pod rotation on the pods vertical axis. This is more or less normal for a center pivot link car. The car does not have a center pivot though. It has a set of links that instead give a virtual center pivot that is very low. The thought here, I am sure, is to lower the rear roll center. The front suspension is completely novel as well with bell crank operated RC18 shocks to control front bump. I have one report from Pro-ten that the rear is planted very well, but not enough to change cars.


Rear Pan Car Roll Center Analogies
I am going to discuss this by bringing up a couple of large car analogies. First the closest recent suspension that is remotely similar to a pan car is trailer hitched to a tow vehicle. There are springs made similar to our center spring that will distribute the load from the hitch on the entire tow vehicle. Here is a link.

Weight Distributing Hitch
http://www.campingworld.com/shopping/product/reese-pro-series-rb-weight-distribution-kits/7030

If you have a light tow vehicle you can tighten these enough to raise the rear of the tow vehicle adding load to the front. You could even remove the rear wheels. The heavy bars are that tough.

Then you have some yaw motion to kill. This is rotation of the trailer on the vertical axis. They make a set of sway controls (actually yaw controls) that are friction operated.

Sway control
http://www.campingworld.com/shopping/item/trailer-sway-control/12701

They act much like side links. You could lock these and then with a front wheel drive tow rig (removed rear tires) you would have our pan car suspension; sprung in the center on the pivot. If the trailer is leaf sprung the rear roll center is the center of the axle. If I move the hitch (or pivot point) up and down. I change the roll axis of car a little bit, but the rear roll center is still primarily like a leaf sprung rear end with rear roll center at the center of the axle. If the trailer had a solid suspension then the spring in the tire as it conforms to the road would be the only suspension. The rear roll center is still at the center of the rear axle.

Let's take another case that you might be able to visualize better. Lets take a late model mustang and cut the car in half right in front of the rear seat. Normally the rear roll center on this 3-link with Panhard bar mustang is at the center of the Panhard bar. If the rear suspension was solid the rear roll center would be the center of the axle. Now we add a second suspension. Lets say a trailer hitch with sway control and load distributing bars. This does not move the rear roll center to the hitch pivot. The rear of the car has its own suspension and roll center in spite of the center pivots position. It is at the center of the Panhard bar.

Now we take the same mustang (still cut in half connected by a trailer hitch) and make its rear suspension solid. The only compliance is in the tires. The rear roll center is at the center of the axle.

This last case is where I'm afraid our pan cars are. As much as we try to change the rear roll center, we are not. It is at the center of the rear axle.

Much experimentation on my part and with the Hatzenbach car and with lowered center pivot link cars and lowered t-plate cars has led me to this conclusion. Quante has a super spot for his Panhard bar as it keeps the weight low and his battery is short enough for it to fit there. Mine would be in the same place except that I am using extra long batteries. I suspect my car will handle as good as with a low Panhard bar as we are not really changing the rear roll center. We are bending somewhat the roll axis in its middle region which does not seem to affect handling much.

John

Quante

iTrader: (6)

Thx for the nice comments all!!
Yep, I know the hatzenbach and its a very nice piece of work (stole the lexan bumper idea from it).
But I didnt quite like the idea of having RC18 dampers on the car (sorry John ) and then having to cut springs to put on them.
It would've been easier to desingn in though cause they're not as "fat" as the TRF shocks.
Lengthwise, the TRF's and the RC18 dampers arent that much different.

On the front end my spring problem is leverage, thx for the idea but the Corally springs you mean are way to soft (I drove a C10 for about 5 years, best car I ever had), atm I settles for 1/8 Nitro springs (uhuh, nitro springs).
I have no idea what rating they are but they go over the hardest asso touring springs I have (copper or something like that).

I'm gonna start thinking on how to mount/build a sway bar on the front just as the C10 had (car is stripped for parts anyway).

Added a few pictures on the front end, you can check out my kingpin. This must be the most creative thing on my car, the Rod of a L2 center damper screwed into a ball from the CRC Bloody knife (used under the springs) all under the pressure of a spring. Zero slop (I really mean 0) and still very smooth and easy to move.
If I bend one I have a big ploblem, I only had 2 L2 center dampers .

elvo

John, great analogy and visualization. Here's the short version: A pan car rear suspension isn't as much a rear suspension as it is a way to make the chassis bend near the center :-)

Quante, goed bezig! Er gaat redelijk wat volk zijn voor een pan car kampioenschap denk ik.

John Stranahan

iTrader: (27)

Thanks for the post guys. Exiting work coming to a close here.

Negative Camber Gain

Negative camber gain can be seen when you push on the front end of our RC cars. The top of the tire may move inward slightly; This is negative camber gain. The camber becomes more negative. The top of the tire may not move in at all to give 0 camber gain. We may even want the left side tire to have a positive camber gain on the oval as it is always on the inside of a turn. The theory is: as the car rolls, the tires flex inward at the bottom, the negative camber gain restores a flat tread for better traction.

I noted that the front suspension on my Superior Spectre Oval car that I most recently assembled and tested had excellent steering traction. With a left offset rear pod, I was expecting a small loss here. So what was the difference in front ends between this car and it's mate the Woods Racing car.

The front ends were both strut types. I went to the shop and re-examined the woods car. It had a Typical old Associated (L4 vintage caster blocks) suspesion with long kingpins. It had a very slight negative camber gain. I pushed up on the kingpin with tire off. I wathched to see if the angle of the axle changed compared to a fixed edge like the battery front or the bumper. There was a slight barely noticable negative gain. Maybe .5 degrees.
See Photo Two


I ran the same test on my Associated Spectre car. This car has a CRC based front suspension with trimmed front arms and trimmed outer plastic rod ends, Associated style long kingpins, machined Delrin steering arms.
See Photo One
This front end had considerable negative camber gain. Maybe 1.5 degrees over the full travel of the kingpin. This is about where I set the negative camber gain of my dual A-arm suspensions. The two movements looked similar to my eye.

I had two other front ends assembled with the same basic setup. Low inner A-arm pivot, 2 degrees caster, 0 degree caster block. The only thing changing is the relative lengths of the upper and lower arms.

A brand new CRC Prostrut front end with All CRC prostrut parts was much like the Associated suspension a very slight negative camber gain. Maybe .5 degrees more negative over the full range.
See photo Three

Finally I have a CRC suspension similar to, but not identical to the CRC long ball suspension. With this suspension the upper A-arm is the typical length, but the lower A-arm is short (CRC size) and there is a little graphite extension plate to be able to use the upper arm long.
See Photo Four
This suspension gave me zero negative camber gain. As some people like this long ball suspension I suspect it sheds traction better with roll.

So in the pic below the suspensions are rated from high to nonexistent negative camber gain. Further adjustment can be made by elevating that inner pivot on the upper A-arm. Tests to come. These four suspensions should have similar low roll centers on an oval car or road car.

Pro ten Holland

iTrader: (1)

I also found that the associated front end has more steering mid-corner compared to the CRC front end.
I think that's why CRC has released the long upper arm conversion.

I think the effects are more evident on a wider car (235mm or 200mm) than on a narrower car (like 12th scale).

Please also note that the ackerman is different from the associated to the CRC front end. That will also change the steering characteristics.