Quante

iTrader: (6)

Hi John,

Yes there are turnbuckles on the front end! I'll be using Team Laje's ( http://www.laje.se/IMAGES/large_SpeedEvil2007.jpg ) aluminum block to connect the links. I found it pretty important that I could do rollcenter changes to the front so I really wanted upper links.
Atm I'm drawing up the front end, havent looked much at the rear end yet.

But I'm glad you like it. One of the problems I have atm is ride height adjustment, with this front I probably am going to mount the complete suspension on a seperate plate which I can shim up and down. But this means a lot of extra weight...

John Stranahan

iTrader: (27)

Quante-The nitro guys as well as myself just crank the shock collars up and down to change ride height. I can also shim mine up or down. It does change roll center to crank the collars, but it seems to work OK without additional adjustments. The roll center change must complement the tire height change. If you take a look at my two shimmable blocks you can see that you can actually make what you want very light. This suspension is not much heavier than an associated front. You waste some weight bridging the center of the car which is not really needed from a strength standpoint.
john

Quante

iTrader: (6)

Its the roll center change I'm afraid of, maybe its worth trying to do it with the springs first before I waste time and material making a seperate mounting plate.
I'll post update pictures as I advance in the design.

John Stranahan

iTrader: (27)

Quante-One more thing you should do. Take a look at the way the Associated TC5 mounts that lower arm. It is almost bullet proof. The little amount of flex those short vertical plastic inner hinge pin mounts protect the pin from bending and the arm from bending. This is also apparent on the associated pan car upper arm mount. That flexible plastic caster block protects the upper arm and pin. We hardly ever break the upper arm. I have tried to make something similar on mine. It is somewhat succesful but the base of my arm is not long enough. In your schematic your arm looks like it has a long enough base.
John

Quante

iTrader: (6)

I want the lower arm to be Carbon Fibre because I'll be able to produce it myself. I dont have the material to create a mold, took the initial design of the arms of a Yokomo YRX2000 and a Corally. Never broke an arm on my old C10 ever (in 8 years of racing it).
The arms will be made of 3 or 4mm Carbon fibre and it will be able to take a punch. I'll be centering the kingpin on the lower arm by means of a "O-ring" (remember it doesnt have to slide). The O-ring will give somewhat in a crash.
Still, thanks for the warning

John Stranahan

iTrader: (27)

Quante-good luck. Keep us informed.

Practice Session
Jeff let me have all the "keys" to the track lap counter. I had audible laps called out as well as the ability to print out the whole session. This let me do a little more accurate testing on some of the real basics on the oval. Gearing, tires and line. On the printout the lowest session is the first one. The most telling numbers are the 20 lap averages so I will concentrate on those.

First test was with 4 fairly short BSR pinks. Gearing was 3.14 inch rollout. 88/40 3.2 inch rear tire. This is exactly what I raced last weekend. The tiimes were similar, 4.56 average for 20 laps, to my race times. I qualified second losing only by .001 second last weekend.

I upped the gear 2 teeth on the pinion to 3.3 inch rollout. One of the guys runs up here. The car felt a little snappier at first, but the lap times tell the tale. The car was slower. That settles my inner conflict once and for all. You can use this taller gear to settle the car down or to make it lug a little more, but it is not faster if you can get sufficient rear forward traction. I had enough with my 3-link car.

I went one tooth below the start to a 39 tooth, gearing 3.07 inch/rev and the car improved. Now this is the gear I like from gut feel. This also happens to be the gear where the motors RPM average is right on the Power peak on the dyno. No slippage factor included. This would be the optimum gear on road as well I suspect. I had some tire spin on the battle axe on corner exit with this gear so it needs to be geared slightly higher.

Next I tested a couple of tire combinations. First I added that typical for oval right front purple to the car. Now the lap times say there was no improvement, but there were some subtle changes in handling. Because there is more grip on the inner tire on corner exit the car corners slightly better. It rotates harder from the left side bias. You can use more throttle on corner exit. The car is more stable without a tendency to slide out into the boards. Apparently from the lap times you must give up some speed on corner entry though. But from the testing there does not seem to be an overall penalty here. If that right front pink tire is wearing too much, then go to a purple or harder tire.

Next I put two pink GRP fronts on. Previous testing has shown these to give slightly less grip than two BSR pink fronts. The car improved again. That last 20 lap average 4.382 is a race winning average at our track.

Fast Lap
I may have mentioned this before, but you have to take the fast lap with a grain of salt on the oval. If you run a good backside of the course and then cut it a little tighter than usual on one turn and then dive for the loop, you can run a fast lap which will ruin the followup lap because you are all out of shape for the turn now. So it might be good to look at the fast lap and average it with the lap following. It will give you a more meaningful number.

Run Line
The best run line on this asphalt oval seems to be a little diamond shaped. Wide in the middle, but not wide the whole length of the straight. The audible lap times help determine this the best. This is a very similar line to what the guys were running during the Roar Carpet Oval Nats.

John

John Stranahan

iTrader: (27)

Oval Practice, World GT class suggestions for wing and runnout.

I performed these experiments on a flat asphalt oval, but I could have just as well have done it on an asphalt road course and which probably would have given similar results.

The first thing I tested was tire size and brand. This is a continuation of Wednesdays test. Firstly my gear ratio is now more settled for 4 cell 13.5 with the small sintered rollout. The car likes to have 3.07 rollout or a little less. This is about .1 lower than I used with the fat tuner rotor. The dyno showed more watts with the small rotor, but you only get best laps with this lower gear.

The first test today was with 2.40 inch GRP pinks (large) up front and 2.2 inch GRP pinks(medium) in the rear. I readjusted the ride height but nothing else. I am going to use top 10 fast laps as some of my runs were a little short on total number of laps. 4.72 seconds. Slower than wednesdays best 4.377 s average (top 10).


Tire size test
I went to very short 2.060 inch front GRP pink(About as small a you can run). Times did improve, 4.62. Now to adjust for tire size on my car I just crank on the front shock collars similar to a Nitro car adjustment. There seemed to be enough compensation there that the small tire drove similar to the big tire, but the small tire was faster. This is conventional pan car wisdom. One reason is that the tires are are lighter when smaller. The car is also a little more responsive with the short front tire.

Duplication of the Best car conditions from Wednesday.
I went to 2.160" BSR rear (medium) pinks duplicating the best run from Wednesday. I achieved my best run again 4.41 s (Wednesday 4.34s. Why the difference. Well today I had only 2 pounds of sugar. I applied four pounds on a wider run line Wednesday. Traction was just this little bit worse today. There was also some dust present from brisk gusts. I am convined the car likes BSR pinks in the back and GRP pinks in the front.

Wing Type Test
Now I did a test on two wing styles. One is a touring car wing which I have used a lot on the oval. See the first pic. The second is the Darkforce wing with KSG mounts and Darkforce Wing buttons. See the second photo. This is the deluxe and expensive wing setup that most guys run on the oval. Now this oval wing puzzles me a little. Our cars are the exact same size as the Nitro 200 mm gas touring car bodies, yet all the big dogs on our Roar Nitro Nats race used a touring car wing similar to the second picture. Mounted on pedestals similar to mine. Their cars, I believe hold our big track lap record, even better than the 1/8 scales who also had a nationals on our track. They do limit the height on touring car wings, but none of them have large side dams, a large flat area behind the back window, nor heavy steel mounts.

So what is the best wing for a 13.5 brushless oval car on flat asphalt. The top three sets of numbers show the result on my car. 4.409 for the touring car wing. 4.514 for the darkforce wing positioned like the instructions Barry pasted in earlier from Custom Works. Flat part even with the roof, kicker angled like the winshield.

I lost some steering. I tried two more positions for this wing. I moved the mounts low on the back window and slid the wing forward on the mounts. This had the effect of just lowering the wing. I got more steering, I reduced dual rate. 4.56. Finally I moved it back to the position in the photo where the kicker is just behind the rear most edge of the spoiler. I was not faster.

I now have numbers to support my choice of wing. On a banked track you are going to go faster and may have different needs. I supect that touring car wing is still going to be faster up to 60 mph. If the car needs straight line stability on the straight your car may need the big side dams. This is not a problem at my leisurely 27 mph on the oval.

I had run these two wings on the Battle Axe previously and came to the same conclusion.

John Stranahan

iTrader: (27)

Torsional Flex
As I like to tinker, I made chages to the car before the race and after my very good Wednesday practice session. My car was 2 ounces overweight from the addition of the RPM for Traxxas Rustler Nylon bumper and BRP blue foam bumper. I trimmed the bumper to two round buttons. This actually extended the bumper further outboard which was good. I trimmed the center out of the Nylon bumper; my chassis was a bit delicate in the middle anyway. I narrowed the front of the chassis to match the front suspension. I removed the rear of the chassis that was basically hanging there supported only by the front; this should improve motor cooling (it was 101F in the shade for Sundays race). What resulted was a lightening of the front end by 1.5 ounces and an increase in torsional flex. The track prep for the race was a dose of sugar Saturday followed by a full dose of sugar on Sunday. I had too much grip and especially too much grip in the back (no steering) from the previous favorite set of tires; BSR pink rears and GRP pink fronts. I replaced the rears with GRP pinks and removed my third shock from the rear which was only lightly loaded applying left down tweak. Now I had plenty of steering. The car felt good. I turned down dual rate. Lap times were not as good as in practice. The second through 3rd heat lap times were not posted so I could make no further progress. I finished and qualified second 2 seconds back.

My lightening attempt had not only lightened the front but it had increased torsional flex. If you grab the front and rear of the car and twist it the resistance is related to the torsional rigidity. On a touring car you can often adjust this with aftermarket parts or by removing screws from the top deck. On my car I added 3 braces. The brace at an angle did the most to remove torsional flex. The side brace on the battery side which I have had on the car previosly allowed me to raised the front end of the battery which tends to sag the chassis down with the weight. As a single support it lacked durabiltiy and would stress the screw in the crashes. I adjusted it to chassis flat with batteries on board. Anyway the chassis is a lot stiffer now. I gained only .6-.7 ounces. I should be able to test it Wednesday. I will put extra sugar down.

More torsional flex generally give you more cornering traction front and back.

The car is very durable now. No breakages on Sunday. Lower arms are strengthened with a graphite plate. Lower A-arm inner hinge pin supports are strengthened with a graphite plate. Rear link screws are all steel now. Front bumper extends outward to touch the body.


On a pan car you can adjust chassis torsional stiffness but usually you cannot return to the previous state. I have heard that superguing all the edges will stiffen the chassis. This includes the inner edges of all cutouts. I have not measured this so I can't tell you if it is really true or not. You can increase the size or number of chassis cutouts to make the chassis more flexible. On cars with a top deck you can add or remove support posts.

Note that that third front body post is extremely helpful in protecting your wheel arches from cracking at the top. I would add this two your road car as well.

I was having trouble with my steering rod end popping off. Generally new parts fix this. Mine did not. I replaced the rod end with an Aircraft type that cannot pop off. This may prevent a DNF if you have this problem on one of your cars.

John

Boomer

A captured ball end (in full-sized racing, it would be a heim-joint (sp?)) - yeah, I tended to go through my cars replacing as many ball joints with these as I could. Cool stuff!

So those three (or really two as you already had one on there?) struts were still lighter than all the trimming you had done? Sweet! Constructive and adjustable weight has to be better than just plain old vanilla weight!

John Stranahan

iTrader: (27)

Boomer-Thanks for the post.

Those heim joints worked well last race. Those three stiffening links added only .7 ounces to the car. I had removed 1.6 ounces. It is certainly a lot stiffer than before for the reason you mentioned. The middle of the chassis does not sag now on the battery side and rub the track (cutting my battery tape). I am 1.1 ounce overweight now. I am hoping my lap times will improve on a high grip surface. I'll find out tomorrow if the weather cooperates. A short test on my concrete driveway showed promise. I put a drop of glue on each ball after I set the car up to be flat. This will prevent tweak from small movements.

It was nice to make the chassis perfectly flat while loaded with the adjustability you mentioned.

Pic shows a small graphite plate that increases the strength of the rearward mounting screw location. The first time I mounted the left side link I had trouble here. There is a long post forward under the graphite plate, but only a short post rearward under that little plate. The screws attach to a tapered G10 frame rail. I added a similar graphite piece to the other side of the car after the pic was taken.


John

Quante

iTrader: (6)

John,

I have a question regarding the Tri-link setup, I like the concept and I'm thinking of integrating it on my pro10 (it'll be this or a link setup).
As far as I can tell the rearpod is held into place by 3 links and 1 link extra to center it (else you can still move the pod left and right), is it possible to dumb the extra link if you put the 2 lower ones under an angle: \ / ?
Do the 2 shocks need to be all the way back? In theory the complete pod is held in place, cant the shocks be mounted in front of the pod because this is a lot easier to mount and you gain access to the motor/ gears.
Could be that this shock- setup asks too much of the upper ballcup...

John Stranahan

iTrader: (27)

It is possible to put the rear shocks in front of axle. I find little difference in performance. See the third pic. The shocks could even be mounted with bellcranks to actuate them and be horizontal. In all of my work I did find that the closer to the wheel the lower shock mount (front or back of the car) the better the car was through the bumps. Front or back of the rear axle is equally close. Bellcranks may not be as effective.

I tried several versions of four links. In one the top links were angle in. The rotation was very much hindered with binding of the links. I straightened the upper links, it was improved but still very much hindered. I did not try angled lower links and straight upper links. The new battle axe does have angled lower links. I would suspect from my work with angled upper links that the side to side motion would be excessive without the Panhard bar if you had angled lower links and a single upper link. You could certainly try it on the prototype before you add the Panhard bar.

The mustang suspesion previous to the latest model had angled lupper links to control side to side motion. The latest model has a superior 3-link with Panhard bar rear suspension. There is no binding with a 3-link as the chassis rolls on the pod.
John

John Stranahan

iTrader: (27)

Problem: GenX 10 rear tire hop on power with 10.5 brushless and 7.4 V. I thought I would post this since it is very relevant to this thread. If you have solved a similar problem please post a solution. Unfortunately I have no other details yet.

I have not run that particular combination of motor and battery. I guess that it has a lot of punch or bottom end. Things to try. Use Corally Jack the Gripper traction compound. You may get the tire to just grip rather than slip and grip. The traction compound also gives the tire a syrupy feel so it slips smoothly. This is what happens on all of my cars including the 13.5, 4.5, 3.5.

Tinker with the gear ratio. I assume this is happening at more than just the start of the race. I would try a lower gear (smaller pinion). See if you can get that rear tire to lift the front end rather than hop at the back. A softer front end with more droop might help this as well.

Chances are this hop is not an up and down hop on both sides at the same time but rather a hop on one side followed by a hop on the other side. It is hard to tell, but this is what I suspect. This happens to me on a bumpy straight. In this case center shock is OK, try thicker dampener lube or chunk those rascals and put on some RC18T shocks or something similar.

Also give me more info. What rear tire are you running. Carpet or Asphalt.

Also do not neglect the slow roll on of throttle to cure corner exit ills. You have to de-touring car yourself.

John

Track Session
My track session today was unsuccessful. I put on 6 lbs of sugar and had good traction. I just could not get the car to turn fast laps. It would handle great after some adjustments. It was very consistent. I removed the diagonal chassis brace. It drove better but was not faster. I put my rear side shock back on to eliminate excessive steering. Still not faster. Tried all the tires I had. I have some double pink fronts Friday coming which may help. I put the car back mostly like it was before the session. This included putting the softer front springs back on. I only left on the left side reinforcing link which will probably hold up now with the rear reinforced a little bit. It helps keep the battery off the ground without adding a lot of torsional stiffness which apparently is not useful on the asphalt oval.
john

lidebt2

iTrader: (21)

Could it be the driver is getting old????????

I would give you a report on the battle Axe BUT I'm waiting on a part from CRC that I ordered 12 days ago which they said was shipped the next day. I called CRC this past Monday and was told that they were JUST manufacturing the part and would ship it on Tuesday. Oh well, still no part. When and IF I get the part I will update my progress. Oh and before I forget, remember the driver setup sheets that Frank from CRC was going to send 1 1/2 months ago, still haven't received them either.

Have fun .... Rick

BlackedOutREVO

iTrader: (67)

How tough is the CRC? I like the lipo mounting down the center

I want to build a pro 10 for next race season