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Old 12-29-2008, 09:54 AM   #451
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John,

Thanks for the reply to my PM. I think I will try to go ahead with the 1/12 three link project.

One other question about the three link for the moment... am I right in assuming that with the upper link parallel to the lower links that in bump movement the pod stays more parallel with the main chassis, rather than acting like a hinge? I suppose if the front attachment of the upper link were low enough, it would be more like a hinge, only with the effective hinge point much further forward than it is with a "traditional" two link/center pivot car? I was running this idea around in my head and it almost seems like you could use the angle and length of the upper link to alter how much the front of the pod moves in relation to the main chassis, and this might give a means of controlling bump stiffness independently of roll... or would that open up another can of worms that I haven't thought of?

I guess that's more than one question... sorry.
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Old 12-29-2008, 11:01 AM   #452
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David
You are right in that the 3-link acts less like a hinge. In my cars the motor can is required to rotate only a little as the pod moves up in bump. In other words its like you say the pod stays pretty parallel with the chassis. Current full size race car design on solid rear axles tend to use long links. The top link on a transam car goes pretty near the driver. That is one reason I use fairly long links on my cars. It reduces the amount of rotation of the motor can (and pod) which is just wasted motion. One benefit is I can run the pod at 3mm ride height even on rough asphalt. The front edge of the pod does not hinge down any more to be worn away.
The main reason to adjust the three link is too have different amounts of antisquat. Raising the front of the lower links is most helpful. Lengthening the upper link while keeping the same angle will give approximately the same antisquat and thus almost the same handling with the exception that there is less wasted motion rotating the motor back and forth. The suspension will be more quick to react to bumps with longer links.
That would be an exciting project. Give us a sketch or a pic of the prototype when you think things out.

Pro ten- you note differences in suspesions #2 and #3 of my pic series although they have very similar negative camber gain. The difference must be elsewhere. Maybe Ackerman like you say. Suspension #1 is distinctly different in having more negative camber gain and may be worth a try. If you have a CRC suspension you have most of the pieces. We may be able to adjust that amount of negative camber gain into any of the suspensions. I will tinker with that today maybe.

John

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Old 12-29-2008, 09:33 PM   #453
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Superior Spectre, Offset Pod + Two motor Spacers left

We had a beautiful day stuck in the middle of gloomy wet weather. It was dry Sunny and almost Summerlike with over 80 F air temp. I treated the asphalt track to medium high traction which guys prefer with sugar water.

The test for the day was to add two 1/8 inch motor spacers to move the motor left in the pod. This is about as many as possible and required longer Motor mounting screws and a pinion extended about as far as feasible. I first drove the car square for a whole battery pack. I could drive it fast and well, but there was some tendency to wiggle toward the inside board on corner exit. I had plenty of steering traction.

Then I added only 1/8 inch of left rear offset. This helped. The car was exiting super straight out of the corner. I coudl drive the wide line much better. I then changed to my FMA packs which are know to be faster than the Orion Pack. (The Orion pack is a dog, but it is a dog with good manners. It has safe chemistry at the expense of some voltage, and excellent cycle life. This is the reason it was chosen for our spec pack.) With the FMA pack on board the car was a rocket for about 12 laps before it settled down. It was near lifting the front wheels on corner exit. Good control was evident. I ran about 20 minutes on the two packs to check tire wear.

Left Rear XXPINK .014 inch wear for the 20 minutes.,.007 for the first 10 minutes without left rear offset.
Right Rear XXPINK .025 inch wear for the 20 minutes, .017 for the first 10 minutes without left rear offset.

So can you get even left and right tire wear. Not without some drastic changes to the car layout. This pod can be offset left some more by offseting the T-plate left. I will need lap times to note any improvements as the car is driving very well.

I am getting a personal lap timer again for a second try. The Spektrum system. It used too much power in my 3.5 powered road cars and they would shut down on occasion from low Battery Eliminator Circuit (BEC) circuit voltage. This car uses much less power with a 13.5 so it should work OK. There is less voltage drop on acceleration.

The RC 18 T rear shocks are working very well as rear side shocks. That modified CRC front end Pic#1, in the front end post above, is working very well.

Pic: Note it took two axle spacers to square the car at 206 mm. I added one more for the second part of the test. I had two motor spacers between the motor and right side pod plate for the whole test.
John
Attached Thumbnails
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-motor-spacers.jpg  

Last edited by John Stranahan; 12-29-2008 at 09:44 PM.
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Old 12-31-2008, 03:48 AM   #454
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John,

Another night awake, but slowly catching up on this thread... Another question too, if that's okay...

In post 439, you mention raising the fronts of the lower links as a means to get anti-squat in the three link rear. Visualizing that in my head, it would seem that raising the fronts of the lower links would introduce some rear-steer ( I've heard it referred to as "roll steer" by 1/12 scale guys.)

On a center pivot link chassis, it's not done often, but some guys will raise the front of the side links to get the car to rotate easier mid corner, but I'm thinking this might lead to a corner exit hooking condition...

Would this "roll steer" be something unique to the center pivot with side links, and not an issue with the three link rear? I'm having a bit of a hard time wrapping my head around this one.

Any advice much appreciated,
David
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Old 12-31-2008, 09:00 AM   #455
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David- Longer links will reduce roll steer possibilities. I found that my setup on the oval with 3 link and center pivot was very similar as far as rear steer was concerned. No objectionable roll steer. The 3-link was just faster. I will take a peek at my wide pan and see if there is any roll steer. I certainly did not find it objectionable on a bumpy road track, as the car was 1.3 seconds faster than typical pan cars. That is huge. Some of this improvement is at the independent front though.

There is rear roll steer on my 3-link wide pan car. It is about 1 degree when fully rolled. They only way to tell if this is helpful or not would be to tune it out by flattening the links. I found in my testing that the car was significantly faster with more antisquat. This plants the rear on corner exit.

John

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Old 12-31-2008, 10:05 AM   #456
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A late Merry Christmas and have a safe New Years, John.
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Old 12-31-2008, 12:02 PM   #457
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Rick thanks. I appreciate it. Same to all. Happy new year.


David- I thought I would detail this rear steer some more in case others are not following. Because the lower links are angled upward in my three links, there is a tendency for one to get longer with roll and the other to get shorter. This causes the links to make the axle become at angle to the chassis, and creates the roll steer.

There is an analogy at the front called bump steer. If you push the tire up through its full range you may find that it points outward with bump. This is called bump toe out. This is my preference to bump toe in. My cars usually have a little bump toe out. As the car rolls the front tire steers slightly to the outside and reduces the steering force. This makes the car behave well when it gets to a grippy spot in a corner. The car rolls a little more; the tire steers out a little to reduce steering. A spin is averted.

Now at the back I would think a correspondingly good trait to have would be bump steer out. This is what the wide pan has. When you roll it to the right, the axle steers to the outside of the turn. This eases up on your rear cornering traction. Should work the same as at the front in that slip angles are reduced on hard cornering keeping the car from gripping too hard. I like the way it feels on the track a lot on the road and oval car. I think you should still strive for big links that will not telescope in a crash, Long links if possible. Links that reach the axle if possible.

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Old 12-31-2008, 06:38 PM   #458
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Once again, thanks for the insight...

And to echo my buddy Rick, Happy New Year to all.

See you Sunday Rick?
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Old 01-01-2009, 08:29 AM   #459
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Spektrum Telemetry, Lap Timer

I don't always have the tracks lap timer available as sometimes it is moved to the offroad track. I purchased a Spektrum Telemetry unit to give me lap times accurate to .01 seconds. On the oval you actually need the precision of that hundreths place as changes you make are small lap time wise but are multiplied by 50 or 60 laps. You also should take at least a 10 lap average to get reliable information. A 20 or 30 lap average is better.

Compatibility
Firstly this unit is not compatible with all spectrum receivers. It is not compatible with any of the tiny pro receivers or DSM2 (second generation) receivers. That leaves you with the large regular receiver S3000 and fuel proof regular size S3001 receivers. I had a large regular Spektrum receiver installed in my primary oval car.

Here is a pic of the installation. I mounted the Infrared receiver with a layer of Parma clear doublestick tape and two tie wraps to the body post. It will pick up light through the left rear window. Cutting the window will probably not be neccesary. In a previous installation on two cars both 3.5r powered the battery voltage on corner exit would low (even with the spektrum capacitor installed) This would shut down the cars on occasion. This time I have only a 13.5 on board. Things should work smoother.

This model is available at lower cost on e-bay shops but appears to be a factory second. The label on the hand held unit is upside down. Not a big problem, but it should be advertised this way.

Pic:Telemetry unit is tiny. It fit on the crossplate for more left rear weight. Infrared pickup is on rear body post. I tried the thin Lexan mount in a previous installation and it gave me nothing but trouble.

Batterry is protected by a graphite battery strap on the T-bone side.
John
Attached Thumbnails
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-spektrum-telementry-lap-timer-resized.jpg  

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Old 01-02-2009, 02:45 AM   #460
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Hey John,

Do you know where I could find a foam bumper for a 235 mm Pro10?
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Old 01-02-2009, 04:59 AM   #461
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Quote:
Originally Posted by Thomas_H View Post
Hey John,

Do you know where I could find a foam bumper for a 235 mm Pro10?

Not sure if it will fit a 235 but I know it fits 200: http://www.lefthander-rc.com/catalog...oducts_id=1099
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Old 01-02-2009, 07:14 AM   #462
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Thanks for the posts.
Thomas H-I like this bumper from CRC. This one and the BSR are not quite wide enough for 235 but they will protect the chassis well. The CRC bumper is not as tall and may fit the bodies like the Peugeot 905 B a little better in the front. The foam on the CRC is quite a bit stiffer than the BSR foam; I like this better.

http://teamcrc.com/crc/modules.php?name=Shopping_Cart&file=product&c_op=v iewprod&prodID=7719030

Here is a pic with my latest installation. I have used 5 short aluminum posts to support the bumper and keep it in front of the graphite bumper. This has been working well and looks nicer than my previous install. I install the bumper over the posts and then install body post and screws to hold the bumper down. It is important to mechanically hold the foam down in some manner. Yes that RF needed some more negative camber;done.
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Old 01-03-2009, 07:34 PM   #463
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Can someone tell me what size driver I need to work on the CRC GenX 1/12th scale car? None of my current drivers fit.
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Old 01-03-2009, 08:22 PM   #464
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.050,1/16,3/32 inch mostly. The motor mounting screw is metric.

http://www3.towerhobbies.com/cgi-bin...&I=LXKTP2&P=ML

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Old 01-03-2009, 08:25 PM   #465
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Quote:
Originally Posted by John Stranahan View Post
.The motor mounting screw is metric.
John
2.5 mm motor screws
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