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Old 01-04-2007, 05:08 AM   #781
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With GRP tires the fronts are both 212mm. The rears are both 235mm. This front width seems to be a good fit to the bodies as it clears the fender lip a little allowing a low front of the body without having to trim the wheel arch excessively for clearance. I measured at the bottom tire edge to tire edge.

Note there is a side by side photo spread of the 3-link vs the center pivot car on the previous page. Also there are some LiPo battery tests results just above.

pic is of the improved rear appearance. I left the screws long to allow for shimming up of the two ends of the Panhard bar.
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Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-three-link-rear-improved-resized.jpg  
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Old 01-04-2007, 08:19 AM   #782
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aha, my front is at 215mm, and the rear at 222. I'll get some wider rear end spacers. That'll increase steering for sure!

John, could you make a small video in which you show how the panhard rear suspension moves?
I'm still trying to figure out how it works exactly.
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Old 01-04-2007, 09:37 AM   #783
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All the panhard bar is there for is to keep the suspended piece (pod) from moving laterally - so it allows (mostly) free vertical movement but limits lateral.

He's got the rod coming from the main chassis secured to the chassis so it doesn't move and the lateral link (the panhard bar) pivots up and down.
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Old 01-04-2007, 10:01 AM   #784
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Take off your center shock on your car replace it with a long steering rod and you have the same movement as a 3 link ~ like boomer said the pan hard bar keep thongs in the center but if you make it so the end of the rod that mounts at the rear pod and on the Chassis side so it can be adjusted up or down and longer and shorter it will change the roll center. this will help in dailing in forward bite or Traction.

And The Dampening is now done by the over the axle shocks and not the center shock or shocks
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Old 01-04-2007, 11:28 AM   #785
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Mathijs-I will add a bit of detail as well. When our pan cars hit a bump the center pivot or T-bar acts as hinge, both the rear of the chassis and the front of the pod move down with a hard bump. If you replace the center shock with a link you will find that the pod is now locked up in bump; it will not fold at the hinge anymore.

When the 3-link car hits a bump only the rear of the chassis (and the frame rail on the left side of the Panhard bar) go down. The pod stays mostly level. The motor does drop a little because I used a short upper link. (The pod has a camber curve so to speak). The pod may go up into bump (off the ground) depending how hard the bump is. Having the shocks directly on the wheel is going to provide a faster return to contact and forward traction. That is my hope.

Using Martys diagram as a guide

When you look at the rear of the car, I push on the left rear shock tower to simulate a hard right turn, The chassis rolls to the left side, the left side of the Panhard bar drops with the chassis left side (the left side has the long frame rail), The pod stays level. Because the Panhard bar is very long the pod and tires are not tugged to the side much causing tire scrub. The roll center is lowered slightly because the bar does go down some.

When I push on the right rear shock tower, the Panhard bar moves very little. The frame rotates around the left side pivot of the Panhard bar as the chassis rolls. The roll center is only very slightly raised as the bar does go up a tiny bit.

When I hit a very hard bump the rear of the frame rail which holds the Panhard bars left side may make first contact with the ground. I can eliminate this contact with a tapered bottom if neccesary.

I don't have the video equipment at hand but I did post a link previously to an animation of the Mustang rear suspension with Panhard Bar. I will repost the link here in a bit.

Here is a link to the animation. Go to the very bottom of the page. Note that with the Panhard bar the tires move a little left and right as they go through full travel. This is much reduced in my car by a very long bar.

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Old 01-04-2007, 11:47 AM   #786
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Ah now I see.
My old 1986 Honda CRX had a similar rear suspension.
On that car the left rear tire sometimes scrubbed the inside of the rear fender on hard sharp bumps because the rear axle moved to the left when compressed.

It's going to be very interesting to see how this setup is going to work. Your pancar is moving to combine the best of the pancar and touring car worlds.

As always: the truth is in the middle!
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Old 01-04-2007, 12:05 PM   #787
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Mathjis-Thanks. I think you have summed it up. This three link suspension is incredibly smooth on the bench. Very little stiction. The only problem may be an overly heavy axle. I'll have to wait and see.



Antisquat

One of the adjustments that the three link axle is going to add is antisquat. I'll start out by summarizing what I know about it. On independent rear suspension RC cars you add antisquat by tilting the front of the rear lower A-arms up a couple of degrees or so. Here is what it does.

The suspension now becomes stiffer on power. Part of the forward thrust from the wheel is directed downward due to the angle.

An offroad buggy now has more traction on the ramp of a jump when you are applying maximum power, this is from the momentarily stiffer rear suspension which increases the rate of weight transfer to the rear.

A touring car will now have a stiffer rear suspension on power. On corner exit this will cause the rear end to be loose. There will be faster rotation. The car will now go poorly though the bumps on power, however. The extra stiffness makes the tires loose good contact. Off power the suspension actually can unload enough to cause an occasional spin if you get off the throttle too much. ( I pretty much don't use antisquat on touring cars for these two reasons). If you setup your springs and shocks right you usually don't need it.

Now this is what is supposed to happen on a full size sedan with solid rear axle: The antisquat will cause the rear of the chassis and body to lift on corner exit. This provides a huge extra bite to the rear tires to aid corner exit on the rear wheel drive only sedan (similar to the buggy on the jump). I have never experienced this on an independently sprung rear suspension RC car.

Maybe this solid rear axle 3-link pan car will behave like the full size car or maybe not. I will have the flexibility to adjust antisquat using the upper and lower link angles with respect to the horizontal. I'll put up a pitch center and %antisquat sketch up later.

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Old 01-04-2007, 04:45 PM   #788
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Antisquat Continued

I took a few measurments from the Three-Link car and made a scale sketch. The green represents the location of the links. You don't need this sketch to tune the car. I was just curious. At the far left is the curve of the front tire and the resulting instant center just behind. The forward traction of the rear tire is applied in the direction of the red line.

If this red line crosses below the center of gravity of the car, but not at the ground then you have some antisquat. 70% in this case because the line is 70% of the way up to the center of gravity. This should cause some chassis lift on throttle. It may improve forward traction out of the corner or it may destroy cornering completely as it is probably way too much. Hard to know with this new 3-link.

If the links are parallel to each other and to the ground then you would have 0 antisquat. The red line from the tire has to go to infinity (parallel to the ground) to meet the lines from the links.

I'll start with 70 % antisquat then reduce antisquat to zero to see if I can notice an effect when I test the car.

I measured the height of the center of gravity by balancing the car on a pencils eraser with the car on its side. Center of the batteries.
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-pitch-instant-center-antisquat012-resized.jpg  

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Old 01-05-2007, 09:29 AM   #789
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so you could make an adjustment by raising the lower links at the rear of the car, right? (at the mounting points) - that would "pivot" the lower line down. . .
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Old 01-05-2007, 02:56 PM   #790
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Just ordered my Pantoura! ....cant wait till it comes in.....BTW John are those lipos wired in series? or parallel?
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Old 01-05-2007, 06:52 PM   #791
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Boomer-yes, both ends can be shimmed. Its exactly as you say. This would reduce the antisquat. The rear of the lower links are as low as they will go but can be raised up; the front are raised up on two 1/8 inch shims so they can be lowered or raised. The top link can be adjusted as well, but see my report below.

slicvicPr87. Exiting days ahead for you. Make sure and take a peek at the first 7 pages of the thread, lots of hints there. When I run double packs at the present time they are in parallel. When I get my new Tekin speed control it will handle higher voltage. I will try them in series with a 6.5 R motor.

3-Link Suspension Maiden Run
I vacuumed about 80 gallons of water off the track. The sun was shining so I thought it might dry. It almost did. Track green slightly dusty Wet in spots, Traction poor.

Well this was not the perfect day to test the Three-link suspension, but I was pretty anxious. I made back to back runs with the Wide Pantoura (Powell chassis equipped) with two MaxAmp battery packs and Novak 3.5R, Novak GTB controller, geared 7.50. I was very pleased with this car except for the parts of the track where the water seeped back up through the cracks. No traction with wet tires.

The Three-link car was equiped with a single LiPo, Novak 4.5 R geared 6.2 and the LRP Competition speed control which revived itself after replacing the big cooling kits capacitor.

With the 3-link car I had
Better Forward Traction, even though I ran only one battery which made the car light for dusty conditions.

The car was Ballistic on the second half of the straight. Very smooth. As if I had a working suspension now. I could see the chassis lift at mid straight when I nailed the throttle (antisquat effect). I'll get Radar numbers later on.

Surprisingly I had better Turn in (front cornering traction on corner entry).
I had to make no adjustments; the car ran great as is. The front end of both cars are setup very similarly except for spring tension.

The pics show the rear of the car under the body at the ride height that I used and at full bump. Because the pod does not drop in the front on the bumps I could run it at 3-4 mm ride height. I only got very light contact on one of the button head screws underneath. The main chassis, I ran at 7.5 mm ride height. There is no new contact with the ground on the main chassis. The little mini truck shocks are working just super. I used the lightest blue springs, 3.0 lb/inch.

Apparently 70% antisquat is working great. I may play with it a little later, but the cornering manners were excellent. I have 3-4 mm of rear droop on the 3-link car.

Eventually I will get lap times with both cars using the same motor.

I look forward to a manufacturer making a production version of this car. If they could work in double front A-arms with single shocks on each front wheel, I would be pleased. Maybe the front end will be my next project. I think there is more turn in to be had with less front end stiction.
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-three-link-rear-view-full-bump-003-resized.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-three-link-rear-view-full-bump-004-resized.jpg  

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Old 01-05-2007, 07:14 PM   #792
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Great Job John I will be working on both front and your rear 3 link over the next 30 days and hope to have a prototype front out to you by that time!
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Old 01-05-2007, 09:05 PM   #793
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Marty-Thanks. Sent you some part numbers.

Mathijs-Now if you add a 6 mm spacer to both sides of your rear end, then your pinion will be extended out as far as mine was with the narrow pod car. I wonder if you will start to eat the outside motor bearing.

I tested a 128/17 (Corally pinion) gear using 64 pitch on the Wide Pantoura with the 3.5R. The mesh is much better. I no longer get a harsh vibration at mid speed on the bench. Very quiet on the track. Interestingly the brakes were now harsh and noisy from gear noise. I still have to look into this.

John

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Old 01-06-2007, 01:51 AM   #794
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John, good work on the suspension! Keep us posted!

I added some spacers to widen the rear end to 235mm. I sure hope I can get some testing in the next few weeks. Weather is still hopeless here.

From what I've tested, the 64pitch gears work excellent. Just make sure you only use brakes in emergencies.
That's also general pancar driving advice: brakes are only to be used when in trouble.
If you need to slow down for a corner just let it roll into the corner. If your setup is about right this won't be any problem.
Using your brakes on a pancar usually ends in stripped spurs.
If coasting into the corner doesn't work you can add a little steering throw and use a full steering lock to slow the car down.
However, a neutral handling pancar needs none of this to enter any corner, just a very brave and precise driver.

I have run 64 pitch spurs from:
-Kimbough: excellent, very resilient, and work with 12 diff balls for a very smooth slip resistant diff. The only downside is that they have a little more drag than HPI and Corally gears.
-HPI: good, last a long time, work with 8 diff balls, low drag.
-Corally: okay, they tend to strip easily because of the very firm plastic compound, work with 8 diff balls. Sometimes they came out the package slightly warped. These gears have the least roll resistance of the gears I have used.
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Old 01-06-2007, 01:56 AM   #795
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John I noticed from the pictures you have some tire scrub on the rear wheel wells of your car's body. See attached picture.
Either cut out the body a bit more, or use heat the body and shape it a little wider around the rear weels.
Also cut out the rear panel more to keep the car more planted to the track at high speeds. I added a cut line in the picture.
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-tire-scrub.jpg  
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