Wheel alignment

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Scobod
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Wheel alignment

Post by Scobod » Tue Mar 29, 2016 10:36 pm

Finishing up my final car for the year. This will be my fourth build. I've learned a lot through my progressions but still have a lot to learn. I'm hoping that this car will finally get me in the < 3.1 Second range. This last car has been giving me a little bit of issues with alignment. Not sure exactly which way to go with it. It's going to be a three wheeled rail rider. On a flat surface when I push it, it moves about 1 inch to the left after about 4 feet. I need it to go to the right as my raised wheel is on the right side. The only reason I'm not changing it is that when I place it on a treadmill at about 8 miles an hour, it stabilizes just right of center which is the correct way it needs to go. Stabilize might be a stretch of the word. It does wobble slightly. Maybe 1/2 inch to the left and right. Does this mean my rear wheels are out of alignment? I've tried to watch videos and read articles on the correct way to align the wheels. Maybe I'm just not finding the right one.



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Stan Pope
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Re: Wheel alignment

Post by Stan Pope » Wed Mar 30, 2016 3:24 pm

It may help if you examine the functions of the three wheels:

Dominant Front Wheel (DFW): may steer the front end away from the car's center line.

Dominant Rear Wheel (the rear wheel carrying the most weight): Determines the path of the rear end relative to the DFW. It may cause the rear to follow to the left of, to the right of or right behind the DFW. The setting may cause the car's center line to deviate from the direction of motion and alter, slightly, the effect of the DFW setting.

Other Rear Wheel (the rear wheel carrying the lesser weight): If aligned with the Dominant Rear Wheel, it just idles. If not aligned, it adds friction to the rear end and its drag may create some turning torque.


Stan
"If it's not for the boys, it's for the birds!"

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Vitamin K
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Re: Wheel alignment

Post by Vitamin K » Wed Mar 30, 2016 5:14 pm

Stan Pope wrote:It may help if you examine the functions of the three wheels:

Dominant Front Wheel (DFW): may steer the front end away from the car's center line.

Dominant Rear Wheel (the rear wheel carrying the most weight): Determines the path of the rear end relative to the DFW. It may cause the rear to follow to the left of, to the right of or right behind the DFW. The setting may cause the car's center line to deviate from the direction of motion and alter, slightly, the effect of the DFW setting.

Other Rear Wheel (the rear wheel carrying the lesser weight): If aligned with the Dominant Rear Wheel, it just idles. If not aligned, it adds friction to the rear end and its drag may create some turning torque.
Stan,

Have you done any experimentation with biasing the ballast in the car to get the weight even (or close to even) on the rear wheels?



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Stan Pope
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Re: Wheel alignment

Post by Stan Pope » Thu Mar 31, 2016 10:03 am

Vitamin K wrote:Stan,

Have you done any experimentation with biasing the ballast in the car to get the weight even (or close to even) on the rear wheels?
Just one go without adequately controlled variables. Result not satisfactory, but I can not ascribe fault.

You didn't ask, but assuming equal cf at all three corners, shifting CM laterally toward DFW side increases the % of drag toward the DFW side. Drag still balances around the CM, but intuition suggests issues if drag on DFW side exceeds drag on the other side.

The "equal cf" assumption may be faulty, since rears are set to roll straight with no sliding friction and DFW is set to rub the rail!

(Incorrect last paragraph removed.)


Stan
"If it's not for the boys, it's for the birds!"

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