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Old 01-27-2012, 05:23 AM   #1
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Questions?? Uneven TC Corner Weight

I used the Integy corner scales last night on the flattest surface I have.

I removed all the shocks etc and use 4 lengths of carbon fibre with two 3mm holes in each piece, they are then attached in place of the shocks in the shocks original position.
The carbon fibre strips have the holes the exact same distance apart so I have effectively fitted four indentical 'solid' shocks.

My theory being that as I have now removed springs and shocks with possible differences in rebound etc there is exactly the same amount of force being exerted on each corner.

My corner weights (from memory) read as follows;
Left Front = 352
Right Front = 218
= 570g

Left Rear = 224
Right Rear = 354
=578g

There is only 8g difference between front and rear and nothing out of the ordinary, but why the big difference in corner weights?

It always seems (including all my previous cars) that the front corner with the servo and the rear corner opposite the motor (against logic) seem to have the highest weights.
Why is this?

Thanks
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Old 01-27-2012, 05:34 AM   #2
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Skiddins

Really not sure what would cause this, but whats interesting, is:

1. As you say Front to Rear is roughly in balance - though i dont think this matters as much

2. Left to Right (in total) is also only 4 grams out - I would put money on if you used the Hudy balancing pins the wight dist would look ok!!

Im interested to see your answer, I dont have the integy corner weight thing, but whenever I use the MIP style tweak station, I always find i have to loosen the rear right and front left collar so surely this is showing the same thing as you??? (seen this on xray and tamoya cars....)
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Old 01-27-2012, 05:52 AM   #3
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One of the first things to be aware of when using scales is scale calibration. Take and change scales at one position, say the left rear. Every scale should produce the same reading at a given position. If not then the height of the scale is off. Take the scale that reads the highest number and record it's reading. Then take every other scale and make it read the same at that position. make the adjustment by adding wide tape to the top surface of the scale. I like to use clear packing tape as it is very thin and wide. When you can put any scale at any position and have them read the same then you can start working with your car. Be aware that tires are not the same diameter and can affect the reading so setup wheels are best for balancing.
I don't know of anyone that replaces the springs with a solid link as you have done. I would put the shocks and springs on and set the cars ride height. Then put the car on the scales. Note the weight differences and adjust the car so as to get equal side to side weight on one end. the split on the other end is the amount of weight you need to add to the light side to balance the car, You may want to move components around to accomplish this instead of adding weight. Always start with no weight in the car and be aware of differences in battery and motor weight. Weight that balances the car should be placed away from the cars center line. Once the car is balanced then add the weight that brings the car up to minimum as close to the center and as low as possible. Always be aware of front to rear weight. I have a Losi XXX-S that is within 2g on each wheel and has 150 g of weight in it to reach minimum VTA weight.
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Old 01-27-2012, 06:01 AM   #4
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Quote:
Originally Posted by old_dude View Post
One of the first things to be aware of when using scales is scale calibration. Take and change scales at one position, say the left rear. Every scale should produce the same reading at a given position. If not then the height of the scale is off. Take the scale that reads the highest number and record it's reading. Then take every other scale and make it read the same at that position. make the adjustment by adding wide tape to the top surface of the scale. I like to use clear packing tape as it is very thin and wide. When you can put any scale at any position and have them read the same then you can start working with your car. Be aware that tires are not the same diameter and can affect the reading so setup wheels are best for balancing.
I don't know of anyone that replaces the springs with a solid link as you have done. I would put the shocks and springs on and set the cars ride height. Then put the car on the scales. Note the weight differences and adjust the car so as to get equal side to side weight on one end. the split on the other end is the amount of weight you need to add to the light side to balance the car, You may want to move components around to accomplish this instead of adding weight. Always start with no weight in the car and be aware of differences in battery and motor weight. Weight that balances the car should be placed away from the cars center line. Once the car is balanced then add the weight that brings the car up to minimum as close to the center and as low as possible. Always be aware of front to rear weight. I have a Losi XXX-S that is within 2g on each wheel and has 150 g of weight in it to reach minimum VTA weight.
I understand what your saying but the Integy system uses one scale and three 'stands', and you have to move the scales from corner to corner etc.
I tried it om different surfaces etc to make sure and it was always withina few grammes.

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Old 01-27-2012, 06:08 AM   #5
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The most important thing is to make sure the scales are absolutely level.
With our small cars a standard spirit level isn't accurate enough. You want either a digital one with a 0,0x read out or a analog one with a sensitivity of 0,05mm/m.

Personally I prefer the analog 0,05mm/m spirit level, we also use these in professional motorsports.
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Old 01-27-2012, 06:19 AM   #6
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Your chassis is twisted. Grab the chassis and twist the heavier corners up. It doesn't take much pressure to do this. Place it back on the scales and re weigh. You also need to do this after a bad wreck just to be sure.

If you haven't balanced the car left to right and front to rear you need to do this first.
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Old 01-27-2012, 06:23 AM   #7
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I think part of your issue is using the carbon fiber pieces instead of the shocks. Think of a chair with 4 legs and 1 leg being slightly shorter. It will stand on the 3 legs, and exert less force on the 4th (to the point of possibly no force if the leg is short enough). It could also be chassis tweak or the level of the scales as mentioned as well.

I'd put the shocks back on it and reweigh to see if the results are repeated.
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Old 01-27-2012, 06:29 AM   #8
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Do this in order with the shocks on to get a better idea of what you are working with.

Balance the car left to right and front to rear by hanging it from string
set all four corners of the car at the same ride height
set the car on scales being sure that the axle passes over the center of the scale. if it does not pass center the readings will be off
if your measurements are close adjust the shock collars to equalize pressure. If you are still way off then twist the chassis and re weigh

be sure your springs are the same on all four corners.different springs will throw off your measurements.
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Old 01-27-2012, 06:29 AM   #9
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Looks to me like a tweaked chassis, did you check the chassis for tweak before doing this? I check for tweak by putting an M4 locknut (or any other equal sized spacer) under each corner of the chassis. I.e. the nuts go between the chassis and setup board to raise the car up, which helps avoid problems with screws, tape or worn areas of chassis. Then lift one end of the chassis up using a knife or balance pin, and make sure each side of the chassis touches the nuts at the same time.

Also, when you say a flat surface, is the surface totally horizonal when measured with a spirit level? I have a home-made setup board with adjustable feet to achieve this.

As you say those numbers are strange, pretty sure on my TC6 the left rear and right front are heavy which is what you'd expect given the position of the motor and lipo. I then counter this by adjusting the shock collars (actually I'm also countering it by making a car with centralised motor and lipo... but that's a different story).
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Old 01-27-2012, 07:11 AM   #10
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Just found the sheet I recorded the numbers on;

FL = 324
FR = 216
= 540g

RL = 228
RR = 310
= 538g

That's actually 2g difference front to rear, less than 0.5%, and the heavier corners weren't quite as heavy as I remembered.
But still a difference.
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Old 01-27-2012, 07:12 AM   #11
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Quote:
Originally Posted by orcadigital View Post
I think part of your issue is using the carbon fiber pieces instead of the shocks. Think of a chair with 4 legs and 1 leg being slightly shorter. It will stand on the 3 legs, and exert less force on the 4th (to the point of possibly no force if the leg is short enough). It could also be chassis tweak or the level of the scales as mentioned as well.

I'd put the shocks back on it and reweigh to see if the results are repeated.
The four strips were nut and bolted together when the 3rd hole (used for mounting) was drilled so all the stripes are as close to identical as you can get.

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Old 01-27-2012, 07:13 AM   #12
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Quote:
Originally Posted by Skiddins View Post
Just found the sheet I recorded the numbers on;

FL = 324
FR = 216
= 540g

RL = 228
RR = 310
= 538g

That's actually 2g difference front to rear, less than 0.5%, and the heavier corners weren't quite as heavy as I remembered.
But still a difference.
Still say a twisted or tweaked chassis.
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Old 01-27-2012, 07:21 AM   #13
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Crack the topdeck screws loose and check again. You have opposite corners heavy/light......the chassis is twisted.
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Old 01-27-2012, 07:28 AM   #14
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Quote:
Originally Posted by Skiddins View Post
Just found the sheet I recorded the numbers on;

FL = 324
FR = 216
= 540g

RL = 228
RR = 310
= 538g

That's actually 2g difference front to rear, less than 0.5%, and the heavier corners weren't quite as heavy as I remembered.
But still a difference.
FL + RL = 552
FR + RR = 526

Even with tweak, scales should rear accurate total front/rear/left/right weights. So it looks like you're heavy on the left side. But that wouldn't cause the tweak.

If the scale height vs. spacer height was off, I'd expect it to affect each corner similarly. So I'm not really buying that theory. I've also never found being out of level to make more than a couple grams difference when using a separate scale under each tire.

So, I'm subscribing to the tweaked chassis theory. But, I don't see a lot of value in using the carbon pieces. If you made them the same length as the free length of your shocks, then you might be forcing the arms down on the droop screws, causing weirdness.

At the end of the day, though, you're not gonna run it that way on the track. If your car doesn't wobble on droop blocks on a flat setup board, it's probably not tweaked enough to sweat it. Put the springs and shocks back on, and balance it that way.

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Old 01-27-2012, 07:48 AM   #15
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I backed the droop screws off to make sure they weren't limiting movement.

I also tried the chassis on balance buttons and it just about stays up central, there is a fractional bias to the motor side which is what your figures suggest

Whenever I have to undo the top deck, I put the whole chassis on my setup board and push down at both ends while doing up the top deck screws.

I will undo all the top deck screws again later and try again.
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