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Old 01-20-2005, 10:46 AM   #1
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Default Using Scales in Setup

I picked up 4 scales from UnderDaHill, nice pieces and a great deal if you are looking for some. I need some help using them though, so if you have used these or other scales to setup your cars for on road (oval experiences may help also), what is your technique?

My Losi XXX-S always seems to have a heavy or light corner no matter what i do. I set the car up to have the same amount of front-rear bias on each side (can't get both fronts and both rears the same...). For example -

LF - 335 RF - 345
LR - 346 RR - 356

I can get it to about 11 grams front to rear on each side. Problem is, the car is all tweaked when it's setup like this, and shock adjusters are all in different positoins. Nearly undriveable turning right. I've tried to get the cross weight similar, but just isn't possible without adding another 20+ grams to the left front, which I haven't figured out how to do reliably. All of my electronics are as far forward as they can be.

I can get 3 corners almost exactly the same, but either the left front is light, or the left rear is light.

Flip side to this is, if I eyeball (no tweak tools) the chassis to be level side to side, the shock adjusters are all pretty even, and the car handles great, but my weights look something like this -

LF - 325 RF - 345
LR - 350 RR - 365
(not exactly, but you get the picture)

I may be rushing through this, and not thinking about it correctly, so straighten me out if I need it!

So what are your experiences?

Thanks for your help!

Mike
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Old 01-20-2005, 10:50 AM   #2
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Is your car over / under 50oz?

If it is under you could add static weight to the light corner and then balance from there...
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Old 01-20-2005, 11:42 AM   #3
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One thing you need to check is if the height of each scale is the same. I have a set of 4 identical scales but the heights vary as much as 1.5MM. If this is the case then you will get a very inaccurate reading. I made 4 pads that are glued to the top of each scale and made sure they were all the same height. This is the only way to use a set of scales.
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Old 01-20-2005, 11:46 AM   #4
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you may want to make sure of a couple things

make sure your shocks aren't in need of rebuild

the shocks are similar in rebound etc...

that shock lengths are the same

none of the hinge pins are bent

arms are not binding at all

on the xxxs it is normal (as with many cars) that the battery side will be heavier. after above is checked then cross weight measurement will provide a good handling car.

the front weight on the xxxs (depending on arm placement) will be just less than 50% and rear obviously just over.

hope this is useful. i run at socal and use scales also if you like stop by and we can talk.
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Old 01-20-2005, 11:47 AM   #5
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check the drupe screws also the car needs to have to up travel in it so it will roll through the turns. and if you have none it will effect the weight on the corners.

easy way to tell is to put it on the setup board and push down on each body post and see if the cross wheel comes off the ground it should not


wvracer
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Old 01-20-2005, 12:00 PM   #6
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Thanks for the good suggestions everyone.

TigeRyan - I'm not clear on how ROAR weights are taken, but with the body, the car weighs in at 1513 grams, just over the legal minimum. The body is not light, so adding weight may be an option with a lighter body. I may do this once I get a handle on how to use these.

teamtamale - this is a good point, I'll measure the scale height to see.

WVRACER - good point. I'll try your method to see what I've got.

rocketron - Shocks are all freshly rebuilt, and checked for length and internal pressure on the Losi tool. Hinge pins are all good. I just replaced all of the ball cups, and the left side is binding a little, but these measurements are very close to what I got before I replaced them. I'll be at So Cal Saturday, hopefully by noon. Lets try to hook up so I can get a lesson!
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Old 01-20-2005, 12:02 PM   #7
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Most sources will say that your percentages and cross weight are more important than 100% equal numbers. Also that a level chassis is more important than the percentages. The most important factor in the whole measuring process being a level floor (or in our case table or setup board).

Also, one more item to note, the RC taboo of adjusting things asymmetrically is reffered to often for full size cars. I say taboo, because some in the RC community swear things have to be 100% level, or 100% equal at a certain component when you are really trying to balance an entire assembly of hundreds of parts, a lot of them moving.

A few interesting web link on the subject. As it it mostly for 1:1 cars, you'll have to weed through the bits you do and don't need. I'm sure more info is available, but a quick search yielded these.

http://www.hotrod.com/howto/113_0309_scale/

http://www.circletrack.com/techarticles/70038/

http://www.eng-tips.com/viewthread.c...=112117&page=1

http://www.specmiata.com/setupguide/...ing%20Tips.pdf
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Old 01-20-2005, 12:10 PM   #8
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Quote:
Originally posted by Erik Shauver
Most sources will say that your percentages and cross weight are more important than 100% equal numbers. Also that a level chassis is more important than the percentages. The most important factor in the whole measuring process being a level floor (or in our case table or setup board).

Also, one more item to note, the RC taboo of adjusting things asymmetrically is reffered to often for full size cars. I say taboo, because some in the RC community swear things have to be 100% level, or 100% equal at a certain component when you are really trying to balance an entire assembly of hundreds of parts, a lot of them moving.

A few interesting web link on the subject. As it it mostly for 1:1 cars, you'll have to weed through the bits you do and don't need. I'm sure more info is available, but a quick search yielded these.

http://www.hotrod.com/howto/113_0309_scale/

http://www.circletrack.com/techarticles/70038/

http://www.eng-tips.com/viewthread.c...=112117&page=1

http://www.specmiata.com/setupguide/...ing%20Tips.pdf
these are ALL very good to read. i also agreed to be careful and to think "outside the box" rc myth will have you doubt yourself.

there are several other good books on suspension, and chassis tuning that are insightful..... see you saturday
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Old 01-20-2005, 01:10 PM   #9
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BTW... 1418 grams is the ROAR legal limit for foam tires 1525 for rubber tires.

Suggestions....

After getting a weight for all four corners, pump the car a bit and make sure the numbers do not change, then rotate the car 180 on scales. If the numbers are not the same as they were before for all 4 corners then you may have a non-level surface or the scale itself may be taller/shorter then one of the other scales. I have not seen this happen with these scales but I suppose it is possible one scale has thicker rubber feet or has more glue under it or something.

After I make sure my scales are level I do the following in this order. This assumes that you shocks are all the same left to right (length, feel, rebound, spring<- hard to check but same color springs can sometimes be different) and that the suspension is not bound up. With the shocks off the a-arms should flop around easily and not stick in any one spot. You also need to make sure you chassis is not tweaked or you will never be able to get ride height perfect on all four coners and still have the right balance. If your chassis is not graphite or carbon fiber it may be tweaked already. It doesn't take much to get a typical stock tub chassis to tweak. I do the following at the start of a race day and before the main if I have time.

A) true all 4 tires to the same size
B) back out droop screws
C) set my ride height on all four corners the way I want it (make sure the center of chassis is also above legal limit of 4mm foam and 5mm rubber)
D) Make sure camber is correct on all tires (it changes with ride height)
E) Put car on scales
F) press on car a few times and start adjusting shocks... press on car a few times after each adjustment below.
G) I try to adjust aposing corners exactly the same amount to add weight then remove exactly the same amount from the other two apposing corners to remove weight. Adjusting one set of corners up then the other down will keep you ride height the same as you get the weights correct.
H) once you get as close as you can adusting all 4 corners in apposing pairs you can do the last bit of fine tuning one shock at a time.
I) Rotate car 180 to make sure the corners still weight the same on different scales.
I) tighten droop screws on all four corners so the spring is not compressed but doesn't move around
J) take off tires and make sure left and right droop are the same (tighten only... do not loosen and let slack back into the spring)
K) Put tires back on and put car on scales. It should still be the same.

The hard part is getting the static weight the same if you car is already too heavy. If you have to add static weight you can always use fans as a functional static weight if you have to add it near the motor. It's better to have too much weight and a balance car then a light, unbalanced, hard to drive car. Lighter electronics a lighter thinner body can give you some grams to play with. Get the car as light as you can (without making it too fragile) and then add static weight to get it balanced.

If your chassis is tweaked you will not be able to get the correct corner weights and still have a flat chassis. If you shocks are not exactly the same you can get a perfect weight balance but when you drive the car it will be different left to right as one shock reacts differently and puts more or less pressure on the tire as you turn left or right. Same thing if the suspension binds at all on one side and not the other. It's like putting heavier oil in the one shock and not the other but it will not be predictable (may bind one time on a turn but not the next time).

Last night I was having some turning problems with the car not being the same left to right but it was balanced and flat. I had air in one of my rear shocks but not the other. It made a noticable differnce and it was only a little bit of air. Another person I race with had the same turning problem and he found a shock that was almost empty and he had a bent rear hinge pin.


Hope this helps,
bob
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Old 01-20-2005, 02:43 PM   #10
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Again, thanks everyone! I think what has already been posted is excellent info, and I should be able to get it sorted out now. Hopefully this answers some questions for other people as well.

Bob - I must have gotten 2wd offroad mixed up with sedan on the weights. I guess with body clips, my car should be pretty close,

rocketron - I'll be be using an apple green BMW, or a white Skoda body, or they will at least both be in my pit on Saturday (along with way too much other crap).

Mike
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Old 01-20-2005, 02:52 PM   #11
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What you need too achieve is a difference in DIAGONALS that is equal or less than the tolerance of you scales.

Of course you need to adjust so that left right weight is as close as possible.

In fact the only time I achieved a left/right balance almost close to 0 on a car was on a XXX-SG+

On my Xray I can't go below a few gr difference ligther on the servo side but the balance on the track is perfect. There's no difference on handlig on turning left or right. When that happens I know it must be angles or shocks or something else, not balance.

Here is the link that explains how the big boys do it

http://www.ground-control.com/?D=e04...ffa901ba6b5aaa

And attached is my file in Excel to calculate the whole thing. You can see the last setting. The diagonals are equal but not all the wheels.

In here you can calculate the weight distribution in the front or the rear.

Hope it helps
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Old 01-20-2005, 02:56 PM   #12
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oops here's the file
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File Type: zip balancas.zip (3.0 KB, 159 views)
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Old 01-20-2005, 04:28 PM   #13
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Default Lazy, Lazy, Lazy..

Ok, Call this the epitome of laziness, or being completely consumed by the thought that R/C cars are different.... but antoniop snapped me back to reality.

I've owned 2 cars with Ground Control suspension, one I still own, and I've spent HOURS on the phone with Jay, the owner, getting the suspension setup on both of them. I never went through a full corner balance on them, but I should have known the information is out there, and it isn't really any different between real and R/C cars. Actually, the information was as close as my email, as a friend of mine had sent me a sheet he built to corner balance his car a couple of months ago....

So, thanks again to everyone for their help, and I've attached the sheet I aleady had. I changed a few things to make it more R/C specific, just enter your weights (in grams) into the yellow boxes and the rest is done for you. The right side of the sheet has some other interesting info that may prove useful as well.

Mike
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Old 01-20-2005, 04:59 PM   #14
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Nice sheet Mike - I have one that is almost exactly the same.

If you guys don't have a laptop at the track and want to figure it manually:

Total weight (TW) = (LF+RF+LR+RR)

LF corner weight as a percentage = LF/TW - repeat for each corner

Front weight % = (LF+RF)/TW - repeat for rear weight

Side to side weight % = (LF+LR)/TW - same for right side

Cross Weight % = (LR+RF)/TW

With these formulas, a value of .23 would be 23% - you can multiply it by 100 to convert it to a whole number percentage if you want to.

My TC4 tends to be about 45% / 55% Front/Rear
and about .5% heavy on the left side.
For best balance, try to get the cross weight as close to 50% as possible
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Old 08-01-2005, 06:08 PM   #15
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Set up the car so that it's absolutely even on all corners, shocks equal and no binding. Make sure the scales are even.
Adjust the weight by moving weight on the car, don't adjust the shocks, if you adjust the shocks you're tweaking the suspension.
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