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Balancing car with weight?

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Balancing car with weight?

Old 07-11-2020, 11:25 PM
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Default Balancing car with weight?

How do you guys balance the car with weights?

I find that with using the preload collars on the shocks(to get both wheels lift up together) caused a difference of almost 1mm on right-height between L/R.
I do have one of those weight scale thingy but i cant seemed to get it right balanced between L/R even though both wheel lift up together.(about 30gramms different)

If i let it to be, the car tends to behave differently between turning right/left.
Is there a SOP for weight distributiojn between L/R?

Any help?
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Old 07-12-2020, 01:33 AM
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Ideally, you would use weights to get the static balance of the car as close as you can first, assuming your car is underweight. I probably wouldn't add weights if the car is already overweight. And look at whether you can lay out the electrics in a different way to get a better balance.

If you've got one of those corner scale thingys, add up the FL+RL and FR+RR totals. You want to get these as close as possible using the static weights. There is also the Front vs Rear weight distribution that is a tuning option, again affected by static weight positions.

Most cars have holes in the bottom of the chassis for you to insert a balancing pin (either an expensive rc tool, or a golf tee), and this is another way of checking left right balance. Some cars have holes in the middle of the shock tower for you to run a string through to hang the car and do the same thing.

Once the static weight is as close as you can get it, you can use the shock collars to get even cross-weights on the car (FR+RL and FL+RR). Although if you still have big differences in the position of the collar I would just check that everything on the car is built correctly and moves smoothly.
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Old 07-12-2020, 04:11 AM
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You cannot use spring preload to compensate for L/R imbalances. You must add/remove weight to do that. Use the corner weights only to verify the balance, and also to make your diagonal cross weights equal through spring preload (compensate for tweak).
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Old 07-12-2020, 06:26 AM
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Thanks for the tips!


So i tried to measure again, this time witht the shock collars all the way up to to make sure the preloads equal on all 4 corners.


FL=277 FR=314

FL+RR=573 FR+RL=647.4

RL=332 RR=295

Left=47% Right=53%


I guess there is quite abit of weight difference there. Seems the L side is heavily unblanaced between F/R. The motor is too heavy and the servo too light.

Should i try to add weights at the FL and RR position to balance it out?

I dont see any rocking movement while the chasdis is on setup blocks, so i guess the chassis is not tweaked physically....or am i doing it wrong?
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Old 07-12-2020, 07:22 AM
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Originally Posted by rko View Post
Thanks for the tips!


So i tried to measure again, this time witht the shock collars all the way up to to make sure the preloads equal on all 4 corners.


FL=277 FR=314

FL+RR=573 FR+RL=647.4

RL=332 RR=295

Left=47% Right=53%


I guess there is quite abit of weight difference there. Seems the L side is heavily unblanaced between F/R. The motor is too heavy and the servo too light.

Should i try to add weights at the FL and RR position to balance it out?

I dont see any rocking movement while the chasdis is on setup blocks, so i guess the chassis is not tweaked physically....or am i doing it wrong?
Looks like you're exactly 609g left and right, 50:50 ratio. Your problem is solely diagonal balancing.

When you're getting these readings, is this just placing the chassis on the scales, or are you compressing the suspension and letting it come to rest after placing it? Do the numbers change much depending on which method you try? If they do, you've got binding in your suspension which will cause wonky handling and give unbalanced values on the scales. Also check your shock length, spring length etc.

If it's all fine, then just add some preload on the front left and rear right and/or remove preload from front right and rear left until the numbers balance.
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Old 07-12-2020, 07:36 AM
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Originally Posted by gigaplex View Post
Looks like you're exactly 609g left and right, 50:50 ratio. Your problem is solely diagonal balancing.

When you're getting these readings, is this just placing the chassis on the scales, or are you compressing the suspension and letting it come to rest after placing it? Do the numbers change much depending on which method you try? If they do, you've got binding in your suspension which will cause wonky handling and give unbalanced values on the scales. Also check your shock length, spring length etc.

If it's all fine, then just add some preload on the front left and rear right and/or remove preload from front right and rear left until the numbers balance.
Did a couple of times with the collars all the way up. Pretty consistent readings within +/-3grams each time. Will check again with the springs loaded next.
Shock length should be okay last i checked but will check again. Havent checked the spring length yet so i'll put that on the list as well.

Coming back to preloads, i need a differnence of almost 3-4 rounds between the Left and Right shock-collars to get the wheels lifting at the same time.....
This translate to about 1mm of ride-height difference between the Left and Right side of the chassis from where i measured. Is this normal?
Due to the previous imbalance behaviour of the car, i thought the ride-height+droop is screwing the handling up. The car tends to swipe out turning right.....or maybe its just driver issues. lol
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Old 07-12-2020, 08:03 AM
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1) Equalize the cross chassis weights with the ride-height collars on the shocks ((RF + LR) = (LF + RR)).
2) Now look at (RF + RR) and (LF + LR) and see which side of the car needs the extra weight.
3) Add weight and repeat 1.

You chassis can still be crooked or with incorrect ride height even thought the cross weights and side-to-side weights are correct. So you can use the collars to get side to side and front and back ride height correct, then repeat 1,2,3 above.

Repeat until you have side-to side and front to back height all 5mm and the cross weights are the same and the side to side totals are the same.

Front "axle" and rear "axle" totals are tuned at the track, or you can use RC Crew Chief and to simulate front and rear weight bias on cornering.
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Old 07-12-2020, 08:43 PM
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try this.

put it on the scales. when balancing dont do anything but diagonal adjustments. if lr and fr are heavy lower the ride height together and also raise the rr and fl together. do this until its balanced.

now go to the ride height gauges. this time do not adjust diagonally. adjust 1 at a time to get the ride height correct.

go back to the scales and do it diagonally again.

you may have to do this series 2 or 3 times for a chassis that looks flat but has never had the ride height and spring compression aligned.

dont read further if this solves your problems.

If your car wasnt flat or has some diagonal preload or one side of the car flexes more than the other this will sequence will make it hard for you to see it in usual ways. it will still jump to one side under acceleration but the chassis will appear flat. you wont get the tale tell signs of tweak. the springs will redistribute the static weight and collar length but under load everything will be off. Be sure the chassis is flat.

be sure the chassis is flat before you do this method. the best way to make sure its flat is on a piece of glass or whatever then to replace shocks with tie rods and make sure the chassis is still flat or level at ride height. if you put a 5mm shim (for example) under the lr tire and the front left (just keep shimming until one of the corners comes off the ground) tire comes off the ground 2 mm move the 5mm shim to the rr and expect the fr wheel to come off the ground 2mm. if it doesnt the car isnt flexing properly or it is preloaded to one side. loosen the top deck and get it to flex even from left to right.
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Old 07-13-2020, 01:05 AM
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Originally Posted by rko View Post
Did a couple of times with the collars all the way up. Pretty consistent readings within +/-3grams each time. Will check again with the springs loaded next.
Shock length should be okay last i checked but will check again. Havent checked the spring length yet so i'll put that on the list as well.

Coming back to preloads, i need a differnence of almost 3-4 rounds between the Left and Right shock-collars to get the wheels lifting at the same time.....
This translate to about 1mm of ride-height difference between the Left and Right side of the chassis from where i measured. Is this normal?
Due to the previous imbalance behaviour of the car, i thought the ride-height+droop is screwing the handling up. The car tends to swipe out turning right.....or maybe its just driver issues. lol
Have you double and triple checked you've got proper droop settings left to right? If they're off, the same-time wheel lift test will give bogus results.

It is not normal for even weight distribution and same-time wheel lift tests to yield a 1mm difference in ride height left to right. That indicates that something is tweaked or binding.
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Old 07-13-2020, 03:15 AM
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Thanks so much for the tips guys! Really appretiated.

I'll double check the droop again! Last i check i gave a tolerance of about 1mm since thats what my gauge's resolution is at. Now that you mention it, it could well be the droop having too much differences!
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Old 07-14-2020, 05:54 AM
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after much doodling over the past 2-3days. I finally found out what was wrong....

The table that i worked on was not parallel to the ground. Checked with a digital angle protactor and found the table to have a 1.5degree gradient!
I had set the scale on the setupboard, which was resting on the table.
Turning the setup board 90degrees and darn, the weights changed by +/- 15gramms on each side. This cause the L/R balance to be off by almost 50gramms and of course a L/R imbalance!

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