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Old 03-12-2013, 02:48 PM   #211
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Anyone else having issues w/ CG calculations? I originally calculated CG at 2" and I was at 20mm but after reading the documents it mentions testing is most accurate at 4-5" I'm around 47mm this way. I've ensured that there is nothing contacting my scales aside from the tires. Looking at the stock tc5 file it shows 30mm as the CG so I find it hard to believe 47mm is accurate. Any opinions? I'm also measuring w/ the body on.

Dave
I had partially the same problem. First of all be sure that the scales are on a flat and absoloutly horizontal hard surface. Disconnect all sway bars and remove all shock springs. Fix a shock lenght limiter on all shock shaft to have the same length on the 2 front wheels and the 2 rear wheels. Verify your downstop screws. Always place the wheels on the center of the scale. If everthing is correct the sum weight of the 4 wheels should be equal to the total weight of the car.
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Old 03-12-2013, 11:31 PM   #212
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I don't understand how removing components will change anything. If anything removing shock springs/etc will skew the results even more (Less weight). Sway bars won't affect front/rear weight distribution which this measurement is supposed to calculate. It calculates total wheel load (weight) vs. combined front tire load at a given height.

My corner weight table is adjustable at all 4 corners and I use bubble levels to ensure itis level prior to any measurements.
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Old 03-13-2013, 06:53 AM   #213
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I tried tests on two cars this morning with the rear raised 2 significantly different heights, 25mm and 102mm. These tests were done body off so with the body on the CG will be approximately 4mm higher. Here are my results.

TRF417
Rear raised 25mm CG height = 25.8mm
Rear raised 102mm CG height = 25.2mm

TC4
Rear raised 25mm CG height = 23.7mm
Rear raised 102mm CG height = 25.0mm

Attached are a couple pics of the setup.

You should not have to remove replace or disconnect anything. The car should be setup just like it would before hitting the track.

I looked at your numbers and can't understand why the front weight is so much higher with the rear raised 93mm than it is with the rear raised 44mm. My measurements only varied by 10gm between the two measurments and yours changed by almost 50gm.

When you test make sure you do the following
  • Keep the car in the same orientation between tests. Meaning do not rotate your car on the board between tests.
  • Press down on the front and rear suspension before taking readings to settle the car in the suspension.
Attached Thumbnails
RC Crew Chief Software-cg_25mm.jpg   RC Crew Chief Software-cg_102mm.jpg  
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Old 03-13-2013, 06:56 AM   #214
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Bob, i'll try without the body. I do always compress the suspension to not only settle the suspension but also ensure there is no interference of the scale w/ any moving parts cuasing an erratic reading. Did you read the other part of my email about the TC5 Y1 measurement? I've done all testing w/ the body on as to get accurate readings but i'll try it w/o the body and report back.

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Old 03-13-2013, 07:39 AM   #215
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Originally Posted by TT_Vert View Post
Did you read the other part of my email about the TC5 Y1 measurement? Dave
Yep, check your email.
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Old 03-13-2013, 09:34 AM   #216
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Well I took the body off and remeasured. Still seems off but you be the judge

Front
355.5 351.9
347.3 347.1

Lifted rer
Height 94.3mm
Weight: 711.4
Calculated CG: 34.36

Now Bob states that the body will raise CG 4MM so I'm at 38MM for CG. Does this sound acceptable? Most of the sample vehicles in this program are signifigantly lower.

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Old 03-13-2013, 11:02 AM   #217
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Well I'm stumped. It's better but I would only expect your CG to be higher by the difference in the tire radius. The only other thing I can think of is to make sure all your scales are reading the same.

Can you send me a pic of the car on your setup in the raised position?

I'll check the program.
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Old 03-16-2013, 08:46 PM   #218
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CG calc update.

Not sure why TT vert was getting strange results but his measurements are now in the correct range. I checked the program and the equations are correct so no issues there. The measurement is very sensitive however so it is important to make sure there is no binding in your suspension and nothing is interfering with the scales. Also I would recommend the test be repeated several times. I did 10 measurements with rear raised and the total weight on the front varied by 1.2gm. That doesn't sound like much in a front weight of 600gm but it makes .6mm difference in the CG height calculation. So take a number of measurements and then average them to improve the accuracy.

If you want to get the most accurate reading possible then you should do as Crashnco suggested above and replace the shocks with fixed links set at ride height. That will eliminate any variance due to friction/stiction in the suspension or shocks, making the measurements much more repeatable. You could also remove the wheels and support the axles on fixed blocks to remove variables to due with the tires.

IMO at the end of the day if the CG height accuracy is .5mm that is about all we can hope for without going to a much more elaborate test setup.
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Old 03-22-2013, 09:17 AM   #219
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BobW,

I just finally got your software, and started initially inputting info for 1/10 scale TLR 22 Buggy. My main question is, with the 25 kick up and 2.5 antisquat not being planar with the bottom surface of the chassis, what will be the effects of these on the calculation output? There is no way for the software to know that the front and rear arms pivot any way other than parallel to the chassis or ground. What is the best way to try and compensate for this in off road?

Thanks,
BK
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Old 03-22-2013, 12:12 PM   #220
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The way to handle this is to take the average hinge pin height. So place the chassis on a flat surface and measure the height of the high point and low point between the hinge pin blocks, divide the sum by 2 and then subtract 1/2 of the hinge pin diameter. That is how my technical reference says it should be measured.
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Old 03-22-2013, 02:28 PM   #221
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Bob, thanks for the quick reply. I kinda figured that would be a decent work around initially as that is how I entered it into the program last night (roughly), I still need to take a car apart and get technical with all my measurements to gain some accuracy. I was thinking though, if the shock is 20% softer by laying it down in relation to vertical, wouldn't the front suspension be a percentage softer by laying it rearward 30? Do you recon we should figure some correction factor?

Thanks again for the response. I think once we get this clarified this is going to be a very useful tool! Thanks for the hard work developing such a comprehensive program!
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Old 03-23-2013, 05:56 AM   #222
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It's the angle of the shock relative to the arm that is important. So if the total kickup on the arm is say 20deg and the shock is laid back 20 deg the angle of the shock relative to the arm in the side view is 90 deg and no correction is needed. If the shock is laid back 30 deg and the arm kickup is the same then the relative angle between them is 80 deg. The correction factor in this case is equal to the sine of the angle squared so sin(80)^2 which equals .97. Not particularly significant. If the kickup was 0 deg then the relative angle would be 60 deg and the correction factor would be .75 which is certainly significant.

If I remember from the last truggy I did the arm kickup and shock layback result in an angle fairly close to 90deg so I would say generally no correction is required. If you have the situation you described then definitely apply the correction factor directly to the spring rate.
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Old 03-23-2013, 08:30 AM   #223
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What is the default track width setting for the 417 ( v5 and x) ? And more importantly is that inuding 0.5 mm wheel spacers?
what is too great a difference between front and rear RC, my current setup has a 3mm difference( -4mm front and -7mm rear)
Also, ive noticed that moving the upper link up inner and outer position by the same amount doesn't effect the values apart from the total roll stifness by 0.01, where as it does actually have an effect on the roll characteristics?
Thanks
And awesome program by the way.
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Old 03-23-2013, 10:06 AM   #224
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The Track width setting can be set to match your car. Just open the Chassis Manager and change the Front/Rear Track width as required. Measure the track width where the rubber meets the road.

The upper camber link position does not have any affect on the roll stiffness only on the Roll Centre position and camber gain. So moving the upper link should show no change in the roll stiffness. The roll stiffness is only affected by the springs and ARB's.

By moving both the inner and outer camber link position by the same amount the angle between the upper and lower arms, which determines the roll centre location, will not change much. Therefore the roll centre position will not change much. The camber gain will be affected slightly as well.

If the Roll Centre position changes slightly you should see a very minor change in Chassis Roll Sensitivity. That may be the small change you noted. The Chassis Roll Sensitivity value uses the Roll Stiffness, Sprung Mass CG and Roll Centre position in the calculation. It is an indication of the overall vehicle roll stiffness relative to the Lateral g load.

Hope that answers it.
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Old 03-28-2013, 05:25 AM   #225
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I'm looking for a couple more users to Beta Test the latest RC3 update which is almost complete. This version provides the ability to simulate Nitro Motors so someone who is experienced with these cars would be good.

I have attached a screenshot of the new Acceleration Page set in "Nitro" mode. Post, PM or email me if you are interested.
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