14 replies to this topic

[Gamester]

Hey guys,

This is something that I have been pondering for a long time and maybe someone here can help me out. Ok, so my dilemma is with calculating scale weight for RCs/Models.

For example, let’s say you have a 1:10 scale RC car made of steel, aluminum, and plastic, exactly like the full size vehicle. Let’s say that the full 1:1 version of the car weights 3500lb. So, the 1:10 car should weigh approximately 1:10th of the weight, right? Nope, it isn't even remotley close in reality. No 1:10 RC car would ever weigh 350lb, not even if it were made of lead.

However, other measurements seem to hold accurate. For example, I have a very detailed and accurate 1:12 scale model of a 1969 Camaro SS. The wheel base of a 1:1 1969 Camaro SS is 108in, so that divided by 12 means my 1:12 model should have a wheelbase of 9in, and it does.

Why is weight scaling so vastly different? Is there some material density or gravity variation that has to be factored in to the division or something?

I am certainly no scientist, so I hope someone here with a greater knowledge of physics behavior can help put my mind at ease

Thanks,
Jason

[speedy_w_beans]

1/10 applies in each of the three dimensions (x, y, z). Therefore, the 1/10 scale RC car uses 1/1000 the volume of the materials. 3.5 lbs (1/1000 of 3500 lbs) suddenly looks realistic if using all the same materials, but scaled down to correct sizes and thicknesses.

-Paul

[Daves956]

Liquids, power source as in a V8 versus an electric motor. If the scale model was in fact made of the same materials and utilized the same technology then the weight would be right but an RC car has no relation to the 1:1 it's patterned after other than looks.

[Gamester]

Ah, that makes perfect sense. I always thought that the scale size would mean everything should be the same scale, not just the measurements.

Thanks for easing my mind guys

[wolfdogstinkus]

Gamester, have you seen madinventor's scale tank?, I think he is factoring the weight of the 1/1 in his build but I could be wrong and just making it up?, lol

[WillyChang]

1/10 applies in each of the three dimensions (x, y, z). Therefore, the 1/10 scale RC car uses 1/1000 the volume of the materials. 3.5 lbs (1/1000 of 3500 lbs) suddenly looks realistic if using all the same materials, but scaled down to correct sizes and thicknesses.

doesn't need to be realistic on the materials... a touring car is 1400-1800g vs 1:1 of 1500-2000kg

If you add fancy lighting and scale details to your 1/10 sedan it'll hit 2kg quite easily.

[Gamester]

Gamester, have you seen madinventor's scale tank?, I think he is factoring the weight of the 1/1 in his build but I could be wrong and just making it up?, lol

Nope, but I can only imagine the fun that could had with a 1:1 RC tank

[WillyChang]

if its got live ammo, i think i'd rather be INSIDE that instead...

[Daves956]

If your working on true scale everything, what about scale speed? The 1:10th scale Jaguar here should top out around 25 MPH

[WillyChang]

25mph is easily achieved

ahh but air/wind resistance (fluid dynamics) doesn't necessarily scale at set ratio proportional to physical dimensions

so the power necessary to overcome drag won't be a simple multiplier proportional to size ratio


there's also a lot of other dimensions that's nowhere scale, like tyre widths which also add to drag.

[Daves956]

By scale the Jag does just a touch over mach 1.

I read an article about prototypical modeling of railroads, How long it took a road gang to lay a single tie and so on. The amount of beer and whiskey you had to consume to be completely accurate didn't paint a pretty picture and adding the beans to the scenario made me give up scale accuracy forever.

[Grastens]

I read somewhere that scale speed for RC vehicles is actually the actual speed multiplied by the inverse of the scale (or divided by the scale), but then divided by the square root of the scale as well. This is supposed to explain why a 1:10 scale car can still handle at 25mph when the real car would be nowhere near as manoeuvrable at the 250mph equivalent, and was originally used for putting the handling of RC aircraft into scale.

The logic behind it is that time is also scaled down for these models, and so a scale speed of 250mph for the Jaguar would actually be closer to 80mph (using 25mph: (25mph x 10) / 3.16, the square root of 10, is actually equal to 79 scale mph. Using 80mph: (80mph x 10) / 3.16 = 253.16mph).

Another resource is here: http://www.ultimater...p/t-151252.html

[stu22]

Simplify the problem.

A 2x2x2 inch cube will have a volume of 8 cubic inches. A 1/2 scale version of the same cube will be 1x1x1 and have a volume of 1 cubic inch.

So, a 1/2 scale version of our original cube will have the dimensions reduced by half but the volume will be reduced to 1/8th that of the original.

[billg4]

safety features to protect drivers and passengers are also not needed in a R/C vehicle

That is why a 70's rear drive luxo "boat" weighed 3800 pounds and todays smaller honda or toymota is close to 4,000 pounds

[WillyChang]

1:1's drivetrain & suspension takes a lot LESS volume than in a 1/10 tourer

if they were scale, 1/10 control arms would be wirey thin like toothpicks
and shocks would be dimensions of a AAAA battery