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MadInventor

Motor / Gear ratio help

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I could do with someone to do some checking on some gear ratio calcs for me to see if I've made an error in them before I start thinking about building the gearbox for my War Rig.

I'm using a baseline for  a sensible speed as my 6x6 truck, which I'm running on a standard 540 with a 3S LiPo. From a bit of poking around on the internet, I came up with an equivilent Kv figure for a standard 540 of around 2500KV (Which might be completely wrong :wacko:).......

Standard 540 ~ 2500Kv, 18500rpm@2S (7.4), 27750 @ 3S

The gear ratio of the king hauler gearbox and axle I'm using is 10.64:1 in 3rd

so the axle is doing around 2608rpm

for TLT-1 (89mm) tires, 1 revolution of wheel = 279.6mm

so in one minute travel 279.6mm*2608 = 729201.35mm = 729m = 0.729km = 43.75km/h = 27.34mph, which seems rather quick for this (See the last run at the end of the vid):

 

 

 

So, for the War Rig motor, which is a 1050Kv motor capable of 6S....


5674, 1050Kv, = 23310@ 22.2V, 25200@ 24V

working backwards


The diameter of the war rig tractor unit tires is 132mm, so distance travelled in 1 rev = Pi*132 = 414.7mm

729201.35mm / minute = 27.34mph, so axle rpm need to be 1758.38rpm.

so for 25200rpm at motor, gear ratio required  = 14.331:1
and 23310rpm at motor, gear ratio required = 13.25

Do these seems like reasonable assumptions, I don't want to build the gearbox and find that the truck either crawls along at 10mph, or is an uncontrollable speed machine with no pulling power (The motor is rated at 2330Watts at 6S, so I think it will probably shift the tractor unit quite quickly if geared too high and not puling much weight)

 

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