Calculate Torque 4wd vs 2wd

I’m trying to find out what kv motor will give equal torque on 4wd as 2wd 190kv. How can I calculate it? Reason is I want max top speed(prefered around 45mph) but still have the same torque as dual 6374 190kv setup. The setup is 107mm wheels, 6374 3200w motor, 12s6p battery, geared ratio 2.4:1 Do you think 4 6374 230kv will have same or better torque thene dual 6374 190kv? (And yes I can footbrake and have good protection, I’m not gonna go crazy in town) Ty for any help!

for the same full throttle vehicle thrust with 4WD as 2WD you can use 1/2 the motor amp limit setting with 4WD compared to the 2WD motor amp limit setting (same kv). torque is directly proportional to the motor current so half the current but twice the motors gives the same thrust / acceleration. since heating is proportional to the square of the current you’d see 1/4th the ohmic heating per motor and 1/2 the ohmic heating overall with the 4WD.

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That’s not what he means, he means what kV motor/ gear ratio should he use in a 4wd as a 2wd to boost speed but maintain torque.

Example of this would be to half the gear ratio and then double the motors, although if worked out with maths I doubt this is exactly correct. Maybe you could help him do this as you seem to be very good with the calculations

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Well to begin with he can reach 45mph with only 2 motors by switching from 2.4:1 to 2.18:1 gear ratio without changing anything else… however this change would decrease the peak vehicle thrust from 60.8 lbs to 55.2 lbs.

(2) 190kv motors, 0.05ohm, 107mm tire, 46v battery, 100% throttle, 95% max duty cycle, 60a motor amp limit, 30a battery amp limit per motor

I’m assuming you’re running 12S voltages. Reaching 45mph on a belted rear wheel drive system is kind of trivial at this point, and you don’t need to go higher than 190KV to do it, as @professor_shartsis (hilarious handle, btw) correctly points out.

However, the question may remain uinanswered because it is NOT recommended to run 12S at over 190 ACTUAL KV. Now… depending on what motors you get… the ACTUAL KV will invariably be lower than the stated KV however the amount of difference will vary.

I would start with motors rated at 200KV and go from there incrementally. The likelyhood that they are actually over 190KV upon being measured on the bench is slim, but they may be higher than the 190KV motors you might have already.

There’s a thread around here that discusses actual KV versus advertised, and there is math and other things you can do to figure out actual KV using BLDC or VESC tool. I don’t have a link handy, but maybe somebody else does.

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Type kv in BLDC/vesc tool debug console and divide number by 7 assuming 7 pole pairs standard on most motors if I remember correctly. Gotta give this a try myself.

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now suppose he changes from (2) 190kv motors to (4) 190kv motors & changes the gear ratio from 2.4:1 to 1.77:1… top speed increases from ~40mph to 55mph & peak vehicle thrust increases from 60.8lbs to 90.1lbs…

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Indeed. I clocked @jayx at 44mph in january on a beast evo built by @Battosaii

just found some footage from that day on my go pro last night. I may get around to editing it.

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Funny you should say that cause that same Evo is going 4wd with quad 6374s and a 12s8p so I doubled up everything lol

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wtf are you dragging the battery behind you in a trailer? lol

this is why i love this place. 12S8P good god. I wouldn’t want to weld that one.

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Haha @Eboosted made me a double stack Evo enclosure I could fit a 10p if I didn’t have to fit 4 Focboxes.

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I just ordered 4 6374 custom wired for higher kv 220kv. Will also use eboosted enclosure and evo board and a 12s6p battery and 4 flipsky vesc 6. 107mm abec 11 wheels. Last to decide if i will go with belt or geared drive… Hope 3dservice release their fatboy soon…

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if you’re looking to maximize top speed with that setup i find you can hit 70mph top speed @ 240a battery amps & 81.71lbs peak thrust w/ (4) 220kv motors, 0.025ohm, 46v battery, 107mm tire, 1.6:1 gear ratio, 70a motor current limit & 60a battery current limit per motor…

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haha then i will for sure kill me i will go with 1:2.4 i think Ty for the calculations!

i believe you’ll hit 45mph & 122.5lbs peak thrust with the 2.4:1 gear ratio, 220kv, 4 motors, 70a motor current limit

the fatboy mini urethane drives should be out soon as I’ve seen the custom hangars and pulleys. Should be a matter of time

How do you calculate vehicle thrust?

60 / (2 * pi * KV) = KT (Torque in Newton Meters Per Amp of Motor Current)

Motor Current Limit * KT = Peak Motor Torque in Newton Meters

Peak Motor Torque in Newton Meters * Gear Ratio = Wheel Torque in Newton Meters

(Wheel Torque in Newton Meters * 1000mm) / ((1/2) * Tire Diameter in MM) = Thrust in Newtons, 1 Motor

Thrust in Newtons, 1 Motor × 0.224808943 = Thrust in Pounds, 1 Motor

Thrust in Pounds, 1 Motor × 0.453592 = Thrust in Kilograms, 1 Motor

Thrust, 1 Motor * Motor Quantity = Vehicle Thust

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I tried to do the math, the numbers got complicated real fast. Thanks for the info anyway.