Weight and current

A question that is interesting me:
What will be the current draw different If I have exactly the same electronics (ESC + Motor) on Truggy and Buggy? (Both are set up for the same speed)

In other words, if the Buggy is 25% lighter then the Truggy should I expect 25% less current consumption then the Truggy? If so, If the Truggy is using 5000mAh 4S battery, can the buggy use 25% lighter battarry (3750mAh) and expect same run time and performance as the Truggy?

[steveo]

remember the ampacity will be smaller unless you use a higher C rating than the 5000mah you have- i dont think your formula will work out quite like you want

if you used a 6s battery with correct rpm motor geared for the same speed then you might be able to use the smaller mah battery making your system more efficient

[simplechamp]

Originally Posted by steveo

remember the ampacity will be smaller unless you use a higher C rating than the 5000mah you have

But the lighter vehicle should draw less current. So yes, a smaller capacity battery wouldn't be able to produce as much current, but it wouldn't need to produce as much since the lighter vehicle presents a lower load.

I don't think the 25% lighter = 25% less current is quite right though either.

[suicideneil]

Yeah, I dont think its quite as simple or straightforward as 25% less weight > 25% smaller batts = same runtime available. As weight increases the power required to maintain a certain desired speed increases at a faster/higher rate- for example:

my Dad's old Vauxhall Astra 1.2L could manage 100mph ( good times ), yet a Veyron with an engine many many times larger and about 8-10 times as much HP can only manage a speed 2.5 times faster....

[nativepaul]

I don't think its quite that straightforward either but I think that was a bad example, drag increases with speed on a cube root basis, so any given car, boat or plane will need 8 times the power to do double the speed, with a veyron engine in your dads astra it would go 200MPH, the fact that the veyron goes 250MPH shows that Verons are more aerodynamic than old astras. Weight makes a negligible difference to either drag or top speed except that a heavy car will accelerate slower and thus may no longer have room to accelerate up to top speed on a given straight, given room it will lumber up to the same top speed.

Acceleration is fairly constant for a given power to weight assuming you can get decent traction and our top speed is gearing limited not power limited so it should be close to 25% less current for the same voltage if you are racing on a short track which is mostly acceleration with a very short amount of time at top speed, the longer the straights the less difference in current you will see, and likewise if your bashing the type of bashing you do will make a big difference sometimes I'm doing small ovals in the road outside which would be near 25% and sometimes I'm just buzzing round the park and the bigger wheels and ground clearance of the truggy would be less drag in the grass and the truggy would have the advantage.

[lincpimp]

I would like to point out that loosing weight in key areas will make much more difference. Dropping 25% of the weight off the chassis will not have the effect that dropping 25% off the wheels/tires will. Try running buggy wheels/tires on a truggy (with correct gearing to compensate) and you will see what I mean. Lighter wheels/tires make a huge difference, a lst with truggy wheels/tires has much less draw then the same setup with 40 series...

[E-Revonut]

Good point Linc! That's why I'm looking at some of the newer VTR tires and rims from proline, even lighter than the LPRs