Throttle vs Heat (And How Gearing Changes Everything)

[safe]

Throttle Verses Heat

I've been wanting to be able to prove this definitively for a while and now I've got the "spreadsheets" to do it. While it's pretty obvious that good gearing increases torque and reduces heat just by "feel" it's possible to show the exact way that heat and torque are related. The following charts show the differences that take place by comparing two gears. The low gear and the high gear are spaced as 2 to 1 compared to each other. The motor is a 750 Watt Unite running at 48 Volts and a 40 amp controller.

Note the "big dots" and compare the values:

High Gear
Throttle Setting - 60%
Speed - 12 mph
Hub Torque - 51 Nm (which is less torque)
Heat - 930 Watts (which is more heat)

Low Gear
Throttle Setting - 80%
Speed - 11 mph
Hub Torque - 79 Nm (which is good)
Heat - 560 Watts (which is good)

So the "bottom line" is that in low gear you create 40% less heat and get 54% more torque. You also are operating at 65% efficiency while in low gear and 46% in the high gear.

If you need to climb a hill good gears really help a lot.

 

[xyster]

I've been wanting to be able to prove this definitively for a while and now I've got the charts to do it.

With few exceptions, charts suggest. Charts do not prove. Now, to corroborate (or contradict) the suggestion, go take measurements of this effect in action.

 

[safe]

This is something that is in a sense "so obvious" that proving it is sort of unnecessary. Everyone knows that gearing improves torque and lowers heat. We feel it as we ride and even hub motors are sold based on the idea. (high torque low speed hub motors verses low torque high speed hub motors)

So it's not like I'm actually breaking any new ground on the theory, but I am giving actual values for a specific motor. (750 Watt Unite)

If you like I could do the same for the 5304? (though any change in gearing would be "virtual" since hub motors are fixed in their gear ratio)

Surely you don't disagree with the "theory"... maybe you might dispute specific data points?

The "Throttle Theory" had cases of imperfect data, but the "theory" was solid as a rock. I'm more concerned with understanding the theory than being a "perfectionist" with data. (data errors "happen")

 

[xyster]

This is something that is in a sense "so obvious" that proving it is sort of unnecessary.

Then what's the point of this exercise?

So it's not like I'm actually breaking any new ground on the theory, but I am giving actual values for a specific motor. (750 Watt Unite)

Ah, so the point is to give actual values for a specific motor. Ok, then the same thing holds. The next step is empirical tests.

If you like I could do the same for the 5304?

Tis okay. I've only got one gear anyway.

Surely you don't disagree with the "theory"... maybe you might dispute specific data points?

No, I don't disagree with the "theory" as I am, like most, quite familiar with its real-world operation already. Until backed up with empirical tests, I dispute the specific data points as a matter of course and general, healthy skepticism for that which I haven't observed tested yet.

I understand testing this may not be feasible for you, as it is not for me right now. I'm just pointing out that these charts are a good starting point, but especially so far as specific numbers, prove nothing.

 

[safe]

Just so that you understand the logic of the comparison better let me explain further.

You start with "High Gear" and you find out at what throttle setting you get the maximum torque for the LOWEST throttle. This gives you the MINIMUM energy requirement to achieve the maximum torque. This is in a sense "as good as it gets" for the "High Gear".

You then take the SPEED value of the "High Gear" and relate that to the speed value of the "Low Gear". You now have an EQUAL comparision. You then look up the values for torque and heat for the "Low Gear" and realize the benefits.

The thing about the "Low Gear" is that you can see by looking at the chart that there's MORE torque available if you really needed it, but you don't need it. You can afford to run closer to the peak efficiency area and still have power to spare.

So low gears have a huge advantage in the hill climbing area BOTH in increased torque and in lowered heat buildup.

40% less heat
54% more torque

 

[TylerDurden]

Ahem...

There is no data yet. Merely hypothesis.

Data errors do not happen. They are created.

Only testing can create real data, only real data can validate hypothesis.


8)

 

[safe]

I know on my own bike all the results I've been getting are very close to my actual experiences. I can now calculate things like at what EXACT throttle setting I get the most torque. On my bike the value is 70%, but on the 5304 the value is 65%. Every motor is a little different depending on how you configure it.

Heating is based on the formula:

Heat (watts) = Current (squared) times Resistance

Controller Losses = (roughly) 5%

If you add the Heat Losses plus the Controller Losses and the Power Output together you get exactly what the Power Input value is.

(this chart is for a different motor, but the same idea)