Hubs vs geared - theoretical performance comparison

Comparison of theoretical performance of some typical hub motors compared to gear reduction drive…

Geared: (2) 190kv, 0.05ohm motors w/ 42v & 100mm tires

Hubs: (2) 73kv, 0.07ohm motors w/ 42v & 84mm tires

^Conclusions: The chart on the left shows that both the 73kv (hub) and 190kv (geared) motors themselves have nearly identical peak performance abilities for a given load assuming proper gearing…

In the case of hub motors with 84mm tires, the chart on the right shows larger diameter tires than 84mm would be needed to “access” the peak performance abilities of the motors for all load conditions below the “1” line… for example at 60a battery limit per motor, larger tires will make the vehicle travel faster on all slopes studied (0% - 25%) while at 30a battery limit per motor, larger tires will make the vehicle faster only on 0%-10% slopes. A specific example is 84mm tire / 0.45 ideal gear ratio = 186mm tires gives 56.67mph on flat ground with 60a battery limit per motor.

The hub motors with 84mm tires appear to be optimized for flat ground ~32mph with 10a battery limit per motor, 10% grade ~25mph w/ 20a battery limit per motor, 15% grade ~26mph w/ 30a battery limit per motor, 20% grade ~27mph w/ 40a battery limit per motor, and 25% grade ~27mph w/ 50a battery limit per motor

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I think we really need a professor corner in here. A place where all the fancy charts, graphs and calculations can hang out. :relieved:

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should we just have a “professor_shartsis” category? I don’t understand most of this, but damn it seems important.

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left chart shows “how fast you could go” in miles per hour after you choose a battery current limit and a slope (colored lines - 0% - 25% grades).

right chart shows what gear ratio you need to reach that max possible speed on that slope. since hubs don’t have gears, if the ratio for the chosen slope & battery current limit (on the right chart) shows less than “1.00” you need bigger tires to go as fast as shown on the left chart— but putting bigger tires will reduce the efficiency in the same manner as lowering the gear ratio.

in other words in many situations the hubs could propel a rider faster with bigger tires, but the bigger tires would also make the board less efficient.

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What’s always confusing about the graphs – is that they move. Why are they moving? It’s not obvious what’s changing to cause them to move. Plus I want to look at them longer and zoom in more before they disappear

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The values entered at the top of the chart changed. 190kv vs 73kv - 0.05ohm vs 0.07ohm - 100mm tire vs 84mm tire

geared:

hubs:

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I’m not specifically referring to “this chart” but more so “the charts you’ve posted in the last year”. Trying to be helpful :slight_smile:

Science is good.

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@b264 re: the moving charts can help do comparisons at a glance… sort of like a blink comparator. For example by looking at the moving chart I can quickly tell that the geared system chosen for this example would have slightly higher peak theoretical performance-- a result of the lower assumed electrical resistance with the higher kv motor. In other words the same-size higher kv motor with lower electrical resistance can “go faster” because less watts are wasted as heat.

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there appears to be what I’d call a sort of “sweet spot” as far as gear ratio as long as the battery voltage is around 42v and using 2 motors…

setting the gear ratio such that the no load wheel speed is about 34mph (regardless of kv, tire size but having 42v and 2 motors) gives both maximum possible hill climbing speed up 25% slopes at 60a battery current limit per motor (~31-32mph), and maximum possible flatland speed with only 10a battery current limit (also about 32mph).

geared:

with this particular gear ratio setup, the rider would want to have at least 10a battery limit per motor for flat ground, 20a battery limit per motor for 5% slopes, 30a battery limit per motor for 10% slopes, 40a battery limit per motor for 15% slopes, 50a battery limit per motor for 20% slopes & 60a battery limit for 25% slopes.

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i purchased a boosted mini x at best buy for $999 to compare the performance with the hummie hubs…

hummie hubs (assumed values): 46v, 0.07ohm, 73kv, 2 motors, 84mm tire, 1:1 gear, 120a motor current limit, 60a battery current limit per motor

boosted mini x (assumed values): 46v, 0.07ohm, 190kv, 2 motors, 80mm tire, 3.5:1 gear, 50a motor current limit, 10.86a battery current limit per motor - these are best guess values since the info isn’t readily available – if anyone has better figures please let me know and i’ll correct it…

^the boosted mini x gets better efficiency at full throttle as can be seen from the green line, top left chart (electrical to mechanical conversion efficiency). top speed 20mph.

the hummie hubs have much more impressive hill climbing performance as can be seen from the yellow line, bottom left chart (vehicle thrust pounds - 2 motors). top speed 31-32 mph or so.

boosted mini x test ride:

hummie hubs test ride:

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chasing hummie on the mini x…

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I have no idea how Hummie can ride on his board with such a narrow stance :smiley: Mad skills!

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After seeing him do it I tried, really comfortable, but almost face planted

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where is that? I have no idea where hummie is.

San Francisco I think?