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In this set of tests, I wanted to understand the relationship between maintaining a steady cruising speed & the motor's avg power consumption over two laps (800M) of a running track. The physics of power consumption on a conventional momentum balanced device (e.g. a bicycle) are well understand, but not so with the single-wheel self-balanced systems. There is some debate over how much, or even if, there is an energy penalty to keep the rider upright, or if it conserved in forward momentum. http://www.gribble.org/cycling/power_v_speed.html (watts) = (1-(Lossdt/100))-1 · (Fgravity + Frolling + Fdrag) · V (m/s) Another question that needed answering was, 'does a more powerful motor have an impact on efficiency & if so, by what degree?' Methods: The two eWheels used for the testing were the Ninebot E, 240Wh battery & the new King Song 800W with the 680Wh battery pack.An inline power meter capturing Volts, current, temperature between the battery pack & the control board, recording at a rate of 50Hz Two laps around the track maintaining speed intervals of 15kph, 18kph (for the Ninebot cannot maintain 20kph), 20kph, 25kph, & 28kphThe average power consumption is taken across a minimum of 2 minutes, removing the start (acceleration) & finishing outliersResults: At the same speeds, 15kph for instance, both the Ninebot & King Song are practically identical at 12Wh/kmThere is no significant diminishing rate in efficiency as the motor is operated at the software defined top-speed of 28kph that can not be accounted for by wind resistance
I recorded the battery states from two rides and display the results below. As the relation between remaining capacity and voltage seems to be close to linear over a wide range,^1 the data seem to be useful to evaluate range and energy efficiency of the device. Device: GotWay 14" MCM2s, 340Wh (unconfirmed), 80kg load, tire pressure ~40 PSI. Method: screen shots of the GotWay app under zero load and zero speed (i.e. stopping for each and every screen shot). The acquired data are trip length, battery voltage, and battery temperature. To estimate efficiency and range, I assumed a (I believe realistic^1) overall available voltage range of 12.5V, e.g. from 65V to 52.5V, with capacity linear in voltage. Full charge is 66.2V (measured), battery empty status is allegedly 51V (unconfirmed). The smallest value I had seen so far is 55V, with already significant change in riding experience. Both trips shown do not start from full charge, but close to full. First, a two-way round trip with small detours and roughly about 50m altitude difference, mostly on smooth sidewalks. The overall voltage drop was 2.5V after 8.6km, that is 2.9V/10km. Estimated range: 43km Estimated efficiency: 12.7km/100Wh or 79Wh/10km Second, a practicing session (round trip) mostly over comparatively rough cobblestone and overall comparatively small altitude differences. The overall voltage drop was 5.1 after 11km, that is, 4.7V/10km. Estimated range: 26.6km Estimated efficiency: 7.8km/100Wh or 128Wh/10km I cannot quite explain the large voltage drops in the beginning of the second trip.The voltage increase observed between 2.5 and 3.1km can not be attributed to energy recuperation, because it was a 600m round trip. I triple-checked the data. I don't have a really good explanation there as well.The -12V/10km episode around 8km were 2x10m eights with sharp acceleration and braking between each U-turn. Given these data are reproducible, we see that a smooth surface makes a big difference (somewhat unsurprisingly) andunder optimal conditions efficiency might be considerably better than 100Wh/10km (somewhat surprisingly), even something close to 50Wh/10km wouldn't surprise me anymore now. Here are a few sources of uncertainty: tire pressure is only an estimate the distance measure depends on the calibration of the wheel+app, on the tire pressure, and on the load, all in all in an (yet) undetermined wayinertia/recoveries in voltage measurements, which apparently leads to voltage increase even over a distance of one kilometer flat. difference between initial and final battery temperature, it seems that 10C temperature difference can make for about 0.5V difference. I don't think they have a game-changing influence for estimating overall efficiency though, can't be sure of course. I wonder: are these data still consistent with a 270Wh battery, or do they positively confirm 340Wh? Suggestion for improvements are welcome. If you are interested I will try to post a few more graphs... ^1: http://lygte-info.dk/pic/Batteries2012/Efan%20IMR18650%203200mAh%20(Purple)/Efan%20IMR18650%203200mAh%20(Purple)-Capacity.png http://www.dampfakkus.de/akkuvergleich.php?akku1=498&akku2=99&akku3=&akku4=&akku5=&akku6=&a=2 http://www.powerstream.com/18650-high-discharge-rate.htm
Here are some energy data on my Firewheel 16". The rule of thumb is 12Wh/km or 19Wh/mile. At lower speeds, it should be possible to get 10Wh/km. With a 130Wh battery, expect to get 11km range. With a 170Wh battery, expect less than 10 miles. There is a mean speed of about 22km/h over a distance of 20km with stops, intersection crossing, slowdowns... so my cruise speed is over 25km/h. Firewheel rocks ! Wheel = 13.6kg, rider = 65kg, total = around 80kg. Tyre pressure = 3 bar. Mean speed (km/h) and distance (km) measured by a "Sunding" bike computer. Energy (Wh) measured by Charge Doctor. Original data here, if you want to convert to other metrics (miles per 1kWh...). https://docs.google.com/spreadsheets/d/1MsuAMM87v9bv4sZ-I58M3dmKV1Iq0hnA0cyzTZ5mwkI/edit?usp=sharing