SlowMo Posted December 15, 2015 Share Posted December 15, 2015 Just now, Oily said: No real surprise - staggered me that it might even be possible ! Sooooo - onwards with my 500W motor & 30km/h board then..... It should be similar to the Gotway MCM2 board. You will surely like the performance. Link to comment Share on other sites More sharing options...
andress Posted December 15, 2015 Share Posted December 15, 2015 Here you were counting with the rated power. There is much higher value for peak power for all those inconsistencies on the road. Link to comment Share on other sites More sharing options...
Jag_Rip Posted December 15, 2015 Share Posted December 15, 2015 Please always keep in mind that the same engine is needed to bring you back to a stop in case of emergency. You cant just install an additional diskbrake and call it a day... So you really WANT to have some excess engine power left over that isnt being used for speed. Link to comment Share on other sites More sharing options...
Jimicycle Posted December 16, 2015 Share Posted December 16, 2015 15 hours ago, Oily said: No real surprise - staggered me that it might even be possible ! Sooooo - onwards with my 500W motor & 30km/h board then..... Wow - a serious explanation (although it now leaves me in a bit of doubt that even a 500W EU will comfortably do 30km/h) ? Thanks for the reply. Olly 500w are specified power. Most motors can have peak power more than twice of spec power. So 500W should be fine for normal riding. Link to comment Share on other sites More sharing options...
Colestien Posted December 16, 2015 Share Posted December 16, 2015 Not that I would ever ride over 32kph, but I would like to be able to. So at least 800w, and hoping for 1000w+ Link to comment Share on other sites More sharing options...
Jimicycle Posted December 16, 2015 Share Posted December 16, 2015 18 hours ago, andress said: Here you were counting with the rated power. There is much higher value for peak power for all those inconsistencies on the road. Yes, most motors can have peak power more than twice of the rated power. However, the power a motor can get is limited by how much power a battery pack can supply. Let us do some battery analysis. Typically, a high drain 18650 battery has internal impedance about 0.05 ohms. It is higher when the battery voltage is at low end of working range. A good brand new battery can be lower. We assume the impedance of other part can be ignored. For a 16s1p (16 series, 1 parallel) battery pack (rated 3.7V each, 59.2 total), the total internal impedance is 0.8 ohms. We assume the motor controller set the low voltage protection threshold at 48V (3V for each battery). At rated voltage of 59.2V, the maximum voltage drop is 11.2V, or the maximum current is 11.2/0.8 = 14A. So the maximum peak power of the battery pack can give at rated voltage is 48V*14A = 672W. With assumption of 80% motor efficiency and 30% spare power for balance, the peak power can really be used to drive an EU is 672W * 0.8 * 0.7 = 376W. This equivalent to about 0.5 hp, or left a 75kg object a half meter per second. This is the reason high speed EUs always use multiple pack (2p or 3p pack) to increase the maximum power. Link to comment Share on other sites More sharing options...
DebboR Posted December 21, 2015 Share Posted December 21, 2015 On 15-12-2015 at 6:59 AM, Jimicyle said: I will explain this with physics. 1 hp = 746w, means to left a 75kg weight one meter per second. The slowest speed A EU can move stably is about 3.6km/h, or 1m/s. When a EU climb a slope, the rising speed (up speed) is tan(Angle) * speed. For a 45 degree slope, the ratio is 1 to 1, i.e., moving forward a meter also rise up a meter. For a 15 degree slope, moving 1 meter would rise 0.268 meters. For easy estimate, we assume that the rider plus the EU is 75kg, the efficiency of an EU is 80%. Unlike other vehicles, a EU always needs to reserve extra power to keep us balance. Usually, it needs at least 30% reserved power. Then for one house power, a EU needs about 746/0.8/0.7 = 1332W power. At the slowest speed of 3.6km/h, or 1m/s, the power needed to climb a 15 degrees slope is tan(15)*1332 = 357W. That is, a 350W EU can barely keep moving on a 15 degrees slope. In order to move at a speed of 10 km/h on the 15 degrees slope, the motor power needed is 357W * 10 /3.6 = 991W. If we really want to push a 350W EU to 30km/h, the max angle it can keep move is arctan(350/1332*3.6/30) = 1.8 degree. That is, at 30km/h, a 350w EU can have just enough power to move on flat road, without the consideration of road and wind resistance. In practice, if we want a super EU that can climb a 20 degrees slope at speed of 15km/h, we need 1332* tan(20) * 15 /3.6 = 2020W These calculations are very useful to get a grasp on the actual 'meaning' of the power rating and where this power actually goes to, but I can't help but notice a subtle mistake in your calculations. The speed as measured and limited by the unicycle, is the speed perpendicular to the plane you're riding on, not the horizontal speed. This means the tan(slope) in your calculations isn't really correct (think about it, if your angle would go to 90°, your calculations would result in an infinite vertical speed and power, while it would actually climb vertically at the 30km/h if you ignore the fact that this is impossible). If you replace the tan(slope) by the sin(slope), your calculations will be correct. I just ran it through the numbers, and this resulted in: 340W for 15° and 1m/s 944W for 15° and 10km/h 1.83° incline for 350W and 30km/h 1872W for 20° and 15km/h This isn't much of a difference, but I'm just putting it out there for the sake of correctness . I still appreciate your effort for explaining these simple calculations to those who didn't know how to do this! We'll all get smarter bit by bit . Link to comment Share on other sites More sharing options...
Mystamo Posted December 22, 2015 Share Posted December 22, 2015 Not sure how well this transfers over since the motor in this application is actively working to keep the rider suspended above the motor axis. But in the ebike world, motor ratings meant little. We would buy 500w motors and push 2 to 10kw onto them for short periods of time. I have a crystalite motor that I frequently ride at 5kw. These euc motors from what I observed from my two, barely even get warm. They can be pushed much further with controllers capable of dishing out the amps. Once we blow the lid off the firmware and limits. It won't be long till you see 350w motors doing 30km/h. There is lots of headroom in those motors for those who wish to push the limits of the motors. Mo Link to comment Share on other sites More sharing options...
Jimicycle Posted December 23, 2015 Share Posted December 23, 2015 On 12/21/2015 at 5:06 PM, DebboR said: These calculations are very useful to get a grasp on the actual 'meaning' of the power rating and where this power actually goes to, but I can't help but notice a subtle mistake in your calculations. The speed as measured and limited by the unicycle, is the speed perpendicular to the plane you're riding on, not the horizontal speed. This means the tan(slope) in your calculations isn't really correct (think about it, if your angle would go to 90°, your calculations would result in an infinite vertical speed and power, while it would actually climb vertically at the 30km/h if you ignore the fact that this is impossible). If you replace the tan(slope) by the sin(slope), your calculations will be correct. I just ran it through the numbers, and this resulted in: 340W for 15° and 1m/s 944W for 15° and 10km/h 1.83° incline for 350W and 30km/h 1872W for 20° and 15km/h This isn't much of a difference, but I'm just putting it out there for the sake of correctness . I still appreciate your effort for explaining these simple calculations to those who didn't know how to do this! We'll all get smarter bit by bit . Yes, you are absolutely right, the whole section is talking about VERTICAL speed, no road and wind resistance at all. With these assumption, NO power is needed to ride on flap surface, even in 300 miles . However even with these ideal condition, a 350W unit can only have 1.83° incline at 30km/h. This is the third part the of the series, I will further estimate how much power is needed at 30 km/h in more realistic condition. Assume that, during a riding, an external force make you out of balance and you are lean forward 5°. The force may be caused by a small step one the road, or simply someone gives you a light push on your back. In order to restore balance, the wheel must accelerate a bit to catch up your center point of your body weight. Or in another point of view, a horizontal force is needed to push you back to 0°. Still use 75kg as example, the force then is 75 * tan(5°) * 9.8 = 64 Newton. The recovery force should be larger than this, otherwise you will tilt even more and need more force to recover and ... a faceplant. Once starting move back, the force needed is less and less until zero. That is, we need a burst of force or power to get back. Note that the power is extra power additional to the power keep you moving. From physics, Power = Force * Speed. So the "30% extra power to keep you balance" in my first section of is too rough, the extra power is actually proportional to speed. At slow walking speed of 1m/s (3.6km/h), to move you back from a 5° forward lean, the extra power is 64N * 1m/s = 64 W For 30km/s, the extra power becomes 64N * 8.3m/s = 533W Consider 80% efficiency of the EU motor, even at flat road, you need at least 666W for a safe riding at 30km/h! Use this result to recalculate the conditions stated in the first section: 3.6km/h, 15° slope, 80% efficiency, 5° forward lean recovery: 1m/s * (746W * tan(15°) + 64W) / 0.8 = 329W 10km/h (2.78m/s), 15° slope, 80% efficiency, 5° forward lean recovery: (2.78 m/s * 746W * tan(15°) + 64N * 2.78m/s) / 0.8= 917W At worst condition, you rush to a 30° slope at top speed of 30km/h, and you are 5° forward from balance, the minimum peak power to ensure you are not down is 8.33 * (746 * tan(30°) + 64) / 0.8 = 5151W To recover from 10° lean, the recovery force is 75kg*tan(10°)*9.8 = 130N, about doubled. Above numbers are 412W, 1146W, and 5838W respectively The conclusion is that, at 30km/h, for a 65kg person, even on flat road and without road and win resistance, we need at least 666w to ride safely. In real world, if we want to ride at speed of 10km/h on a 15° slope, with 10° forward lean recovery ability, we need at least peak power of 1150W (at this speed and slope, the road and wind resistances are small). Link to comment Share on other sites More sharing options...
electric_vehicle_lover Posted December 23, 2015 Share Posted December 23, 2015 By he way guys, we just run the motor for the first time with our OpenSource Firmware. We can now make a test to run it at max velocity and measure it and see if is much higher than the 16km/h limited velocity of originals firmwares. Link to comment Share on other sites More sharing options...
playdad Posted December 23, 2015 Share Posted December 23, 2015 Wow that sounds awesome. Keep us updated. Link to comment Share on other sites More sharing options...
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