The boost comes from the current noise on the VESCs sensors for current at around 85% duty cycle. Vedder mentioned that already. And if you have contentiously 2000 Watts from a stand still till close to max speed that would not result in a even acceleration. It would throw you off the board when you start and would be controllable at higher speeds.
To accelerate 80kg from
0 km/h to 10 km/h in 1 second needs 308 watts
10 km/h to 20 km/h in 1 second needs 925 watts
20 km/h to 30 km/h in 1 second needs 1542 watts
30 km/h to 40 km/h in 1 second needs 2160 watts
And wind, rolling, belt and bearing resistance is not even involved.
As I explained in one of the topics that he showed the math, we donât want constant power, we want constant acelleration
Torque is directly proportional to current, and power is voltage times current in electrical terms or torque times rpm in mechanical terms, with that and devins math, with a high power in low rpm it equals to off the chart torque that will throw you off the board
Thatâs the beauty of current control, your acceleration remains almost constant, the current remains almost constant and power rises as the board speed up (in an ideal scenario, without drag forces)
@Pedrodemio LOL, we posted in the same second. But you are absolutely right. Itâs really strange that most of the times the wrong answer gets accepted by the community.
And when we add drag forces then we would need the opposite of Devins theory to have a even acceleration. But to set the Motor max higher then the battery max is quite nice because you have extra power at lower speeds without stressing the battery. And when the battery max sets the limit at higher speeds it is a smooth process instead of a boost.
Also it would not be a boost, it would be a loss of power.
Exactly, for constant power we have a decreasing acceleration as speed increase
Another problem that has to be considered is efficiency, if we pump 200A at 37V in our small motors and expects that all of that power is going to be converted in mechanical power weâre going to have a bad time, just look at the power/torque/efficiency plots that @Mellowhas been doing of some boards, the efficiency at low rpm is very bad, we are basically cooking the motors
To drive the topic back to watts / amps abit more, I think I can remark here that some of these âold eboardsâ especially with these heavy Pb batteries still achieved 20-30kmh even if their motors were brushed and 400-800w.
Of course I dont know their gear ratios and other stats but I think it should be left here that even such âseemingly low powerâ eboards were able to achieve such speed. I dont know their acceleration and sluggishness but I still think this proves the point.
First evolve boards also did not use top notch motors but I think it once again proves it that if you are not after top stats/performsnce, it is possible to live with less.
Similar like comparing ferrari and perhaps some old 90âs car. Both will get till 65mph/90kmh the difference will be in top speed and how fast they will get there + the durability too, probably.
300 watts is enough to reach 30 km/h on the flat. It only takes long to get there and you have a problem with hills.
If you want to know now how many watts you roughly need for which speed you can use this formula.
(New speed / 30) * (New speed / 30) * (New speed / 30) * 300= watts at New speed
Please donât stone me to death if this is wrong.
So how big battery (in terms of discharge) should someone get for going max 30-40kph with 8s setup and longboard wheels?
My âestimateââ is that 40-45A should be plenty already⌠this gives a power output of:
~1150W (40A x 28.8v)
~1300w (45A x 28.8v)
~1720w (if 60A x 28.8v)
What Im still not sure though is, how much power hills might require?
I tried to go up some very steep hill⌠and max power I saw on my wattmeter was 42A with 6s setup, that is ~910w (@21.6v). And I dont have longboard wheels
So I think with 8s, the amps might be in ~30A range?
(900w / 28.8v = 31.25A)
My speed was not the highest though⌠I think I managed to push 15kph instead of regular 25kph that i can do on flats.
â
Maybe @Ackmaniac and @rpasichnyk can share some data? U should have seen plenty of vesc data from the app you use
on experience, i use 20A max on 10s and can climb 10% with ease, but no full speed
The problem in estimating the torque in a given moment is that most people use different battery and motor limits, and since the torque on the motor is directly proportional to the motor current, the max torque depends on the duty cycle
I donât know what the duty cycle is proportional to, the guys you mentioned should have a better take on this
[quote=âOkami, post:28, topic:16121, full:trueâ]
What Im still not sure though is, how much power hills might require?
I tried to go up some very steep hill⌠and max power I saw on my wattmeter was 42A with 6s setup, that is ~910w (@21.6v). And I dont have longboard wheels
So I think with 8s, the amps might be in ~30A range?
(900w / 28.8v = 31.25A)[/quote]
I was surprised to find my 12S setup only needed about 1000W (20-25A) to climb the steepest hill near my place. I go into the hill around 20mph and there is some slowdown. But I bought wider belts/pulleys, and the enhanced torque transfer should allow me to pull enough power to maintain my speed up that steep hill
Some of it would be to voltage sag, but itâs primarily a slipping issue. I had to throttle back my battery amps to limit the current/torque. The SK3 6374 149kV can produce more power than my belt can transmit. Itâs a 3/8" XL belt, which from my memory is only rated for something like 1-1.5 hp. Replacing them with 15mm GT2-5mm (improved version of HTD-5mm), which are good for 3 hp
1.34 hp is 1000W, so those charts I stored somewhere in the back of my brain seem to match reality
ah okay - it sounded like you just went on full throttle and still slowed down. That is why I said voltage sag is the issue here. If you indeed have the belt slipping then you obviously have to take care of that first
@saul Thanks for the info! The more info we gather, the better!
So the one who builds 8s setup and has some hills to conquer, could go with 60A battery to have some headroom for the hills, even if general riding on flats, probably, wont take more than 20A day to day.
Would you be kind enough to pinpoint in which location / region you reside?
Or at least pinpoint how steep hills you got, since the geography around the world seems to shift quite dramatically in regards to terrain
