This is where logging becomes really useful.
I rarely see over 70A drawn from my 12s5p battery with 2x6374 190kv sealed Maytech motors set at 60A each. Even when I increase the motor amps, it does not make a significant difference in the battery amps.
I say set your battery to 90-100A and forget about it.
I guess I’m a shitty planner. I’ve settled on finding my limiting reagent and working backwards. My tattu 10ah 25c 12s pack is good for 250a on paper/marketing. I decided 200a for 4wd. 200/4=50 per esc.
In reality, I only touch peak total amps of 140 on metr telemetry. My limiting factor is really my skill and fear.
Clearly you are trying to avoid the trial and error approach. But sometimes it be that way.
I recommend pouring over your telemetry and matching corresponding actions/feels to the EEE stuff and maths.
20% grade
2.4:1
170kv
110mm tire
160lbs rider -> 190lbs vehicle
top speed on flat 42mph -> battery current to sustain 40mph on flat vs 20% grade:
53a motor current limit per motor:
18a motor current limit per motor:
^results:
40mph on flat ground: 32.2a battery amps total (1610.2w electrical total)
40mph on 20% grade: 98.53a battery amps total (4926.9w electrical total)
4926.9w/1610.2w = ~3.05
*correction on the charts, the battery voltage shown in the charts is 50v, but the charts mistakenly say 46v at the top
the assumptions are:
50v battery, 0.05ohm, 170kv, 2.4:1, 110mm tire, 53a motor limit vs 18a motor limit
Wow beautiful. Gonna study this like crazy, thanks for the reply, it’s above and beyond.
I think i got my gear ratio wrong, motor gear 15t and wheel gear 36t is what it is. 3d servisas says its 2.4 so idk, I think my top speed is closer to 35mph rather than 40mph.
15t motor 36t wheel is 2.4:1
36/15=2.4
your actual riding voltage is probably lower than 50v, that’s why I had to boost it for the chart
Thanks, it’s a little above my head at first glance but it’s making sense. I have a feeling a lot of people over do it on their batteries because they overlook this part.
I think I fudged the chart ever so slightly, I multiplied the 5% grade slope force lbs@ 40mph * 4 to get the 20% value, it’s close, but this was a bit lazy and I think it isn’t exactly correct.
I use max battery amps as a way to limit maximum system power. So I set my motors to the maxium they can do then set the battery amps quite low. Then increase the battery amps a bit at time till its enough power for my needs.
High motor amps only effects slow speed acceleration. Motor amps are much lower at speeds below 60kph.
Peak amp draw happens during acceleration, so limiting battery amps will limit acceleration.
On my system 12s1p, under load (heavy acceleration) my voltage drops to 46.2v X 32a (battery draw) = 1478 watts is my peak system power.
My two vesc battery amps are at 17.5 amps, I will only see 32a (battery) under heavy acceleration for a second or so then it starts to drop. My motor amps are 65a in vesc tool.
To answer your question I feel any difference in increasing the battery amps with the way I set mine up.
I like to run the battery amp limit low as a way to keep the acceleration from being too savage and to save my battery from unnecessary wear.
I agree.
I also don’t like the high battry amp setting.
It has a large voltage sag.
distance is reduced.
I can not control if the acceleration is too sharp.
If I can hit the fastest and climb the hill without inconvenience I’m fine.
I think that more battery amp is unnecessary.
But why buy a thorium 4wd and then limit the batt amps to 10A? Honestly makes no sense. Even the 2WD would be too much for you.
But back to boards…
If you used 60a bat limit per motor @ 50v with these 2 motors in a race, you wouldn’t want to use 2:4:1, you’d want to use 2.15:1 for 45.10mph on 20%…
and in fact, anyone with the same voltage and battery amp limit on the same grade will get the same speed to a close approximation regardless of kv and tire size as long as their gear ratio gives a 48.31mph no load virtual ground speed.
That’s interesting, I need to learn more about gear ratios. What are you using to make your graphs?
the mosf interesting part is:
8082.063923094534641801 motor rpm @ peak mechanical power
^peak mechanical power is 10746.218459832w @ 8082.063923094534641801 motor rpm
A = meters per second = XX.XXX
B = drag coefficient = 0.75
C = frontal area = 0.6m^2
D = fluid density of air = 1.225kg/m^3
E = wind drag force in watts
F = sine of 5% slope = sin(atan(5/100)) = 0.04993761694389223373491
G = acceleration of gravity = 9.80655m/s^2
H = vehicle mass in kg = 90.7184kg = 200lb / 2.20462lb/kg
I = mechanical watts required for constant speed up slope with no wind drag
J = mechanical watts required for constant speed up slope including wind drag
K = H * G * F
L = (1/2) * D * C * B
E = ((1/2) * D * C * (A^2) * B) * A
I = H * G * A * F
J = E + I
J = (((1/2) * D * C *(A^2) * B) * A) + (H * G * A * F)
J = (1/2) * D * C * B * A^3 + H * G * F * A
J = (L * A^3) + (K * A)
^this can be rearranged to:
A=(sqrt(3) * sqrt(27 * J^2 * L^4 + 4 * K^3 * L^3) + 9 * J * L^2)^(1 / 3) / (2^(1 / 3) * 3^(2 / 3) * L) - ((2 / 3)^(1 / 3) * K) / (sqrt(3) * sqrt(27 * J^2 * L^4 + 4 * K^3 * L^3) + 9 * J * L^2)^(1 / 3)
we know:
J = 10746.218459832w peak mechanical
L = 0.275625 = (1/2) * D * C * B
K = 44.42622815547907982077 = H * G * F
therefore:
A=(sqrt(3) * sqrt(27 * 10746.218459832^2 * 0.275625^4 + 4 * 44.42622815547907982077^3 * 0.275625^3) + 9 * 10746.218459832 * 0.275625^2)^(1 / 3) / (2^(1 / 3) * 3^(2 / 3) * 0.275625) - ((2 / 3)^(1 / 3) * 44.42622815547907982077) / (sqrt(3) * sqrt(27 * 10746.218459832^2 * 0.275625^4 + 4 * 44.42622815547907982077^3 * 0.275625^3) + 9 * 10746.218459832 * 0.275625^2)^(1 / 3)
A=32.32551993764664323864 meters per second
I have one doubt. In the Focbox UI App, when I limit Max battery amps, is this limit for the whole battery or is it per VESC?
If I set the limit to 35A, would the Unity be draining in some moment 70A (2x35A) or just 35A? My BMS is 60A rated.
I’ll just leave this here as it seems relevant. I was trying to decide between 10S5P and 12S4P. I went 10S5P, I think it just edges out in most categories probably because of the two extra cells total.
Make sure you are on the latest firmware, it was suspected for a while that is was “per VESC” and later confirmed that it was a bug. The newest firmware fixes this to be battery total.
ITs per ESC. So on a unity, you’d limit it to the full amount, and on twin focboxes youd limit it to half the full amount.
Ok, I have the last firmware version on my Unity, so should be total the total amount then.
thanks you both!
