Calculating 0 to 80kph acceleration times. Are my Grin Tech Calculations Correct? QS 205 3T vs. 4T

[mbgjt1]

Hi all,

So, I have been using the Grin Tech motor simulator to simulate what my acceleration will be like from 0 to 80 kph.

The simulator does not have an option for the QS205 3T 50H V3 so I have gone with the Cromo 5004 and changed the kv to 15.6 (rpm/V).

• 17" rim, 24" outer diamter wheel.
  140 kg total weight of rider and vehicle.
  0% grade.
  80V nominal, 39Ah 22s13p battery.
  200 battery amps, 450 phase amps controller.

Simulation results attached.

As you can see it would take 9.26 seconds to accelerate from 0 to 80.7 kph. Does with match up with real life results? It seems abit slow. How can I reduce this time to 5 seconds or less? The motor will be mounted at the back wheel as a hub configuration, not a mid drive.

Any advice? What am I missing?

I've noticed it takes about 4.299 seconds to accelerate to 66 kph, which is still slow. I am hoping to achieve sub 5 second acceleration to 80 kph. Is this unrealistic in this configuration?

Thank you,

[MadRhino]

Those numbers are estimate, not reality checked. Your build can do better, or worse.

Best acceleration is achieved with: smaller wheel, lighter weight, lower aero drag.

[markz]

"4.3 seconds is still slow"


You building a drag strip ebicycle?

[serious_sam]

As you can see it would take 9.26 seconds to accelerate from 0 to 80.7 kph. Does with match up with real life results? It seems abit slow. How can I reduce this time to 5 seconds or less? The motor will be mounted at the back wheel as a hub configuration, not a mid drive.
Any advice? What am I missing?
I've noticed it takes about 4.299 seconds to accelerate to 66 kph, which is still slow. I am hoping to achieve sub 5 second acceleration to 80 kph. Is this unrealistic in this configuration?

I think the grin simulator is pretty accurate, but the parameters you use make a big difference. For example, battery internal resistance makes a big difference in that calculator. You used 0.2ohms. Where did you get this figure ? Look what happens when you change it to 0.1 ohms (for example). Oh and also you could use maximum battery voltage if you're looking to figure out maximum performance. The calculator will adjust for sag (based on the IR). See here: https://ebikes.ca/tools/simulator.html? ... &kv_b=15.6

Where did you get your spreadsheet data from ? It's a bit hard for us to verify it without looking at the actual data.

FWIW, my bike (26" wheel, 20S5P VTC6, 140kg, MXUS3k4T (Kv=9.2rpm/V, kt=1.04Nm/A), Nucular 12F @ 150Ab & 250Ap, field weakening on) does:
0-20km/h @ 1.4 sec
0-40km/h @ 2.8 sec
0-60km/h @ 4.9 sec
0-80km/h @ 8.6 sec
0-100km/h @ 20+ sec

Field weakening really changes things (it really boosts torque in the upper rev range) and unfortunately you can't replicate that in the motor simulator. This is my (non-FW) setup in the simulator, and it's pretty close to reality (you'll just have to trust me on that, I don't have any saved data to show you a comparison): https://ebikes.ca/tools/simulator.html? ... &wheel=26i I have compared it in the past, and if I recall correctly, it's within about 10 or 20%. It'll really depend on data you use in the simulator, and conditions during your road test.

This is logged data (with FW on) vs the simulator data (non-FW). As you can see, it's apples to oranges:

sim vs logs.jpg (46.31 KiB) Viewed 481 times

If you take your simulator plot and overlay mine (and add a bit of top end for field wekening), they're pretty close, so I'd say your estimated times (which are pretty close to my logged data) sound like they're in the ballpark of 0-80 in 8-9 seconds.

But I strongly doubt you could half that 0-80 time like without difficulty. It would require a significant increase in power.

[MadRhino]

You building a drag strip ebicycle?

Sure not with a hub motor.

Drag does need that kind

[mbgjt1]

Those numbers are estimate, not reality checked. Your build can do better, or worse.

Best acceleration is achieved with: smaller wheel, lighter weight, lower aero drag.

Hey man, I want to accurately determine if it is possible to get these speeds. There are people out there bragging that they can reach 0 to 100 kph in 3.5 to 4 seconds with the QS205 as a mid-drive motor, but I want to achieve this in a rear hub configuration.

I need to get this build right since I don't have the money to mess up, and having a sub- 5 second acceleration time would be awesome !

[mbgjt1]

"4.3 seconds is still slow"


You building a drag strip ebicycle?

I would love a 4.3 seconds 0 to 100 kph / 60 mph!

I can't seem to get a proper answer with regards to whether or not I can achieve this with a QS205 hub motor

[mbgjt1]

As you can see it would take 9.26 seconds to accelerate from 0 to 80.7 kph. Does with match up with real life results? It seems abit slow. How can I reduce this time to 5 seconds or less? The motor will be mounted at the back wheel as a hub configuration, not a mid drive.
Any advice? What am I missing?
I've noticed it takes about 4.299 seconds to accelerate to 66 kph, which is still slow. I am hoping to achieve sub 5 second acceleration to 80 kph. Is this unrealistic in this configuration?

I think the grin simulator is pretty accurate, but the parameters you use make a big difference. For example, battery internal resistance makes a big difference in that calculator. You used 0.2ohms. Where did you get this figure ? Look what happens when you change it to 0.1 ohms (for example). Oh and also you could use maximum battery voltage if you're looking to figure out maximum performance. The calculator will adjust for sag (based on the IR). See here: https://ebikes.ca/tools/simulator.html? ... &kv_b=15.6

Where did you get your spreadsheet data from ? It's a bit hard for us to verify it without looking at the actual data.

FWIW, my bike (26" wheel, 20S5P VTC6, 140kg, MXUS3k4T (Kv=9.2rpm/V, kt=1.04Nm/A), Nucular 12F @ 150Ab & 250Ap, field weakening on) does:
0-20km/h @ 1.4 sec
0-40km/h @ 2.8 sec0-80km/h @ 8.6 sec
0-100km/h @ 20+ sec

Field weakening really changes things (it really boosts torque in the upper rev range) and unfortunately you can't replicate that in the motor simulator. This is my (non-FW) setup in the simulator, and it's pretty close to reality (you'll just have to trust me on that, I don't have any saved data to show you a comparison): https://ebikes.ca/tools/simulator.html? ... &wheel=26i I have compared it in the past, and if I recall correctly, it's within about 10 or 20%. It'll really depend on data you use in the simulator, and conditions during your road test.

This is logged data (with FW on) vs the simulator data (non-FW). As you can see, it's apples to oranges:
sim vs logs.jpg

If you take your simulator plot and overlay mine (and add a bit of top end for field wekening), they're pretty close, so I'd say your estimated times (which are pretty close to my logged data) sound like they're in the ballpark of 0-80 in 8-9 seconds.

But I strongly doubt you could half that 0-80 time like without difficulty. It would require a significant increase in power.

Hey mate thank you for your thorough reply

It looks like it is fairly similar to the simulated results which is abit of a shame. There are people out there saying they can get under 4 second acceleration 0 to 100 kph using a QS205 as a mid-drive motor, but maybe they can achieve this with a high torque sprocket?

I would like to achieve this with a QS205 mounted as a rear hub but I'm not sure if this is possible, and was hoping that someone would share a build that is able to achieve this. Why are you only using 5P? With the VTC6, max discharge current is 30 Amps so you're getting 150 Amps max out of that battery pack... you could probably dump doulble that current into the motor. I wonder how things would change if you start running at 21s10p of VTC6!

Regarding the 0.2 Ohms, this was the standard on the simulator so I did not know which value to use. You're right, changing it to 0.1 ohm changes the speed quite a bit, less voltage loss I presume?

[serious_sam]

Why are you only using 5P? With the VTC6, max discharge current is 30 Amps so you're getting 150 Amps max out of that battery pack... you could probably dump doulble that current into the motor. I wonder how things would change if you start running at 21s10p of VTC6!

The problem is heat. If you just want to do one launch 0-100km/h sure more battery would be faster. But the problem is that these motors can only run a few kW continuously. Anything above that is only in short bursts. And that's with hubsinks and statorade. The motor is the weak link, not the battery.

The qs is a little bigger than the MXUS, but they're comparable.

Running a smaller wheel or geared mid drive would help, but there are still limits to what is possible.

[MadRhino]

Building a drag bike with a wheel motor is delusional. Acceleration does require gearing down to achieve competitive numbers. It does require a geometry design to be able to take full advantage of such acceleration. Then, the bike becomes a one-purpose specially that does not Make a good ride for anything else.

The fact is, we don’t need competitive acceleration numbers to be ahead in the city with an ebike. There are so many other factors that are giving us the advantage. I am laughing at other users of the streets who have much faster acceleration capability than I, simply because they can’t actually use it in a city context. They are not competing on fair grounds, against our highly maneuverable freedom and silent power. The higher the density in urban environment, the less power you need to be ahead when you have the advantage of freedom and maneuverability. A plain pedal bike can beat any motorcycle in dense downtown trafic. My fast ebike can beat any motorcycle anywhere in the city, unless the motorcycle rider doesn’t care about having all the police resources deployed after him. The fact is, drag racing times can only be an advantage in situations that are suitable for this. Most of the time, it is at disadvantage because of other factors.

[markz]

Buddy is going to end up with 3 ebikes, the first being a dragster, second beach cruiser and third mountain bike trail rider. Yet he doesnt have the money to mess up his drag bike. Something seems amiss tbh but we play along.

BTW people can brag all they want, do they have evidence is the question to ask those braggarts. Because that fish I caught the other day was a 12 pound Pike, and when I took a leak behind that big oak tree I must've made my mark 10 feet radius, standing still on that no wind day.

[mbgjt1]

Why are you only using 5P? With the VTC6, max discharge current is 30 Amps so you're getting 150 Amps max out of that battery pack... you could probably dump doulble that current into the motor. I wonder how things would change if you start running at 21s10p of VTC6!

The problem is heat. If you just want to do one launch 0-100km/h sure more battery would be faster. But the problem is that these motors can only run a few kW continuously. Anything above that is only in short bursts. And that's with hubsinks and statorade. The motor is the weak link, not the battery.

The qs is a little bigger than the MXUS, but they're comparable.

Running a smaller wheel or geared mid drive would help, but there are still limits to what is possible.

Very true, the only issue is I haven't had much experience with this motor so I don't really know how much it can handle before it is fried! I'll def try to use hubsinks and statorade, coupled to a 20" wheel instead of a 24.. hopefully it won't heat up during 8 second accelerations

[mbgjt1]

Building a drag bike with a wheel motor is delusional. Acceleration does require gearing down to achieve competitive numbers. It does require a geometry design to be able to take full advantage of such acceleration. Then, the bike becomes a one-purpose specially that does not Make a good ride for anything else.

The fact is, we don’t need competitive acceleration numbers to be ahead in the city with an ebike. There are so many other factors that are giving us the advantage. I am laughing at other users of the streets who have much faster acceleration capability than I, simply because they can’t actually use it in a city context. They are not competing on fair grounds, against our highly maneuverable freedom and silent power. The higher the density in urban environment, the less power you need to be ahead when you have the advantage of freedom and maneuverability. A plain pedal bike can beat any motorcycle in dense downtown trafic. My fast ebike can beat any motorcycle anywhere in the city, unless the motorcycle rider doesn’t care about having all the police resources deployed after him. The fact is, drag racing times can only be an advantage in situations that are suitable for this. Most of the time, it is at disadvantage because of other factors.

You're right, although I won't be in the city much, most of the driving will be done in areas where the speed ranges from 60 to 80 kph, so quick acceleration bursts from 50 to 90 kph are a must! But very correct, I guess I can't be too picky, especially when I am designing a bike that does 0 to 100 in under 10 seconds, and is also able to go offroad and in between traffic, and is less than half the weight of a motorcycle

Its still nice to be able to brag aobut super quick acceleration times, and to be able to beat any motorcycle and car from 0 to 80 kph

[mbgjt1]

Buddy is going to end up with 3 ebikes, the first being a dragster, second beach cruiser and third mountain bike trail rider. Yet he doesnt have the money to mess up his drag bike. Something seems amiss tbh but we play along.

BTW people can brag all they want, do they have evidence is the question to ask those braggarts. Because that fish I caught the other day was a 12 pound Pike, and when I took a leak behind that big oak tree I must've made my mark 10 feet radius, standing still on that no wind day.

fair point.. I guess I havent' seen proper evidence to back up their claims of super fast accelerations

[Chricious]

It's not that hard to achieve times under 5s to 100km/h with the QS250. Especially if it is the 50H version and the rider weight is well under 100kg. You just need to follow this guideline:

1. You need to decide which parameters you can change and which not.
1.5. The parameters which are influencing the 0-100km/h time are motor size, KV, controller, battery voltage, P-groups, cells, wheel size, tire tread, wheel weiht, over all weight, temperature, soil texture, wind, wheel base, weight distribution, rider skill level.
2. If the motor is not a variable and you want to stick with the 205 you need to make sure that your KV matches the V of your battery at 100% charge incl. sag to top out just over 100km/h.
3. If you can't choose the KV of the motor you need to adapt either the wheels size or the battery voltage to fit your purpose and a controller that can handle the voltage.
4. If you set up your, motor, wheel, controller and battery, you just need to increase the phase current until you achieve your desired numbers.

You could face several problems during this procedure. I.e. your battery is saging too much. So you would need to add more parallel groups or use better cells. I would recommend VTC6 18650 cells for a maximum power output.
If you max out the current of your controller you need to upgrade it to a BAC 8000 i.e.
If you top out under 100km/h you need to increase the tire diameter, or lower the motor KV or higher the battery voltage, or use FW.

If everything works fine and you are able to keep your front wheel down, but you experience wheel spin, you could change to a street tread and pre heat the tire and/or use a sticky drag strip for launching.

If you eliminated all the problems but you are still just a couple tens too slow you can heat your battery to ~50C to get the most power out of it.

If it's still not fast enough, you need a new motor and/or a new battery/controller, or loose weight.

But I'm pretty confided it will be possible for you to achieve those times with the 205, if you are following the guideline.

I'm able to get from 0-50km/h in about 5s on my ESK8 and e-scooter with 2kW. So it shouldn't be a problem to go 100km/h in the same time with 4-5x the power.

A guy with a modded Surron on YT claims he goes in 1.9s to 50km/h and in 5-6s to 100km/h using the BAC 8000 and a 72V Litespeed battery.