Stark Varg: Gearing for optimal range

[Erwin P]

Is there a significant range to be won with taller gearing and thus lowering the RPMs?

I do 2 hrs races with some of them actually having some quite long fast sections on them where we reach over 60 km/h.
I was wondering if adding some taller gearing would help me push another lap out of the battery since now i can do 1-1.5 hrs of the 2 hrs race.
Then i move to my 300 2 stroke and switch back to the Stark as soon as the generator put in enough juice for the rest of the race. The Stark is actually 30-45 seconds faster on 7-12 minutes laps so the second pitstop of around 45 seconds is well worth it. Would be cool though to get an extra lap out of it and thus even have a bigger performance gap over the total race.

Also i might move over to a Stark EX at the end of the year wich would be doing OTR events with fast open sections where battery capacity would be at it's very limit. Having a few percent more range would be a huge peace of mind.

 

[Philip]

The "sweet spot" for PMSRMs, often occurs at a mid-range RPM (e.g., 3,000–6,000 RPM for automotive applications.

https://grok.com/share/bGVnYWN5_9857d3c6-b356-4851-84f9-0b97f0b9cfbb

This is 30-60 km/h for the Stark Varg.

What is the average speed in your race?

 

[Erwin P]

Average speed last race was 40km/h incluiding the slow obstacle course where average speed was low going over logs/concrete obstacles etc.

In the OTR events that i would run in the future average speed wil be around 60, with top speeds close to 110/120km/h on the corn fields.

 

[Philip]

You have to run a computer simulation then!

 

[DaveAusNor]

Please let us know if you do the real life experiment and find you get more distance out of the bike with different gearing. I'd assume your races times on the same track would be similar or slightly improved.

 

[Erwin P]

Hard to tell though. All these races run once a year per specific track. Most are even prepared for just 1 day and are setup slightly different each year.

The race i did last weekend was the same i did a year ago. Then we had snow and hail around freezing with deep sucking mud. This year we had sun, 18 degrees, loose sand and a full year of Stark updates (plus me actually getting a bit better). So it's hard to compare the 2.

There is 1 track though where i could do some testing on CrossCountry (wich with us is a mix of MX and Enduro) but that doesn't really have long fast sections.

Also average speed might be a bad indicator. Because in the slow sections you don't cover a lott of ground so efficiency isn't all that important. In the fast sections you cover lot's of ground.
I think a better measure would be how much of the distance is high speed (>60 km/h), how much moderate (30-60 km/h) and how much is slow stuff (<30 km/h).

Too bad the Stark phone saves about 10% of the rides and somehow mostly those from home to the van so i have no data on most races.

 

[Theo]

The "sweet spot" for PMSRMs, often occurs at a mid-range RPM (e.g., 3,000–6,000 RPM for automotive applications.

https://grok.com/share/bGVnYWN5_9857d3c6-b356-4851-84f9-0b97f0b9cfbb

This is 30-60 km/h for the Stark Varg.

What is the average speed in your race?

I like the idea of considering in which rpm range the motor is the most efficient, but I think that the AI has confused things here, since as far as I know the Varg motor is a purely permanent magnets motor, while the permanent magnets reluctance motor is a special hybrid solution used in Teslas. When asked which kind of motor is used in the Varg, the AI replied permanent magnets but in its last answer it said that the Varg motor is an example of permanent magnets reluctance motor.
A pure permanent magnets motor should have the highest efficiency in the first half of the rpms range, as far as I've learnt.

Also average speed might be a bad indicator. Because in the slow sections you don't cover a lott of ground so efficiency isn't all that important. In the fast sections you cover lot's of ground.
I think a better measure would be how much of the distance is high speed (>60 km/h), how much moderate (30-60 km/h) and how much is slow stuff (<30 km/h).

A simplified way of looking at the situation is to state that what the powertrain and battery do is to convert the chemical energy into kinetic energy. Kinetic energy depends on the square of the speed, so in order to accelerate from 0 to a certain velocity v you need a third of the energy needed to accelerate in the same time from v to 2v, for example.

Spoiler: calculation

ΔK=Kfinal-Kinitial
K=v²m/2
ΔK from 0 to v = (v²m/2)-0=v²m/2
ΔK from v to 2v = (4v²m/2)-(v²m/2)=3v²m/2

Since we don't ride at constant speeds, we should worry about energy consumption while acceleraing and accelerations at higher speeds will be more energy consuming. Aerodynamic drag also increases not linearly.
So I guess that average speed might indeed not be a good indicator and that if two sections have the same time duration, the one with higher speeds will be more energy consuming.

Bottom line: in order to optimize efficiency, I would choose a gearing that really minimizes time spent beyond the first half of the rpms and see whether the bike still has an acceptable acceleration.

 

[Philip]

I like the idea of considering in which rpm range the motor is the most efficient, but I think that the AI has confused things here, since as far as I know the Varg motor is a purely permanent magnets motor, while the permanent magnets reluctance motor is a special hybrid solution used in Teslas. When asked which kind of motor is used in the Varg, the AI replied permanent magnets but in its last answer it said that the Varg motor is an example of permanent magnets reluctance motor.
A pure permanent magnets motor should have the highest efficiency in the first half of the rpms range, as far as I've learnt.

I see your point, you are right. I asked Grok again and the answer came out better tailored but still similar to what it said before. Its efficiency likely peaks (e.g., 94-96%) at a mid-range RPM (perhaps 5,000–7,000 RPM).

https://grok.com/share/bGVnYWN5_51db0bfb-2da9-41d5-bda3-5920f132f68e

 

[Erwin P]

I used around 10.3% per lap (8 laps used 83%, each lap rougly 7:30 min). However in the fast farmland section i could see it drop 4% in just under 1 minute. So that short sprint eat up an over reprecented part of the battery. In the obstacle section i couldn't catch in right before and after on the video, but 1:30 min took 1% of battery.
If i could win 10% efficiency on the fast bit and loose 10% on the slow part that would be a huge win.

Acceleration is not so much an issue. I could always go for a higher HP setting and it's about me lasting 2 hrs, so full power all the time is not only a waste of battery, but also of my body. So the times i go full throttle are very rare.

Also actuall speed might be good enough in street racing, but here with all the sand there is actually quite a bit of wheelspin, just less thottle would cost a lott of stability so that's not really an option. I'm too much of a novice in E motors to know if there is a huge loss at ''freereving'' at higher rpms. So maybe that should also be taken into concideration that actuall RPM's are higher than the ground speed in quite some sections.

This is the last race i was talking about. The first lap and an average lap.

 

[Johnny Depp]

I’m convinced this is the way, better rideability and range. RPM and wheelspin is the enemy.
Waiting for someone to prove it. Sprockets are cheap, ridiculous torque to pull it.
It’s also likely that dialing down regeneration would have similar effects. Braking is the enemy, rolling momentum is desirable. The drivetrain already has a lot of built in drag.
It’s also likely to have less heat and thermal limiting.
The advantage vs gas is more defined in lower rpm ranges, up in the rpms the advantage is less.

 

[OpaTsupa]

.... Then i move to my 300 2 stroke and switch back to the Stark as soon as the generator put in enough juice for the rest of the race. ...

Off topic:
I'm curious to know how this is working for you. It's what I plan to do if Varg's range isn't enough for certain rides.
How is the transition to shifting, foot-braking and engine noise when racing?
Perhaps you could say a few words on how 2T 300 (Beta?) compares in general to the Varg.
Do you ever ride somewhere that isn't flat and bellow sea level.
Thanks.

 

[Erwin P]

I’m convinced this is the way, better rideability and range. RPM and wheelspin is the enemy.
Waiting for someone to prove it. Sprockets are cheap, ridiculous torque to pull it.
It’s also likely that dialing down regeneration would have similar effects. Braking is the enemy, rolling momentum is desirable. The drivetrain already has a lot of built in drag.
It’s also likely to have less heat and thermal limiting.
The advantage vs gas is more defined in lower rpm ranges, up in the rpms the advantage is less.

I could experiment a little on one off my regular bigger MX tracks. Wouldn't be the best comparison to my races, but at least we'll see a difference if there is any. I have 12-13-14-15 sprockets on stock (shares those with our Beta's).

Maybe on a quiet day (so the ruts don't change too much) do 2 or 3 laps at the time with camera focused at the dash an see how it performs with each front sprocket.

Shame it's not road legal. On the road it would be much easier to compare the exact same lap with the exact same speeds.

 

[Erwin P]

Off topic:
I'm curious to know how this is working for you. It's what I plan to do if Varg's range isn't enough for certain rides.
How is the transition to shifting, foot-braking and engine noise when racing?
Perhaps you could say a few words on how 2T 300 (Beta?) compares in general to the Varg.
Do you ever ride somewhere that isn't flat and bellow sea level.
Thanks.

It's a Beta RR 300 Racing from 2021. So KYB in front, Sachs in the back.
From 23 onwards they have MYB front and rear and should be a better transition with the Stark.
However being an enduro bike it's far softer with all pros and cons. For racing i would love to set it up the same, but the Beta is my abroad enduro travel bike as well.

I have mixed feelings, the Beta is a wonderful bike, but it feels so outdated compared to the Stark.

Shifting isn't really an issue, i gear it low'ish at 13-49 so it doesn't stall anywhere. The vibrations sure are annoying the first lap (even though it's quite the smooth engine for an ICE), but workable. Noise is a bit annoying in singletrack, but doesn't really bother me and really like it blasting higher speeds.

The real issue is switching from hand to foot brake. When riding my 300 on bigger rides it's no issue, but switching takes some time. Especially in "panic" breaking where you pull the clutch instead of the rear brake making everything even worse.
I have now installed a dual brake on my Stark to make it an easy'er transit (and braking hard is easy'er on the body with a foot brake). Only ridden that once and was in the mentioned race though so should be getting used to that in the future.

The Stark i have only used once in hillclimb terrain at Pascuet Enduro domaine, same for the 300. But my previous Beta 250 2 stroke i've used in the mountains of Pascuet, the Balkans and Spain. It hardly suffered from less air at 2200m altitude.

Edit: Hillclimbs i had the shitty stock rear tyre of the Stark on, but it was a huge help to not have to shift while climbing. The suspension was on the hard side though where the Beta Racing shines for being compliant.

 

[Upinsmoke57]

Are the stock MX bikes still shipping with a 14 sprocket where the Enduro models ship with 13? If so that kind of says something right there. I ordered the enduro but it came with a 14 which the dealer later told me was the wrong one for my bike. I don't think it really makes that big of a difference as I now have the 13 on and I'd be lying if I said it was noticeable. The terrain is the furthest thing from consistent so how would one be able to measure efficiency? My main goal was to minimize wheel spin and I wasn't sure if that made a difference. I also had this discussion with a friend who's an engineer at Lucid. He said, in short, as long as you're in the useable torque curve it shouldn't make much difference in terms of efficiency. But I also think he was dumbing it down a lot for me to understand as I'm sure it's not that simple of an answer.

 

[Erwin P]

Well that's a reason why i would love to have a roadlegal Varg. That way you could test under the exact same circumstances.
I do have the feeling on the really fast bits (not in this video/track) of ''over revving'' the engine. Almost as if you get past a powerband.

Here is a dyno chart from a very early Stark MX 80 hp comparing to a YZ450. You can forget about the lower YZ450 line, but the upper one is interesting. The 80hp being full power actually shows it's peak performance and thus efficiency.
Below it we have the same dyno showing hp per 10hp setting.

It however isn't the full picture yet since actually the torque is the efficiency and with the curves in those lines it doesn't seem to be fully lineair.

 

[Erwin P]

I also found one on the torque that someone calculated from the HP dyno from above video:


If we take this to be true one would say the peak efficiency ends at 43 mph/69km/h.
If you with my riding involving 70 km/h as is now (and far more when it would be road legal in OTR events) you would think a higher gearing would actually shove this point to higher speeds and thus being more efficient.

I do also wonder if the taller gearing would stop wheelspin from happening that often. If the bike has to work harder at the same RPM you would think it had less power to spin away.

 

[OpaTsupa]

It's a Beta RR 300 Racing from 2021. So KYB in front, Sachs in the back.
From 23 onwards they have MYB front and rear and should be a better transition with the Stark.
However being an enduro bike it's far softer with all pros and cons. For racing i would love to set it up the same, but the Beta is my abroad enduro travel bike as well.

I have mixed feelings, the Beta is a wonderful bike, but it feels so outdated compared to the Stark.

Shifting isn't really an issue, i gear it low'ish at 13-49 so it doesn't stall anywhere. The vibrations sure are annoying the first lap (even though it's quite the smooth engine for an ICE), but workable. Noise is a bit annoying in singletrack, but doesn't really bother me and really like it blasting higher speeds.

The real issue is switching from hand to foot brake. When riding my 300 on bigger rides it's no issue, but switching takes some time. Especially in "panic" breaking where you pull the clutch instead of the rear brake making everything even worse.
I have now installed a dual brake on my Stark to make it an easy'er transit (and braking hard is easy'er on the body with a foot brake). Only ridden that once and was in the mentioned race though so should be getting used to that in the future.

The Stark i have only used once in hillclimb terrain at Pascuet Enduro domaine, same for the 300. But my previous Beta 250 2 stroke i've used in the mountains of Pascuet, the Balkans and Spain. It hardly suffered from less air at 2200m altitude.

Edit: Hillclimbs i had the shitty stock rear tyre of the Stark on, but it was a huge help to not have to shift while climbing. The suspension was on the hard side though where the Beta Racing shines for being compliant.

Thanks.
That's pretty much how I imagined it.

I also have a 2021. Beta 300 RE.
If you care to tune the Beta for hill climbs then consider the S3 Extrem Head. It turns it into an EV, and I don't say that lightly.
All I ride is hills, and where I had to shift, clutch and leg-peddle, now I can tractor up in any gear. (13-48 sprockets for me)

 

[Johnny Depp]

I could experiment a little on one off my regular bigger MX tracks. Wouldn't be the best comparison to my races, but at least we'll see a difference if there is any. I have 12-13-14-15 sprockets on stock (shares those with our Beta's).

Maybe on a quiet day (so the ruts don't change too much) do 2 or 3 laps at the time with camera focused at the dash an see how it performs with each front sprocket.

Shame it's not road legal. On the road it would be much easier to compare the exact same lap with the exact same speeds.

I think a lap time comparison would also be revealing. I'm not sure you could accurately measure battery usage in a few laps?

 

[Johnny Depp]

I also found one on the torque that someone calculated from the HP dyno from above video:
View attachment 13439

If we take this to be true one would say the peak efficiency ends at 43 mph/69km/h.
If you with my riding involving 70 km/h as is now (and far more when it would be road legal in OTR events) you would think a higher gearing would actually shove this point to higher speeds and thus being more efficient.

I do also wonder if the taller gearing would stop wheelspin from happening that often. If the bike has to work harder at the same RPM you would think it had less power to spin away.

Now you are getting what I was saying. With a gas bike like my Beta 480, the rideability goes up with taller gearing. Less wheelspin and clutch and shifting, just cruise and it's got so much torque and flywheel stalling isn't an issue. The optimum spot for me is 15/48 which for most is considered street gearing (I go to 45 on the street). This won't work with a smaller bike with less torque, you need massive torque to pull it off, exactly what the Stark has in spades. The Stark has more torque at the first crack of the rpms than the YZ450 has at any point in any gear. It can absolutely pull the tall gearing, and tuning with the tallest gear the bike can pull has always been my go to.

 

[Erwin P]

I think a lap time comparison would also be revealing. I'm not sure you could accurately measure battery usage in a few laps?

Not quite sure though. Lap times may be interrupted badly by messing up 1 corner. Also another feel to a bike might slow you down at first, so might be misleading.

As for battery usage on a few laps. It's a 2:30 to 2:45 min lap on a sandtrack. Just 35/40 minutes is needed to drain the battery. So just 16 laps will do 95-10% Wich would be roughly 16% in 3 laps. It might be a bit short to get a good measurement, but doing much more would drain my own energy too much to actually produce a good outcome for al 4 front sprockets. Doing it over different days the sand track would change too much (you'd be amazed by how much the corners change per day). Hardpack would be much easier to get proper results.
I can ride much longer than 4x 7,5 minutes, but for the results i need to be the same for all 4 runs + a scouting run to not get any surprices into my first session.