Grin's rear all axle motor!

E-HP said:

This motor is starting to look interesting. Seems that with the 0.35mm laminations, it would be at least as efficient as my Leaf, and I'm guessing it could take 4kW-5kW or more for short bursts of acceleration. But, the couple of things that I really like are, the ability to use a quick release axle and skewers with my current frame, which would make flat repairs while on a ride a possibility; and the paired spoke holes for lacing my 24" rim radially.
Being able to use a cassette is nice, although I never shift anyway. But as long as it's serviceable (I wore out one freewheel, but that's an easier replacement than replacing a freehub), seems like a step in the right direction.

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I think this should realistically be capable of a bit more than 1kw continuous.

Do consider that it's got a 27mm wide stator, and so, it is at a disadvantage, efficiency wise, because it has a higher 'end turn loss to copper doing useful work' ratio than the 35mm leaf ( the 30mm/28mm leaf also lose efficiency )

Peak efficiency on the motor is around 88%, and this is actually impressive for a 27mm DD so i would say it's a particularly efficient motor considering that.

This is about as much power as you'd want to run continuously in an upright bike:

Motor Simulator - Tools



I wouldn't call it exactly up to the task of 4-5kw, maybe 3kw for very short periods of time. If you need to go below 70% efficiency during bursts, i think that's a sign you need a bigger motor. At 3kw, we're at 79% efficiency already.



The motor should be very good on a small wheel in a recumbent. There's a surprising amount of benefit from high RPM of the small wheel here. A pair of these on a trike would haul ass and have plenty of spare torque to climb hills.



Compared to the MAC motor i'd say that it is a better motor at equal weight because it's more efficient. If you need better heat dispersion, you could add ferrofluid also, whereas with the MAC, you can't.

I am surprised at how it maintains it's efficiency as you increase RPM. This may have to do with less eddy current losses VS a 35mm hub.

Honestly, i think it would be a killer motor for a semi/full recumbent, and a quite good motor for an upright bike. I'd pick it over a MAC for either.

Good info!

I just ran a simulation for using a Leafbike 4T in the rear at 144V/150A/10kW max, and two Grin 5T at 144V/150A/3kW max, running off a 144V 12.6AH pack of Molicel P42A in a 40S3P arrangement at 135A max total pack current, Mitas MC2 16x2.25" tires on each wheel. Assumed 320 lb laden weight, Crr value 0.009, and CdA value of 0.10 m^2.

We get the following:

0-10 mph: 0.7s
0-20 mph: 1.5s
0-30 mph: 2.4s
0-40 mph: 3.5s
0-50 mph: 4.8s
0-60 mph: 6.2s
0-70 mph: 8s
0-80 mph: 10.1s
0-90 mph: 12.5s
0-100mph: 15.5s

1/8 mile drag: 9.6s @ 76.6 mph
1/4 mile drag: 14.7s @ 97 mph
Top Speed: 23.9s @ 108.8 mph

So its acceleration performance would be on par with a new Subaru BRZ or new Mazda Miata. It would be slightly faster than the standard police Dodge Chargers, as well as significantly faster than the police Ford Explorers. Except it would be AWD, and the complete vehicle would weigh somewhere around 120-140 lbs(light enough to pick up and carry into a building in a pinch).

Human power was not accounted for. 500W of hard pedaling could easily cut 0.5s off the 0-60 mph time.

I'm intrigued. I should eventually build this.

The Toecutter said:

I only need to do so for about 15-20 seconds at a time. I'll be at 110 mph on flat ground by the time that has elapsed, considering there will be another Grin motor running the same input and a Leafbike running 10 kW peak.

I don't know if the Grin can handle 5 kW or not. Perhaps it could only do 2 kW peak, even with ferrofluid? Even so, that would still be quite usable. Temperature sensors with the CA3 set to dial the power back to prevent overheating will be a necessity.

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OK so you are basically using it as a motorcycle. Don't crash.

neptronix said:

I think this should realistically be capable of a bit more than 1kw continuous.

Do consider that it's got a 27mm wide stator, and so, it is at a disadvantage, efficiency wise, because it has a higher 'end turn loss to copper doing useful work' ratio than the 35mm leaf ( the 30mm/28mm leaf also lose efficiency )

Peak efficiency on the motor is around 88%, and this is actually impressive for a 27mm DD so i would say it's a particularly efficient motor considering that.

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I'm only talking about hard acceleration in bursts. Before swapping in the Leaf, I fed my 1000W MXUS ebay motor 4.5kW-5kW for short periods without any issues. Doing so for more than that and it would get hot. My thought is that the better efficiency would allow a bit longer bursts and with the temp sensor installed there'd be a way to rollback power when necessary.

richj8990 said:

OK so you are basically using it as a motorcycle. Don't crash.

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It's getting a roll cage.

The Toecutter said:

It's getting a roll cage.

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E-HP said:

I'm only talking about hard acceleration in bursts. Before swapping in the Leaf, I fed my 1000W MXUS ebay motor 4.5kW-5kW for short periods without any issues. Doing so for more than that and it would get hot. My thought is that the better efficiency would allow a bit longer bursts and with the temp sensor installed there'd be a way to rollback power when necessary.

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I’ve got an all axel on a globe3t scooter with a phaserunner. 72 volts and I pump 3500 watts. This seems to be an upper limit. The motor builds a lot of heat after about 10-15 minutes of thrashing and the phaserunner starts to dial back. I still have a blast on it. I might add a second motor to the front axel. It’s not like a big crystallite or mxus. Its lighter and heat soaks quickly. The stator can take the watts just not for long. I think the all axel could run even 4500watts but I would want to add a band of cooling fins around the outside of the motor. It seems if you are running a grin controller with the grin motor and you leaving the thermal protection in place then you are reasonably safe from doing damage.

Carlkoski said:

I’ve got an all axel on a globe3t scooter with a phaserunner. 72 volts and I pump 3500 watts. This seems to be an upper limit. The motor builds a lot of heat after about 10-15 minutes of thrashing and the phaserunner starts to dial back. I still have a blast on it. I might add a second motor to the front axel. It’s not like a big crystallite or mxus. Its lighter and heat soaks quickly. The stator can take the watts just not for long. I think the all axel could run even 4500watts but I would want to add a band of cooling fins around the outside of the motor. It seems if you are running a grin controller with the grin motor and you leaving the thermal protection in place then you are reasonably safe from doing damage.

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Thank you for that.

In my case, I'll be at top speed during full-throttle acceleration within less than 15 seconds, then the power will scale back because of BEMF buildup/flux saturation, with the Leafbike 1500W in the rear wheel providing the lion's share of the thrust. I'm only going to need about 4 kW electrically applied split between all three motors to hold somewhere around 90 mph on flat ground. I think I could get away with 4,500W without cooling on each all-axle motor in this context, because it will soon be below its continuous current rating once top speed is reached. It will also be extremely rare for me to demand that much power from any of the motors. And with built-in temperature sensors, it will scale back the current to prevent overheating anyhow.

So long as your coefficient of drag is under .1 you might make it. On my diggler scooter with a big crystalite motor I can sustain 40mph on about 1800 watts but it takes about 3200 watts to sustain 50.

Carlkoski said:

So long as your coefficient of drag is under .1 you might make it.

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He won't get there. That kind of Cd takes obsessive attention to both shape and surface finish, plus getting taped into your bike before a run.

Chalo said:

He won't get there. That kind of Cd takes obsessive attention to both shape and surface finish, plus getting taped into your bike before a run.

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I have a Milan SL velomobile in my possession with a Cd of 0.08 to copy the proportions of. It has a frontal area of 0.41 m^2. Overall CdA value is 0.03 m^2.

I need an overall CdA value of 0.10 m^2 or less to pull the above 4 kW @ 90 mph off. If I end up with a frontal area of 0.58 m^2, then that corresponds to a Cd value of 0.17 or less. Which is double the Cd value of the Milan in my possession.

My second body shell had a 0.20 m^2 CdA value according to data obtained using coast-down tests via the RChung method. It has outboard/open wheels which are very bad for drag. Based on this, I think cutting drag in half is a realistic goal considering the wheels are going to be enclosed this time.

The Toecutter said:

I have a Milan SL velomobile in my possession with a Cd of 0.08

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Claimed.

That's 60% of the Cd of an Aptera, from something that wobbles, flutters, and has wheel gaps in it. In the real world, it won't have the same Cd as a clay or foam model in a wind tunnel.

I think chasing unsafe speeds in an unsafe-at-any-speed vehicle with imagined drag numbers is a folly and a waste of time. But don't let me stand in your way.

Chalo said:

Claimed.

That's 60% of the Cd of an Aptera, from something that wobbles, flutters, and has wheel gaps in it. In the real world, it won't have the same Cd as a clay or foam model in a wind tunnel.

I think chasing unsafe speeds in an unsafe-at-any-speed vehicle with imagined drag numbers is a folly and a waste of time. But don't let me stand in your way.

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The Milan neither wobbles nor flutters. That thing is surprisingly solid, and remained so even when I careened down a steep hill at 89 mph. The steering does get twitchy after 40 mph or so, but it never felt as if the monocoque itself was unstable in the least. Being able to hit 50 mph on a flat section of Highway 141 with a mile and a half of full-effort sprinting and no motor suggests that the designer's claimed drag figure is somewhere close to what it is in the real world. Getting my custom build to replicate those results won't be easy, and is definitely not happening with coroplast, but I don't need to be as efficient as the Milan anyway.

Most of the Aptera's drag comes from its exposed axles, control rods and outboard wheels(although the fairings help minimize the penalty). If it were mostly sealed as certain high-end HPVs are, its Cd value would be significantly lower than 0.13.

My folly so far has yielded a flimsy kayak of death that can accelerate like a car and hold 50 mph. And I love it.

I have been running my V2 rear for 680 miles and it has lots of torque, runs about 10-15 degrees C cooler (it has ferrofluid) than my GMAC equipped bike. They both weigh about 52 lbs with the battery. The V2 is on a K2 full suspension 26" mt bike and the GMAC on a 29" Specialized Rockhopper. I have run both a little off road on gravel trails and both climb good, but the GMAC quickly over heats. Even riding on the paved bike path it is easy to get the GMAC hot. I have them both set for 3 profiles on the CA. I have a economy 350w, Legal 750w and fast 1500w settings. I am running 52V on both bikes.

zog1gig said:

I have been running my V2 rear for 680 miles and it has lots of torque, runs about 10-15 degrees C cooler (it has ferrofluid) than my GMAC equipped bike. They both weigh about 52 lbs with the battery. The V2 is on a K2 full suspension 26" mt bike and the GMAC on a 29" Specialized Rockhopper. I have run both a little off road on gravel trails and both climb good, but the GMAC quickly over heats. Even riding on the paved bike path it is easy to get the GMAC hot. I have them both set for 3 profiles on the CA. I have a economy 350w, Legal 750w and fast 1500w settings. I am running 52V on both bikes.

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Nice, I am thinking of getting a rear All Axle on a 29" bike. Do you suggest getting the slow winding for a big wheel like that? I live in the PNW so there are some hills around but I don't ride anything too steep.

mexican_amigo said:

Nice, I am thinking of getting a rear All Axle on a 29" bike. Do you suggest getting the slow winding for a big wheel like that? I live in the PNW so there are some hills around but I don't ride anything too steep.

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You might want to consider the RH212 for such a tall wheel. The higher pole count produces more torque, which a larger wheel needs. You may find the All Axle a little anemic in a 29" due to it's lower pole count.

Worth playing around with the ebikes.ca motor simulator to see the effect in action.

There is now a 3T wind version of this motor available. My two side All-axle motors for my KMX have been ordered, as has a 5T wind rear All-axle for my Milan SL velomobile.

I just looked on the website. Can you link the 3t version? I couldn't find it

I think there's currently a bug in the website. I went to their hub motors section, where it says there are 40 items, and get the message "We can't find products matching the selection." I'm unable to select any of the hubmotors they have available at this time. They may be in the middle of an update.

I let them know and it got fixed.

All axle on a 23" wheel sounds like my idea of a good time. I'm surprised it doesn't melt in this condition.

neptronix said:

All axle on a 23" wheel sounds like my idea of a good time. I'm surprised it doesn't melt in this condition.

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The all-axles all come with Statorade already in them, right?

That's not the case.
This is the effect of moderate 'gear down, volt up'.

Things get really crazy with a 20"

I've put in a deposit on the 45mm wide version. I'm super excited for it -- I had a DD45_FST that got stolen (along with the bike, lol) and miss it bunches, I'm betting the AA45mm is going to blow that one out of the water.

neptronix said:

All axle on a 23" wheel sounds like my idea of a good time. I'm surprised it doesn't melt in this condition.

View attachment 346902

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That's pretty awesome. I'd love to make a superlight EUC with an all-axle motor... I wonder how it would handle steep hillclimbing and the like though, might be asking a bit much when comparable motors all weigh a lot more (though I guess the relevant metric is copper weight..)

After many years of begging Justin for a rear motor version.. my wish is finally granted
Extremely impressed! great fit and finish + wheel build quality. Seen is a 24" Alex Rim.



Love the printed diagram on the motor! ( it's sharper than pictured, my phone camera is a bit crap )



What i dig most about this motor is that it shouldn't be any drama to change a flat tire due to the quick release and single bolt torquearm. The lower weight than a typical DD makes for easier manhandling on the side of the road to change a tube.

I remember the 16lbs leaf with 2 torque arms was a bear to replace a tube on. 5 bolts to free the motor. The fit was so tight that you had to hammer the motor in/out of the dropouts.

This hassle + the fact that my area has lots of tire flattening objects is what discouraged me from ebiking for a long time... i'm very happy to own a big part of the solution to that



I am still awaiting my em3ev battery. Should have first ride impressions in a week or two.