Grin's rear all axle motor!

[kuromaku]

Has anyone tried to push the motor to its limits and discovered its real-life limitations?

Maybe not "to the limits," but here's my dual (narrow) GAA setup with a 14S battery stack at nominal:


(edit: wrong image pasted in)

The design was to climb an ~8%, 10km hill at 40°C ambient carrying up to 10kg of additional mass in luggage. I'm assuming the motor simulator temperature rise is assuming a 20°C ambient, so it predicts ~73°C steady-state temp, and I'm seeing about 66°C on both motors at the top of the hill with ~30°C ambient we've been experiencing lately, so I'll call that good.

It'll get me to 40kph in about 3.5 seconds on flat ground, and still produces enough torque at a standstill to get started reasonably quickly on a 15% grade:

 

[neptronix]

That's kind of disappointing for a dual motor setup @ 20% efficiency, and with smaller wheels too.

Ever since Justin told me about dual motor shengyi setups, i haven't stopped thinking about them.



Geared motors are a lot stronger in the low RPMs. Look what happens when we combine the two motors



Strangely enough, we're kicking the leafbike 1.5kw's ass here with the same total motor weight.. in this situation, the motor is making 1.5kw of heat, lol..

 

[vladrov]

Hi, when ordering the All-Axle motor custom wheelbuild, there is a field for "Spoke Colour x32." The options are:
- none
- Sapim Strong Spoke, Butted 13-14 Silver
- Sapim Strong Spoke, Butted 13-14 Black

Am I correct in assuming that the "none" option is a mistake and that you should always choose one of the other options? It seems like you are not actually selecting a color, but rather choosing whether or not to include spokes. With "none," there would be no spokes, which doesn't make sense.



Do you refill ferrofluid? I live in Europe, and the shipping from Canada is expensive. I would like to buy some now to avoid having to search the European market for ferrofluid or pay for costly shipping from Canada in the coming years, in case a refill is necessary.

And lastly, although it probably doesn't matter for my order because there are no alternatives, are the Alex rims that Grin offers of good quality?

 

[Epithemeus]

Hi, when ordering the All-Axle motor custom wheelbuild, there is a field for "Spoke Colour x32." The options are:
- none
- Sapim Strong Spoke, Butted 13-14 Silver
- Sapim Strong Spoke, Butted 13-14 Black

Am I correct in assuming that the "none" option is a mistake and that you should always choose one of the other options? It seems like you are not actually selecting a color, but rather choosing whether or not to include spokes. With "none," there would be no spokes, which doesn't make sense.

View attachment 359060

Do you refill ferrofluid? I live in Europe, and the shipping from Canada is expensive. I would like to buy some now to avoid having to search the European market for ferrofluid or pay for costly shipping from Canada in the coming years, in case a refill is necessary.

And lastly, although it probably doesn't matter for my order because there are no alternatives, are the Alex rims that Grin offers of good quality?

The none option is for those building their own wheels or using it for non wheel purposes.

From what I remember ferrofluid refills are a thing that needs to be done, but only like... Every 5 years kind of timeframe.

 

[vladrov]

I am playing with the motor simulator and found that the All Axle with standard winding with ferrofluid on 96V delivers high efficiency results. It can also be pushed to very high power for short periods of 1 to 5 minutes.

The higher efficiency can be observed with the standard motor winding; the voltage itself does not affect the efficiency. Voltage only influences the maximum speed of the motor.

The improved efficiency is due to the increased copper fill in this version of the motor.

Here is what Justin from Grin Tech wrote to me:

The primary reason for this is due to the standard 8x8 winding having a slightly higher copper fill factor than the fast wind in this case. 8x8 is 64 strands in each slot, vs 12x5 or 60 strands in the fast motor (same as the stanard motor at 10x6). So there is more copper in an 8x8 winding than a 12x5, 10x6, or for that matter 6x10 winding. A 9x7 or 7x9 winding is quite close at 63 strands.

The difference is fairly marginal, but it is there. A bit more copper means in each slot means a bit lower copper losses for the same motor torque and hence a slightly higher efficiency. The resistance of the cable lead from the windings to the L10 connector plase a small role as well, as this gauge wire does not scale with the motor winding but is fixed across all of them.

At first, I was a little confused because, on the Grin website, the standard version is described as 6T, not 8x8, as Justin wrote. I contacted Grin again, and they told me that they use different terminologies on their website. I'm not sure what that really means or how there can be different terminologies for turn count, but I trust that the higher efficiency of the standard winding is real.

The standard winding of the All-Axle motor is indeed slightly more efficient compared to the slow and fast versions due to a higher copper fill. Justin's description of the standard version having an 8x8 winding is accurate. The confusion might stem from different terminologies used on our website.
- To clarify, the standard version with an 8x8 winding is approximately 1-2% more efficient as indicated in our motor simulator.
According to Grin, the motor can handle high torque.

According to Grin, the motor can handle high torque.

Here is my question and the response from Grin:

Would operating the motor up to 115 Nm be technically problematic, assuming temperature is monitored and automatically throttled?

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

The All-Axle motor will perform up to 115nm just fine. Although it appears like you are trying to build a motorcycle, this is a bicycle motor and we will not be taking any responsibility for the damage caused by running such high power at such a high speed.

 

[neptronix]

115nm can happen, but at a great efficiency loss under high load.
You will make quite a bit of heat too.

Also we have all the torque on one of your chainstays instead of on both.. seems dangerous to me.

if you want that kind of torque i'd consider a leafbike 30mm or RH212 with dual torque arms. Both should be able to take short blasts of 3kw here and there

 

[vladrov]

115nm can happen, but at a great efficiency loss under high load.
You will make quite a bit of heat too.

Also we have all the torque on one of your chainstays instead of on both.. seems dangerous to me.

Hmm, good point. I haven't really considered whether the bike frame can handle that. I'll think about it more and report future developments here.

 

[neptronix]

Yeah.. dual torque arms on a bigger motor makes for a safer distribution of load.. consider if you have an aluminum frame, that frame has a finite amount of motion until it snaps.

Personally i like the Grin v7 torque arms for this, with the downside of the tire change being a pain in the ass. ( sealant would be a good idea )

The 5 minute burst rating for the RH212 is as such, about 60nm.



Versus the Grin All Axle Standard winding at 50nm.



I would honestly not go past 90nm peaks on the All Axle. The phaserunner at maximum settings is pretty well matched to the motor.

 

[fenomeno]

Hi
Do you think that the torque arm is indispensable for this rear motor?
Up to what level of torque do you think it is the limit to avoid it usage?
Thanks.

 

[gromike]

The all-axle has an integrated torque arm. You shouldn't need to add one on the other side, unless you plan to run crazy amps through it.

 

[fenomeno]

Thanks
What do you mean for integrated torque arm?

 

[neptronix]

Hi
Do you think that the torque arm is indispensable for this rear motor?
Up to what level of torque do you think it is the limit to avoid it usage?
Thanks.

The rear dropouts of a bike are not built for this kind of power and will be ruined in short order if you don't use a torque arm.

I would start thinking about torque arms at 500w ( peak, not continuous )
I would start thinking about 2 torque arms above 1000w.
For the grin all axle, the single torque arm it comes with is sufficient.

 

[offGridDownUnder]

Thanks
What do you mean for integrated torque arm?

The All-Axle includes a torque arm designed just for it:
https://ebikes.ca/pub/media/wysiwyg/GrinHub/Axle_Interfaces.png

 

[fenomeno]

The rear dropouts of a bike are not built for this kind of power and will be ruined in short order if you don't use a torque arm.

I would start thinking about torque arms at 500w ( peak, not continuous )
I would start thinking about 2 torque arms above 1000w.
For the grin all axle, the single torque arm it comes with is sufficient.

Thanks neotronix.
Then behind or equal to 350w continuous (350w / 48v =7,2 amps) you propose mot to use torque arm.
Do you think that a thru axle carbon frameset will withstand the load. A profesional biker applys 400w in a uphill. Me 250/300w plus the motor.
Which Throttle % domyou think are 7,2 amps For this motor? Frankly speaking I do not need much more to follow my colleagues, they are almost profesionals.

 

[neptronix]

Carbon frames? i wouldn't use them. They can fail spectacularly without warning during non electrified usage. Not worth the risk to save a few pounds with one of those frames vs an aluminum frame. Motor + human power = more forces against a type of frame not known for being resilient.

A few pounds also won't matter with your human power doubled at all.

If you have a programmable controller, 350w could = 100% throttle if you programmed it as such.

The grin all axle motor requires use of a torque arm by design.

If you just want to double human power, i'd suggest you get a cheap bike with oldschool 135mm quick release, run a 4-5lbs dual reduction motor at 300w with no torque arm, and enjoy.

$299 for this bike. The +5 lbs versus your carbon bike won't matter at all. Will include low tier parts but this company produces quality frames that are made in Taiwan.
Save up to 60% off new Hybrid Bicycles | Adventure Hybrid 29er Bikes Elite Adventure Sport Trail

 

[fenomeno]

Carbon frames? i wouldn't use them. They can fail spectacularly without warning during non electrified usage. Not worth the risk to save a few pounds with one of those frames vs an aluminum frame. Motor + human power = more forces against a type of frame not known for being resilient.

A few pounds also won't matter with your human power doubled at all.

If you have a programmable controller, 350w could = 100% throttle if you programmed it as such.

The grin all axle motor requires use of a torque arm by design.

If you just want to double human power, i'd suggest you get a cheap bike with oldschool 135mm quick release, run a 4-5lbs dual reduction motor at 300w with no torque arm, and enjoy.

$299 for this bike. The +5 lbs versus your carbon bike won't matter at all. Will include low tier parts but this company produces quality frames that are made in Taiwan.
Save up to 60% off new Hybrid Bicycles | Adventure Hybrid 29er Bikes Elite Adventure Sport Trail

If you have a programmable controller, 350w could = 100% throttle if you programmed it as such.
Thanks but I tried to mean for the motor with baserunner controller. Which % Of the throttle are 7/8 amps 350w?

The grin all axle motor requires use of a torque arm by design.
An external torque arm? Why?

 

[neptronix]

It depends on how many amps you set in the controller. Set the controller to draw 7.2 amps and you get 350w at 100%. Set the controller to draw 72 amps and you'll get 350w at 10%.

The grin has an external torque arm so it can fit whatever weird dropouts you want. That means we can't use the standard rectangular axle shape that fits a bike with quick release dropouts. More details are on the product page for it.

The motor needs a torque arm because it's a 1000w rated motor. Would be an uncommon choice for someone to order one that's looking for 350w. It also does regenerative braking, and you really want a torque arm for that no matter the power.

 

[offGridDownUnder]

Then behind or equal to 350w continuous (350w / 48v =7,2 amps) you propose mot to use torque arm.

Without something to restrain the motor, it will just wind itself around until it pulls the electrical cables out. The motor has a section that turns (usually the spokes come out of this to the rim, etc.), and a part that must remain stationary relative to the frame - fork or rear dropouts.

But the torque the motor makes goes both ways, so there must be something to hold the stationary part. The classic bicycle design did not have this problem - just the problem of mounting the axle to the frame. So there is a hole in the frame large enough for the axle. But wait - you need to be able to take the wheel and axle out and put them back - so there is a slot instead of just a hole. 3/8" originally, which translates well to 10mm.

So, at first, people tried to restrain the motor axle using that 3/8" or 10mm slot by using a 12mm axle with flats - because the slot was already there and they didn't know any better. This is horrible leverage against the axle and beyond the tiniest motor there is a great likelihood of spinning the axle in the slot, which machines the fork or dropout into a bigger circle (and destroys your motor, as above). It's really not worth it - that part of the bicycle frame is just not designed for the job.

Use a torque arm instead of buying a new frame every few months. Don't try to nickle-and-dime it, just put on a torque arm and then you won't need to worry about it.

Grin and some others design torque arms so they have a slot at the end of the arm, so dropping the wheel only requires loosening one extra small bolt - it can remain in the fitting so it's there when you put the wheel back.

Do it right once and then you don't need to think about it again.

 

[neptronix]

 

[fenomeno]

The motor needs a torque arm because it's a 1000w rated motor. Would be an uncommon choice for someone to order one that's looking for 350w. It also does regenerative braking, and you really want a torque arm for that no matter the power.

Then I reached the point I wanted to 350w/1000w = 35% of the throle...

I knew that we were going to reach this point in the conversation. What in hell are you focusing on this product? It is pricy, weighty, 1000 watt!!!
I own this BMC with Mahle X20 bike. It works fine but I can't hack the speed limit. I ride with semiprofesional people (they ride 10.000km per season) and I'm not. It is hard for me to follow them with a 13 kilos bike, in flat terrain at 35km/h riding in a short steep slope after 100 kms of route. Then as it is impossible to hack what I own and after a season being able to follow them in the uphills, something that did not happened in the past, I want to DIMyself electric bike. If possible I'd like to focus in a thru axle rear hub motor (it is the next future) I'd like to focus in a cassette torque sensor (it is the next future) I'd like to focus in a light motor 250w continuous with no overheating (almost impossible for a geared)
And this where I am. It seams that I will have to wait until truckrun put the RN04 properly in the market or not if you give me your advice... (There is also this Bofeili rear hub motor but being honest I do not trust on them)

I you want to share your knowledge I will be more than greatfull...

Thanks

 

[fenomeno]

Without something to restrain the motor, it will just wind itself around until it pulls the electrical cables out. The motor has a section that turns (usually the spokes come out of this to the rim, etc.), and a part that must remain stationary relative to the frame - fork or rear dropouts.

But the torque the motor makes goes both ways, so there must be something to hold the stationary part. The classic bicycle design did not have this problem - just the problem of mounting the axle to the frame. So there is a hole in the frame large enough for the axle. But wait - you need to be able to take the wheel and axle out and put them back - so there is a slot instead of just a hole. 3/8" originally, which translates well to 10mm.

So, at first, people tried to restrain the motor axle using that 3/8" or 10mm slot by using a 12mm axle with flats - because the slot was already there and they didn't know any better. This is horrible leverage against the axle and beyond the tiniest motor there is a great likelihood of spinning the axle in the slot, which machines the fork or dropout into a bigger circle (and destroys your motor, as above). It's really not worth it - that part of the bicycle frame is just not designed for the job.

Use a torque arm instead of buying a new frame every few months. Don't try to nickle-and-dime it, just put on a torque arm and then you won't need to worry about it.

Grin and some others design torque arms so they have a slot at the end of the arm, so dropping the wheel only requires loosening one extra small bolt - it can remain in the fitting so it's there when you put the wheel back.

Do it right once and then you don't need to think about it again.

Fully understood.
But I'm sure it can be defined a Torque / amps limit to the motor behind it the motor do not slips and can stay in their original mounting position with the help of the thru axle lock. Don't you think it can be calculated? I'd like to avoid the installation of the external torque arm. I'm road bicycle enthusiast.
There is another question that what in the hell to use this motor, if you are going to limit it's power...

 

[chuyskywalker]

I knew that we were going to reach this point in the conversation. What in hell are you focusing on this product? It is pricy, weighty, 1000 watt!!!

Because that's the motor this thread is about. If you would like more general advice, build info, etc, you should probably start a separate thread.

 

[offGridDownUnder]

what in the hell

Did you intend "why in the hell" here?

Assuming, then this is the only thru-axle motor I know of. I used one on my Cruzbike conversion (rear of the Cruzbike, using a front wheel - they're backwards). I don't know if the clamping force for a thru-axle matches the force of nuts or a QR skewer - perhaps you already know this?

If you don't like a torque arm because of the aesthetics, think about having a 220mm drum as your hub - that is the outer envelope of an All-Axle - perhaps the torque arm isn't the most visible aspect? I doubt people would remark on the torque arm and miss the motor casing.

Two variants of the v3 rear incorporate torque sensors in the freehub, Grin rates it at 250W in a scenario they say meets Euro/Asia specs, and at 4kg, it's heavier than a small Bafang, but much lighter than most other DD motors. Grin provides nothing that mates an All-Axle with a drop-out slot for anti-rotation.

I'd like to avoid the installation of the external torque arm. I'm road bicycle enthusiast.

Well, you suggest you can't use your BMC, so you'll need to pick something else. But you also want to avoid gears - that cuts out the small Bafangs and the SX2. The DD (Direct Drive, just so we're on the same page) Crystalyte SAW20 works for 75mm front forks only.

Actually, if you are bothered by a torque arm because you are a road bicycle enthusiast, why is the boost motor and bits on the BMC acceptable? What is it about the torque arm that is an issue that the boost motor and fittings isn't?

I'd reconsider about the small Bafangs and buy a couple of extra gear assemblies against the day. I bought a spare gear assembly for my SX2. I replaced the SX2 with a v3 All-Axle, and it's true that the SX2 is quiet (compared to the previous GMAC), but the All-Axle is quieter still. I haven't run a Bafang hub, but they are reputed to be quiet.

Another option is to paint the torque arm so it blends in? Others may not notice it as much as you think they will, but you know your friends.

A concern if you try to use a motor restrained by axle flats - your drop-out must be well fitted for the job, and that is not a design requirement for any higher-end bicycles - they aren't interested in your (or my) DIY. You're stuck with what they provide, and you had best shop with that in mind to get the least-worst drop-out slot.

And further along that path - if you enable regen on a motor held by axle-flats, you had better search for a very good and very tight fit between drop-out and flat. I'd want steel axle, steel nuts, and steel frame, and think about seriously over-torquing the nuts before I trusted that that arrangement wouldn't loosen itself during a ride.

But try it if you want to. I'd be interested in hearing of an approach using your requirements that works - let us know.

 

[fenomeno]

Did you intend "why in the hell" here?

Assuming, then this is the only thru-axle motor I know of. I used one on my Cruzbike conversion (rear of the Cruzbike, using a front wheel - they're backwards). I don't know if the clamping force for a thru-axle matches the force of nuts or a QR skewer - perhaps you already know this?

If you don't like a torque arm because of the aesthetics, think about having a 220mm drum as your hub - that is the outer envelope of an All-Axle - perhaps the torque arm isn't the most visible aspect? I doubt people would remark on the torque arm and miss the motor casing.

Two variants of the v3 rear incorporate torque sensors in the freehub, Grin rates it at 250W in a scenario they say meets Euro/Asia specs, and at 4kg, it's heavier than a small Bafang, but much lighter than most other DD motors. Grin provides nothing that mates an All-Axle with a drop-out slot for anti-rotation.


Well, you suggest you can't use your BMC, so you'll need to pick something else. But you also want to avoid gears - that cuts out the small Bafangs and the SX2. The DD (Direct Drive, just so we're on the same page) Crystalyte SAW20 works for 75mm front forks only.

Actually, if you are bothered by a torque arm because you are a road bicycle enthusiast, why is the boost motor and bits on the BMC acceptable? What is it about the torque arm that is an issue that the boost motor and fittings isn't?

I'd reconsider about the small Bafangs and buy a couple of extra gear assemblies against the day. I bought a spare gear assembly for my SX2. I replaced the SX2 with a v3 All-Axle, and it's true that the SX2 is quiet (compared to the previous GMAC), but the All-Axle is quieter still. I haven't run a Bafang hub, but they are reputed to be quiet.

Another option is to paint the torque arm so it blends in? Others may not notice it as much as you think they will, but you know your friends.

A concern if you try to use a motor restrained by axle flats - your drop-out must be well fitted for the job, and that is not a design requirement for any higher-end bicycles - they aren't interested in your (or my) DIY. You're stuck with what they provide, and you had best shop with that in mind to get the least-worst drop-out slot.

And further along that path - if you enable regen on a motor held by axle-flats, you had better search for a very good and very tight fit between drop-out and flat. I'd want steel axle, steel nuts, and steel frame, and think about seriously over-torquing the nuts before I trusted that that arrangement wouldn't loosen itself during a ride.

But try it if you want to. I'd be interested in hearing of an approach using your requirements that works - let us know.

Thanks a lot for your time.
This is my quick reply to your answer because your post has tons of info that I'd like to squeeze and learn.

If you don't like a torque arm because of the aesthetics

It seems that I am under pressure by the aesthetics because I purchased a high end BMC bike. This is not the case. I'm sure that the torque arm will damage a carbon fiber frame. I prefer it because for long rides they are much more comfortable than the aluminum ones. I'm considering this one (Aluminium frame) also.

Another option is to paint the torque arm so it blends in? Others may not notice it as much as you think they will, but you know your friends.

No problem with a good painting job. Friends laugh at me when a drop from the bunch in a hill.

I'd reconsider about the small Bafangs and buy a couple of extra gear assemblies against the day.

I do not understand this proposal

You're stuck with what they provide, and you had best shop with that in mind to get the least-worst drop-out slot.

Fully agree with you. I thought DIY before purchasing the BM but I decline the option due to my lack of time to train and also to manage the project.

Two variants of the v3 rear incorporate torque sensors in the freehub, Grin rates it at 250W in a scenario they say meets Euro/Asia specs, and at 4kg, it's heavier than a small Bafang, but much lighter than most other DD motors. Grin provides nothing that mates an All-Axle with a drop-out slot for anti-rotation.

That's the point 250w in the external label. No problem in Spanish roads. All-Axle although it is expensive and weighty is a good option to last 5 years in my bike...

I don't know if the clamping force for a thru-axle matches the force of nuts or a QR skewer - perhaps you already know this?

The Mahle X20 do not have external torque arm, this is the only thing I know. the truckrun also. I bet that the limit is in the 30s Nm of torque but ... ... will be nice to calculate it, but it is really difficult. The motor stays in the postion due to friction forces I guess...

 

[vladrov]

Create your own thread; this isn’t the right place to discuss your project. However, share a link here for those interested in reading further and commenting.

Upload photos of the dropouts and the hub in the new thread and I’ll get back to you there.