Sram Sparc Geared Hub Motor

[Freddyflatfoot]

Hi.
After researching some different SRAM products, I came across this interesting looking geared hub motor from SRAM.
The reason I say it is interesting, is that it combines a hub motor, and an 5 speed internal geared hub.
Not sure of the performance aspect of the motor, but wouldn't expect too much from the relatively small 16.8v NiMH battery, but the concept does look sound.
Also looks like the controller is built into the motor, so dunno how modding the motor would go.
Would probably suggest that the motor is on the low end of the power scale.
Has anyone come across this motor in their travels?
The SRAM site is the only place I have seen it.
Here is the site, click USA, then Products, and the SPARC will be on the drop down list,
http://www.sram-imotion.com/
Cheers!

 

[Dr. Shock]

I have SRAM (formerly Sachs) Spectro S-7 internally geared hubs on two bikes. I have had very poor luck dealing with SRAM. In fact, they generally won't even talk to their dealers. I asked three local dealers to get some parts for me out of SRAM's current product catalog, and only one of them could even get a reply from SRAM. They were told SRAM didn't actually sell the parts (despite the fact they were listed in the current catalog) but they'd send a free "parts bag" to the dealer, which might or might not have the parts they needed. In fact, they never sent anything.

I finally found a shop in Wisconsin that specializes in these hubs, the Yellow Jersey (google them) and they had everything I needed. They say the hubs are built very well and they have been working on them for years, so maybe they have an "in" with SRAM.

Anyway, I'd be a little hesitant to buy their hub motor just because of the lack of support for their other low-volume products. It would also be nice if their website told us some details about the product.

 

[rkosiorek]

the Sram Geared Hub motor is less than 200W and AFAIK a pedelec only. i have never seen one for sale. i have only seen them in pictures of a couple of different concept bikes.

other than ad hype for the concept bike i have not seen a review of it anywhere.

it comes in 4 versions. first there is a European version that is higher speed than the US version which is limited to 20mph. Each of those come in two different gear ratios one set for 20" wheels and the other for 26".

though at about $1000 without batteries or wiring, me thinks i would rather have a BionX

rick

 

[safe]

Very interesting...

200 Watts
5-speed gearhub with 251% range
NiMH, 16.8 V, 8 Ah

 

[recumbent]

Finally we have gears integrated into the hubs, welcome to the 21st century.

 

[safe]

Finally we have gears integrated into the hubs, welcome to the 21st century.

I agree.

Especially with the way the laws are designed where you are limited in peak power so you are basically giving away 25% in power when you run a fixed hub motor verses something like a 5 speed hub motor.

From the "Hub Motor vs Gears" thread a while back the conclusion that I arrived at was:

Gears give 25% more power.
Gears give 25% less heat.
Gears give 33% better overall efficiency.

...so this really makes the hub motor fully competitive.

If they could make these in an American 750 watt version then we would have the perfect foundation for a road racing class because you would have everything you needed in one product.

I would like to see stories of people overvolting this hub. If it can be overvolted to boost the power to about 750 watts then it might be a really fine product. For me I need a lot more power out of my bike than 200 watts.

For europeans and australians this looks like an excellent choice... but for canadians or americans we are allowed more power than this...

 

[Rassy]

I could not tell if the internal hub gearing applied to the motor, or just to the peddaler. Does anyone know for sure?

 

[josh]

I've seen some threads & details on this system & IIRC the motors in the hub (there are two, I believe?) don't drive through the gears, so single motor gear only and peak power output is also on the low side, even for lower speed, road legal electric bikes in Europe, so not the best for hilly areas. Some owners seem very happy with them, often as a quite compact & medium-powered pedal assist system in small bikes & folders, I believe, but I recall some debate over the quality of the design of at least the earlier versions of the SRAM Sparc (a search for those terms will throw up more precise info) & there's some difference of opinion as to its value.

 

[Freddyflatfoot]

I did find that this system was used on the Dahon Roo Electric folder, but couldn't find any more details.
Apparently the system uses two 100 watt motors, and are used either in series, or parallel mode, depending on whether you want torque, or speed.
I still can't confirm whether the motors drive through the 5 speed gearbox, but the literature indicates that they do.
I still think the concept has merit, and as suggested, a higher power output would be better.
Would like to see how one of these would go at either 350 or 500 watts, at say 36 volts.
Maybe someone with some engineering knowhow, could adapt a hub motor around an internally geared hub?
Sounds like a doable project.
Safe, any ideas? Got the juices flowing?
I'm thinking that this could be the absolute answer to the simplicity of a hub drive, and the gearing flexibilty of a geared drive system.
I'm already enjoying my geared hub motor, but ultimately, it is still a 'single' speed motor.would be even more efficient with a geared hub!
I wonder if one of these SRAM, or even Nexus hubs can be grafted into the inside of a hub motor?

 

[Dr. Shock]

One of my SRAM S-7 hubs did duty as the transmission for a chain-drive ebike, but it quickly succumbed to the stress and began shifting spontaneously, and finally didn't engage at all. This was on a geared down 300w scooter motor rated for 24v and run at 36v--not the most overpowering setup imaginable. I concluded that these hubs were not up to ebike power levels, though one trial is not a good sample. Also the 5 gear version may have more robust gears than the 7 speed. My current setup has a hub motor in the front and a high geared internal gear hub handling the pedal power. That way, if either system has a meltdown, I can still ride it home.

 

[josh]

Hi Freddy,

You're right, the sparc system does seem hard to find details on, kind of obscure & maybe not the highest production numbers either, but searching around I'm pretty sure now that its a low power, single gear-reduction system and the hub gears are separate - for pedalling only. Mathurin also posted in that 'hub motor vs gears' debate that the motor is single speed. There's a rather long thread here with some details of inner workings & links & images, aswell as an intended mod of the motors, though no significant power boost that I can recall. Apparently it climbs hills ok, but at low speed. I guess with a little more power & higher gear ratio you could get some good speed & torque out of it, but whether the design is strong enough to take it I don't know.

Actually, for ebikes with limited speeds up to say 25-30mph, motors might only require 2 or 3 gears at most for adequate efficiency & reduction in unnecessary power interruption for gear changes, and theres a way to achieve that by modifying the planetary gears in hub motors at the construction stage, so that would still be a relatively simple hub motor but with simple gears too! I don't know which motor you have, but 'geared' hub motors like the Ezee & puma kits for example, do have quite broad power curves already, so either more pedalling at low speed, or 1 or 2 added motor gears would suffice for improved efficiency. The friction of the gears themselves does seem to reduce efficiency a little over direct drive hub motors at 'cruising speed' but adding more gears to an already single-geared hub should only increase efficiency of power usage over all speeds .

To DrShock: I recall reading that SRAM hub gears can fail under heavy load - they're apparently not really engineered to deal with such high forces as high power chain drives, as you say - I recall that some Giant/Lafree Twist (Panasonic transmission drive) owners who changed their hub gears found some SRAM hub gears not strong enough for that system, which is only around 300W peak I think, so you're not the only one, not that thats much consolation I guess .

 

[safe]

Normal human pedaling produces peaks and valleys of torque. A professional level cyclist might produce an average of 400 watts of torque over the course of an hour, but their peak torque will be as high as 750 watts. In a sprint situation you would expect up to and beyond 1000 watts of peak torque.

...so you have to figure that any hub should be able to handle a constant torque value that compares to this level of power. In order to make the translation you have to convert from the concept of "power" to "torque" and to do that you need to know the "gearing" because:

Power = Torque * Gearing (rpm)

If you go through all that then you can figure out how much torque a typical hub should be able to handle. I'm under the impression that different hubs are better than others when it comes to the ability to hold a gear and not skip or freewheel when you don't want it to. The Sturmey Archer hubs make strong CLAIMS about the ability to not produce miss-shifts and I will see if that's true in future bike testing.

As for this 5 speed hub motor... if it DOESN'T translate the electric power through the gears then it's just a hub motor... no advance having been made.

 

[josh]

Interesting safe & a good point about peak torque/power: I hope this doesn't drift too far OT but the latest version of the panasonic (transmission drive) pedelec system uses hub gears and has a peak power output of around 340W which is delivered in a 1:1.3-1.5 ratio between pedal input & motor assist, so 'flat out' for the motor would require around 226W rider input (thats flat out for many riders too!) to which the motor adds its power i.e. 1.5 x 226W = 340W, giving a total (peak) power of 566W through the gears: if you pedal any harder, that would be added on but the motor is all-out at 340W.

If you are putting more power than that through the gears, like a professional cyclist would, I think you'd be using derailleur anyway since they are more efficient than hub gears? Whether they are stronger I don't know, but I guess they must be .

 

[Drunkskunk]

Normal human pedaling produces peaks and valleys of torque. A professional level cyclist might produce an average of 400 watts of torque over the course of an hour, but their peak torque will be as high as 750 watts. In a sprint situation you would expect up to and beyond 1000 watts of peak torque.

Not to take us too far off topic, but if a professional cyclist produced torque like that chart, he wouldn't be a professional.

A skilled rider using cliped pedals distributes the workload through the whole pedal cycle. when your feet are cliped to the sprocket, you have the advantage of pulling up on the pedal as hard as you push down. but in addition, you can use your calf muscles and feet to pull back on the pedal at the bottom of the stroke, and push forward on the top of the stroke.
lance and others don't produce 450watts by pushing down harder on the pedal than the rest of the world. they produce it by applying power through the entire stroke.

 

[Dr. Shock]

"To DrShock: I recall reading that SRAM hub gears can fail under heavy load - they're apparently not really engineered to deal with such high forces as high power chain drives, as you say - I recall that some Giant/Lafree Twist (Panasonic transmission drive) owners who changed their hub gears found some SRAM hub gears not strong enough for that system, which is only around 300W peak I think, so you're not the only one, not that thats much consolation I guess ."

Yes, you'd think it would be a function of the number of gears they try to jamb into the hub. Each gear has to be narrower for a given design with more gears. That said, my LBS has a higher opinion of Shimano 7 speed hubs than SRAM, though the people at Yellow Jersey stand by the SRAM, and they've been dealing with them a long time.

Based on my admittedly anecdotal experience, I wouldn't want to be an early adopter of an expensive SRAM hubmotor, even if I were satisfied with the power output, which actually sounds pretty aenemic.

 

[Jeremy Harris]

You can't express torque in watts, the watt is a unit of power so it doesn't make any sense to talk of torque in this way.

Torque is expressed in units of distance x force, so can be Newton-metres for those of us in metric-land, or pounds-feet for those still using good old Imperial units.

Power is torque x radial velocity, so, using metric units, if a wheel is spinning at 200 revs per minute and has a torque applied to it to keep it spinning at this speed of 40 Newton-metres, then the power will be:

200 revs/min = 20.9 radians/second

power = 20.9 x 40 equals approximately 837 watts.

We could have equally had a power required of 837 watts, but at only 50 revs/min of the wheel. In this case the torque needed to deliver this much power at this rpm would have been 160 Newton-metres.

Jeremy

 

[josh]

Cheers Jeremy, can get confusing all these terms & units

(In case anyone finds it useful In order to try to relate the maths/mechanics to the real world, I try to think of torque as resulting from the power output, gearing & revs: a high gearing requires high power to get moving (i.e. increase revs) from a low speed, i.e. requires high torque - like starting off on a bike in high gear is hard work, and low gearing needs only low power (hence low torque) for the same situation. In both gears, the torque needed decreases as speed (revs) increases, so that the high gear becomes more 'comfortable' but the torque required in low gear becomes uncomfortably low i.e. spinning like an egg-whisk & top speed is thus limited, so upshifting the gearing is needed to both return the torque to a more optimal level and increase the speed/revs if wanted.

In an attempt to relate this to the SRAM Sparc, I think I'm right in saying that the torque characteristics of a hub motor and its speed range depends on the combined gearing of motor and wheel, given by the combination of internal geared reduction, if any, and the wheelsize (smaller diameter = more torque but less speed & vice versa) aswell as power output. Thats why motors with already quite high rpm but moderate torque at low rpm at voltages like 36-48V work best in smaller wheels when you up the voltage. The same limitations don't necessarily apply to higher torque geared motors which can provide good torque at lower rpm & also reduce the max rpm of the motor, both factors which make them well-suited to larger diameter wheels like 24"-28".

PS For anyone who wants to know, to convert revs/min (rpm) to radians/second (units of radial/angular velocity), just multiply by 2 pi & divide by 60 i.e. ~6.28/60 = ~0.1047.

Good job this is the technical forum, eh?

 

[Miles]

Normal human pedaling produces peaks and valleys of torque. A professional level cyclist might produce an average of 400 watts of torque over the course of an hour, but their peak torque will be as high as 750 watts. In a sprint situation you would expect up to and beyond 1000 watts of peak torque.color]

Safe, please use the right units, for goodness sake

 

[Freddyflatfoot]

Ok, this thread has attracted some discussion, and maybe the SRAM internal hub gears are not up to the task?
Someone mentioned that maybe a three speed is all that is needed? he old Sturmey Archers have a good rep for reliability.
So back to the original premise. Is it possible to graft an internally geared hub into a hub motor?
This premise is going to suit those countries that have lower power ratings.
A geared system works well, but they are usually complex and a bit weildy, and maybe the not the most reliable system.
If we are going to have e-bikes suitable for the mainstream population, they have to be legal, and suitable for a variety of terrains. I believe a geared system is the best way to accomplish this, and an internally geared hub motor would help to make the system foolproof.

 

[josh]

I'm no engineer but I think grafting hub gears in would be very difficult technically. If you're interested how 2 or 3 gears could be relatively easily included at the design & construction stage (you might need funding or contacts to make this happen though!) take a look at this thread a few pages in: the gears are essentially made by using the existing planetary gears of geared hub motors to drive the wheel in different gear ratios, one of which is direct-drive which might also allow the geared hub motor to run as efficiently as non-geared hubs when in that gear, due to no efficiency loss through cogwheel friction .

It might be useful for countries/states with power limitations on ebikes as you say and is an aesthetically pleasing & practical way to combine the efficiency of gears (and no more than necessary) with the simplicity of hub motors .

 

[safe]

Safe, please use the right units, for goodness sake

Hey, I know all about the torque verses power relationship. It's more about conventions being used... people prefer to think in terms of power. Torque you don't know unless you can figure out the gear ratio and rpm, so it gets more confusing.

If you begin with a basic assumption:

"All torque is estimated in relation to a 'standard gear ratio' that is typical for a bike."

...then these ballpark estimates using Watts aren't so bad.

But I agree... to be really accurate you need to get the old spreadsheet out and setup all the relationships and produce a graph that describes the torque across the entire powerband. After all the torque VARIES depending on the rpm a great deal. (you end up having to guard against PEAK torque more than peak power because they occur at opposite ends of the chart) Every time I post a chart (which is technically a superior representation of the data) people complain about that, but then when I generalize too much people complain.

Maybe people just like to complain a lot?

Hmmmmm..... :wink:

 

[Miles]

I Know that you know what you mean, but just imagine how confusing it is for people still learning.....

If you must use watts, at least add something to qualify it....

Your supposed to be "the teacher"

 

[Jeremy Harris]

I certainly wasn't complaining at all. As has already been pointed out, if you set out to try and teach others then it's important to be factually correct, otherwise any advice given could be misleading and lead to the opposite effect to that desired. If the post was not intended as an unasked for lesson in simple mechanics, then perhaps less authoritative phrasing might make it clearer that the advice being given was to be treated with caution by any reader.

Calculating torque from a pedal system is fairly straightforward, as the maximum force on the pedals will be around that resulting from the riders weight, plus what ever pull the rider might exert on the bars. Knowing the length of the pedal crank the peak torque is easy to determine.

Calculating average power requires measurement of the crank cadence and knowledge of the torque change with crank angle characteristic.

Jeremy

 

[safe]

Calculating torque from a pedal system is fairly straightforward, as the maximum force on the pedals will be around that resulting from the riders weight, plus what ever pull the rider might exert on the bars. Knowing the length of the pedal crank the peak torque is easy to determine.

This would actually make a good "educational thread".

I've done many of these, would it be too much to ask you to create a new thread based on this?

Maybe even throw in a chart or two so I don't feel alone in doing such things. :wink:

We tend to express everything in terms of watts because that's how our electric motors are measured, but torque is often misunderstood. The idea of the INTERACTION of motor torque and human cyclical torque is actually a very complex thing. In some ways you have to worry about the "rogue wave" situation where a low end motor torque combines with a cyclical pedaling peak to produce an instantious torque load that might snap parts that can easily handle the average power requirements.

Would you volunteer?