SRam Sparc -> how does it work (technically, two motors ?)? how in practical use

[rooel]

Thanks for the explanations, Coops. I am afraid all I can say about the Sram Sparc system is that it provides a very pleasant cycling experience for my needs, a few miles, up and down a couple of hills every day to collect the morning paper, with occasional off-road tours on tracks and trails. The hills by the way have been deliberately incorporated in the daily ride as I enjoy riding them with the assistance of the Sparc.

I have liked the system so much that I have bought further Roo Els, and indeed recently transferred the system to a Speed P8 for the reasons stated here in the Dahon forum

 

[coops]

Thanks for the information and recommendation, rooel: it may not be for everyone, I'm sure, because of the relatively low level of power assist compared to some bikes, but I'm glad it works for you : I haven't really come across it at all, here or elsewhere, so any information you can provide is most welcome you can even post a review if you like! I am intrigued, I must say, as to how it works, but I'll have to get my technical head on again to begin to understand that .

Stuart.

 

[kraeuterbutter]

@coops:
"taking your trehad a bit off-topic"

don´t see it that way.. is very interesting
i hope now that it is the new sparc... (most likely will not happen)
the new one seems to be lot better.. quieter, more power, more rigid


however:
i think the worst mistake i made: i looked into the endless-sphere.com - forum..
man, they have another definition of power..

e-bikes with 750watt-hub-motors are "weak motors"
the funn starts with 1500Watt-watt...

some suck over 2000Watt out of there batteries when going up 15% hills with 25 or more mile/h

very impressive:

Randy Draper with his custome made bike..

he went up over 10.000feet hight-meters at volcano Haleakala (37miles long road) with one charge..
(in flat he can go over 100miles)
he started after all the race-byciclists and still could go ahead all of them..
(1600Watt peak, 750Watt average)
he was driving with jeans on the mountain

see the short articel about the event here:
ELECTRIC CYCLES AND CYCLING, SOLAR AND BATTERY (ASSISTED) ELECTRIC CYCLE ENDURANCE RECORDS - SOLAR NAVIGATOR CATAMARAN WORLD ELECTRIC NAVIGATION CHALLENGE, NELSON KRUSCHANDL, BLUEBIRD ELECTRIC LAND SPEED RECORD CARS

same bike goes 47miles/h in flat

1500Watt - (there is a discussion about that in that forum) - seems to be no problem for most bikes (i mean solutions,where the bikes gearing is used as well)

but: i want a bike that does assist...
when the bike has over 1000Watt power --> why should i pedal anyway ?!? with 1000Watt my added 100-150watt are worthless...

so: a bike that adds my power 1:1..... i think i would be pleased..
AAAND: up to know i have only bikes with 0Watt assistance...
so anything over 100Watt i guess should be feelable for me and good...

maybe in 1-2 years i will feel and want more (as it is always in life)

because i have some Lehner and Kontronik-Brushlessmotors here
(a good brushless-motor with rare-earth-magnets in this categorie costs around 200Euro, so i doubt that there are 2 of them included in the new sparc)
and also controllers i think i will - if i will - try it witht he componentes i have already here (and if they fit from space, and the RPM is in a reasonable region)

batteries: i will use of course the batts i already have here..
5s1p A123 Fepo4 -> good for testing because robust..
light (less than 400g)
powerfull enough (500Watt continouse, 1000Watt peak)

and can be recharged within 5min (5min for 90-95% charge-state) if i have too

 

[flecc]

As those US preferences show kraeuterbutter, the power level is very much a matter of personal preference.

For a bike to be assistable, you need to know how much power is needed in total, and that will depend on the steepness of the hills you have to climb, and the speed at which you want to climb them.

For a typical 25 kilo electric bike with a rider of 75 kilos, the power needed for hills up to 12% will be around 465 watts for a climb speed at the point of the bike's maximum torque, which falls at about 13.5 kph (8.5 mph) on a bike capable of driving to the 25 kph (15.5 mph) EU limit.

Therefore, if you can provide 165 watts of that, the motor will have to provide the other 300 watts. If the motor cannot provide that much, the climb speed will have to be slower. For example, in the same case but at 9.5 kph (6 mph), a total of 328 watts is needed, which after the 165 watts we assumed you could give, leaves the motor needing to provide 163 watts.

To work these out for yourself for any hill, the formula is:

P = 9.81 x Mass in kg x Velocity in metres per second x Gradient.

the gradient expressed as a fraction of change over distance, for example, a 12% hill is 1 in 8, expressed in the formula as 0.125.

The 9.81 is a constant, and the mass in kg is the combined total bike and rider weight. This formula doesn't allow for losses from wind resistance, rolling resistance or friction, but those will not normally be large at hill climb speeds.
.

 

[penguin]

As an ex-Sram Sparc owner, I feel the need to share my own experience.

First the negatives.

I could not get the battery pack to attach to a bike rack without bungee cords, due to this it detached itself more than once when hitting potholes, causing damage to the case and it's rather Heath Robinsonesque power cable connector. The best thing to do is to put the battery pack into a waterproof pannier to keep the thing safe.

It is a noisy beast, making a high pitched whine.

Such sound and fury signifying nothing meant that I soon started thinking of the Sparc as 'She who must be obeyed ' for like the same lady, you are left with the feeling that this was fun to begin with but a lot of work to look after.

I realised that something was wrong. Yes, the Sparc was running out of our relationship!

Up even moderate hills, the dual motors scream away, but as you get nearer to the peak, it stops delivering the goods, and it is up to you to get there yourself - no doubt this is true of the over geared Torq also, the reason why the Sparc fails to deliver is its sheer lack of efficiency, you can audibly hear it.

It is not a good sign that the twin motors make so much noise, for that is energy wasted from the battery which has to made up for by you, and with such a tiny battery to begin with, one begins to see that it's use is really for very short trips as a bit of fun.

The battery would not last the full 15 mile commute to work and back, in most cases I would get 10-12 miles on its economy setting. Moreover, the battery power would deplete alarmingly overnight left uncharged- I work ten hour shifts.

Probably uncoincidental to the alarming drop in charge was that of it's equal propensity to overheat. When this happens, you usually end up having to unhook the wire from the battery, try again, and more than often than not, waiting a minute or two for it to cool down, not much fun when it starts raining.

My 7.5 mile journey to work one way would vary between 35 - 40 minutes on the way to work, 50 to 70 on the back. Why such a difference on the way back? I would be tired and the machine would 'not' augment my power as the battery had depleted to nothing on the all important journey back home in the post-graveshift early hours of the morning.

Compare this to:

The Giant LaFree Comfort, which would consistently be 30 minutes on the way in, 35-40 way out.

The Giant Revive Spirit, consistently 35 minutes on the way in, 40-50 way out.


Now the positives.

It is light. Very light indeed.

On the flat it is rather good, 17 miles per hour easily possible.

It is folding bike friendly. You can take the (now severly battered and dogeared) battery off the bike rack, stick it in your backpack, and Bob's your uncle.

Hope that helps,


Chris (Penguin)

 

[rooel]

Chris, as a happy user of the Sram Sparc as fitted to the Dahon Roo El, I would be interested to know what bicycle your kit was on, and if it was the 12 volt lead acid system or the 16.8 volt NiMh.

The Roo El comes with a special rear rack whose rails accommodate the battery box and hold it very securely, and the 16.8 system should give at least 15 miles with the motor driving at full power all the time, and up to 30 miles with intermittent use.

The figure you quote of 12 miles even on the half power economy setting is exactly what was claimed by the manufacturers for the earlier Roo El with the 12 volt system, which was powered by the sealed lead acid battery. My experience of NiMh batteries is that they lose power at a slow rate when not in use, whereas I suspect the lead battery does decline in the way you describe.

 

[kraeuterbutter]

@Penguin:
hmm.. sounds not that good (noise)

i know now, that i have bought the 12V (so, old) version
its currently shipped to me, so on its way

nevertheless:
i think 112 Euro is not that bad.. (have to considere that i get a 5speed-gear with it , so the electric drive for that is nearly free)

i will not have any battery-problems... i will go straight for the A123 i already have..
there is no problem with self-discharging or loose of power or what ever

first i will dismantel it and make some pics of the inner things and post here

 

[kraeuterbutter]

got it today...
so:
now i have to "spoke" it

went to a bikeshop (a shop were the cheapest bikes start at 2000Euro .. have seen there bikes over 5000Euro and i think thats not the limit)

its near to me, and the gay who works there is very nice

so: he told me: "spoking" (don´t know how it is called, i call it now this way) will cost 50 Euro without material -> i think thats ok

the problem: he told me, i would need a strong rim because of the short spokes..
AND: the short spokes are not common..
there are short spokes, but they are thin and from a weak material, would easily break
so he said, that he thinks that we would have to make new, special spokes specialy for the sparc..

hmm.. i have forgotten to ask how expensive that would be, but
"we have to make special spokes" sounds not cheap ;(

any idea ?
(or has he such high demands (riding 2000-5000Euro bikes) that he is not "from this world" anymore ?)

what do you think ?

 

[flecc]

He's not of this world kraeuterbutter.

There's overwhelming evidence that thin spokes are not less strong, and you don't need an extra strong rim.

Spokes are available in a huge variety of lengths in 1 or 2 mm steps. Here's a UK link. Track through those options and you'll see there's a huge range of lengths, qualities and thicknesses available.

St Johns Cycles
.

 

[rooel]

Or go to the UK Dahon distributors

Fisher Outdoor Leisure Limited: Search for a product

where they list the real thing, although that is no guarantee they will be able to supply them, and they are not cheap.

 

[kraeuterbutter]

thx for the links !
i will check them monday
but i have the plan to get parts i need from Austria (or Germany if it are sparc-related things, because sparc is build in germany, isn´t it)

so: i will check the links and see if i can find similar parts here..

now i have to prepare for friday night skating
(police shuts down streets (even the biggest main-streets) for some minutes and so we can drive through vienna and enjoy the city by a way you never else have the oportunity too do..
now for 5years, every friday, from spring to end of summer, from ten till midnight (or longer when it is a long route)... so cool !
today only a small round, 14km... last week 24km )

 

[JohnInStockie]

How very 'civilised'

 

[kraeuterbutter]

--- Warning for modem users (who read this notification through email):
i will now post LOT of pictures..
(so if this is a problem for you, don´t follow the link) ---

i have got now the SRam Sparc..
and disassambled it

first: i was told, that it is the 12V Version
another indic for this: inside there is a hand-written date that says: 29.01.2002

because iam only able to post 4 pics per posting, i will have to use several posts,so: to be continoued

 

[kraeuterbutter]

now: flecc, you said something about a belt-drive ?
there is no belt inside

so no belt, no pulley.. all gear/pinion-driven

-------------------------------

for the motors:
some previouse pages ago I made the guesswork, that there are maybe a cheap silber-can-motors used..
i was right..

here on the picture you can see the two original motors (550er sice)
compared to a 550er Titan from my E-Maxx (a 4,5kg RC-monstertruck, using two of this motors for reaching ~40km/h, the cheap stock motors.. meanwhile of course replaced by Brushless)

 

[kraeuterbutter]

picture of the Titan

Titan with build-in fan for cooling

sparc-motor with build-in fan for cooling

 

[kraeuterbutter]

the motors are non-serviceable (so you can´t open it, you can´t change the brushes),
the motors have no ball-bearings !
only bush-bearings

at least you can say: you can get this motors for ~10-15 US$

so no high-quality motors, just motors which run from band-conveyor in china every day, hundret and hundret thousands times

----------------------------------------------

my idea with the Lehner Motors:

here you can see for comparisment my Lehner 1930-8

the lehner is here configurated in star-configuration

 

[kraeuterbutter]

don´t wonder about the ugly looks of the lehner (scratches, dirt)
its normaly used here in this 10year old CRONO buggy,
doing races (Peakpower: a little over 1000Watt, battery: 4s Lipo with 4.4Ah)

(driving in dirt, jumping 3meters high and 10-12meter far, beating many of the pro-nitro-powered 1:8scale-buggys here in my area)


BUT:
BACK to the SRam Sparc:
you can see: the Lehner is same size like the 550
it has the same mounting-holes in front
but it has more than 4times the power of one of this 550 silber-can-motors
(and costs also about 10times as much )

(it accelerates my 4.5kg heavy E-Maxx RC-Monstertruck to about 90km/h speed (Peaks in the 1200Watt region))

 

[kraeuterbutter]

for the electronics:
does not look in any way "expensive"
iam not a electronic expert..
but it seems not too use much expensive parts on it

there are no parts on the backside of the platine

when removing that platine, there would be far enoug place for a Kontronik BEAT 80-6-80

here for size-comparisment:

some features of this controller:
6-25Volt
80A continouse !
100A 15sec. peaks
120A shorter peaks
and some featurs like: Current limiting, Active free wheeling circuit, Overtemp. protection, Short circuit protection, Reverse polarity protction, False start protection, ....

this controller can handle far over 1000Watt continously..
nevertheless its tiny and would easily fitt into the sparc-hub as you can see on the picture

here you can see, how the hub is connected with the outer world

 

[kraeuterbutter]

now to the gearbox:
no belt..
the teeth-count is:
9 teeth on the motor-pinions
then 36 teeth
the next pinion 9 teeth again (but bigger modul)
then 37 teeth
on this is another spur mounted (the black one) with the one-way inside and 34 teeth
this is running in the hub (108 teeth)

count all this:
we have:
9:36 * 9:37 * 34:108
which results in a gearreduction of
4 * 4.11 * 3.17 = 52.1:1

(just some calculation:
for 25km/h with a 26" wheel we need 630rpm of the wheel -> so with an 52.1 reduction the motor needs to spin 32823rpm to reach that)

so when i look on the measured diagramms provided by Lehner Motoren on there homepage
(here the values http://www.lehner-motoren.com/diagramm/1930-8.13v_liste.txt )
you see: the motor 1930-8 i have fits this requirements prodigiously well.
only downside: the motor is made for power..
it starts to get in his good efficience-range above 400Watt (so to keep it efficient you should use the power )
nevertheless: also on low power its still more efficient than this sliber-can-sparc-motors

the one-way

 

[kraeuterbutter]

finaly to the bad things:
the plastic used inside the sparc is realy of cheap make !!!
i realy don´t know why the sparc is that expensive
(cheapest motors, cheap controller/electronics, poorest plastics)

even on the cheapest rc-cars (more toys than cars) the plastic is more robust than this inside the sparc which helds the motors:

effect:
the motor-holding plastic-parts are broken !

its broken on a wide range, i think 70% of the material that holds down the motors is broken of the ground-plate !!

i don´t think that this comes from the little torque the motors provide..
its - like on rc-cars - from g-forces..
(when jumping a car 0.5m high and landing, the weight of the motor has to be absorbed by the motormount.. a cheap plastic-motormount can break on this..
instead: a high-quality carbon-kevlar-improved plastic will survive landings from 3-5m hights !)

so i think, the bike with the sparc mounted was going over curbstones by the previouse owner..
this was enough, so that the ~220g heavy motors cracked the motor-mount..

here would be a part made from higher quality plastic (improved by carbon-fabrics/fibers like on rc-car-chassis) very nessessary...

question is:
will i get a replacement part (maybe worth 5 US$) by SRam, or will they want me to send in the sparc to replace it ?
(that would cost me all together (sending to Germany, sending back, price for repair) maybe 100US$

before i send in all the parts, i will try to fix it myself with carbon-fibres, CA and or epoxyd-glue
combined with fine cotton streak

so..
first conclusion when looking to the dismanteld things:

i think the gears look very rigid.. should not fail
the mounting of the gear-shafts seems also to be rigid enough that tourque does not kill there anything

a big problem is the weak plastic, that can not support the weight of the motors (g-forces when driving on a not that clean road which causes agitation makes the plastic break under the load of the little 220g motors !)


the motors + gears + electronics + cap weights only 837g

(the motors themselfs: 220g each)

for the Lehner-MOtor:
mounting itself should not be a problem (same mounting holes, same diameter, same length)

Problem maybe to find a suitable pinion for the motor, because the lehner has a 4mm shaft
(a 3.17mm shaft like the sparc-motors would break at peak-powers of ~2000Watt what this motor is able to handle)

another thing: i wonder why there are nowere ball-bearings used...
on such an expensive part i thought ballbearings should be standard..

next steps:
* repairing of the plastic
* mount it on the bike..
* first testruns with desition if i need and want to modify it with stronger, brushless motor

Flecc: mounting only one motor would not be a problem at all, as said: no belt