Convert my Rockhopper help

Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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Hi all,
I'm looking at getting a kit for my bike and could do with some help.
I've got a nice year 2000 specialized rockhopper which has been fettled over the years from it's original spec.
runing a triple chain ring at the front and 9 speed on the rear.
I'm 11 stone, pretty fit and cycle to work daily on my road bike.
However my MTB is not getting enough action! It's quite a heavy old girl. I reckon about 30lbs in fighting trim.
on the flat and downhill she's lovely but uphill is a slightly less pleasant experience.
predominant use will be off road. I'd like both an assist option and a straight throttle only option.
Ideally I'd like to keep her full functionality so I'm assuming mid drive is out as I'd lose my front derailleur?
I was looking at the 350w rear drive kit on woosh's site but I'm worried 350 is not going to be up to the job off road.
can anyone advise?
bike should be pictured below.
007 (2).JPG
 

jackhandy

Esteemed Pedelecer
May 20, 2012
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'Orses for courses and all that...
Stay legal with a 250w rear hub; Ezee kit for maximum grunt; 8fun kit for minimum money...
Or put a 500w Bpm2 in the back wheel, with a S12s controller & good quality battery in a backpack (Ezee 14ah flatpack in mine ) & really have a blast! :)

The only practical alternative position for the battery on that frame is under the down tube, where it may well compromise clearance - seatpost rack Not recommended :( Will definitely bu##&r up the balance & could crack the post, or even the frame .

Go for a low-speed wound motor.
 
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Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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Cheers Jackhandy,
I've got a couple of bikes for playing on the road.
This is just a toy for the dirt so the 250w road legal bit is a non issue.
I more interested in finding a kit that will meet my needs.
 

Nealh

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Aug 7, 2014
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First thing is to think where the battery is going(back pack already suggested), to keep original spec than a nice 500w cst with reasonable torque probably no more than 250rpm.
 
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Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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There are a couple of water bottle bosses on the lower edge of the down tube which would put a bottle type battery in the gap between the bottom bracket and the front wheel. I suspect though that this would probably foul the front wheel if I go with a battery large enough to give me a decent amount of amp/hours.
I'll probably go with either a back pack battery or possibly a slimmer double battery pack custom mounted either side of the top tube behind the stem.
Both of these though will raise the centre of gravity a fair bit. (although the stealth bomber gets by okay that way.)
The back pack option would require some sort of quick release safety connector for the inevitable unintended dismounts!
If possible I'd like the battery on the bike but appreciate I may have to compromise.
 

Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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oh yes, its a hollowtech 2 bottom bracket as well if that makes a difference.
 

jackhandy

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May 20, 2012
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Those bottle bracket lugs won't take the weight of a battery, so you'd need to strap it round the frame too.

A backpack battery doesn't raise the CoG - You've already fallen off before that becomes an issue ☺
Mine has 30a Anderson connectors, which pull apart satisfactorily when I fall off or forget to disconnect before walking away:
You'd need to add some form of strain relief so the lead doesn't chafe where it exits the battery & controller; and solder, not just crimp the Andersons.

My Octalink bb has a 22mm axle & my Isis 18mm - both handily allowing a standard square-taper pas magnet ring to be reamed out with a step-drill.
 
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Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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this is all sounding promising.
my bank account is already starting to tremble!
what hub motor are you using?
Having never used an e bike I'm tempted by the woosh complete kit with the 350w bpm motor as I've got almost everything from a single supplier in the uk.
I'll have to sort out something for the brake switches as I'm on hydraulics but other than that it's 'almost' plug and play.
 

Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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Hmmm, I've just mocked up the woosh 15ah battery sizes in cardboard and tried it under the frame. if I sit it flush with the angle of the down tube it sits too low and will get clouted every time I go over a ridge. I also don't like the look of the bike with it hanging there either so it's either going to have to be two packs slung either side of the top tube that are narrow enough that my knees don't clout them whilst pedalling or the back pack job I think unless there are some other suggestions. I normally hit the trails wearing a camel back anyway but wonder whether the weight of the battery as well will become tiresome.
 

JohnCade

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May 16, 2014
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Cheers Jackhandy,
I've got a couple of bikes for playing on the road.
This is just a toy for the dirt so the 250w road legal bit is a non issue.
I more interested in finding a kit that will meet my needs.
Actually it is unless you are using it on private land with no public access. It's still a common mistake to think that legal is only applicable to public roads and cycleways, even if the real situation is reiterated on sites like this one.

I'm not trying to tell you what you can and can't do BTW. Just clear up any misconceptions.
 

jackhandy

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May 20, 2012
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IIRC this bike is for recreation only, as is my bouncer.
I have a Bpm2 500w in the back wheel & s12s controller in the dinky frame triangle, with both pas & throttle.

If this was your main bike, I'd definitely recommend going for a complete kit from Cyclezee to have the peace of mind of a 2-year warranty & peerless after-sales service.
The 2 kits have pretty much identical grunt.

The controller's a big beast, so you'd need to do a mock-up again to make sure it'll fit somewhere sensible.
You'll find all dimentions & spec. on the Bmsbattery website, which is where I bought mine.

Bear in mind there's effectively No Warranty with it, as you have to pay shipping back to China, which is more than the kit's worth.
Although I ordered a 201rpm motor for low-speed grunt, I received a 250rpm/code 12, which still gives bucketsfull & is quicker than I'm comfortable with on singletrack.
Make sure you get a hight discharge rate battery/ies.
Don't make the mistake of thinking 2 cheap ones will be equivalent to 1 good 'un.
You'll almost certainly need to dish the motor wheel & check spokes for tension, as they are often left slack for shipping.

There' a lot of posts on here from people that have done similar builds, so I'd advise searching bpm2 & having a read.
 
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Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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Thanks, I had forgotten about the 'public access' bit.
lots to think about and inevitably none of the off the shelf kits appear to cover all the bases for what I think I want at this time.
 

trex

Esteemed Pedelecer
May 15, 2011
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The positioning of the battery is particularly difficult in this case because of the lack of space inside the triangle.
I would look at the possibility to mount a rack battery to the seat stays.
 

Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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Cheers JackHandy,

yep, this is totally a toy for dirty fun ;)
I've got my normal alu framed commuter roadie and a full carbon 'sunday best' roadie also for day to day commuting and road based rides.

I'm pretty much looking for a push bike based equivalent of a green laner motorbike. So assistance on the off road, uphill stuff and un-powered free fall for the downhill squeals and inevitable crash.
 

Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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Being a bit of a tart I really like the look of the old girl so don't really want to add racks if at all possible. would like to keep the lines as clean as possible.
I may end up longer term getting something custom built to house the batteries either side of the top tube if I can't find an alternative solution.
At the moment it's looking like a backpack with quick release connectors as the favourite option.
 

Andrew2505

Finding my (electric) wheels
Oct 27, 2014
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so spec'ing kit I'm thinking
The 36v 500w CST bpm2 motor (this will let me use my existing 9 speed shimano slx cassette and retain my nice slx shifters also)
The matching s12s 500w controller
The compatible lcd 3 display unit all from BMSB in the US

then from the uk
thumb throttle.
this alone would get me riding without PAS presumeably

and if I want PAS then add
PAS sensor ring and sensor.
sort out some brake switches for my hydraulics to cut out the PAS instantly if I stop pedalling and apply the brakes.

then it's just batteries and charging.
Batteries
I'm figuring a pair of these lipo packs in series gives me 37v and 8amp/hours
https://www.hobbyking.com/hobbyking/store/__34830__Turnigy_nano_tech_8000mAh_5S_25_50C_Lipo_Pack_UK_Warehouse_.html

Charging
I already have one of these in the shed from an old project.
figure a second one would then let me charge both packs simultaneously with full balanced charging each time.
https://www.hobbyking.com/hobbyking/store/__14857__HobbyKing_8482_50watt_5A_X_Charger_Balancer.html

Can anyone see any problems with this kit match up?
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
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I'm no battery expert but think you will need a bit more than that, some one with more knowledge will advise.
 

jackhandy

Esteemed Pedelecer
May 20, 2012
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BmsB are in China & you'd just as well get your throttle & pas from them in with your order. Get a couple of spare throttles & pas sensors & rings + a few spare spokes. They cost peanuts.

A couple of people on here have cobbled brake cutoffs using sub-micro switches or hall sensors on the handlebars.
 
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trex

Esteemed Pedelecer
May 15, 2011
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Motor, controller and LCD: no problem there.
you may need two chargers. Each HK6 does only 50W charging at most.
You also need 10 cell monitors to avoid draining too much on the batteries.
 
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