Need help for my first ebike setup! DH bike to go uphill!

[glump]

Hi, I live in a small village in the south of France that has a hill with very cool trails on it. (Here).
I’d like to go bicking there but because I've not being doing any sport for many years, the steep hills are too big for me.
My normal bike is normally light but for this project I want to use my DH bike which is quite heavy (18kg) but of course very good to go downhill. i weight 85kg.

My ebike should be able to climb steep trail hills but doesn’t need to go fast on flat.
I’d like to be able to ride for 40 km with 20 of them on hills from 5 to 15 %

I was thinking on buying a Mac hub motor from Cell-Man on a 24 inches wheel (to lower the bike because it is a bit big for me) but I’m not sure on the winding. I’ve seen many 8 turns examples on DH bikes on the sphere but I’m hesitating with a 10t version.
Another option was to go with a GNG mid-drive to avoid the gearing /winding problem but I don’t want to be bothered with chain problems and stealth is important for me.

For the controller I’m thinking on getting the 12 fet controller that EM3EV offers.

For the battery I’m not sure. I’d like to use a backpack with Lipos from HK. But I’m not sure witch? How many? Do I need a BMS for them? How will I charge them?

If anyone can help me choosing, i'll be happy to hear any advice / experience i can get !

 

[MattyCiii]

GNG looks like a good choice, see http://endless-sphere.com/forums/viewtopic.php?f=6&t=44623

Batteries in the back pack? You have some nice space in the triangle there above the shock. Maybe enough to take the edge off the uphill grades. If you need more power than the room you have, then add more (either in a back pack, or elsewhere).

 

[glump]

Splitting the battery pack is a good idea ! like 2x 6s Lipo in the frame and if needed two more in the back pack.

For the GNG i think it is theoretically the best solution but i'm concerned about the reliability of the system. I can't decide between the simplicity of hub in the wheel that might hurt the balance of the bike when going down and the neutrality of Mid-drive solution knowing it has some weaknesses...

 

[pchen92]

Salut,

je te conseille un MAC si tu as besoin d'un système facile à monter. Le 10T parait bien en 44V 10Ah. Tu peux espérer 36-38km/h sur le plat en 24" je pense.

 

[MattyCiii]

Splitting the battery pack is a good idea ! like 2x 6s Lipo in the frame and if needed two more in the back pack.

You might be able to get 4 * 6s in that space, two fore & aft by two wide. Make a fake battery box out of card board. Find size specifications for packs on HobbyKing web site. Add about 10mm to width, height and depth dimensions for your battery box, and wiring runs. Then tape that sucker into place and go for a ride - see if it interferes with pedaling.

I'd suggest doing rough calculations for a mid-sized LiPo brick (5 amp hour) and a big one (8 amp hour) - doing so will ensure you get the biggest pack that can fit in that space.

The cardboard box "battery simulation" will also show you if you're getting in the way of the suspension/shock - so make the box rigid and go off a curb or two to test that.

 

[dogman dan]

10t at least on the Mac, if you intend to ride slowly up steep hills. One issue with steep trails, is that though you can build a bike to run up those hills fast, can you hang on if that trail is ridden that fast?

If you can't handle those trails at 15 mph, then you gotta build for slower, perhaps even going to the 12 T.

 

[glump]

with all your comments i'm reconsidering the GNG option. But what about reliability with it ?

for the 6s lipo from HK how do you charge them if wired for 44V ?

 

[MattyCiii]

for the 6s lipo from HK how do you charge them if wired for 44V ?

There are many ways to charge. Personally, I always balance charge at 6s with a BC-168 charger (charging through the balance taps). As a result I've set up my two bikes as follows:
1) Parallel packs first, then series them (so a 4 battery pack is two pairs paralleled, then these two sets are put in series()
2) When I charge, I disconnect the series connecter. First! Then double check I disconnected it.
3) Then I plug all the balance taps into parallel and charge.

This way, everything is balanced every time. At 8 amps per channel max, this can be a slow process. And, if you ever forget that middle step... fireworks and toasted gear.

Again, there are many ways to charge...

 

[winkinatcha]

Hey Mate

Couple of things to consider if going for rear hub motor on a sweet bike like that.

There is a very high chance the space between the disc and the motor will be an issue with the hub motoor "straight out of the box"... most if not all motors I have come across (MACs, Magic Pies, 9c, Cohnis, MXUS) have this issue. there are ruber/plastic spacers available to bring the disc out from the wheel, and various washer solutions, though not ideal, can also be used... Personally I am about to try cutting down a shitty old disca to use as spacer.s..) Keep that in mind it can be a pain to sort.

Torque arms are probably a good idea... I suspect with your dropouts and de railler there may be space issues... I beleive Grin technologies are the go.

Dropping wheel size in the rear can cause serious problems in terms of pedal to ground clearance... this can partly be fixed by shortening crank length but a big caution as the clearance issue can be quite dramatic.

now personally I have used a 24v (6s) 500w (20-25 amp controller) cohnis dd rear hub (peaking at max speed 25kph) on a light Front suspension hardtail hour after hour on all sorts of terrain without any probs with overheating.. on steeper grades, though not fit and of the same weight as yourself, I find I can actually assist the bike really well with low gear peddling, and still have great control, where on pedal only attempts uphill on the same terrain I had a lot of trouble pedalling and keeping the front end down... but I digress...

A recent thread I have watched by Kudos: http://endless-sphere.com/forums/viewtopic.php?f=3&t=38218 shows how he tackled the common issues of motorising a good downhill MTB.

Bon Chance dude and keep us in the loop

joe

 

[glump]

Couple of things to consider if going for rear hub motor on a sweet bike like that.
...

Thanks for the feedback !

I was thinking on the problem with the ground clearance if going on 24 inches and the hub solution appears to be more complicated than i thought.
Considering every thing that has been said here i think i will go with the GNG brushless kit and keep my 26 inches wheel.

For the GNG it seems not very reliable but the problems seem to be easily fixable. I work at an EV company and we have good belts, pulleys and laser cutting providers so i should be ok with it.

My next step is to figure out precisely my battery / charger setup !

 

[bzhwindtalker]

Hello, I have a GNG and after having built many ebikes, it really fullfils my needs for a offroad/trials bike. It can be pushed a lot with a chain drive, it can probably take 2000-2500w brusts easy. I cant get it hot at all on 1200w. It took me quite some time to get the system reliable but it's now spot on, no chain issues and massive torque, it climbs 45° ramps with no initial speed. The only issue is noise but my primary chain drive is really far from perfect.
The gen 2 GNG seems to be a really good option too, but I dit not test it yet.
If you plan to use the motor only for climbing, a slow MAC with a high quality rim and good torque arms will work well!

 

[glump]

Thanks for your feedback !
The thread on your bike convinced me that GNG is the way to go !
Could you tell me more on your battery setup / consumption ?

 

[N!co]

for the 6s lipo from HK how do you charge them if wired for 44V ?

There are many ways to charge. Personally, I always balance charge at 6s with a BC-168 charger (charging through the balance taps). As a result I've set up my two bikes as follows:
1) Parallel packs first, then series them (so a 4 battery pack is two pairs paralleled, then these two sets are put in series()
2) When I charge, I disconnect the series connecter. First! Then double check I disconnected it.
3) Then I plug all the balance taps into parallel and charge.

This way, everything is balanced every time. At 8 amps per channel max, this can be a slow process. And, if you ever forget that middle step... fireworks and toasted gear.

Again, there are many ways to charge...

Would it be possible to leave your packs in series and charge them from 2 BC168's that have separate and isolated 12V powersupplies?

 

[glump]

I just ordered the GNG brushless kit.
Now i need to figure out the battery etc...

 

[bzhwindtalker]

You should get a 14s lipo setup, you will really have more power while stating in the stock controller range. On the other hand 12 s makes charging easy.

 

[glump]

if i go with a 12s2p setup, is this a good selection from HK ?
For the power supply of the charger i will use a pc or a big truck battery.


Uploaded with ImageShack.us
What do you think ?

(i didn't really understood how to charge in parallel.... and most of all what do i need ?)

bzhwindtalker how do you make a 14s pack ? 2x6s+1x2s ?

 

[glump]

At the end I went for an easy setup for my furst build so i bought a 48V10A LiFepo pack from ping battery to put in a backpack.
I built a box on the frame to make a clean assembly of the controller, the watt-meter and the cables.

I went for test to the boulangerie, close to work 1.6km away. Pedalling a bit i had this:

Going t the boulangerie 32.3 wh 34 km/h average

and back 27.3wh and 32 km/h average

(altitude seems wrong, it is uphill first and going down on the way back)

so it makes about 18.5 w/km full throttle with every thing stock

Over data:
weight: bike: 23.5kg, battery+backpack:6.1, me: 88.3= 118 kg

Peack power of the bike on the watt-meter 1050w

Result : the belt is already dying !!