Help with part selection for my first e-bike

[elmo78]

First of all I would like to say hello and big thanks for being such a great community. I have been reading this forum for a few weeks and I have finally decided to write my first post.

I don't want to reinvent the wheel so I've decided to ask for your opinion on preferred motors and batteries. There's quite a big choice of components so it's really difficult to make a decision.

MY GOALS:

1. Full suspension bike
2. No pedals
3. Top speed around 40-50kph (30mph)
4. Range minimum 30km while off-roading and having fun and 60kmh commuting on flat ground. The more the better.
5. I need torque and acceleration more than top speed.
6. Free wheel. I don't think I will benefit much from regen.

MY POSSIBILITIES:
1. Can weld aluminum
2. Know a lot about suspension and bicycles
3. Can solder stuff
4. Can work with fiberglass (like for a battery shroud or container)

I am in the process of completing the bicycle parts and the electric stuff will come next. The bike is a Giant Warp with Marzocchi Bomber fork, hydraulic disc brakes. As in the photo below.


MY MAIN QUESTIONS:

1. Which motor should I choose? Depending on the motor itself I can connect it directly to the sprocket by the rear wheel (a big sprocket like in motocross bikes). I can buy a motor with an integrated reduction. I can also use the bottom bracket to install a secondary reduction. With no pedals and cranks I can weld the footpegs slightly above the bottom bracket. So the engine cantransfer power to its own primary reduction which is attached to the BB, and on the other side of the BB is the output which then connects to the chain going to the back wheel.

2. Should I use Headway LiFePO4 batteries? Each one of them has 10Ah/3.2V. My initial plan is to use around 18 batteries for 57V and 10Ah. Is that enough? Or maybe there are other battery options which give me more flexibility and lower weight? I have no experience so I can't really tell whether I need more voltage or more ampere-hours in my case.

I also have a plan to use two sprockets side by side, like in a typical bike cassette. They will have a large difference in teeth count. By using a spring-loaded chain tensioner, I can either have more torque and low speed (30pmh) and by popping the chain by hand onto the other sprocket, I could increase speed and range and decrease torque (which is not necessary for longer commuting on tarmac).

I would be grateful for any help

Below is the photo of my bike. The blue circles are the batteries and the red rectangle is roughly the space I have for the engine and reductions (15x25cm). I can double the battery count by placing them on the sides of the frame if need be. But will it be too much weight.

 

[amberwolf]

I use much heavier bikes/trikes so I might be off a bit in my estimates, but this might be useful for range/battery calculations:


At a rough guesstimate, you'll probably need about 1/2Ah per mile at 20MPH for "48V" system on flat ground.

At the faster speeds you're after, especialy since you can't add any human input, you'll probably need a third to half again more Ah per mile, at least, possibly more. If there's a lot of hills or stops and starts you'll need more; the more often you have to accelerate the more capacity you'll use up.

 

[Mündawg]

I do not believe a 570wh battery would be enough for the distance you want, not without pedaling. I get around 20miles (with a little left for emergency) from my 650wh battery, up in the mountains, with a good bit of pedaling effort.
Maybe your motor and battery will be more efficient than mine. And you may not have the same intense hills i do.
But i would err on the side of 20Ah for the distances you want considering you can not pedal with your design.
Good luck mate!

 

[elmo78]

Thanks a lot for the replies.

I am thinking about the cyclone 3000W motor. Seems pretty simple and if I install a big cog in the back it might even run only on its incorporated planetary reduction.

Are there any other battery options which can be a match to LiFePO4?

From what I see on the internet people have some small battery packs tucked to the frames and seem to have a lot of fun. This is why I assumed that a bunch of bulky LiFePO4 batteries would make me happy.

 

[amberwolf]

Sure you could have fun with a small pack, just not for very long (and if the pack is not made of cells that can handle the loads it won't last as many cycles as it should either).

 

[Mündawg]

Are there any other battery options which can be a match to LiFePO4?
.

With your frame it's tricky. I stuck with a softtail frame with a large opening between in put a big ol battery. You maybe could put a second battery on top of your frame in that V crevice. Wire them in parallel.

 

[g725s]

MY GOALS:
1. Full suspension bike
2. No pedals
3. Top speed around 40-50kph (30mph)

When finished with your eMotorcycle please only ride it like the Motorcycle it will be, not a bike. Riding it fast in bike lanes or bike paths like legal bike or eBike will give eBikes a bad rep.

But have fun riding it like a motorcycle once done.

 

[elmo78]

ride it like the Motorcycle it will be, not a bike

No worries about that. I plan to use my bike on the streets and it's legal here. I live in a residential area with little traffic so riding my bike just like a motorbike or car will be safe for me and other people. My house is adjacent to a large forest with singletracks and wider gravel tracks and this is the off-road place where I can have fun.

With your frame it's tricky.

Well, yes it is, but bear in mind that there are no pedals so the knee area can be wider and my pegs can be wider. There's absolutely no problem putting 20Ah of batteries.

But I am still thinking if the LiFePO4 batteries are the right choice? They are safer than LiPO or Li-ion, the3y can withstand more charging cycles but they are probably not the best choice when it comes to power-to-weight/size ratio.

I have been looking at the A123 systems batteries in 26650 format (3,3V, 2,5Ah) but I would need over 100 of them to come close to 50V and 20Ah. Getting close to $1300
If I choose the Headway batteries in 38120 format (3,2V, 10Ah) I can reach 20Ah and almost 60V with 36 cells. Paying less than $700.

Any other battery suggestions? What I like about the Headway batteries is that they have screws on the terminals. I can use thick copper strips and drill them in the right places.