3kw eBike Build Questions

Hi everyone,
First time poster here. I've been contemplating a build for the past few years and I've now got a fairly good idea what I want but have a few questions.
I'll likely be selling my motorbike (93 dr350s) to fund this project, and my goal is to have this bike basically be able to replace that bike. Not in speed and power but more that its something I can ride to uni everyday (very short commute), explore suburban roads/paths, and the odd dirt road/track.
So I've decided that what I want is something along the lines of a 3 to 5kw hub motor, dual suspension mtb. I havent bought the bike yet, but I'm thinking of going with something like an early 2000's downhill bike (something similar to a norco vps or old kona), as they have good suspension and brakes, and will hopefully be fairly stable.
To mount the motor I'm going to cut some steel plates that bolt on around the dropouts and slightly extend the wheelbase. I have access to a waterjet cutter, so I can very neatly cut the plates out of, say, 10mm steel.
Batteries, I'm thinking of using lipos and (depending on whats on special when I buy them) I'll likely be using three 6s 20Ah packs in series. Main reason I'm wanting to use lipos is that the bike likely won't have a big space for a battery, so it'll be easier to distribute three smaller sized batteries. I'll probably end up rewiring the cables with a bms, so that I can charge the bike with one charger, although maybe I am better off just starting with 18650s then?
My main questions are around the motor and controller setup. Top speed wise I'm not after anything too crazy, 60 to 70 km/h would be heaps. I do want it to be fairly torquey though, so I'm thinking somewhere in the 3 to 5kw range is good?
What I'm unsure about is how it should be configured. I could use a low kv motor, and give it heaps of volts and not so much current, or a could use a high kv motor and do the opposite. Both would result in similar speed and torque, but I'm sure that one of those setups in more preferable.
Hence, what I'm asking is what specific motor meets my requirements, and what battery setup with it?
I'd like to get a motor laced to a 26" bike wheel, as I'm doubtful that the bike's swingarm will clear a motorbike rim/tyre, but will pushbike spec spokes and rim be strong enough for that power level?

Thanks for any help.

How much offroad use do you expect?

Grantmac said:

How much offroad use do you expect?

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Not much proper off-road stuff. Lots of paths and few dirt tracks. Back wheel won't be leaving the ground much, but I'm sure I'll appreciate the dual suspension

You won't need the 3kw 45H motors, the Leaf 1500W will be fine, or the cheaper 1kw hub motors, while you buy a 48V or 52V 40A controller.

You also dont want any bicycle that sticks out, or is colorful to draw attention while your in class at the university.
Hiding a rear hub behind dirty pannier bags and having a removable battery would be the top priorities.

The issue is the unsprung weight of the hub. Any offroading will be severely compromised.

jacobm906 said:

What I'm unsure about is how it should be configured. I could use a low kv motor, and give it heaps of volts and not so much current, or a could use a high kv motor and do the opposite. Both would result in similar speed and torque, but I'm sure that one of those setups in more preferable.

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If it helps, a system that needs more current is harder on it's batteries, and/or needs to have more parallel cells to keep from doing that.

jacobm906 said:

3 to 5kw hub motor, dual suspension mtb

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Hub motors, especially heavy ones, thoroughly compromise suspension performance.
If you find the advantages of a hub motor compelling, best to fit it in a hardtail frame.
Conversely, if you find the advantages of full suspension compelling, best to build it as mid-drive.

The consensus for 70kph and dirt roads will be full suspension.

^or motorcycle

The University student OP just needs a normal ebike going normal speeds.
Literally anything will do, unless there are some steep hills to climb.

Probably best for a one stop shop where you get a quality built battery along with a quality laced quality rim and the kit.
https://ebikes.ca/shop.html

Thanks for the responses.

I'm not looking at building a cheap way to get to uni. I'm living close enough that I can walk or ride a push bike, or yes a normal ebike. But I'm wanting to build a high power dual suspension bike, for many more uses then getting to uni. Something that I can replace my motorbike with, in that I can go hoon around the suburbs, do up to 70km/h with plenty of torque for the hills, and hit the odd dirt track on it.

I was considering just going with a bbshd, and I'm aware this would have many benefits on a dual suspension bike, especially for off road use. But I think a hub motor suits my needs better. The idea of going that fast on a hardtail doesn't sound very comfortable. A softtail with perhaps a stiffer spring and good anti-squat geometry would be preferable I believe.

I do appreciate all the responses, even the ones suggesting other options. Please keep them coming if anyone else wants to chime in.

BBSHD won't do what you want and a hub won't either. You need to consider the Lightning Rods LHD or a similar build.

jacobm906 said:

Thanks for the responses.

I'm not looking at building a cheap way to get to uni. I'm living close enough that I can walk or ride a push bike, or yes a normal ebike. But I'm wanting to build a high power dual suspension bike, for many more uses then getting to uni. Something that I can replace my motorbike with, in that I can go hoon around the suburbs, do up to 70km/h with plenty of torque for the hills, and hit the odd dirt track on it.

I was considering just going with a bbshd, and I'm aware this would have many benefits on a dual suspension bike, especially for off road use. But I think a hub motor suits my needs better. The idea of going that fast on a hardtail doesn't sound very comfortable. A softtail with perhaps a stiffer spring and good anti-squat geometry would be preferable I believe.

I do appreciate all the responses, even the ones suggesting other options. Please keep them coming if anyone else wants to chime in.

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I build an ebike based on Giant Trance. With a battery it weighs 38 lb.

It can climb any hill, but the top speed is only 50 km/h.
I'm in the process on building a bike based on Orbea and it will do about 70 km/h.

What are those cell holders?

Sent from my Nexus 6 using Tapatalk

john61ct said:

What are those cell holders?

Sent from my Nexus 6 using Tapatalk

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These are custom made. I call them gatling gun style. 10S in this case. They can be any S and I might make 4P sometimes in the future just for fun.

Nice, would you be willing to upload the print files somewhere?

john61ct said:

Nice, would you be willing to upload the print files somewhere?

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Do you have capability to make these type of parts?
What equipment do you have and were are you located?

Just talking about as an open source resource for the community, for myself it would just be a "maybe someday"

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john61ct said:

Just talking about as an open source resource for the community, for myself it would just be a "maybe someday"

Sent from my Nexus 6 using Tapatalk

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I posted questions on this, Vesc and esk8 forums and haven't got a single answer.
I gave donations and got nothing in return. So, at this point my reply in no.

Ecyclist said:

john61ct said:

What are those cell holders?

Sent from my Nexus 6 using Tapatalk

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These are custom made. I call them gatling gun style. 10S in this case. They can be any S and I might make 4P sometimes in the future just for fun.

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No offence but that pack design is stupid, the cells located near the connection between parallel groups will suffer a lot. That.s probably Ok Because you dont draw that much current.

atkforever said:

Ecyclist said:

john61ct said:

What are those cell holders?

Sent from my Nexus 6 using Tapatalk

Click to expand...

These are custom made. I call them gatling gun style. 10S in this case. They can be any S and I might make 4P sometimes in the future just for fun.
Battery 1.jpg

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No offence but that pack design is stupid, the cells located near the connection between parallel groups will suffer a lot. That.s probably Ok Because you dont draw that much current.

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You don't know shit from shinola, but I will give it to you for someone who doesn't know much you are cocky little frog. 8)

I actually like the design, in abstract anyway, precisely because that group connection could be located at the hub centre, therefore equidistant for each cell within the group.

Would work well for packing a tubular case, but otherwise does not optimise overall energy density.

I designed it for a very specific reason and put a lot of thinking behind it. I will not go into details, but I will just say that without it I could not achieve my goal of flying to Japan with my build electric bike and tour island of Shikoku. I have this pack for two years now and it is still working perfectly. This thing can be disassembled and assemble back in two hours with just one coin and one phillips screwdriver and it seamlessly fits inside frame of my bike.

So why not go into details?

I need modular packs like Justin's LiGo that comply with airlines' 100 Wh restriction

That what you mean?

Patent pending or going on sale soon. Dont matter either way, if it sells good it will be copied and knocked off.

I had a DR350. It was a fun bike. I think mine might ave been a 93 too? Maybe a '92. Anyway, it was a fun bike.

You aint touching the power level of that bike with any off the shelf mid drive. YOu might get close to the on road performance with a big hubby.

There is a line between ebike and emoto. My current bike borders that line. You have to choose if you want a bike-like bike, or a moto-like bike. Then build to suit.

I had a BBS02 Mid drive but it was nt the best design ( Chinese production) and was hard on the bicycle components. if you are not into fixing your bike consonants every week, get better components. My BBS02 fun ran out at 1200 miles after fixing the dirve twice with major downtime. They just cannot handle hard riding. They are for light trails at lower than 20mph. I can blast up trails with my modified hub motor.

Then I build a hub bike, 100w QS motor ( like the 1500w Leaf motor recommended above, a clone) and this bke was 100x more fun, and I take it everywhere.

Checkout my hub bike build thread and others here. Gives ya an example of what you can do. Lipo energy density is a compromise... and there art cells that whomp them if you oknw what to look for.

DR was a fun fun bike. Soozokiz I had a few.

My hub build: Newbie.

https://endless-sphere.com/forums/viewtopic.php?f=6&t=103648&hilit=Newbie

markz said:

Patent pending or going on sale soon. Dont matter either way, if it sells good it will be copied and knocked off.

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You hit the nail on the head. Obviously you understand how things work. Someone design and start production of a new product. After a while Chinese copy it with cutting all corners including quality of material. And voilà you have junk available on Alibaba or EBay for half the price and everybody is happy. Even our government is happy. It collects patents fees for doing absolutely nothing in return. What's not to like?