Critique my mid-drive build plan

[sjtrny]

Hi guys,

Sorry if this is the wrong place to post. Wasn't sure if this sub-forum or the mid-drive sub-forum was more appropriate.

I am looking for any advice, suggestions, approval or mockery for my proposed build.

This will be by first build. BUT I am quite experienced with RC and electronics (build my own planes, quadcopters etc) so I've found everything pretty easy to understand so far.

Goal:

• Daily commute to train station to/from train station 5km each way and quite hilly.
• Commute without breaking a sweat
• Occasionally take it out to do some light off road work

The plan:

• Donor Bike: Trek 810. It's a hard tail I've had since I was a kid. Just needs new tyres AFAIK, hasn't been ridden in a long time.
• Motor/ESC: Cyclone 3000W
• Monitoring: Cycle Analyst v3
• Battery: 18S (72V) 6-8Ah Lipo (probably from Hobbyking)

Obviously 3000W isn't street legal (here in AU it's 250W pedal assist, please correct me if I'm wrong). So I would like to use the CA to put the bike into a street legal mode if Police or other authorities take any interest.

Does this seem like a reasonably straight forward/sane build? Or am I going in the totally wrong direction?

 

[Drunkskunk]

Welcome to the forum. We don't sugercoat shit here. Your plan has flaws.

Starting with the Trek, Good choice. The 800 series are what many give as an example of the "ideal" doner bike. The only way to improve an 800 series is with fatter tires, and Koolstop brake pads. That's pretty much it, they are good to go as is. However, this design of bike isn't built for speeds over 50kph. The geometry is all wrong and wouldn't be stable, and the parts aren't built for that kind of stress. a 3000w bike might push up to 70 kph. The bike would eventually come apart at those speeds.

A 3000 watt cyclone as a commuter bike's power plant is another story. If you had years of experience building ebikes you might be able to set up a 3kw Cyclone that would only need maintenance every few days and get you to work without breaking down and making you late 29 out of 30 times. You don't have years of experience. You aren't going to be that lucky.
It's an awesome motor. It would be a phuqing riot on the trails. it's not something you can rely on for commuting. And there are a lot of reasons for that. For example, the drive sprockets, chain, bearings, and axles were designed for 1 human power. An average person produces around 100 watts sustained, an Athlete can sustain 200 watts. 3000 watts from a motor is 30 times the power from an average person.

If you want a reliable commuter, slap a 1000w hub motor in that bike. It's pretty much the ideal match, and will thrash pretty well on the trails.
Then build a second bike for just the trails with the Cyclone kit and go have a riot with something that sometimes will get pushed home, but you won't care, because it will be epic.

 

[timk]

Are you in Brisbane? If so you could take my bike for a ride to see if your power needs are overstated.

I'm running a Bafang BBS02 with a dolphin pack full of 18650 cells, apart from needing to be retightened once, it has been reliable.

I have just clocked over 500km, I commute 40km a day.

Cheers

 

[Wheazel]

I would advise a new member of the ebike community to go the direct drive hubmotor route for reliable commuting.
A middrive or any setup that requires some kind of transmission of the power, will be more prone to cause problems over time.
It is trickier than you think to build a rock solid system with one or two transmission steps. A DD hub is more forgiving.

I have tried a lot of configurations, and my hubmotor cargobike is by far the one that has caused me the least problems.
So far 6500kms of riding since the end of July 2015. Never gotten delayed to work due to the bike.

Edit* I use a leafmotor 1500W that I am giving 2500W tops. Most riding is done at 600-1000W.
And this is on a heavy bike with bad aerodynamics. Basically the only downside is the unsprung mass of the hub.
Which in my book is a minor problem for a commuter bike.

 

[flat tire]

First, you don't want a ESC from a RC craft, you want a good sine wave controller like the one in my sig.

Second, don't listen to anyone who tells you to get a hub motor if your bike will see significant use off road or in any situation where handling is important. The mid drive is obviously a lot better for handling and off road use due to heavy wheels being HORRIBLE off road, and also offers a lot of versatility as far as climbing hills and still getting decent speed on straights if makes use of the bike's gears.

If you mostly want to ride on roads, I'd advise a gearless hub motor like the one in my sig over a mid drive. Reason being it will be much quieter, simpler, and offer more raw power than a mid drive for high speed cruising. My 1500W nominal motor can cruise at 45 MPH, hits a 56 MPH top speed on a fresh charge and gets best range between 30 and 35 MPH.

Third, a good 18650 battery will offer better cycle life and energy density than LiPo but less raw output and more voltage sag under extreme output demands. For your power needs LiPo doesn't really offer any advantage. If you can't spot weld or solder (dangerous) your own 18650 pack I would go with LiPo just because they're much easier to assemble. Whatever you do, make sure you balance charge, and you're better off with NO bms and a decent balance charger than a crappy BMS.

Fourth, GET A CYCLE ANALYST. I didn't have one at first and it's not an absolute necessity to ride but it will make your rides 1000% easier and more informed.

 

[izeman]

i would choose the BBSHD over all other solutions. it's reliable and serves well on- and offroad.
18s is not needed, get a 13s/14s 18650 pack. 10Ah are more than enough for 2x 5km rides.

 

[sjtrny]

Wow thanks guys. Great to hear some wisdom from experienced e-bikers (is e-bikers a thing? I'm sticking with it).

I think if I was to summarise what you're saying it would be:

• You don't need 3000W
• Bike won't tolerate the power
• Use a hub motor to start with OR get a smaller mid-drive

So in response I have some questions/thoughts

Too much power

I wasn't anticipating to be taking full advantage of the 3000W. Is it not possible to run at a lower voltage or current limit with the CA v3?

Also I'm unlikely to ever go faster than 50km/h as that is the speed limit on the roads I will be riding.

Hub Motor

I have read that Hub motors are often not up to the task of large hills. Is this true or would a 1000W hub motor be fine?

Smaller Mid-Drives

Annoyingly the BBSHD and BBS02 are more expensive than the Cyclone 3000W kit, which is why I ignored them. Are there more affordable options?

I just noticed the Mini cyclone on lunacycle but it's still more expensive than the 3000W kit. What's the deal with that?

 

[Chalo]

Second, don't listen to anyone who tells you to get a hub motor if your bike will see significant use off road or in any situation where handling is important. The mid drive is obviously a lot better for handling and off road use due to heavy wheels being HORRIBLE off road,

The Trek 810 is a hardtail bike; all its weight other than the front wheel is unsprung. What does it matter where the motor is? As long as it isn't high or stuck outside the wheelbase, I don't see what difference it's likely to make.

 

[izeman]

you only need a 3000W kit if you want to ride 3000W. no need to spend more money than needed.
just imagine that top notch ebikes like haibike have a nominal 250w (peak around 500-700w) limit and can climb the steepest hills. 1000w is good enough to let you ride 45km/h w/o pedaling on the flat for sure. if you are way over 100kg or have strong winds, your speed will be lower of course. a mid drive using gears will always be able to climb steeper hills at the same power level than a DD, for a longer time (not necessarily at a higher speed of course).
yes. the bbshd kit is more expensive, and a high quality 18650 battery is expensive as well. but i have built quite some bikes, and i can only recommend: do it once right, or twice wrong for more money.
you may go the super cheap road and buy a little bafang front/rear hub, some cheap rc-lipo, but then you have to learn all the stuff about wiring, battery maintenance, etc ...
installing a bbshd kit (eg from em3ev or luna *ggg*) will get you running in a very short time, and i can almost gurantee that you will be happy with it.
if you still tend to go the do-it-all-yourself route, we'll be happy to guide you through all the stuff you need to know.

 

[izeman]

Second, don't listen to anyone who tells you to get a hub motor if your bike will see significant use off road or in any situation where handling is important. The mid drive is obviously a lot better for handling and off road use due to heavy wheels being HORRIBLE off road,

The Trek 810 is a hardtail bike; all its weight other than the front wheel is unsprung. What does it matter where the motor is? As long as it isn't high or stuck outside the wheelbase, I don't see what difference it's likely to make.

that's absolutely correct. still a mid drive adds the benefit of using the gears, at cost of more complexity and a possible higher failure rate because of more components.

 

[sjtrny]

you only need a 3000W kit if you want to ride 3000W. no need to spend more money than needed.
just imagine that top notch ebikes like haibike have a nominal 250w (peak around 500-700w) limit and can climb the steepest hills. 1000w is good enough to let you ride 45km/h w/o pedaling on the flat for sure. if you are way over 100kg or have strong winds, your speed will be lower of course. a mid drive using gears will always be able to climb steeper hills at the same power level than a DD, for a longer time (not necessarily at a higher speed of course).
yes. the bbshd kit is more expensive, and a high quality 18650 battery is expensive as well. but i have built quite some bikes, and i can only recommend: do it once right, or twice wrong for more money.
you may go the super cheap road and buy a little bafang front/rear hub, some cheap rc-lipo, but then you have to learn all the stuff about wiring, battery maintenance, etc ...
installing a bbshd kit (eg from em3ev or luna *ggg*) will get you running in a very short time, and i can almost gurantee that you will be happy with it.
if you still tend to go the do-it-all-yourself route, we'll be happy to guide you through all the stuff you need to know.

The thing is that the 3000W kit is cheaper than BBSHD. I'm right on 100kg and will sometimes carry up to 15kg of gear with me (multiple quads (drones to the uninitiated) and a stack of lipos to power them).

I'm used to wiring and battery management/care. I do it every day with my quads. I'll be soldering at least once a week doing repairs and charging/cycling or storage charging my lipos. Electronics is the easy side for me. The mechanical stuff is the hard part.

 

[izeman]

i know. the kit is cheaper. many ppl use it, so it should work for you as well. i just don't have any experience with it.
as you fly quads you probably know everything about lipos, balancing and stuff (i fly a 450 quad as well).
there should be no BIG difference between installing the bbs and the cyclone kit. each of them can be hard or easy to do, depending on your experience.