Long time rider/engineer building 2wd fatty.

Gramslam

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Hello all,
Gramslam here.
I’ve been riding xc/dh 35 years.

Looking to start build on 2wd fat e-bike
Wondering where a good place to start is. I’ve built one bike. $4k dh bike.
But want a good alternative to driving cars.

Any suggestions would be most welcome! I know nothing of fatty measurements, so not sure what I can use from my DH.
Mainly I’m looking for good compact front and rear hub motors. From what I’ve seen, the bafang stuff looks well built, but that’s just me judging a book by its cover…

Cheers all,

Keep the rubber side down!
 
If you're looking for alternative to car driving, mostly on-pavement operation, 2WD would be mainly serve to obtain high top speeds.
Unless you plan on riding in snow that require extra traction with 2WD.
Any specific battery range that you would like to have? With two motors, you're likely to need extra battery capacity, too.
Finding location on a DH rig for extra battery capacity maybe difficult.

For a front/fatty hub motor, you will need at least a 135mm spacing on the forklegs.

You can get some ideas from these pre-bult dual motor, dual (or triple) battery ebikes:


 
I did a full writeup on doing 2wd ebikes. I've done multiple generations of them, starting out with dual geared hubs and graduating up to mid in the back and hub in the front when I more or less learned the limitations of geared hubs the hard way. My latest is my daily driver at home that I just put into service a couple of months ago.

The link is the intro explainer that gets into three separate examples in detail, where I went in a different direction for each.


Get a sandwich before starting those 4 articles and maybe branching into the Lizzard King build series that goes into a lot of specifics.

In a nutshell, 2wd ebikes are awesome. When you distribute traction to two wheels you gain abilities that you can never approach simply by applying more power to the back wheel.

You'll also see what is wrong with the commercial examples. In a single sentence: they sell the platform short with compromises and shortcuts.

The motor you want for the front on a fattie is the Bafang 750w... The 'bigfoot' 750 that has the oversized internal core. These motors are unicorns now and I know of only one seller, who I bought a motor from a few months ago to replace one I killed on my sand crawler.


With a motor like this, you want the matching 35a controller the same seller sells (they also have a display). Then you set the motor to slow-start so its still safe to use.

Matt @ Bicycle Motor Works Dot Com has built custom batteries for me that have hi capacity BMS' that can handle the draw of two motors at once. If you are building the bike, do yourself a big fat favor and stay away from dual batteries. Also stay away from parallel'ing two packs to make one big one... that works very well but it also introduces a level of risk that you should avoid unless you know exactly what you are doing. Far better move is to buy a single big battery and split its output to the two motors.

Happy to answer questions and shoot down any bad ideas you care to toss out. :D I have a pretty low opinion of the manufactured 2wd ebikes on the market and you will get the gist of why on that opening article. The sellers are making version 1.0 mistakes, or they are cutting corners because they have to make a buck and doing it right doesn't allow that.
 
If you're looking for alternative to car driving, mostly on-pavement operation, 2WD would be mainly serve to obtain high top speeds.
This is incorrect. 2wd does not provide a speed increase (with a minor exception noted below). Just for starters, geared hub motors have rpm limits and those don't change. So the motor spins as fast as it is going to spin regardless of how many of them you hook up in a line together.

With that said, a 2wd dual-Bafang G060 bike with twin 35a controllers - one for each motor - hooked up to a single battery (52v, 30ah with a 90a continuous BMS) on 26" fat tires will peak at just barely 34 mph. Using just one motor on the same bike, its peak will be 32 mph. The 2wd will take a bit to get up to 34 from 32 as well.
img_20170923_172230[1].jpg
img_20180831_101645[1].jpg
img_20190405_181817[1].jpg


On pavement, what WILL increase is your level of acceleration to any speed from zero to the peak. In the left turn lane on my hub+hub commuter, I need the granular control of dual throttles to keep myself from running into the bumper of the car in the turn lane in front of me. Its safest in that one scenario to stay away from dual PAS and use throttle initially to be sure you control your start. Rear throttle only for a blink, then hit the front. 2 seconds in your pedaling takes over and you lift off both throttles and complete the turn without running into anything.
Unless you plan on riding in snow that require extra traction with 2WD.
There is much more to it than that.

Two motors working together... one alone will get too hot to touch. Two together and they are barely warm. The linked video in the opening explainer above gives the specific reasons why this is not an illusion and there really is a large synergistic effect in terms of heat reduction.

Here's one more 2wd benefit: My 'sand crawler' was a flat-ground commuter for about its first 1300 miles. That was my first mid+hub 2wd, built because I learned a hub+hub (the orange one above) was not survivable long term in steep hill country. I discovered the front motor completely wipes out any increased drivetrain wear that comes from a high powered mid drive in the back: The mid is never hauling the bike up from a dead stop anymore. On flat ground I found I had no need to downshift at stoplights, and could start off and stay in the 11T cog. Despite doing this, that ($7) cog lasts about 1000 miles instead of the 50-200 you'd expect from pulling that shenanigan with a rwd mid-drive.

pxl_20210929_013039030-e1633137296875[1].jpg


Wear is reduced on the entire drivetrain. My green cargo bike just crossed 3000 miles and it is still on its original KMC e11 chain (and steel cluster). It still shows good on the wear gauge.

Improved, distributed traction provides benefits in all types of terrain. Its the most obvious to the outside observer in deep sand, snow and mud, but to the rider the appreciation of the benefit on basic pavement is instant. 'effortless' is the best way to describe the feel of it.

And another: I have a load of gravel to pick up again today. 100 lbs. Distribute some of the pulling load (traction) to the front wheel and the amount of pain and suffering the entire drivetrain goes thru to get the job done is markedly improved. I'll be taking a steep hill that a geared hub would never survive, 2wd or no.
 
WOW!!! You guys are awesome! Thank you for so much information!. I will be using it in snow, mud, and whatever else I can throw at it without killing it. I also want to do a kayak trailer for it :) For a battery, I was thinking https://a.co/d/5dgwbnc with a transformer. I use that battery to power my kayak and my dive hookah. Will likely get two more...
I will have to make a few sandwiches, and perhaps a few redbulls to go over all the info you guys have provided!
Thanks!

If anyone ever tells you guys that you are good people, tell them "screw that" Gramslam says I'm Awesome!
 
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Thank you for so much information!.
No problemo. Here's something to watch out for with that motor I linked you to: Bafang has used the same two standard motor connectors for years... and lucky you they just changed them. Look at the linked motor's screw-on connector. These are brand new pics on a listing they have had up for awhile so you will absolutely want to email them and ask if they still have a matching 35a controller as the page says, or if a) the motor does not use that new connector despite the pics or b) sorry charlie their controllers don't match anymore.

If you get b), that means you are going to have to rewire the plug connection yourself. This is not quite as bad as it sounds, but relatively speaking its bad. Not shown in the electrobikeworld web page is that you get the other side to that wire. I did a look around for another option and found none (but I looked for months before I found a 750 and a 500 so keep looking and be patient). However I found an AliExpress ad for the same motor that does show the other side of the wiring that you get.


The blue, green and yellow wires are hall sensors. You would have to find a pinout of the standard plug the controller uses (they exist but I don't have one handy) and get out your nippers and crimper stuff.

I was thinking https://a.co/d/5dgwbnc with a transformer. I use that battery to power my kayak and my dive hookah.
That monster is not going to work on an ebike unless you put it on a trailer and tow it behind you, both because of its size and weight (11 kg). I love LiFePO4 for its safety, forgiveness for being left in a hi charge state and the huge cycle count it can handle vs. the Li-NMC that everyone uses in 18650 and 21700 packs, but LiFePO4's energy density sucks in comparison, which means to solve that you have to do big and heavy batteries... which by and large are way too big for an ebike. And we haven't even addressed the weight of the added gear you will need to step up the voltage. By the time you finish adding a trailer etc. etc. you've lost any hope of having a bike that makes sense. AWD is a weight increase as it is, with a second motor, a need for a bigger battery, a controller etc. etc.

Realistically you want a 48v or 52v battery. Preferably 52v. Not for speed but because 52v provides a wider range of usable volts as it drains down. A 48v battery is actually 54.6v at a 100% charge. A 52v is 58.8v. Not much difference, so 48v systems work fine on it, but the added bit at the top end gives you longer run time.

This is far and away the most visited page on my site. Check out the 48v and 52v charts. They each have a Usable Volts column. 48v is 14.5 until its drained. 52v is 15.8v.

 
Links to Amazon may include affiliate code. If you click on an Amazon link and make a purchase, this forum may earn a small commission.
In the land of cyberspace, Where electric bikers roam, I sought advice from a wise man, To build my dream bike home.

On ebikesforum.com, I posted my inquiry, And waited for a sage to come, To help with my quandary.

Then came a man named "m@Robertson", With knowledge to impart, He shared his wisdom freely, Straight from his ebike heart.

He spoke of gears and motors, Of tires and rims and chains, Of batteries and controllers, And how to beat the pains.

I listened to his every word, And followed every guide, And soon my bike was built and purring, With joy I couldn't hide.

So here's to "m@Robertson", A hero of the net, For giving me the gift of knowledge, And my dream bike, no regrets.
 
So 750w front, what should I go for in rear? 1500w?
What is the best way to connect two controllers?
I’m going to order the front motor you posted.
Then rear and controllers….
My experience is with flight controllers in drones.
 
So 750w front, what should I go for in rear? 1500w?
When I did hub+hub, I did identical front and rear. You will find tons of rear G060 motors. Its the front one thats hard to find. When I went past that and used mid drives in the back to make them basically able to handle anything, I used BBSHDs. Two totally different motors but there is no reason to match them. But if you do, you gain a common parts list between them (controllers, throttles, PAS sensors and so on).
What is the best way to connect two controllers?
The best way is to not do that :) Two entirely separate systems that only share a common battery (or do separate batteries for a v1.00 result. A single common one is a far better solution). My hub+hub bike thus had two individual 35a controllers, so 70a total which makes for acceleration so strong it makes you giggle, but if I'm being truthful is unsafe, which is why you set each of them to slow-start. Two motors on slow-start are still faster off the line than a single powerful one, and the bike remains completely controllable.

Look at the articles that describe the individual bikes. I am pretty sure I included talk about the Y plugs I used to split the brake cutoffs to both controllers, and the PAS Y plug that sent the signal from one sensor to two controllers. The last thing you want is a single throttle and I get into why in the introductory article.
I’m going to order the front motor you posted.
Then rear and controllers….
If I were you I would tie together the controllers and the motor purchases. Electrobikeworld has been selling this stuff for years and if it were me I'd want to keep them on the hook for compatibility. Its that or you dig in and expect to do a lot more work potentially getting compatibility together. Putting compatibility on EBW makes an already complex project just a little simpler.
 
Hello all,
Gramslam here.
I’ve been riding xc/dh 35 years.

Looking to start build on 2wd fat e-bike
Wondering where a good place to start is. I’ve built one bike. $4k dh bike.
But want a good alternative to driving cars.

Any suggestions would be most welcome! I know nothing of fatty measurements, so not sure what I can use from my DH.
Mainly I’m looking for good compact front and rear hub motors. From what I’ve seen, the bafang stuff looks well built, but that’s just me judging a book by its cover…

Cheers all,

Keep the rubber side down!
Check out Eunoeau defender. S. Lot of bike for resonal money
 
This is incorrect. 2wd does not provide a speed increase (with a minor exception noted below). Just for starters, geared hub motors have rpm limits and those don't change. So the motor spins as fast as it is going to spin regardless of how many of them you hook up in a line together.

With that said, a 2wd dual-Bafang G060 bike with twin 35a controllers - one for each motor - hooked up to a single battery (52v, 30ah with a 90a continuous BMS) on 26" fat tires will peak at just barely 34 mph. Using just one motor on the same bike, its peak will be 32 mph. The 2wd will take a bit to get up to 34 from 32 as well.
View attachment 8291View attachment 8290View attachment 8288

On pavement, what WILL increase is your level of acceleration to any speed from zero to the peak. In the left turn lane on my hub+hub commuter, I need the granular control of dual throttles to keep myself from running into the bumper of the car in the turn lane in front of me. Its safest in that one scenario to stay away from dual PAS and use throttle initially to be sure you control your start. Rear throttle only for a blink, then hit the front. 2 seconds in your pedaling takes over and you lift off both throttles and complete the turn without running into anything.

There is much more to it than that.

Two motors working together... one alone will get too hot to touch. Two together and they are barely warm. The linked video in the opening explainer above gives the specific reasons why this is not an illusion and there really is a large synergistic effect in terms of heat reduction.

Here's one more 2wd benefit: My 'sand crawler' was a flat-ground commuter for about its first 1300 miles. That was my first mid+hub 2wd, built because I learned a hub+hub (the orange one above) was not survivable long term in steep hill country. I discovered the front motor completely wipes out any increased drivetrain wear that comes from a high powered mid drive in the back: The mid is never hauling the bike up from a dead stop anymore. On flat ground I found I had no need to downshift at stoplights, and could start off and stay in the 11T cog. Despite doing this, that ($7) cog lasts about 1000 miles instead of the 50-200 you'd expect from pulling that shenanigan with a rwd mid-drive.

View attachment 8289

Wear is reduced on the entire drivetrain. My green cargo bike just crossed 3000 miles and it is still on its original KMC e11 chain (and steel cluster). It still shows good on the wear gauge.

Improved, distributed traction provides benefits in all types of terrain. Its the most obvious to the outside observer in deep sand, snow and mud, but to the rider the appreciation of the benefit on basic pavement is instant. 'effortless' is the best way to describe the feel of it.

And another: I have a load of gravel to pick up again today. 100 lbs. Distribute some of the pulling load (traction) to the front wheel and the amount of pain and suffering the entire drivetrain goes thru to get the job done is markedly improved. I'll be taking a steep hill that a geared hub would never survive, 2wd or no.
I see a lot of mid drive bikes using 8 and more gears at the rear. Wouldn't make more sense to reduce the number of gears which would allow a stronger chain and gears?
 
No problemo. Here's something to watch out for with that motor I linked you to: Bafang has used the same two standard motor connectors for years... and lucky you they just changed them. Look at the linked motor's screw-on connector. These are brand new pics on a listing they have had up for awhile so you will absolutely want to email them and ask if they still have a matching 35a controller as the page says, or if a) the motor does not use that new connector despite the pics or b) sorry charlie their controllers don't match anymore.

If you get b), that means you are going to have to rewire the plug connection yourself. This is not quite as bad as it sounds, but relatively speaking its bad. Not shown in the electrobikeworld web page is that you get the other side to that wire. I did a look around for another option and found none (but I looked for months before I found a 750 and a 500 so keep looking and be patient). However I found an AliExpress ad for the same motor that does show the other side of the wiring that you get.


The blue, green and yellow wires are hall sensors. You would have to find a pinout of the standard plug the controller uses (they exist but I don't have one handy) and get out your nippers and crimper stuff.


That monster is not going to work on an ebike unless you put it on a trailer and tow it behind you, both because of its size and weight (11 kg). I love LiFePO4 for its safety, forgiveness for being left in a hi charge state and the huge cycle count it can handle vs. the Li-NMC that everyone uses in 18650 and 21700 packs, but LiFePO4's energy density sucks in comparison, which means to solve that you have to do big and heavy batteries... which by and large are way too big for an ebike. And we haven't even addressed the weight of the added gear you will need to step up the voltage. By the time you finish adding a trailer etc. etc. you've lost any hope of having a bike that makes sense. AWD is a weight increase as it is, with a second motor, a need for a bigger battery, a controller etc. etc.

Realistically you want a 48v or 52v battery. Preferably 52v. Not for speed but because 52v provides a wider range of usable volts as it drains down. A 48v battery is actually 54.6v at a 100% charge. A 52v is 58.8v. Not much difference, so 48v systems work fine on it, but the added bit at the top end gives you longer run time.

This is far and away the most visited page on my site. Check out the 48v and 52v charts. They each have a Usable Volts column. 48v is 14.5 until its drained. 52v is 15.8v.

I would recommend sticking with high quality 21700 cells, preferably Samsung for your battery.
 
I see a lot of mid drive bikes using 8 and more gears at the rear. Wouldn't make more sense to reduce the number of gears which would allow a stronger chain and gears?
Only if you are breaking chains, which should never happen if the builder does their job right and the rider does the same. Especially on a 2wd where a big part of the 2wd benefit is splitting the load to two wheels, which in turn eliminates the wear and tear on the drivetrain that a high power mid drive creates.

But about that part on stronger chains... On my green Bullitt, I just crossed 3000 miles on its original chain: A KMC e11 and yes that means its 11s. Do some googling and you'll find 11s chains testing out to be stronger than 9s, which has sort of been the DIY standard for some time. Its counterintuitive but boils down simply to the fact that by the time 11s drivetrains came out, chain manufacturers got better at it.

I just scored four Connex 11s chains for only $24 each at Jenson USA, in case anyone else is in the market. They are normally around $100 each. Usually I buy the SRAM EX1 which is 8, 9 and 10s compatible, meant for ebike drivetrains and is normally priced at $25.

Fewer gears become a benefit if you are throttling but not pedaling. Throttling, you are trying to make the motor happy and the cycling experience isn't so relevant, so fewer gears are a benefit. If you want exercise though, the variation necessary to allow meaningful pedaling remains and you are right back to wanting more gears.

My white Bullitt is using an AdventX drivetrain, just changed from a Box Prime 9. Almost all of the reason I changed is I wanted more gears and I thought the differences in the hardware might give me more than just a single extra. Turns out I guessed right and I got two. That frame has very short stays so its impossible to run a mid drive and have a chain be usable across the whole cluster. Not because the derailleur can't get there, but because pumping so much power thru a skewed chain is a recipe to break it.

Here's the bike a few days ago. Thats 100 lbs of gravel (100 lbs sure doesn't look like much). Plus my 250 lb self. And I have steep hills between the store and my home. No broken chains and to get up those hills I really appreciate the gear variance to give me the cadence I want on whatever the slope is.

20230406_150404.jpg


My Surly Big Fat Dummy, which I retired for the white Bullitt, negotiated the same terrain with the same loads and has only a single BBSHD and a 215-link KMC 11e chain for its 11s drivetrain. Its at I think 1600 miles and counting; no issues.

Lastly, I have been building mid drives since I think ... 2016? Many thousands of miles on both daily drivers and singletrack toys. I have never broken a chain. I've cracked an 11T cog and worn a few others out, but never damaged a chain, using motors that typically peak at 1750w (BBSHD) and go as high as 4 kw (Cyc X1 and Cyclone).
 
I would recommend sticking with high quality 21700 cells, preferably Samsung for your battery.
Under the floor of the white Bullitt, initial test fit. Custom made-to-size with Samsung 50S 21700's. 14S8P and the available room turned out to mean a 35ah pack. Hi-po BMS to handle the dual motors. The second box, empty in this pic, houses the front motor controller and onboard charger.
20230114_143102[1].jpg


Under the green one. 2 years earlier. Final fitment before bolting the floor on. Samsung 40T 21700's, 14S8P but a bigger pack (no 50S available back then). 70a continuous BMS to accommodate both motors. 32ah. You can really see the improvement the 50S provides in that pack's smaller size and larger capacity, which allowed me to completely hide the battery behind the frame rails and between the crossbars rather than having to put it underneath.

pxl_20210501_201129667-e1620856648406[1].jpg
 
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