DIY Dual Motor EMTB/Cargo Suggestions

[SCIFIcrab]

I am relatively new in the world of ebikes, but have good experience working on bikes from my time working at a bike store.
My current ambitious project is to build an ebike capable of hauling up to or near 100 pounds of cargo in off road condition similar to a bike packing mtb setup, but with more weight.
Idealy I would want this bike to function more like motocross style bike with pedaling not used very much but it might be necessary to give the required power for steep hills.
I am not too sure what would be the best type of motor + controller for this application, but would love to hear some suggestions!

 

[m@Robertson]

I've got a little experience with this . I've done the awd thing and the super heavyweight cargo thing.

Dual Motor AWD Electric Bikes (the good and bad)

I like to build top-quality-component ebikes from the frame up. Quite a few of them are dual motor or AWD or 2WD or whatever you want to call them. Why would you build an AWD ebike?

talesontwowheels.com

I can tell you without hesitation your best motor choice will be a BBSHD in the back and a fat hub in the front. the problem with that is there are no fat front hubs available on the market at this time (If you find one, please let me know). In fact I just went a few rounds with a Chinese seller who was advertising 135mm Bafang G060's (the gold standard) and it turns out they are out of stock, likely never had them in the first place.

When looking into carrying serious weight, you need to realize what you are getting into. Myself personally, with a heavily modified Surly Big Fat Dummy (super strong custom wheels, BBSHD, custom wideloaders) I have crossed 565 lbs in total system weight. The issue is balance. Put 120+ lbs even low on wideloaders that are perfectly balanced and you are essentially in for the ride of your life at 5-8 mph, and even with the best brakes, your challenge when slowing is not about stopping, its about the risk of losing your delicate balancing act and crashing over. When a 500 lb bike falls over, stuff breaks.

Only one kind of cargo bike - other than a tricycle which is sub optimal for bikepacking - can handle these kinds of loads without balance issues - a frontloader.

Mid Tail, Long Tail or Front Loader (which cargo bike do I choose)?

I never planned on building three different classes of cargo bike, but I did. What are their strengths and weaknesses?

talesontwowheels.com

And a frontloader is not ideal for bikepacking, either.

I presently have my Surly BFD set up for overland riding in the Lower Sierras - where I am in the forest or running along mostly granite mountainsides - no actual trails. The bike use in that environment is wood gathering. So I can get it pretty heavy, but its not any 200 lbs of cargo heavy. A BFD or a Salsa Blackborow are the two production bikes you want to look into for this kind of work and guess what? Both are out of production. Blackborow's are unicorns, but if you Join the Surly Big Dummy and Big Fat Dummy group on Facebook you can find them on sale used.

There are no pics of it set up like this, but I now have a 36T front chainring to go with the 11S rear setup. If I were starting over (the SRAM 11S group with CSMS7 steel cluster is plenty strong) I would use either a Box 2 9 spd with a Microshift Advent 46T steel cluster, or if that cluster won't work with the Box derailleur (which is a beauty) do the full Microshift Advent transmission group. Bear in mind a bike like this will need a lot of chain (I am at 210 links IIRC) and you really REALLY want to use a proper badass ebike chain. As in go ahead and break the bank and get a KMC e9. However the SRAM EX1 has 144 links and even though it is a 10s it should work on a 9s drivetrain - it was specified by SRAM for their EX1 drivetrain which I have on my enduro. Why do I mention this? They are only about $25 each. I am doing the Advent upgrade on my mid tail maybe as soon as tomorrow and I can't find e9's closer than the UK so I have a couple of the SRAM chains and we'll see how they do.

The Surly Big Fat Dummy Project

Prologue (you are here)Episode 1: 138L (each) Panniers… Seriously?!Episode 2: Big Fat Dumb WideloadersEpisode 3: Kickstand KaosEpisode 4: Add a Flight Deck. And a HangarEpisode 5: LeftoversEp…

talesontwowheels.com

Beyond those choices we're talking custom frame, I think.

or do a trailer to get around the balance issue.

 

[SCIFIcrab]

Thank you for the in depth block-o-text. Your article outlines the exact reasons why I am going down this dark path, so may I pick your brain a little?

First though I want to share my design goals and ideas:

I am not attempting to design a regular bike. This build is from an engineering challenge program that I am taking part in, where my challenge is to design a jumpable ebike suited for the military. It seems to be a impossible challenge getting a bike small enough to be strapped to someone's chest yet carry upwards of 300 lbs total load. In my research I am now looking for experts to tell me good luck have fun that's not going to work. It wouldnt be a challenge if it were easy.

The bike must be reliable, lightweight(not over 100lbs), have long range, carry ~150 lbs of gear, and be good a tough terrain. This is a gear hauler at heart so top speed is not really a major priority.
Simplicity is the key to reliability, so I want to keep this think down to as few parts as I can. That is one reason why I don't want a mid drive, but I also know its hard to get the required torque without gearing. If it can break easily I don't want it (looking at derailleurs mostly).

As of now I think that a Crystalyte UFO motor would be a good fit but tbh don't know enough about them to justify that decision.

As for frames I'm putting that off for a later date because it will need to be custom, and I need to prove that the electronics work before I an move on in the project.

Thankfully funding is not much of a concern so my budget is pretty high.

I will make sure to post my progress, because like your blog post its a lifesaver for anyone trying to do something similar.

 

[m@Robertson]

Yeah sure no problem on the brain-picking.

What you are doing is going to require quite the budget so its good you are not trying to work so much with general marketplace equipment.

Given your weight carry requirements, you had best look to custom wheels and hubs.

The typical way you do the things you are trying to do is to use steel so it can carry the load and bend (flex) vs. break. So steel everywhere. Clusters, forks. Frame. But thats not compatible with your carry weight. I've done titanium and I don't think its durable enough. It likes to flex. My 2wd hub bike and my 2wd mid+hub are both Chumba Ursa Major frames, with one being chromoly and the other being ti. I think the chromoly is going to have a longer life. Way too much lateral flex in the rear triangle.

DD hub motors are heavy suckers, and they are light on torque. only way I can think of to even try and make this work is to do very small wheels front and rear. You get a torque advantage from say a 16" wheel and its less likely to be impossible to jump out of a plane with it strapped to you. Notice I did not say possible.

 

[SCIFIcrab]

Yeah sure no problem on the brain-picking.

What you are doing is going to require quite the budget so its good you are not trying to work so much with general marketplace equipment.

Given your weight carry requirements, you had best look to custom wheels and hubs.

The typical way you do the things you are trying to do is to use steel so it can carry the load and bend (flex) vs. break. So steel everywhere. Clusters, forks. Frame. But thats not compatible with your carry weight. I've done titanium and I don't think its durable enough. It likes to flex. My 2wd hub bike and my 2wd mid+hub are both Chumba Ursa Major frames, with one being chromoly and the other being ti. I think the chromoly is going to have a longer life. Way too much lateral flex in the rear triangle.

DD hub motors are heavy suckers, and they are light on torque. only way I can think of to even try and make this work is to do very small wheels front and rear. You get a torque advantage from say a 16" wheel and its less likely to be impossible to jump out of a plane with it strapped to you. Notice I did not say possible.

Take a look at this crazy picture, pretty sure those are at least 26" wheels.

 

[SCIFIcrab]

Going on about the motors, are you saying that any hub motor with the power and torque to get all that cargo moving would need to be something massive like what they use on those moto cross style bikes?

Also for the frame I think steel will work plus its much easier to find someone to build it.

 

[m@Robertson]

Going on about the motors, are you saying that any hub motor with the power and torque to get all that cargo moving would need to be something massive like what they use on those moto cross style bikes?

Also for the frame I think steel will work plus its much easier to find someone to build it.

Then use his bike if it works so well . If all you have to do is put a rider on it thats a different set of rules. Once that guy finishes with his chute it looks like he has little else besides his jumpsuit to carry along, and I see neither a motor or a battery. Regardless, if its a viable platform use that. Otherwise ...

Motor size: Not that big, but it could not be small. What you have to pay attention to is the Nm torque rating of the motor, and figure out how much that is going to be affected by your battery size, voltage and the controller amperage. In particular, controller amperage = torque, as in more amps = more torque. But the motor itself can only give out so much before it either gives no more or bad things happen to it.

This is where you start to run into the words 'impossible'. Hub motors are by their nature single speed. Up a steep hill they provide the same gearing as they do on flat ground or downhill. Or on pavement vs. sand up past the rims. Two hub motors will help immensely with the problem, but it is inherent in your chosen platform. So you have to overpower it to be able to do the same job a mid drive can thanks to the fact it can use gears (think of how your life would suck if you were the motor (i.e. the rider) and were riding single-speed).

Consider this: A heavy electric cargo bike is doing good carrying a rider and 100 lbs of cargo. You want to shrink the platform and have it work in conditions that are far worse than any cargo bike application. Oh and it has to be folded, worn on the body and take whatever stresses go along with a jump. If you want just an ebike, never mind the heavy cargo capacity, thats a pretty tall order as it is.

If you haven't done it yet, I suggest you get on a bicycle - a normal electric one - and ride it in singletrack or overland terrain with 100 lbs of gear. Once you realize from experience what you are up against, work from there. Just for starters: Fat tires to handle the weight. And because fat, probably 20". I learned in auto racing (working with an engineer from Hoosier talking to me thru a back channel, because lawyers) about sidewall height and tire pressures, and it carried directly forward into cargo bike hauling. Its why I graduated up to a Surly Big Fat Dummy when I was carrying 100-125 lb loads. And after the first ride I knew it was the right move. Given your constraints, plus your usage, you absolutely need 20" or smaller wheels (torque advantage) and the fattest rubber with the tallest sidewall you can muster.

FYI when the Sondors Fold XS was in development, it was originally going to get the same 25a controller the 26" fat tire XS was going to get. But thanks to the smaller wheel diameter 25a turned the bike into a wheelie machine, which is bad for ma and paw who just want to have a peppy ride around the neighborhood. So they used less power. This same torque advantage thanks to the smaller wheels is something you can take advantage of to help you move closer to your goals.

 

[PedalUma]

In my opinion you will need to start where you are at and get some experience with a real bike and not a theoretical one that will not ever happen unless you have experience with a real bike first. The Motague Paratrooper is a proven design. Install a mid-drive so you have the torque advantage of gears. By the time parts arrive you will be riding within two weeks of today. By Valentines! Chalk up some hours riding it and experimenting. Then you will have a visceral feel of the physics. That is how birds fly. They do not need a blackboard with calculations and they fly perfectly well. Further design inspirations will flow from actually doing it. All the best. Please include photos of your Valentines 2022 ride.

 

[tomjasz]

For giggles I used Barent Hoffman's 2WD wiring and two 10T MAC motors and Grin controllers. A real beast IMO. But massive overkill so they ended up on two bikes. I'd think about doing a pair of MAC motors again if I needed a heavy hauler. Although several pedicab sellers use BBSHD motors with very good reliable results.

 

[PedalUma]

I am about to jump on this bike for a crosstown house call appointment with someone with a failed BionX on their Mundo. This pictured Mundo carries 220Kg on the rear rack. That is some wiring diagram! A Mundo with a failed BionX can be had for $450. It is also a good place to start a project.

 

[PedalUma]

In follow up the failed BionX person has ordered a new non motorized rear wheel. After riding the one in the photos there was no going back. Also BionX has not been supported for five years. I just emailed him back proposing doing a bike swap so he can ride this week. My problem is that I have six lost batteries in transit form early December. By early next week I will be out of motors and batteries and my suppliers are taking two week vacations. I guess I will be too.

 

[tomjasz]

In follow up the failed BionX person has ordered a new non motorized rear wheel. After riding the one in the photos there was no going back. Also BionX has not been supported for five years. I just emailed him back proposing doing a bike swap so he can ride this week. My problem is that I have six lost batteries in transit form early December. By early next week I will be out of motors and batteries and my suppliers are taking two week vacations. I guess I will be too.

Yup, here we go into Chinese holidays. As if the supply chain isn't normally F'ed up at the time. I can count the number of reliable suppliers willing to take orders and ship on 1 finger.

NYE and SF create more delays after the holiday with the backed-up orders. Adding a few days to recovering for the holiday.

for anyone making orders from China...
(For optimal display of the table, we recommend using a desktop PC or tablet.)

Public Holiday	Date	Duration	Compensation Days
New Year's Eve	01 Jan – 03 Jan 2022	three days	-
Spring Festival	31 Jan – 06 Jan 2022	seven days	29 Jan & 30 Jan 2022
Qingming Festival (Tomb Sweeping Day)	03 Apr – 05 Apr 2022	three days	02 Apr 2022
Labor Day	30 Apr – 04 May 2022	five days	24 Apr & 07 May 2022
Dragon Boat Festival	03 June – 05 July 2022	three days	-
Mid-Autumn Festival	10 Sept – 12 Sept 2022	three days	-
Chinese National Day	01 Oct – 07 Oct 2022	seven days	08 Oct & 09 Oct 2022

The reason for having so-called „compensation days" in China is that weekend days are swapped with neighboring non-holidays in order to create a longer, uninterrupted holiday period.

 

[kmccune]

Take a look at this crazy picture, pretty sure those are at least 26" wheels.View attachment 112664

I believe my bike would ride its own chute down. That buddy system likes like a prime injury going somewhere to happen.( spoke through heart anyone?)

 

[PedalUma]

I believe my bike would ride its own chute down. That buddy system likes like a prime injury going somewhere to happen.( spoke through heart anyone?)

Those Montagues were used in the first Desert Storm. The idea is you can land lightly and move quickly with stealth. No heat signature. The military has one design of a motorcycle that uses almost any fuel. It is diesel and can run on anything peanut oil to aviation fuel.

 

[Ebiker01]

OP, u r looking to make a Gocycle with 3x more power and 3x frame strength.

It's possible with the TQ Motor (150nm, 3-4lbs), Grin Phaserunner 72v controller and a 2, maybe 3kwh 72v battery pack. Will be $$$$ to make it.

Webstore US

Gocycle G4, G4i and G4i+ set a new standard for performance in the portable e-bike segment. Buy the award-winning G4 electric bike now.

gocycle.com

 

[m@Robertson]

I believe my bike would ride its own chute down. That buddy system likes like a prime injury going somewhere to happen.( spoke through heart anyone?)

What @PedalUma said. At one time they were literally military issue for jumpers. I think (but this could be wrong as I am not that up on folding bike history) they were the inspiration for all of the first budget Chinese copycats that hit the market years ago.

I've never been all that appreciative of the integrity of a folding frame or that particular bike, but after they came up in this thread I went back and took a look at them closely and they do appear to have a pretty solid mechanism. Nothing like the commercial crap out there. I do think the Sondors hydroformed frame is one of the best examples of a sturdy folding 20"-wheel frame out there. But the OP's specs seem to preclude using it. Honestly I think the only way to meet those specs is to specify some tech that does not yet exist. Particularly lightweight, high energy, high density battery storage.

 

[PedalUma]

does not yet exist

This is why he should do a real world project. It is the difference between a kid at the back of the bus talking about a theoretical girl the the guy who is talking with a girl.

 

[m@Robertson]

This pictured Mundo carries 220Kg on the rear rack.

You sure about that? The Mundo is rated for 550 lbs / 249kg, but that is total system weight, which means rider included. 550 lbs is still a whole lot - roughly 100 to 150 lbs more than the rated system weight of pretty much all competitors, which typically max out at 400-440 lbs. My Big Fat Dummy for instance is 400 lbs.

Just yesterday I was chatting with someone who has discussed carry capacities with the honchos at Larry Vs. Harry (the Bullitt). That frame is stressed for well over its 400 lb system weight limit. Thats not the limiting factor. Neither are the wheels which can be beefed up significantly (I sure did with mine)...

Its the tires that limit the weight capacity of the bike. And while on mine I went to a 32mm internal width rim so I could put on a 2.4" front tire (vs. the spec'd 1.75) the rear triangle cannot go more than a 2" tire... so thats the end of that insofar as upgrades are concerned.

When I put carbon fiber rims on my Big Fat Dummy, shod them with 4.8" tires and then loaded that bike to about 560 lbs, it was clear that the BIG tires - pumped to about 18 psi - made all the difference in the world. I just downsized my mid tail to 2.2" tires from 2.8" (temp wheel switch to fix a broken spoke) and the degradation is enormous. I am totally going back to the big tires.

 

[m@Robertson]

This is why he should do a real world project. It is the difference between a kid at the back of the bus talking about a theoretical girl the the guy who is talking with a girl.

Yup. I mentioned above that he should go get a real bike, load it up to the capacity he wants to and then try and ride it like that. Forget about all the build specs. Just ride a bike that is carrying 100 lbs. That learning experience alone will dramatically inform him insofar as a reality check is concerned.

 

[PedalUma]

You sure about that? The Mundo is rated for 550 lbs / 249kg, but that is total system weight, which means rider included. 550 lbs is still a whole lot - roughly 100 to 150 lbs more than the rated system weight of pretty much all competitors, which typically max out at 400-440 lbs. My Big Fat Dummy for instance is 400 lbs.

Axle strength is very important. These bikes have very strong wheels. Thanks fort the tip in tires.

You could be right. I was thinking payload as being like a pickup truck. Here is a photo of a screw up. These bikes amplify the sound of motors. I have since learned how to do it right. In this case Great Stuff shot out weep holes and on to the rear disc.