Special 6-seater bike build

[mrpr39]

Hello guys,

i've stumbled across this board while searching for potential solutions for a special project. So far i've already collected some tips, did some calculations and made a generall plan. But before ordering components i wanted to collect some opinions on the choosen parts and my thoughts so far.
So first of all a general project description. The vehicle i want to electrify can be seen below:

It's a 6 seater bike with no connected rear axle, each wheel is driven separately by three of the passengers.
The bike was not designed for driving uphill which is why there is now a need for a conversion, as there are a lot of hills around here
It should be possible to drive the bike completely electric so there will be a lot of power required. I'm calculating with a combined end wheight with passengers of around 800kg.
Now my idea is to connect each separate axle (each wheel on the rear has one, they are just not connected in the middle) with an electric motor.
So some key facts for the build that are given:
- targeted speed: 6-7km/h
- targeted manageable slope: 12% / 7°
- end wheight: 800kg (based on my calculation that makes 1200Nm necessary for driving uphill)
- one separate motors for each wheel

From my calculations i think i require two motors with at least 4, better 5 Nm of torque.
An additional problem is the targeted speed. I can only fit a sproket with around 50 theet on the axle because of the limited space. To get to my desired speed with the current wheelsize the motor shouldn't have more than 500-600rpm, so i'm somewhat limited to motors with a build in gearing.
Now to the parts i thought about using:
Battery:
Aliexpress

Motor:
Aliexpress
I would use the 48v version. Also this motor has the advantage of a build in gearing which together with the sprocket i think i can get to a gearing of 1:30. Although the seller suggests a possible load of 1000kg for a single motor, i'm not sure if that's realistic based on my calculations above.

I'm happy to hear about alternatives and am grateful for any feedback i can get on my plans and will update on the build making progress.

 

[RunForTheHills]

I can't read German, but does that motor have a clutch (for coasting or peddling while the motor is idle)? Since the chainring is mounted on the left side of the bottom bracket shell on the right side of the vehicle, you might be able to mount a BBSHD updside down on that side. Or a CYC X1 Stealth or TSDZ2. Or you could install hub motors like the Grin All Axle. What size are the wheels?

 

[mrpr39]

Ah sorry, this is the english link: Aliexpress
Sadly the motor doesn't have a clutch so i'm not exactly sure how it will behave when coasting. The feature of peddling isn't that important to me, it wouldn't be a problem to remove the chain of the motor just in case the battery will run out one day. And while it's charged i guess no one wants to peddle .
However about the mid mounted motors there is one concern i have. Mounting them probably would work, using one of them upside down. But as they would be connected to the axle with the same freewheel as the people peddling, the freewheel probably can't hold the power. I already had to replace it twice with just the people peddling breaking it.
The hub motor is something i haven't thought about in depth, as my concern there was that it's not suitable for the targeted low speeds. But maybe you know some solution that could make it work. I will look into that later today and also look up the weehlsize let you know about it. Thanks already for the suggested options.

 

[RunForTheHills]

I guess I misstated that. The freehub on the wheel would allow you to coast. It is just the pedaling that would be coupled to the motor drag. But if you are breaking freehubs, are you just planning to mount a fixed cog on the rear wheels? You didn't say what your target speed is. I believe that Amberwolf has built three wheel vehicles designed for cargo hauling and Chalo builds pedicabs. I am pretty sure both of them used hub motors. I don't really much insight into this kind of project.

I don't know if it would work, but the All Axle is available in a single side mount kit for trikes and quads and they will lace it into a 16" wheel. It would have to go on the front wheels. Here is the motor simulator for two All Axle motors pulling 400Kg each.

https://ebikes.ca/tools/simulator.h...ass_b=400&hp_b=0&bopen=true&grade=0&grade_b=0

 

[RunForTheHills]

Here it is with a 24V battery:

 

[mrpr39]

Thanks for linking the two graphs.
I think the suggested motor will not be suitable for the targeted low speeds of around 7km/h (4,5mph), as there seems to be a bad efficiency for any (hub)motor without proper gearing.
I now measured the wheel diameter which is 14".
Now the main problem then is probably the combination of these figures, low speed, wheel size, slopes of around 10% and the weight of the vehicle.
In order for the motor not to overheat there will probably be something special necessary. I'm not sure if any available hub motor can manage that. Even though a hub motor would probably be the easiest solution to build.

 

[mrpr39]

And about the general setup, my idea was to mount a second sprocket on each left and right axle which i would then both connect to a separate motor. The sprocket for the pedals would still have the freehub. If i can also use a freehub for each motor would be up for testing, but as mentioned i don't trust them to be able to transfer the power.
Concering the battery, i would use two of the mentioned batteries in series which would leave me with 48V and a constant current of up to 100A.

 

[APL]

There are better freewheels to be had, but at a cost of course. White Industries freewheels are considered the best by many, and their jackshaft or mid drive units for tricycles and gas bikes are top.

Some ES freewheel discussion, there are many others ; https://endless-sphere.com/forums/viewtopic.php?f=28&t=25153

Hub motors sort of run in the 400 to 600 rpm range,.. depends on the volts you use, more volts more speed. If you flip a hub motor and run a freewheel on the left side, then the thread direction works out for a freewheel. (just reverse two phase wires to change direction) Pedaling won't turn the motor that way, but the wheel will rotate the chain at all times.

Power comes from gear reduction, and since you're not going very fast, you can gear it 2:1 or 3:1,.. the more the better of course.
Here's a simple mid drive calculator to use, just put in wheel size and fool around with gear sizes until you get the speed you want.
https://electricscooterparts.com/motorwheelgearratio.html

Personally, I think two hub motors would move that thing along nicely, although your in a new territory with the mechanical stress's
involved. Next is to determine the average trip distance and the battery size needed to comfortably do so.

The brakes on that machine are friction and could use an upgrade, any plans for adding some bike disc brakes to it?

 

[amberwolf]

As long as the motor itself is wound for the speed you'll be using it at full load at, then it would work fine that way.

It's when you use a motor wound for a much higher speed at a lower speed but at the loading it should see at the higher speed, is when overheating gets to be a big deal. (if you play around with that simulator, you can see how this works).

There aren't many "common" ebike / scooter motors wound for the speeds you're after, but some companies, like QSmotors, will wind them however you want.

QSmotors also makes much better axles/etc than the other typical hubmotor stuff I've worked with, and since you're using single-sided axles, that could be very important. Many of the other hubmotors I've used had axles that couldn't handle these kinds of loads even mounted from *both* ends--I can't imagine any of those other companies (especially MXUS) making something that could do it from one side successfully. QSMotors even makes "car" style hubmotors, designed specifically to be mounted from just one side, with a big disc brake rotor mount on that inboard side as well. They have a sale thread here on ES, and that has their contact info and websites as well.

There are also internally-geared hubmotors, but the clutches in these that allow them to freewheel aren't always all that strong, and could fail under the loads...so you'd probably need to get ones made like the GMAC, without a clutch, so the motor has no built-in freewheeling. The regular DD Direct Drive hubmotors are much simpler and less prone to overheating or mechanical failures, however.

Either way, the only "easy" way to use any hubmotor is to do it on the front wheels, making them a completely independent drive system from the pedals.

I think the suggested motor will not be suitable for the targeted low speeds of around 7km/h (4,5mph), as there seems to be a bad efficiency for any (hub)motor without proper gearing.
I now measured the wheel diameter which is 14".
Now the main problem then is probably the combination of these figures, low speed, wheel size, slopes of around 10% and the weight of the vehicle.
In order for the motor not to overheat there will probably be something special necessary. I'm not sure if any available hub motor can manage that. Even though a hub motor would probably be the easiest solution to build.

 

[amberwolf]

There are a number of ways to get freewheeling action other than just bicycle freewheels with pawls.

There's one called a dog-clutch that can be used this way, where it more or less has a disc on the axle with pins in it that gets shoved over by a fork so the pins engage the drive mechanism. The disc is driven by the traction source (motor, people, whatever). Thud here on ES made a two-speed transmission using this type of clutch to engage and shift the gears; there's at least one thread about it somewhere with pics to give you some idea of what I mean.

There are also sprag clutches, which are a kind of roller-bearings (like needle bearings but shaped so they slip in one direction and grab in the other). These come in different sizes and have different torque and wear ratings; McMaster-Carr and Grainger and the like should have bunches of them.

A form of roller-clutch is often used in internally-geared hubmotors as a freewheel (but the way they make them they are prone to failure under shock loads or even just heavy loads, and there is no good way to get into the motor to maintain them without taking the motor apart).

Ah sorry, this is the english link: Aliexpress
Sadly the motor doesn't have a clutch so i'm not exactly sure how it will behave when coasting. The feature of peddling isn't that important to me, it wouldn't be a problem to remove the chain of the motor just in case the battery will run out one day. And while it's charged i guess no one wants to peddle .
However about the mid mounted motors there is one concern i have. Mounting them probably would work, using one of them upside down. But as they would be connected to the axle with the same freewheel as the people peddling, the freewheel probably can't hold the power. I already had to replace it twice with just the people peddling breaking it.
The hub motor is something i haven't thought about in depth, as my concern there was that it's not suitable for the targeted low speeds. But maybe you know some solution that could make it work. I will look into that later today and also look up the weehlsize let you know about it. Thanks already for the suggested options.

 

[APL]

If I look at it in watts, you have 6 people pedaling at roughly 100 watts each at the moment, according to this Google search.



If 600 watts of power is enough to make it move on pedal power, then 1200 watts will double that performance, and it's easier to figure what 2400w or 4800w of power will do. (48 people pedaling!)

Two 1500w hub motors could do it easy, I would think, considering burst watts, and geared 2 to 1, twice as much .. you'll probably need more than that to get down to 8 mph..

 

[calab]

Please
Do
Not
Under
Power
Your
Ebike

Its easier and cheaper to limit power then it is to make more, higher power.
I was going to say Leaf 1500w hub motor if you want two motors, or a single qs 3000w hub motor

 

[Chalo]

Its easier and cheaper to limit power then it is to make more, higher power.
I was going to say Leaf 1500w hub motor if you want two motors, or a single qs 3000w hub motor

If all he wants is sub-5 mph, power isn't really the issue. It's gearing.

Leaf motor is a great choice because he can get 11t winding for maximum copper fill but really low RPM/volt. Then use 16t sprockets to however large a rear axle sprocket is feasible.

 

[calab]

No cup holders on that thing

 

[mrpr39]

No cup holders on that thing

No worries, as a German i made sure to have some. It's the grey tubes in front of every seat

Its easier and cheaper to limit power then it is to make more, higher power.
I was going to say Leaf 1500w hub motor if you want two motors, or a single qs 3000w hub motor

If all he wants is sub-5 mph, power isn't really the issue. It's gearing.

Leaf motor is a great choice because he can get 11t winding for maximum copper fill but really low RPM/volt. Then use 16t sprockets to however large a rear axle sprocket is feasible.

About the suggested motor from Leaf, do you have a link to a specific model. I searched there website and there is quite a large amount of different models. And i also couldn't find any configuration for the winding of the motors, would that be someting that i can just add as a request during checkout? And where could i find the available options for windings?

A concern i have about a hub motor is how to mount it considering the current peddals should still be working. Here is a picture of the axle(s). Now for the hub motor mounting would be a problem because of the whole axle is spinning, or am i missing something?

 

[mrpr39]

The brakes on that machine are friction and could use an upgrade, any plans for adding some bike disc brakes to it?

You are right about the breaks, just friction based. I thought about some upgrade, but for now they were working alright. Enough breaking power to block the wheels. Maybe with the electric conversion it would then still be a good time to also include some disc breaks, we'll see.

 

[RunForTheHills]

A concern i have about a hub motor is how to mount it considering the current peddals should still be working. Here is a picture of the axle(s). Now for the hub motor mounting would be a problem because of the whole axle is spinning, or am i missing something?
rear axle.png

It seems like the logical place to put the hub motors is on the front wheels. I don't think it would be easy to convert it to disc brakes though.

 

[calab]

Ah yesss I see the cup holders now, very interesting placement of the cup holders. Smart move hiding them behind a wind break, of utmost importance is being refreshed while riding hard, using that throttled thumb can be difficult, finger or hand cramps you know. It can be real tough, maybe thats why lots like to use pedal assist.

 

[Chalo]

About the suggested motor from Leaf, do you have a link to a specific model. I searched there website and there is quite a large amount of different models.

The model is 1500W, freewheel rear version is probably best for what you're doing (because you can mount a sprocket on either the disc brake side or the freewheel side). The default winding is I think 5 turn, and optimized for about 45 km/h. In the comment section of the order form, you can specify any other winding count or desired top speed/RPM you want. The slot accommodates 66 strands of whatever magnet wire they use, so 3 turn, 6 turn, and 11 turn get maximum fill. 5 turn (and hypothetically 13 turn) get next best fill percentage, and 4 or 8 turn are next best after that.

The slower the winding, the less maximum power you can extract from the motor. But that power may be at a much more useful speed for you than if you use a faster winding.

If you design a reduction gear and you know what RPM you want, you can ask the sales representative at Leaf for advice about what winding to use.

 

[RunForTheHills]

The model is 1500W, freewheel rear version is probably best for what you're doing (because you can mount a sprocket on either the disc brake side or the freewheel side).

But if you look at the picture, the freewheel is mounted on the axle inside the frame about 3 or 4 inches from the wheel. The wheel is fixed to the axle and the chain runs on the inside of the frame. That is why I suggested putting the hub motor on the front wheels.

 

[RunForTheHills]

If not the All Axle, maybe something like this single shaft motor from Qsmotor.

https://www.qsmotor.com/product/3000w-single-shaft-motor/

MTA: It says 80Kmh, but if you run it on lower than the recommended 72 volts and ask for a custom winding, you can probably get it into your speed range.

 

[Chalo]

The model is 1500W, freewheel rear version is probably best for what you're doing (because you can mount a sprocket on either the disc brake side or the freewheel side).

But if you look at the picture, the freewheel is mounted on the axle inside the frame about 3 or 4 inches from the wheel. The wheel is fixed to the axle and the chain runs on the inside of the frame. That is why I suggested putting the hub motor on the front wheels.

Looks to me like there's a gap between the frame and the wheel that could be used to fit a 48t (or whatever appropriate size) sprocket. Instead of a spacer, there could be a keyed carrier for a chainring.

 

[RunForTheHills]

Looks to me like there's a gap between the frame and the wheel that could be used to fit a 48t (or whatever appropriate size) sprocket. Instead of a spacer, there could be a keyed carrier for a chainring.

Yes, but then you would have to move the chainrings and chain to the outside of the frame. Maybe it is doable, but it looks like the brake mechanism would get in the way of that.

 

[Chalo]

Looks to me like there's a gap between the frame and the wheel that could be used to fit a 48t (or whatever appropriate size) sprocket. Instead of a spacer, there could be a keyed carrier for a chainring.

Yes, but then you would have to move the chainrings and chain to the outside of the frame. Maybe it is doable, but it looks like the brake mechanism would get in the way of that.

Another prospective location is underneath the rear two seats, with the motor chains and large chainrings running through openings cut in the floor plate (or that section of the floor removed entirely). In that case, it probably would be a good idea to install a kick plate between the front edge of the seats and the floor.

 

[APL]

Are the wheels 14" from top of tire to ground? They look taller than that to me, what's the diameter?

If I use the 14" wheel size you gave, and use a 400 rpm motor 'as a guess', and enter it into the speed calculator using your 50T max
gear, I get 5.3 mph. A little faster than the 7 kph or 4.3 mph you wanted but at least doable with single stage gearing.
https://electricscooterparts.com/motorwheelgearratio.html




I used a 16T drive cog, because that's the smallest six bolt, bolt on bike cog that will work with a larger chain, And with the 3 to 1
reduction that it would have, mechanicals will need to be on the robust side .

One 1500 watt motor geared 3:1 has the equivalent torque of 4500w, so one motor would probably handle it, with one controller and less cost, but you have more stress on the chain and only one drive wheel. (unless you use a differential)

If you use two motors then you need to control them evenly with one throttle , so there may be some problems there too.
Two motors have twice the cost but half the mechanical stress, and you get two wheel drive.

Just some things to think about I guess..