Advice on MXUS Turbo build

Hello. I’m looking to put an electric bicycle together over the next couple of months, and was hoping to get some feedback. Once I get hold of some parts, I will document the build.

[EDIT] Change of plan. I was planning on building a bike for commuting, but my work circumstances have changed, so now I will build a bike for off road instead [/EDIT]

I won't have any problems putting the bike together, I'm an engineer with plenty of experience with mechanical and electrical systems. But since I have no experience with electric bicycles specifically, I'd like some constructive criticism on my selection of components.

This is my plan so far:

https://www.ebikes.ca/tools/simulat...h&k=1&frame=mountain&autothrot=true&throt=100
(The motor simulator has got to be one of the best tools on the web. Thanks to the geniuses at Grin Tech. You rock).

Donor bike:
A downhill mountain bike, around 5-10 years old. I’m currently looking at a Norco Atomik or Norco A-line. The A-line has bolt-on dropouts, which I imagine will make modifications for mounting the motor much easier. It appears that downhill bikes are well suited because they are quite robust (suited to withstanding higher torques), and have better stiffness and geometry for higher speeds.

Dropouts:
I will design some clamping style mounts that could bolt onto (or in place of) the original bike dropouts. Machined in 7075-T6, or 4140 steel as an alternative.

I understand dropout/clamp material is a contentious issue. The upside of the 7075 is the lower cost to machine, and better appearance of anodising (relative to painted or rusty steel). The downside is the significantly lower modulus. Even though it has a slightly higher hardness than mild steel, deflection at the contact surfaces under high load can cause fretting and possibly yielding. I can see this compounding into a real problem when running regen. However, if I can get the clamping arrangement just right, it might be ok. I think this is the highest risk component, so I will do some analysis in this area to justify the decision either way.

Motor:
MXUS 3k v3 4T. I figure the 4T will give me a good compromise between speed and heat output. I will add FF (but no heat-sinks, at least at this stage). I will try to set a current limit so torque is limited to 200Nm. I think this is a realistic safe target for a bicycle.

Wheels:
Go to 24" motorbike rims. Either redrill the hub flanges to suit 14G spokes, or use brass washers and the original spoke holes. Not sure yet.

Gearing:
Single speed freewheel. Not much point havnig gears if I am going to rely on power 100% of the time. Pedalling a DH bike is hard at the best of times. I'd rather not do it with a 10kg hub and 5kg battery pack.

Battery pack:
20S5P of Sony US18650-VTC6. Actually, 2x 10S5P in series, each with its own BMS. That way I can charge them in parallel using a Meanwell HLG-320H-48A. Originally I wanted to run 24S, but the controller I was also planning on using is limited to 88.8v. The total weight should be around 5kg, and I will put it in a back pack. If the frame had a bigger triangle, I would think about frame mounting them, but I don’t see it as a big issue. Time will tell.

Controller:
I was looking at the Mobipus 72200. I like the industrial style construction, and from what I’ve read, it is relatively user friendly. The only problem is supply. I have tried to get in contact with SamD from Ballarat Ebikes, but he has only responded once to my emails (he only asked where I am located). I responded to him. Then no response back. His website is still operational, and advertising parts. Does anyone know if this is normal for him, or has anyone been in contact with him lately ?

So, I am kind of at a loss for what controller to use. Does anyone know of a comparable power level controller that is available in Australia ? It is costly to ship to Australia, so I would prefer to buy locally if possible ? But that might really limit my options.

Anyway, that’s the current plan. If anyone has any suggestions, I’d be thankful for your words of wisdom. Cheers.

And here's a spreadsheet I've been using to keep track of everything.

At 200nm, a DH bike is a back flipper.
No game for a newbie rider. I suggest that you make your custom clamping dropouts with integrated brake mount on the left, and chain tensioner mount on the right, so you can make them longer to stretch the wheelbase 2 or 3 inches. That would give the bike stability in acceleration.

You are planning too much power for the speed that you wish. I mean, unless you want to ride at 100+ kmh, or stop and go up steep hills, there is no need for a heavy setup.

MadRhino said:

No game for a newbie rider.

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This is my first ebike, but I've been riding motorbikes almost since I could walk, so it won't be a problem :thumb:

MadRhino said:

I suggest that you make your custom clamping dropouts with integrated brake mount on the left, and chain tensioner mount on the right, so you can make them longer to stretch the wheelbase 2 or 3 inches. That would give the bike stability in acceleration.

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I think you are correct, if I move the axle location, then I will have to transfer the brake and tensioner mounting points to the dropouts I make. Not too sure about extending the wheelbase too much though. I was thinking 1-2 inches. I didn't want to change the handling of the original bike too much.

MadRhino said:

You are planning too much power for the speed that you wish. I mean, unless you want to ride at 100+ kmh, or stop and go up steep hills, there is no need for a heavy setup.

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Do you mean that I should use a smaller motor to achieve the 70km/h target ? My calcs match the motor simulator for estimated top speed (around 70km/h when sitting upright). In reality I don't plan on going any faster than 60km/h, but having the extra torque is handy for climbing hills and accelerating. I'd rather have "too much" power than not enough (as long as the bike can safely/structurally handle the torque).

To ride the streets with high power, stretch the wheelbase to 51 or 52 inches. That is very compact already for a street bike but still, it will make it possible to use the power in acceleration. If it is too short, you will have to stand and lean over the handlebar to keep the bike from backflipping when accelerating full power. That may be good off road, but on the street it is preferable to be able to accelerate seated.

If you ride your bike like a motorcycle, and you have motorcycle background, then go for the big motor, controller, and RC lipo for a battery. I never regretted having more power than needed, and I have the priority keeping the bike sub 100 lbs.

Change of circumstances. I will no longer be able to use the bike for travel to work. I was expecting to move to a new work facility sometime in the next couple of months, but it's not happening anymore. It won't be practical to ebike my current work commute (+40km with highway driving).

But, I am still set on building a bike, so I will build one for off-road use instead. I have access to some decent properties good for mountainbiking. I think the plan will remain the same, with the following differences:
- Single speed freewheel instead of multi-speed.
- 24" motorbike rims instead of 26" MTB rims.

Do you still think stretching the wheelbase is a good idea ?

And remember that Australian fuzzies only allow for 200W no matter if someone is a 80 pound crack head, carrying their 200 gram crack pipe, or a 500lb Sumo wrestler carrying 125lbs of groceries because Sumo wrestlers do require a ton of food to maintain their lively-hood.

MadRhino said:

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In mountain trails, you need the bike compact. 50 inch wheelbase is the max I would like.

I don’t like to build with motorcycle wheels. It is a compromise some have to live with, for reliability when the terrain and conditions are too hard on bicycle wheels, and tires especially. I have no thorns or sharp rocky terrain here, so I can enjoy the extra performance of light weight DH wheels.

Remember to ebike in a courteous and safe manner.


Sam seems to be building a nice rig, the 4T motor should be good, and in a smaller rim you get more torque. But there comes a point where you may be biting off more then you can chew. Go ahead and buy that 4T MXUS V3 motor with 2 sets of hall sensors, then buy your main controller with regen and a spare generic controller (like ebay seller HKsunwin), a few throttles, torque arms, multi-meter, spoke tool, special freewheel tool to use on the motor, ferro fluid, ignition is nice to have for a quite run into the corner store, ebike brake levers to activate the regen braking/abs braking, buy a soldering iron, solder, wires, connectors.

Do you plan to pedal at all?
I have heard some people have not installed a chain and have been riding for months and months, too cheap, too frugal to get a running drive train going.


Regen braking is good to have so you dont have to spend money on vbrake or disc brake pads.

You do realize there is a MXUS 5000W motor right, not sure of the price comparison between that motor and the QS motors.

One thing I would do, if I was buying a new second mxus 3kw motor is spray paint the inside with an appropriate spray paint, https://www.grainger.com/product/SPRAYON-Red-Insulating-Varnish-1D276 but since you are using Ferro Fluid, then its probably a good idea to see if the ff would affect the ins varnish.

serious_sam said:

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MadRhino said:

I don’t like to build with motorcycle wheels. It is a compromise some have to live with, for reliability when the terrain and conditions are too hard on bicycle wheels, and tires especially. I have no thorns or sharp rocky terrain here, so I can enjoy the extra performance of light weight DH wheels.

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That makes sense. I figured the moto wheel would get more traction, but the MTB wheel would definitely be more nimble.

markz said:

Remember to ebike in a courteous and safe manner.

Sam seems to be building a nice rig, the 4T motor should be good, and in a smaller rim you get more torque. But there comes a point where you may be biting off more then you can chew. Go ahead and buy that 4T MXUS V3 motor with 2 sets of hall sensors, then buy your main controller with regen and a spare generic controller (like ebay seller HKsunwin), a few throttles, torque arms, multi-meter, spoke tool, special freewheel tool to use on the motor, ferro fluid, ignition is nice to have for a quite run into the corner store, ebike brake levers to activate the regen braking/abs braking, buy a soldering iron, solder, wires, connectors.

Do you plan to pedal at all?
I have heard some people have not installed a chain and have been riding for months and months, too cheap, too frugal to get a running drive train going.

Regen braking is good to have so you dont have to spend money on vbrake or disc brake pads.

You do realize there is a MXUS 5000W motor right, not sure of the price comparison between that motor and the QS motors.

One thing I would do, if I was buying a new second mxus 3kw motor is spray paint the inside with an appropriate spray paint, https://www.grainger.com/product/SPRAYON-Red-Insulating-Varnish-1D276 but since you are using Ferro Fluid, then its probably a good idea to see if the ff would affect the ins varnish.

Click to expand...

From what I have read, the Mobipus controller is very reliable, so that's one reason I wanted to go in that direction.

I wasn't going to set up regen to start with. Maybe once I get everything else sorted.

Probably wont pedal much, but will still have drive train.

What is the purpose of the varnish ? Waterproofing ?

I'm not sure of the weight of the MXUS 5k. I think the 3k is probably a good compromise for weight and power ?

With the weight of motorcycle wheels an tires, no motor is too big. Most builders are not conscious of the performance penalty of motorcycle wheels on an ebike. Heavy wheels are consuming a lot in acceleration, making for the need of a bigger battery. They also have higher cynetic energy, making for poor braking distance, thus eventually require motorcycle brakes. That is the escalade of weight, where one heavy component is calling for more and more heavy components, transforming a powerful ebike into a lame motorcycle.

Weird build, everything is way heavy and overkill and expensive for 60kmh

Look at getting leaf 1500w, 24" bicycle rims and 18 fet infineon

tolkaNo said:

Weird build, everything is way heavy and overkill and expensive for 60kmh

Look at getting leaf 1500w, 24" bicycle rims and 18 fet infineon

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True. That is what a conscious builder would do for 60 kmh. Yet, building for serious off road has no limit. I was building 10k$ DH bikes without a motor.

tolkaNo said:

Weird build, everything is way heavy and overkill and expensive for 60kmh

Look at getting leaf 1500w, 24" bicycle rims and 18 fet infineon

Click to expand...

I can see where you're coming from. And I totally agree with you, if the only criteria was to reach 60km/h.

Originally I was thinking more along the lines of this analogy: it'd be nice to own a GT3 Porsche. Sure it can do 300km/h, but you'd never actually drive it that fast on public roads. But it's still a sweet car to drive, and nice to have that power on tap, just to give it a squirt every now and then. Hard acceleration is fun, even if you don't go over the speed limit. And once in a while you could take it to a track and stretch its legs.

Once I changed my plan to make something for offroad, the reasoning changed, but the conclusion didn't: DH bikes are designed for fast off road riding. They are tough and stable, and eat bumps like nothing. I think too much power is never enough, so I should choose a motor that has plenty of grunt, but at the same time doesn't over-load the frame or upset the balance "too much".

I hope that makes sense.

serious_sam said:

tolkaNo said:

Weird build, everything is way heavy and overkill and expensive for 60kmh

Look at getting leaf 1500w, 24" bicycle rims and 18 fet infineon

Click to expand...

I can see where you're coming from. And I totally agree with you, if the only criteria was to reach 60km/h.

Originally I was thinking more along the lines of this analogy: it'd be nice to own a GT3 Porsche. Sure it can do 300km/h, but you'd never actually drive it that fast on public roads. But it's still a sweet car to drive, and nice to have that power on tap, just to give it a squirt every now and then. Hard acceleration is fun, even if you don't go over the speed limit. And once in a while you could take it to a track and stretch its legs.

Once I changed my plan to make something for offroad, the reasoning changed, but the conclusion didn't: DH bikes are designed for fast off road riding. They are tough and stable, and eat bumps like nothing. I think too much power is never enough, so I should choose a motor that has plenty of grunt, but at the same time doesn't over-load the frame or upset the balance "too much".

I hope that makes sense.

Click to expand...

It's gonna be barely any faster though, the leaf and that 3k mxus will both be able to handle the burst current from that 5p battery you're planning

Then adding heavier 3000w motor, heavy moto rims, moto tires, only to go 60kmh which is about 1800w? The whole thing doesn't work together

Ultimately up to you though, if anything id stay with the mxus 3k but i think you could get away with the leaf, then 24" bicycle rims and a lighter cheaper controller like an infineon

I am still waiting on parts for my first ebike build, but I have built many non-electric bikes. There are two I built without compromises, not worrying about what was popular or cost. I built exactly what I wanted and I love them. I will grant that the first effort or two is usually a learning exercise, but after that you should know what makes you happy.

tolkaNo said:

It's gonna be barely any faster though, the leaf and that 3k mxus will both be able to handle the burst current from that 5p battery you're planning

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Those cells are rated to 30A. I figured 150A would be enough. What size battery would you recommend ?

serious_sam said:

tolkaNo said:

It's gonna be barely any faster though, the leaf and that 3k mxus will both be able to handle the burst current from that 5p battery you're planning

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Those cells are rated to 30A. I figured 150A would be enough. What would you recommend ?

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They're not rated to 30a? And why are you splitting such a small pack into 2 pieces with 2 bms?

https://www.candlepowerforums.com/v...st-Review-of-Sony-US18650VTC6-3000mAh-(Green)

Granted, they won't last long at 30A, but they are rated to produce that for short durations (the link above tested them @ 30A for about 3 minutes continuous before they hit 80degC).

I wasn't planning on running them that hard, but short bursts should be ok.

I've seen the Meanwell HLG-320H-54A has good feedback on the forums, so I was thinking of using that to charge the 2 packs in parallel, effectively as 10S10P. For $130AUD, that's a pretty good deal. Not sure what charger is rated for 20S packs ? Do you have a suggestion ?

Thanks for your feedback.

serious_sam said:

https://www.candlepowerforums.com/v...st-Review-of-Sony-US18650VTC6-3000mAh-(Green)

Granted, they won't last long at 30A, but they are rated to produce that for short durations (the link above tested them @ 30A for about 3 minutes continuous before they hit 80degC).

I wasn't planning on running then that hard, but short bursts should be ok.

I've seen the Meanwell HLG-320H-54A has good feedback on the forums, so I was thinking of using that to charge the 2 packs in parallel, effectively as 10S10P. For $130AUD, that's pretty good deal. Not sure what charger is rated for 20S packs ? Do you have a suggestion ?

Thanks for your feedback.

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You're looking at >12v of sag trying to pull 150a out of 5p vtc6, it's not gonna happen, you're massively over-estimating that tiny pack

There's chargers all over aliexpress for 50 bucks that can do 20s

tolkaNo said:

Then adding heavier 3000w motor, heavy moto rims, moto tires, only to go 60kmh which is about 1800w? The whole thing doesn't work together

Ultimately up to you though, if anything id stay with the mxus 3k but i think you could get away with the leaf, then 24" bicycle rims and a lighter cheaper controller like an infineon

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I'll look into the 24" MTB wheels. Thanks.

tolkaNo said:

You're looking at >12v of sag trying to pull 150a out of 5p vtc6, it's not gonna happen, you're massively over-estimating that tiny pack

There's chargers all over aliexpress for 50 bucks that can do 20s

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Thanks. I'll have a look for the chargers.

What motor/controller/pack do you run ?

serious_sam said:

tolkaNo said:

You're looking at >12v of sag trying to pull 150a out of 5p vtc6, it's not gonna happen, you're massively over-estimating that tiny pack

There's chargers all over aliexpress for 50 bucks that can do 20s

Click to expand...

Thanks. I'll have a look for the chargers.

What motor/controller/pack do you run ?

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Cheapo ebay 1000w DD, 12 fet em3ev infineon, 18s5p samsung 30q

tolkaNo said:

Cheapo ebay 1000w DD, 12 fet em3ev infineon, 18s5p samsung 30q

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Sounds like the 30Q are good cells. Are you happy with that setup ?

serious_sam said:

tolkaNo said:

Cheapo ebay 1000w DD, 12 fet em3ev infineon, 18s5p samsung 30q

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Sounds like the 30Q are good cells. Are you happy with that setup ?

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Yeah im happy with it, the 1500w leaf would be a way better choice motor wise but im gonna use this one until it melts :lol: