Most powerful midmotor option below 10kg/23lbs

Sparfuchs

1 kW
Joined
Nov 22, 2020
Messages
305
Hello EV Friends,
I'd like to covert a downhill bike into a e-dirtbike hybrid with all the normal bicycle components (cranks, gears ect.) but with a dirtbike seat, a 24 inch rear wheel and a powerful mid motor to do burnout drift, powerwheelies and fast acceleration or hill climbing. I don't need it to be faster than 70 kph/45 mph.
I don't really need it to be super light but as I think the power is anyway limited by the stability of the bike chain, the swingarm and the spokes I won't benefit from a motor with more than 10,5kg/23lbs like the cyclone 18kw (also has way more power than I could use without damaging or bending parts I guess). A DHB is quite robust but still not a dirtbike.

First I was thinking of a cyclone 3kw (nylon gears) used with way more power and optimized cooling and temp control and a gear ratio (aside the gearbox) of 13t freewheel to 53t chainring, then 32 chainring to a 11t-52t cassette. That would give me a ratio of up to 6,65 right. So with the gearbox I'd get at 52t gear a torque of 864 Nm (130 nM x 6,65) at a speed of 135 rpm (900 rpm / 6,65). Am I right so far ? So that a lot of torque (maybe more than the bike or the nylon gears can handle ) but I'm more worried that the acceleration might be bad because of the reduced speed ? In case I use the mentioned set up: First I thought of a 16s battery because I don't need to much top speed, but do you think I'd need a 20s because of the big speed reduction ?

As I could do a speed reduction of up to 6,65 I thought that a more powerful motor without a gearbox would give me better results ? So what motor do you know that could do the job ? A criterion that must be considered is that the motor can't be wider than the cyclone (171,5mm) because of the cranks. The only option I found was the cyclone 18kw with 178mm and 10,5kg... but less power and weight would be better. The most interesting wold be the motor Kuberg uses (8 to 15kw), or of the bykstar dirtbike (also 8 to 15kw), or maybe one of the lightning rod motors ? But I wasn't able to find any details to these motor or where to buy them.

So what do you thing I should use ? I also appreciate solutions I didn't think of yet but please no motors that cost more than 1000 €.

Thanks a lot for your help
Best regards Sparfuchs
 
j bjork said:
Maybe QS surron replacement motor?
https://endless-sphere.com/forums/viewtopic.php?f=10&t=114340
Thanks a lot for your reply j bjork,
it's a great motor but unfortunately like all the qs motors to wide (310mm) to get it between my cranks.
 
I'm working on building something like you describe and planning on going with a Lightning Rods motor. Seems like the best option but I think 10kg worth of motor is going to be way too much. I'm planning on probably a Small Block motor and a low top speed for mostly technical riding and it seems like I'll have way more torque than I can ever really use. A Big Block or XL motor will probably give you that torque at a higher top speed but it seems like the XL will be seriously pushing the components. The nice thing about the Lightning rods motors is they are IPM so you can use field weakening to get that top speed and gear it for more low end torque, not a great idea if you'll be spending a ton of time in field weakening but not bad for some occasional runs up there.
 
scianiac said:
I'm working on building something like you describe and planning on going with a Lightning Rods motor. Seems like the best option but I think 10kg worth of motor is going to be way too much. I'm planning on probably a Small Block motor and a low top speed for mostly technical riding and it seems like I'll have way more torque than I can ever really use. A Big Block or XL motor will probably give you that torque at a higher top speed but it seems like the XL will be seriously pushing the components. The nice thing about the Lightning rods motors is they are IPM so you can use field weakening to get that top speed and gear it for more low end torque, not a great idea if you'll be spending a ton of time in field weakening but not bad for some occasional runs up there.
Thanks a lot for your reply scianiac,
I absolutely agree that 10kg is way too much if you don't make benefit of it.
As mentioned I was also considering lightning rod motors but haven't found a website with the specs or anything like that. The website that seems to be the original site is really bad designed and not informative at all. Do you have a link for me that helps me out ?
 
Just https://lightning-rods10.mybigcommerce.com/ but there is a lot more info in the Lightning Rods thread and you can ask specific questions about the drives there if you don't find your answers. I believe for torque estimates all you need is Kv (from which you can calculate Kt) and phase amps. It seems though the listed phase amps are a fair bit lower than what you can push these motors to.
 
scianiac said:
Just https://lightning-rods10.mybigcommerce.com/ but there is a lot more info in the Lightning Rods thread and you can ask specific questions about the drives there if you don't find your answers. I believe for torque estimates all you need is Kv (from which you can calculate Kt) and phase amps. It seems though the listed phase amps are a fair bit lower than what you can push these motors to.
Thanks a lot, i already found this page but didn't get that i've to click on "show more details" to see the specs :D
Does anyone know who produces those motors or what motor it usually was ?
 
Sparfuchs said:
j bjork said:
Maybe QS surron replacement motor?
https://endless-sphere.com/forums/viewtopic.php?f=10&t=114340
Thanks a lot for your reply j bjork,
it's a great motor but unfortunately like all the qs motors to wide (310mm) to get it between my cranks.

Really, 310mm?
I thought it was something like 130mm
 
j bjork said:
Sparfuchs said:
j bjork said:
Maybe QS surron replacement motor?
https://endless-sphere.com/forums/viewtopic.php?f=10&t=114340
Thanks a lot for your reply j bjork,
it's a great motor but unfortunately like all the qs motors to wide (310mm) to get it between my cranks.

Really, 310mm?
I thought it was something like 130mm
I think so. On QS website it says 33cm x 33cm x 31cm.
 
If you follow the link in the thread about the motor I linked to you get more accurate numbers:
https://fr.aliexpress.com/item/1005003835665401.html?srcSns=sns_Copy&spreadType=socialShare&bizType=ProductDetail&social_params=40198197322&aff_fcid=39ac67eba1e04ded8a8604781d169514-1657083542169-04501-_Dlc7on5&tt=MG&aff_fsk=_Dlc7on5&aff_platform=default&sk=_Dlc7on5&aff_trace_key=39ac67eba1e04ded8a8604781d169514-1657083542169-04501-_Dlc7on5&shareId=40198197322&businessType=ProductDetail&platform=AE&terminal_id=0639d9568488409b91d244682d87f35b&afSmartRedirect=y

It should probably not be very hard to find dimensions for the surron to compare to. As it is a replacement they should be rather similar I think.
 
Seems Vasily from Nucular has been pushing the QS165 up to 450 phase amps. It is a hell of a powerful motor for the size.

I use an AT12070 motor, I can hit mid 40s mph without it getting hot at 140phase amps 60kV. It does not respond well to field weakening. I can climb a 30degree gradient easily.

Does anyone know the volts/rpm constant or flux linkage for the QS-165 motor? I really want one, but it almost looks from the graphs like you have to start field weakening from 1000rpm at 60V.
 
Issue with powerful mid drives is that it will blow out derailleurs and rear hub ratchet mechanisms- they are designed for human power. Most of the e dirt bikes use either a large direct drive rear hub or a left drive chain.
 
j bjork said:
If you follow the link in the thread about the motor I linked to you get more accurate numbers:
https://fr.aliexpress.com/item/1005003835665401.html?srcSns=sns_Copy&spreadType=socialShare&bizType=ProductDetail&social_params=40198197322&aff_fcid=39ac67eba1e04ded8a8604781d169514-1657083542169-04501-_Dlc7on5&tt=MG&aff_fsk=_Dlc7on5&aff_platform=default&sk=_Dlc7on5&aff_trace_key=39ac67eba1e04ded8a8604781d169514-1657083542169-04501-_Dlc7on5&shareId=40198197322&businessType=ProductDetail&platform=AE&terminal_id=0639d9568488409b91d244682d87f35b&afSmartRedirect=y

It should probably not be very hard to find dimensions for the surron to compare to. As it is a replacement they should be rather similar I think.
you were absolutely right. Here it says on the drawing its 152,6 mm wide and has a diameter of max. 188,6 mm. So it might be an option.
Screenshot (30).png
 
electric_nz said:
Issue with powerful mid drives is that it will blow out derailleurs and rear hub ratchet mechanisms- they are designed for human power. Most of the e dirt bikes use either a large direct drive rear hub or a left drive chain.
Thanks a lot for your reply electric_nz,
I absolutely agree. But as I want to keep the derailleur to switch gears and to be able to pedal home when battery is empty. That's why I'm trying to reduce the force on these parts as much as possible by using a 24 inch wheel and going from 32t to the 52t cassette. If anyone has an other idea to reduce more force please let me know.
 
I've thought about and researched that a lot and using the bike gears is a tricky concept. If you just want to be able to pedal the bike home then you don't need gears, you'll just be peddling slowly and that's not a huge problem for occasional poor battery planning. If you want to actually change gears for the motor that's a bit tricky to work out if that's a good idea or not. The debates about gears vs no gears are very long and in depth but my personal opinion on the matter is that gears are only useful for very specific use cases. The rest of the time it's always better to just spend the weight on more power. If you have a very limited motor power like a commercial ebike the gears are required, but we are pretty far away from that and talking about power levels where gears become a waste of weight and just limit your performance.
 
mxlemming said:
Seems Vasily from Nucular has been pushing the QS165 up to 450 phase amps. It is a hell of a powerful motor for the size.

I use an AT12070 motor, I can hit mid 40s mph without it getting hot at 140phase amps 60kV. It does not respond well to field weakening. I can climb a 30degree gradient easily.

Does anyone know the volts/rpm constant or flux linkage for the QS-165 motor? I really want one, but it almost looks from the graphs like you have to start field weakening from 1000rpm at 60V.
have you got a link? thought the nuc could only do halls and the qs was encoder?
 
sn0wchyld said:
mxlemming said:
Seems Vasily from Nucular has been pushing the QS165 up to 450 phase amps. It is a hell of a powerful motor for the size.

I use an AT12070 motor, I can hit mid 40s mph without it getting hot at 140phase amps 60kV. It does not respond well to field weakening. I can climb a 30degree gradient easily.

Does anyone know the volts/rpm constant or flux linkage for the QS-165 motor? I really want one, but it almost looks from the graphs like you have to start field weakening from 1000rpm at 60V.
have you got a link? thought the nuc could only do halls and the qs was encoder?
Older ones are hall sensor only due to filtering on the inputs but iirc new ones have a different arrangement.
https://www.patreon.com/posts/encoder-motors-61616083
 
Hillhater said:
If anyone has an other idea to reduce more force please let me know.
As said previously,…..Just use a left side direct drive with a freewheel.
Thanks a lot for your reply hillhater,
but are there solutions for the disk brake ? Because if i have my cassette on the right side I'll have to mount the sprocket on the left INSTEAD of the brake disk right ?
 
scianiac said:
I've thought about and researched that a lot and using the bike gears is a tricky concept. If you just want to be able to pedal the bike home then you don't need gears, you'll just be peddling slowly and that's not a huge problem for occasional poor battery planning. If you want to actually change gears for the motor that's a bit tricky to work out if that's a good idea or not. The debates about gears vs no gears are very long and in depth but my personal opinion on the matter is that gears are only useful for very specific use cases. The rest of the time it's always better to just spend the weight on more power. If you have a very limited motor power like a commercial ebike the gears are required, but we are pretty far away from that and talking about power levels where gears become a waste of weight and just limit your performance.
That's a great point of few. When i said "I want gears" the main reason was that I thought that's the best way to get maximum torque and acceleration out of it and thought it's necessary to get enough top speed (70 kph/45 mph) when using a big reduction of 52:13 and then 52:32. But if there is a way to have same or even better results without having to shift i'd like it much more.

My best case scenario would be If I'd find a way to mount a 18x1,4 or 1,6 dirtbike rim on my normal downhill swingarm. I've one with a thru axles an one with a "slotted dropout" i could use. Then i could also use a motorbike chain and sprocket and go crazy with the torque. But how to mount and what about the brakes ?

And do I have to divide the (RPM x V) by the gear ratio to calculate the top speed at the rim size to know what rear sprocket i need or how do i make this decision ?
 
The way to use left hand drive is to have a wider swing arm than rear hub. This is because you will have a sprocket behind the brake disc. So you need more room on the left side. I remember around 15mm out spacing to clear the caliper to the sprocket last I checked on my setup. Just measuring as thinking about a possible future project…
 
Skaiwerd said:
The way to use left hand drive is to have a wider swing arm than rear hub. This is because you will have a sprocket behind the brake disc. So you need more room on the left side. I remember around 15mm out spacing to clear the caliper to the sprocket last I checked on my setup. Just measuring as thinking about a possible future project…
Thanks a lot for your reply Skaiwerd,
so I'd have to brutally bent the swingarm of my downhill bike ? :D Because there are to many individual swingarms I don't think there is a wider swingarm to buy that fits for my bike or how would you solve that ?

And do you have names of the parts I'd need to buy or a picture that shows what a left hand drive looks like ?
 
Now I'm also thinking of using a rear rim like sur ron does because i've read that they might be slim enough to fit in a dh dropout. Maybe I'll need a axel adapter but I haven't figured it all out yet. So if someone has anything helpful about dirtbike rims on dhb please let me know
 
Sparfuchs

There are examples of left hand drive on the cyclone page, bikes and motorcycles are shown. Zoom in at the rear wheels in the pictures. Some show a belt drive on the left which for me would be crap.
https://www.cyclone-tw.com/product/2

On the lightningrods web site he shows one there. Although it uses a 219 chain.
https://lightning-rods10.mybigcommerce.com/l-r-swingarm-big-block-drive-for-qulbix-76r-and-140r/


Oh sorry direct answer is put a smaller hubed wheel into a swingarm that’s wider. So 177mm into 197mm. Or a custom swingarm, way it is. A pre made frame has its limitations.
 

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Skaiwerd said:
Sparfuchs

There are examples of left hand drive on the cyclone page, bikes and motorcycles are shown. Zoom in at the rear wheels in the pictures. Some show a belt drive on the left which for me would be crap.
https://www.cyclone-tw.com/product/2

On the lightningrods web site he shows one there. Although it uses a 219 chain.
https://lightning-rods10.mybigcommerce.com/l-r-swingarm-big-block-drive-for-qulbix-76r-and-140r/


Oh sorry direct answer is put a smaller hubed wheel into a swingarm that’s wider. So 177mm into 197mm. Or a custom swingarm, way it is. A pre made frame has its limitations.
Thanks a lot for the pics and the explanation.
I guess I'll have to find a way to mount a dirtbike rim (like sur ron) on my dhb and use a sprocket instead of a cassette.
 
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