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electric motor guru

2K views 13 replies 7 participants last post by  titan 
#1 ·
I may be starting a new job soon. the job means a 70 mile commute one way, i have done this in a car and it takes about 2hrs, on a bike it takes about 1hr 20. i have been mulling over the idea of building an electric mountian/MX style bike. i wouldnt be using it all the time but figured it was a good range to give me the motivation to give this a go.

done a bit of research into motors and this seems to be about right sort of spec for the application. ( it what seems to be the style used in most motorbike Ebike, that dont use a hub motor)

https://www.miromax.lt/en/m-6/c-39/...wer_5kw86kw__67hp115hp__400_cm3#photo_gallery

and using basic understanding of youtube i have gathered that at around 48v avg speed will be around 45mph ( at the engine ) i figured i need to achieve that as an avg speed for 2hrs to garentee me hitting the distance of the commute. so would probably need to run at more 72v.

here is where i get stuck.....
how do i work out what batteries would be best, 18650 vs flat cells (RC car style) and what batterys i need, also what configuration would i need them to be in to create the cells i require to achieve this??

plan is to take something like this



and make something like this, that can go around 45-50mph avg for 2hrs ....

 
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#2 ·
Idk. Where’s Mike Kelly? He’s been building electric pedal bikes.

To me, someone who was enthused about and selling electric Dirtbikes, 45 mph for 2 hours sounds like a lot to ask. . . Altas could run that. Though they had a rather large power cell. They were max run time of 4 hours on the low power setting...and as low as under an hour in max power mode (doing Motos) .
 
#4 ·
I imagine you'd need a full size electric motorcycle to get that sorta range
 
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#7 ·
most electric bike are only just pushing that range but if i can keep the weight down.... most city cars are just about pushing 100miles on pure electric (zoe, smart etc)

The battery pack would be huge weigh a ton and cost two... And the end result would not be an ebike but a speed pedelec that will need to be registered as a motor vehicle and insured and taxed accordingly, plus riding one will require you to use a motorbike helmet, not to mention it would not be permitted on bicycle lanes as it would be seen as an electric motorbike.

Say you're using 1000w@72v, that's 13.8A. https://m.aliexpress.com/item/4000042967041.html?trace=wwwdetail2mobilesitedetail&spm=a2g0o.productlist.0.0.52c568a6FHjkuj&algo_pvid=7a425f94-222c-4ee5-8ad7-e86d33e1c964&algo_expid=7a425f94-222c-4ee5-8ad7-e86d33e1c964-10&btsid=81836b94-30a7-4750-9080-37459cc43e44&ws_ab_test=searchweb0_0,searchweb201602_4,searchweb201603_60

For example using these cells you need 23 of these to reach 73.6v, that gives you 24Ah which would give you an hour and a half-ish of full tilt, that pack would cost 455€ and weigh over twelve kilos, wiring BMS and casing not included. On top of that you need the motor the controller all the throttles displays and whatnot you're reaching motorbike money in no time flat, not to mention you'd need to recharge it at both ends so you'd either need an onboard charger that's another space drain and an extra lump to carry around, or two chargers and they're not cheap.

I've lusted over sth like this for years just to arse around the backyard forest but the cost is just too high.

Oh and most definitely use a hub motor that's a looot easier since you don't need to allocate space for it and you don't have to worry about busting a chain, if a bit more expensive though
weight of 18650 would save me about 100g over that (roughly for the same AH and v but more indervidual batterys) so a total of 2.3kg over the 23 (using my simple math), i can 3d print holders to put the batterys in multiple places rather than one large single bank. i been reading about raspberry pi as a BMS and they are tiny (if i use a Zero) although it would mean a good amount of coding and thats not my strong point, also they have minimal drain with just a plug in display for testing, use LED idoit lights style indicators on the bike.

need to have a better look at hub motor

it early days yets lots more reserch needed before i pull the pin and spend money. so far i think £2k is close to a sensible budget, but that still £2k less than anything you can buy worth spending money on.

i may be shooting for the stars with the range and avg speed (less important over distance really) but got to have a goal. i think just getting one to move under its own system is the best approach, then take it from there.
 
#5 ·
The battery pack would be huge weigh a ton and cost two... And the end result would not be an ebike but a speed pedelec that will need to be registered as a motor vehicle and insured and taxed accordingly, plus riding one will require you to use a motorbike helmet, not to mention it would not be permitted on bicycle lanes as it would be seen as an electric motorbike.

Say you're using 1000w@72v, that's 13.8A. https://m.aliexpress.com/item/4000042967041.html?trace=wwwdetail2mobilesitedetail&spm=a2g0o.productlist.0.0.52c568a6FHjkuj&algo_pvid=7a425f94-222c-4ee5-8ad7-e86d33e1c964&algo_expid=7a425f94-222c-4ee5-8ad7-e86d33e1c964-10&btsid=81836b94-30a7-4750-9080-37459cc43e44&ws_ab_test=searchweb0_0,searchweb201602_4,searchweb201603_60

For example using these cells you need 23 of these to reach 73.6v, that gives you 24Ah which would give you an hour and a half-ish of full tilt, that pack would cost 455€ and weigh over twelve kilos, wiring BMS and casing not included. On top of that you need the motor the controller all the throttles displays and whatnot you're reaching motorbike money in no time flat, not to mention you'd need to recharge it at both ends so you'd either need an onboard charger that's another space drain and an extra lump to carry around, or two chargers and they're not cheap.

I've lusted over sth like this for years just to arse around the backyard forest but the cost is just too high.

Oh and most definitely use a hub motor that's a looot easier since you don't need to allocate space for it and you don't have to worry about busting a chain, if a bit more expensive though
 
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#6 ·
What Matty said... It's in no way an electric bicycle if it'll do what you need it to. It's a home made electric motorbike.

Basing it off a bicycle frame also doesn't sound like a great plan. Bicycle brake pads and going to last you like a week, if the discs hold out for that long. Bicycle forks, even good ones, typically have plastic bushings, which aren't going to last long. By the time you paid for a durable enough bike, might as well get a motorcycle for the duty. Given the speed you're planning for, anything from 125 up will be suited. That 125 off roader you were messing with a while back would do it, for example.

Edit: just zoomed in n saw you want to use a rigid bike. Not even a front suspension, at 45mph? I'd say dude YouTube it, but that sounds like a snuff movie.
 
#8 ·
riding along at 50mph I bet 90% of drag is aero rather than rolling friction
 
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#14 ·
Mate, you seem to be reinventing the wheel here.
Believe it or not there is a whole community building these things, much like what we do with bikes I just fancied putting my own spin on one with out paying out a few £k from the off. It may well never get further than a list of parts and this thread but a worth while conversation never the less.. it's the future [emoji23][emoji23]

Reading up on the rules for pedal power I would be limited to 15mph on battery so that's out the window so if I did do it it would have to be an electric motorbike



Sent from my SM-G973F using Tapatalk
 
#12 ·
The other option to boost your range is to reduce drag. At 45 MPH, aero drag is a HUGE battery killer for a light vehicle.

To make significant gains there you need to ditch the upright bike and go recumbent, to minimize frontal area. Even better if you can do a full fairing. That quickly leads you to a form factor more like a small pedal car (maybe one that leans in corners) - often these are called "velomobiles" and they are actually pretty damn near ideal for commuting. Electrify one of those and you might hit the range & speed target you have in mind, but it will still need a pretty big power pack.

Me, I go 25 miles to work and could plug in next to the welders... hmm.
 
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