Low cogging torque / drag motor advice

[drebikes]

I just can't stop making new threads but I have so many questions.

As I said in other posts I am trying to design a light weight high range ebike to help me to ride just that little bit faster on long trips. The power needed is quite low, 200W DC or less continuous, so 4 amps DC for a 48V battery.

I have looked at quite a few motors, starting with a pretty powerful 800W from kellycontroller before realising a 500W from em3ev should do the job better since it's lighter. But if the battery turns flat then I'd appreciate a low cogging torque motor. My first question is if you have any data about the cogging torque values of the direct drive 500W motor @em3ev or if you have run with it (or the equivalent C9) with the battery flat and how it was.

Otherwise which hub motor would be low drag and:
*should have at least 200W
*preferably under 200$
*can work with 16s lifepo4 battery

P.S. I was loking at the falco motors and thechnically they fit the bill, but they are out of budget.

 

[dogman dan]

Get the Mac, the internal freewheel in those will eliminate cogging when the motor is not powered. It will not do regen with that freewheel, but you will roll fairly frictionless.

It won't be quite as frictionless as a good road bike, where you can spin the wheel and watch it turn forever. But it won't be getting any cogging, just the resistance of cheap hub cover bearings and the internal clutch. Enough to stop a wheel lifted in the air soon, but you won't feel it. You will feel the weight of the motor and battery, just like you feel any cargo carried.

If you went DD motor, the ones EM3ev sells are known to be pretty low cogging types. You feel very very little resistance at 0-8 mph speed. As you pass 10 mph, you start to feel it, and by 15 mph you feel it very much. If coasting downhill, each winding type will have a max coasting speed. The fast motors will feel less resistance until going faster. I find it very hard to exceed 25-mph when using the very slow motors descending steep long hills. The fast motors will max out coasting about 35 mph.

To make the cogging of a dd motor vanish while you pedal it in with a low battery, just start conserving BEFORE you run completely out. Just a tiny 50w tickle of the throttle is all it takes to completely eliminate cogging so you can pedal it home easy. So you could pedal for one hour, getting 10 miles down the road at 10 mph on a mere 50wh of battery. Start conserving when you are down to the last available amp hour, and you have it made. I've done this hundreds of times, because it was cold, windy, or I took the long way home. If you have a wattmeter, shame on you if you get surprised by a low battery.

So, get the Mac will work. But you are on a budget. That makes the dd motors' price very attractive. Get the slowest model of the DD that EM3 ev sells. On 200w of 48v, you will get about 15 mph. Or you can do 20, which will be your max possible speed on about 400w. That slow motor will run very very efficient on hills, and startups, and is ideal if you are only going to want to use 200w. No matter what motor you choose, at 48v, 200w will never get you more than about 15 mph average. But the slower motor will save you battery wattage by making less heat on starts and hills.

So the best thing you can do, is ride the slow motor at 200w, and make that battery last longer so you can forget about cogging being a problem. If you need to really stretch range, ride with 50w showing on your wattmeter, and you won't feel cogging.

 

[d8veh]

I must admit that i don't quite understand your question where you say you want low power, like 200w, and long range, but you combine that wiith 500w and 800w motors. Normally you start with how fast you want to go, how far you want to go, and how hard you want to pedal.

There's lots of 200w, low drag motors that have free-wheels inside so no cogging at all. The lowest drag ones come from Outrider and Keyde. Nearly as good, but a lot cheaper is the Q100.
http://www.keyde.com/?do=product&lang=en&event=list_2
http://www.h9.com.cn/en-p1.asp
http://www.bmsbattery.com/rear-driving/353-250w350w-q-85100sx-motor-e-bike-kit.html
or with cassette spline:
http://www.greenbikekit.com/index.php/e-bike-cassette-freewheel-hub-motor-36v-250w-light-weight-high-speed.html

 

[drebikes]

I may end up spending more than 200W in cruise, this is an estimation. As to why a 800 or a 500W DD motor, the reason is quite simple: cost. There are good motors available, but the cost of shipping to Europe is prohibitive, order of magnitude 100$ motor-only by plane. Chinese suppliers seem to have access to slow shipping by boat that is often free, which alows within a give budget (for example) a much better battery for the whole system.
That said, I am working to find a solution, but the supply chain is a problem. I'm looking into RC motors now to get a clear picture of what is achievable with them, since I could add on the pannel quite a few sellers.

As a system I'd like this ebike drivetrain to boost the speed I can already acheive on long trips, which is 12-15 MPH. If such a system would boost me to 20MPH I'll be a very happy cyclist The low cogging torque would be desirable if I'd have to just pedal as I do now in case of flat battery. dogman, keeping a few Wh for emergency isn't a bad idea like the emergency tank in any motorbike; it's good that I could do 10MPH without really feeling the cogging torque, it's perfectly acceptable for what I have in mind. The thing was I don't want my less techincal friends and family for who I'd have to build some ebikes feel the stress of needing to look at the battery gauge "or else". d8veh, I'll look into the links you posted.

I'm also looking into RC. As far as I see their big disadvantages would be (in order) : no / difficult assist on start from standstill and lower continuous power compared to a Hub. On the upside they're lighter and cheaper and seem to push enough continuous power for what I need

 

[dogman dan]

There is virtually no disadvantage to running a 1000w motor at 200w, except for the 1000w motor weighs more.

But the weight is worth it to me, because I don't normally fry 1000w motors unless I give them 3000w My climate is harsh, and the rocky mountains are steep, so I cooked off both of the smaller wattage motors I ever owned.

My typical ride nowdays, a 150 pound cargo bike, plus me, plus groceries. Call it 350 pounds. I have a motor on the bike easily able to put out 3000- 5000w, a 5304 clyte. But I ride it about 20 mph, and use about 600w doing it. When I have a need to, I put on full throttle, and use 2000w to go 33 mph. Nothing wrong with the big motor running at a pace it could do for years continuously without overheating.

IMO, if price is the issue, go with the cheaper direct drive motors, or less powerful gear motors than the mac. If you aren't climbing huge mountians in desert conditions, the smaller motors like the cute or bafang should work fine for you.

Only if you need the power, and the freewheel, do you need the mac. For 300w and under, the tiny gearmotors work fine. I just can't get up my hills on 300w. That's why my monster cargo bike has a motor able to do 2000w all day.

 

[drebikes]

I see, you have a bit of weight to push up a hill. I think in my case the bike and me shouldn't pass 200 pounds. There are some hills around me, but let's say if I have some boost it's bonus.

The cost issue is interesting. For me and the lady I'd pay more, but I want at least the first prototype to be representative for a small series that I'd build for a few friends and relatives. The other thing about the cost as I said is that the most appreciated motors are in the US or Canada and if I buy from there shipping is half of the motor price; by principle it doesn't seem right.

DD it is then. Unless it's RC motor? Probably I have to make another thread for that once I understand better RC ebike drivetrains.

 

[LockH]

"Anti-Cogging Algorithm Brings Out the Best in your Hobby Brushless Motors"
http://hackaday.com/2016/02/23/anti...-out-the-best-in-your-hobby-brushless-motors/

[youtube]Rp8YyCMY4vs[/youtube]

 

[Hummina Shadeeba]

Maybe the eflight with its very high kv means weak magnets and that’s why low cogging torque

I guess drone motors with their many poles are for less cogging so as to have better control? Is that it, is that necessary?
I don’t see the extremely low cogging torque 21n22p used anywhere.

 

[dogman dan]

FWIW, with the worst cogging dd motor out there, just the tiniest tickle of power to the motor eliminates this. With some kits, riding with the display set to level one power does exactly this. And a 10 ah battery used on level one power might last 100 miles.

In addition, you add about 8 pounds of motor and 8 pounds of battery to any bike and pedal motor off, why it feels exactly like a 16 pound heavier frame. Picture your nice road bike tires on a 50 pound beach cruiser frame. Yep, it sucks.

Soooo, you might find riding around no power with that extra sixteen pounds not so great. But,,, happily, you can get a simple planetary geared motor that is pretty light, ride it at low power, using the PAS, most of the time, and it will coast down a hill just as fine as a naked bike. And then when you need power, just punch the button on the display, and switch from level one power to level 5.

Believe it or not,, some pretty good engineers in china have been working on this about 20 years. You won't improve on their work much.

But trying to is real fun! But again, if you build something homebrew, just the tiniest tickle of power makes the cogging go away, and barely impacts your range at all. Take a 500wh battery and discharge it at 50w, and it lasts 10 hours. If you ride 10 mph, that's 100 miles. So tickle the motor and forget about cogging being a problem.

When riding down a big hill, like 3000 vertical feet, cogging is your friend.