1000w Front Hub Motor ebike Build Question(s)

[cyberalien82]

I apologize if I haven't researched this very well, but I'm not confident about where/how to look for information next. I'm looking to put a front hub motor on a steel (cro-mo) frame Pure Ayer 5 speed igh (belt, disc brakes, 650 wheels, 100mm dropouts, link below). I weight 175, am hoping to achieve 60+ miles on flat terrain using the lowest level assist at a speed between 20-25mph. I'm guessing this might not be possible with only a 5 speed, but I'm having a hard time finding an igh 8 speed bike for a reasonable price.

I've already balanced the pros & cons of the three different motor setups, so I've already decided on the front hub motor & I'm strongly considering the mac kit at lunacycles (link below, 1000w, 48/52v). Before I get into more specific questions, is there anything wrong with this setup? If not, the best I figure is that I need a minimum of a 20ah battery to get the distance I'm wanting, but will have to find that elsewhere as lunacycles is sold out of the larger battery they would sell with this kit. Also, lunacycles doesn't list a 27.5 (650mm) rim build for this kit.

While I work with my hands, my knowledge of electricity is only that of installing outlets & of functional safety, as I'm a firefighter by trade, so for the sake of safety, please assume I'm a total noob. Where do I go from here? After reading the FAQ I *think* this is the appropriate place for this, but am prepared for the burn if it isn't Thanks for any help.

https://lunacycle.com/bare-mac-high-performance-hub-motor/
https://www.purecycles.com/products/urban-commuter-belt-drive?variant=12350875074633


Jonathan

 

[2old]

Looks like a great system for a conversion and the MAC should suffice for you, but Luna hasn't had a controller for this motor for ages and no telling when they will. Look at em3ev for the motor and battery; your biggest decision will be the appropriate Mac motor (winding) for your needs, but they provide excellent assistance. IMO, don't worry about "only" five speeds; you won't need more (probably less) with that motor. I would consider two torque arms for the fork.

 

[Chalo]

Don't worry about your 5 speed hub; it will work fine. You might have to change the primary ratio if it isn't high enough, which could imply switching out the belt for a chain.

20mph will take at least 300W output (pedals plus motor) and 25mph will take at least 550W. If your system is well matched to your cruising speed and runs efficiently, that means about 450W and 800W respectively of battery power if you're not pedaling.

If you really want to go 60 miles at 25mph, and the terrain is flat with no wind-- ideal conditions-- that implies an almost 2kWh battery, which is pretty big. That's about three times the capacity of a pretty big downtube mounted e-bike pack. And that's assuming you're okay with running the battery all the way down, which isn't a good idea.

There's no good way to accommodate that much battery on the bike you have.

So let's say you're good with 20mph for 60 miles. That will consume 1350Wh from your battery in ideal conditions. That's a pack that you could probably fit better onto your bike-- the equivalent of two downtube packs.

Any effective pedaling you do will reduce the load on the motor, and extend your range, possibly by a lot. You probably won't be supplying half the power to ride at 25mph for two and a half hours, but you could pretty easily provide half your power requirement to cruise at 20mph. So you can both reduce your quantity of batteries and give them an easier job to do if you pedal ambitiously. To help ensure this happens, you'll need to use a system that has pedal activation (PAS).

The advantage of the MAC motor over similarly powerful direct drive motors is that it coasts freely, so you can ride the bike with only pedal power without incurring drag from backdriving the motor. The disadvantages are slightly lower efficiency, louder operation, and less tolerance of overheating at high power. But once you load up 60 miles worth of batteries, I doubt you'll be pedaling the thing anywhere without motor help. So you might as well use a more efficient and fault tolerant direct drive motor like the Leaf Bike hub.

Both MAC and Leaf hubs are available in different windings, meaning they can make their rated power in different speed ranges. By choosing the right winding, you can match road speed to wheel diameter to motor RPM to get efficient cruising at your desired speed.

 

[Bigwheel]

I have over 3 thousand miles on 1000w front hub motors and on flat ground maintaining speeds over 20 mph will require between 400-800w and you will be burning in the high teens wh/mi wise. If you have the complimentary pedal gear ratio to assist that is. Just riding a throttle will be more. Keep in mind that the faster you go the more air you will be pushing against and the more power necessary, even on flat ground.

I use Grin components and have been well pleased with their service and performance. I have 9c and an AnyAxle DD motors running statorade @ 20A 52v which I find is the best combination of enough power for my needs and range. I can squeeze 30 miles out of a 10ah, 520wh, battery on flat ground but rarely averaging in the 20's.

As mentioned make sure you use a good torque arm system and keep an eye on the axle nuts, especially if you use regen which is something to think about as it is a good feature. I don't use PAS, just a throttle in conjunction with the Grin CA3 display that allows me to set the throttle like a cruise control.

Sorry I don't have any input on where you are going to get a 20ah battery. But you could get two 12ah HL types and swap them out and have the option to only use one for shorter missions.

 

[dogman dan]

Agree with both above. Including some reserve, figure on .75 amp hours of 48v per mile, going full 48v speed of above 25 mph. At about 15 -18mph, you can get 2 miles per amp hour, or half an AH per mile. You will never believe how much farther you go on an amp hour at 18 mph, vs 20 mph. This is because the amount you get from your pedaling increases incredibly as you slow down.


As I rode along, keeping track of my wh/mi, the target was to hit below 25wh/mi average, to make it across 60-70 miles of desert road.


I did lots of 60 mile rides, and they always took about 1500 watt hours. 48v 30 ah, 36v 40 ah. For convenience carrying that much battery in panniers, think in terms of two 48v 15 ah packs. Or one in the triangle, and one on the rear rack.

 

[donn]

You will never believe how much farther you go on an amp hour at 18 mph, vs 20 mph.

According to the simulation, if you can make 60 miles at 20 mph, you could reach about 78 miles at 18 mph, pedaling at 100W. Add several miles to that, if you use a hub that's more optimal for that speed, instead of the stock configuration.

(That "if you can make 60 miles" means, in terms of your real battery capacity, so it would be less than the simulator's "range" figure, which uses the nominal capacity of the configured battery.)

 

[cyberalien82]

I truly appreciate the time and information you've shared.

I need a day or two to think this over, but I have no intentions of sitting on this bike and ever using the throttle. I'm actually getting ready to finish the last leg of my yearly state-by-state bike across the US in May-- Maine!-- and the idea of not at least spinning at any time just feels wrong.

So, assuming I get the Leaf or the Mac motor-- and two torque arms for the cro-mo fork-- what's my next step for components? Or, at least, which two or three sites might be best for ordering the rest of what I'm wanting in the same place?

 

[dogman dan]

Actually, for the longest possible range, there is no way you can beat controlling the motor with a throttle. Unless the bike has torque sensing PAS.

But, its possible to select ordinary PAS low enough, that you just pedal 60 miles while carrying the extra weight, doing more effort than you would with a naked bike.

 

[donn]

Actually, for the longest possible range, there is no way you can beat controlling the motor with a throttle. Unless the bike has torque sensing PAS.

But, its possible to select ordinary PAS low enough, that you just pedal 60 miles while carrying the extra weight, doing more effort than you would with a naked bike.

Interesting topic, technique/technology for minimal battery use. It makes sense to me too, that would be a throttle - with a cruise control feature, running at ordinary bicycle speed. Any reasonable performance goal has to allow for some real advantage to having a motor, so the motor has to kick in on hills.

 

[Bigwheel]

Although I only have a throttle on my hub bikes it is how I operate it that makes the most sense for the way I ride. I am a long time cyclist and pedal 99% of the time but on the road I find the PAS systems don't always allow for me to regulate my input/cadence as I have grown used to over the years. It is either too much like magic legs or fiddling with the assist level to find the right feeling I want. So I find that using a throttle in conjunction with a Cycle Analyst's ability to set as a cruise control along with the ability to set wattage limits in segments and a front hub motor that isolates the motor from the drive train totally allows me to pedal however I want at all times. So what I do is get into the gear I want and set the throttle to what compliments it and my desired speed over ground. I can then go up and down gearing to deviate my input as I want without affecting the motor output. It is like riding a tandem with a really strong stroker.

Although I have a 1000w motor I find myself using the 500w limit, of the 250, 500, 750 and 1000w settings, as the best combination of power and range for my needs on a daily basis, my average average is 15wh/mi, but if I am going for ultimate range I will scale back to 250w and vice versa if I want more power. Sometimes it is convenient to give the throttle a blip to keep momentum but I rarely use it for constant forward motion. It is easy to override the cruise function by blipping the throttle or hitting the regen button I have set up also.

 

[dogman dan]

Big wheel said it real good. Only a human brain controlling the throttle has the maximum ability to tweak the lowest wh/mi out of a battery, and still assist to the maximum. Again, you can set pas to level one, and get 10 pounds of weights worth assist, but you just put 25 pounds on the bike. So that is just pedaling your bike with extra weight, not getting assist.

The way to ride best is this.

Pick a speed.

Pick a gear that goes that speed at your ideal cadence. (This is very personal, and cheap hall sensor PAS settings rarely fit every rider.) I only downshift if the hill is very long and very steep. But in whatever gear, whatever speed, I set my cadence the same, and the pressure on my foot the same. A steady cadence is the key on really long rides.

Use the throttle, to give yourself assist at your ideal cadence. If on the open road, a half twist throttle can be jammed against the grip making it sticky at the chosen setting, for a crude cruise control.

This is the only way I know, without torque sensing PAS, to give an 80 mile ride with the lowest possible assist level every inch of it, yet be able to instantly react to anything that causes resistance, like gusts of wind, rolling hills, etc.


The downside? Yeah, you gotta learn to ride efficient. It can take a lot of time to learn to avoid throttle creep that costs you wh. Pedaling is the key, and soon you learn to sense the foot pressure, and stay in the right gear for your chosen speed. But yeah, you gotta actually pay attention while you ride. Its worth it when you take off on a ride, and the next drink of water or plug is going to be across 80 miles of desert.