off road rear hub as mid drive build blog

[John Bozi]

EDIT: 5/01/15 Have renamed this thread again as I have changed direction of my next build.
EDIT: 27/9/13 Have renamed this thread as I have changed the direction of my build.

Below is the original first post:

I am looking for a HUB motor for climbing about 10-20 minute single track only. Not interested in mid drives. Gravity does it back down. Imagine the fittest cross-country rider alive and the speed he climbs at, not straight lines but going around corners and obstacles. I couldn't careless about going fast as most climbs are winding and errors on throttle could be neck braking.

Basically I will park my car at the base of the mountain, use up most of the battery to the top and enjoy the ride down unelectrified. Possibly have back up battery set ups in the car, for each different run so I don't have to cart it around.

I think I am planning to put the slowest winding motor in a 20" wheel.

Considerations I see are weight, bump handle factor and heating. I live in a subtropical area. I will of course be trying to be stealth as possible as mtb riders don't like electrics. Might look at back packing as much as possible.

Portable chairlift.

guesses: Mac 12t from cellman (anything better than this for pumping higher voltages or amps?)

or from a dogman quote on another thread: http://endless-sphere.com/forums/viewtopic.php?f=1&t=49136#p727424

My favorite though, is the extremely slow 2812 motor, which I run on 72v. 25 mph top speed, but able to climb crazy steep hills for a mile or so before melting down. By limiting the wattage to 1500w I have no problems, but I have at times doubled that to 3000w. At 3000w, with a 72v 40 amps controller, you pretty much never pedal unless it's up a grade of 30%.

 

[miuan]

Hub motors are good for anything but what you intend to do. Your MTB will feel crappy with 20 inch wheel. The hub motor must be big to handle that type of riding, and then it's no longer stealthy... you may be better off with GNG drive.

 

[skeetab5780]

you can try to hide your wires, but your not going to hide a rear hub. Also the newer hubs seem to be louder now..

Use an x5405 xlyte and you wont overheat ever.. it will take up most of the 20" rims space and will weigh 20lbs but its a nasty motor.

good luck finding one..
(p.s sellers ill pay more )

 

[dogman dan]

You'll get away with more power in Em3ev's 10t dd than you will in a Mac. They just shed the heat better. But others with trails easier to ride up at 20 mph do prefer the bigger motor approach, compared to my slow motor approach.

If you can maintain 15 mph up that trail without crashing, then an EM3ev DD in the slow winding will do. It sill will be able to climb some pretty steep stuff no problem, like 15% slopes for 20 min. But it won't overheat much at all if you can maintain 15 mph enough. In that winding, 48v would get you 20 mph on the flats with a 26" wheel. keeping it under 2000w, you could go as much as 40 amps. Re 26", I wouldn't want to ride hard bumpy trails with a radial spoked hubmotor. 26" wheel for me. But a 24" could work ok.

Tip, get two of the motors. You'll melt the halls in one from time to time, so a spare you can slap on quick is the way to go.

But, it's just too bad that the new Clyte crown motor does not seem to be available in the super slow windings the old 5300 series used to be. If you see a used 5306 for sale on your continent, snap it up!!!! Then you'd have a super slow motor easily able to take 3000 w for long periods.

 

[zombiess]

Can yo provide details of how steep the climb is?

A cromotor will probably do it, but are you willing to go single speed freewheel on the rear with a 26lb motor? Its the highest torque motor I know of that can be fit into a bike that has 150mm drop outs. Doesn't mean its the correct motor for your application though. Will you be jumping? How rough is the terrain? What about battery size and placement as weight distribution effects handling?

 

[d8veh]

Using two lightweight motors rather than one big one is much easier to handle when climbing. Traction is better and there's less tendency to wheelie or flip. The motors are smaller and quieter. Throttle control is better, so when you're on tight slippery turns, its dead easy. Twin 250w motors should be enough - Q100s if you're not too fat. I've built four 2WDs: It's very easy. In fact easier than installing a single larger motor. Here's a Giant I built with twin Q100s and a 20aH battery. Total weight about 23kg. Click on the link in my signature to see my Rocky Mountain that's more for off-road:

 

[dogman dan]

To give the best advice, we do need detailed info on how steep this 20 min climb is.

The stuff I do, I maintain about 15 mph up most of it, but believe it or not, there are guys who pedal it faster. The problem is the last steepest bit, only about a half a mile or so, but steep enough to fry hubmotors in that distance, unless they are big and fast, or take it slower and have the winding to not overheat going 10 mph. Up top, going up at 10 mph is a challenge. The hard parts, just hanging on for it is the main problem. Very hard not to wheelie off going up a rock staircase. So the blast up it wasn't the best option for my particular mountain trail. I DID try it. A 5304 in 24" rim flew up it fine, I just couldn't hang on for it, and kept heating the motor by riding it slow enough for me to handle it.

But if your ride is mellower, then you can put 72v to a 28mm 10t motor, and ride up it a 15 mph with little heating. Up to about 15% grades is fine. It depends a LOT on the character of the trail. However steep, a smooth and relatively straight trail can be handled by a big enough motor. Just power up it, and never stall the motor. But the Rocky mountains I ride in, are called the rockies for a good reason. Having to slow down, or stop when you bucked off, creates a problem for hubmotors.

 

[davec]

cro/54xx/53xx in a 20" will do you good/ or a 2wd-

 

[dogman dan]

Hell yeah it will. But I couldn't hang on to that blasting up my local trails at 20 mph. We didn't ride that area years ago on motorcycles unless we had trials gearing, and even then it was mighty hard to stay on.

That's why I became such a fan of the slow motor approach, fly off those trails, and your landing will always be in cactus thorns.

A super slow winding monster hubmotor would rock. Still looking for a used rear 5306 for sale.

If he can ride down those trails at 20-25 mph, then the big motor haul ass approach will work great. In general, you can go up trails faster than down, at least as far as staying on the bike goes, IMO. If nothing else, wheelie off beats over the bars.

 

[John Bozi]

sorry haven't replied for a while although I have lurked, been overly busy and tired.

A few of you guys helped me with choices when I first came on here earlier this year. I started a thread with similar thoughts but got totally side tracked by the limitations of hub motors and also their strengths. I kind of gave up on my mountain biking and got in to going faster around corners on bitumen. Lots of fun too!

For the type of terrain hit my video signature (homepage video is purely mtb) imagine going up the hill I rode down. It's not steep on single track only on firetrails.

My onroad bike has the 4065 and that just wouldn't work for how I am hoping to ride. The other is to take a smaller lighter approach, I'd like the slow method, smaller packs (happy to let them have a shorter life span).

Rear hubs don't look that unstealthy to me, it's more wiring, controllers and battery packs that destroy the smooth look of the mtbs. I plan to possibly have aluminium forks so front hub is a no go.

 

[dogman dan]

Looks to me like that terrain is not perfect for the blast it at 30 mph approach. Hard to tell from vids, stuff looks very flat. But it appears at least the equivalent grade to the trails in my area. Just enough rocks to make too fast a problem for your rims, tires, and maybe face. There's the question of how fast you choose to hit a tree as well.

2812 would work, but you can't buy one, unless somebody drops one on the used market. Since the 2810 dd motor is available at EM3ev, and it's cheap, I'd say try that at 48v first. Vent holes in the cover so when you do heat it, it cools faster, temp gauge inside. Big deal if it melts. Then if it really is too fast a wind, maybe try the 12T Mac.

 

[torker]

I love my 2810 in 20 inch it only does 25 mph. @ 60 volts but it gets there really quick. I haven't tortured it though. Not sure what it would actually take.

 

[dogman dan]

Anything in 20" beats 26". The big problem with hubmotors and steep trails that are too tricky to ride 20 mph, is 26" wheel can't go 10 mph at 2000w without smoking motors. The slow winding helps a lot, but in 26"wheel, I still want to go faster than 10 mph under heavy loads with a 2810. My 2812's can handle a lot of 10 mph, but 5 mph up 15 degrees will smoke em.

So it becomes a bit of a question of can you hang on at 15 mph, over rocks, logs, etc.

 

[bowlofsalad]

Anything in 20" beats 26".

Excluding top speed and comfort.

The two smaller motor suggestion sounds up your alley, keeping it cool is still going to be an important concept though. Some put oil in geared motors. The suggestion of using a vented motor or two is probably what I would recommend. If you really need stealth, panniers and things like that would probably do a great job of hiding things.

I don't know what you mean by mountain bikers don't like electrics, what are they going to do? Watch you ride away? Shun you? Meh. Those would shun you because you rode an ebike up a hill probably aren't worth your time. "HOW DARE YOU DESICCATE THIS MOUNTAIN WITH YOUR ELECTRONS!"

 

[dogman dan]

The implied meaning was, 20" rim beats 26" rim for torque, when using hubmotors. You can slap 20" wheels on a DH bike, but you'll hang your crank on every rock for one. Hence the tendency to use 26" wheels, and cook off a few motors in the learning curve.

What will the other bikers do? Sick Ranger Rick on you in some places. Or take action themselves if they are like the surfers in dogtown. Hey dude, is this your carburetor?

 

[bowlofsalad]

I thought it would be worth mentioning wheel size for comfort a softer ride, I assume he is going to be going pretty intensely fast down a mountain, I imagine larger wheels might be pretty important even with great suspension, but I am probably be wrong.

I've heard of this torque and efficiency argument on wheel size several times. The only thing that makes most sense to me for that is a decrease in rolling weight as well as an idea that I don't really know how to talk about with a short phrase. Imagine a spinning ice skater or sitting in a spinning chair, when their legs are out and they pull their legs in, they start to spin faster. What I am suggesting is, the larger wheel might take more energy not just based on weight to get up to speed. Every situation I've tried setting up in any simulator doesn't change the torque output with a change in wheel size. Only voltage and maximum amperage seems to achieve an increase in torque. I suspect that a smaller wheel will accelerate more quickly, giving the impression of increased torque. I don't know if you have the same amount of weight spinning around the hub motor on a 26vs20 inch wheel if you'd see the same rate of acceleration, my theory is that the 20" wheel, due to how far out from the hub motor the wheel is, would still accelerate more quickly, but that is due to some phenomenon that I don't have a word for. This is a theory or guess.

 

[Miles]

Every situation I've tried setting up in any simulator doesn't change the torque output with a change in wheel size. Only voltage and maximum amperage seems to achieve an increase in torque.

You don't get more torque output.... The torque requirement is lower to achieve a given linear force.

Yes, the torque requirement to accelerate a smaller wheel up to speed, in a given time, is less, too, but the crtitcal thing is the level of sustainable torque, not the short term peaks....

 

[John Bozi]

One of my riding buddies bike has 24" and it is barely noticable that they are smaller unless you look to study the bike. The frame made for 26" wheels doesn't look strange is what I am trying to say. Running 20" wheels however, will look rather odd IMO and attract attention.

Maybe a middle of the road 22" might be a bit of a better compromise between, hill climbing ability, comfort and "normality".

22" in with fattest rim and tyres I can find should push near the 24" look and feeling too.

Anyone want to suggest the most suitable Lipo combination? Voltages or continuous amps I should be aiming for a 10 minute climb? I really don't want to carry more weight up than I need for each climb, as almost all the trails lead back down to the carpark where I could have another pack ready waiting to change over.

If the Mac 12t is the slowest available I will look at getting it. Flying up the hill to fast is very dangerous not just for me but also other riders coming down fast not expecting anyone coming up that fast.

Almost had a nasty accident yesterday on the firetrails like this. This is the 4065 doing very well for firetrails with urban tyres

[youtube]JbY0jp-g3pk[/youtube]

 

[John Bozi]

Izeman's build is pretty close to what I want.

Very stealthy http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=32267

scrap my last idea of 22" because they've only got 20" or 24"

I'm bit worried about 20" for chain clearance over roots now...

 

[dogman dan]

RE the battery, the voltage you want depends on the speed you want. Using the 10T from EM3ev for example, 36v gets you about 15 mph max, 48v gets you about 19 mph, 72v gets you about 30 mph.

I liked 48v for the 10t myself, for trails. Up a steep hill, say 15%, you could stay in that butter zone of 10-15 mph, and never get too hot. It couldn't climb the really crazy steep hills like the 12t on 72v though. Both windings overheat on crazy steep stuff. Also a problem if you keep having to slow to 5 mph, just to stay on the bike over rock steps. Enough repeats of 5 mph or even worse steep uphill start ups, and you melt down.

This is all 26" wheel data.

10 min shouldn't melt you down though, It generally takes 30 min of real punishment to cook one off.

As for the size, 5 ah might be enough. 10 min is very short. If not enough, you will know then if you need to add 3 ah more, or 5.

 

[John Bozi]

I won't buy anything until I can also make on a decision for the bike.

I want to build an offroad bike right the first time (dreaming) not keep going for second best.

I will stick to the smallest wheel back idea but need to find a solution for ground clearance. I plan to get those tripple crown or clamp forks which will lift the front up (also offer an easy place to attach a battery) and possibly have something like a slightly larger front wheel than the rear. Not too different as they end up just looking dumb for me.

I see the peddles more to just help the motor on starts and steep, am not looking for long ranges of going fast, so the peddles are more to just make it more "legal looking" so not too worried about efficient heights of the bike, or cranks really.

It might end up looking a bit like a dj bmx with big ass suspension.

I just am having trouble visualising how say 15cm of rear suspension will compress, how low will the cranks or bottom bracket get to the ground after a drop off a log.

I do wonder how strong the mac is.

I also consider building my own frame. I am waiting to see how the raptor boys go once they get them, but I feel for the bike I am trying to make they have too much battery space. I would love single speed concentric so I can do away with the tensioner which also be another thing low to the ground to get damaged.

Lots of thoughts.

I am most impressed with this guys 18" rear with 22" rear.

more pics here : http://endless-sphere.com/forums/viewtopic.php?f=28&t=47054&start=175

although it is not a rear hub, he will be doing another version with a rear hub and concentric pivot point. I am keen to learn what happens as it look like almost perfect for me.

 

[dogman dan]

Definitely a different critter there in the pic. Once you go non hub, you get to pick your gearing.

Don't listen to what I learned about hubmtors. A 10T direct drive hubmotor in 26" wheel run at 72v works really shitty. It fails to climb 20 degrees. Degrees bro, 20% is no problem.

 

[John Bozi]

Definitely a different critter there in the pic. Once you go non hub, you get to pick your gearing.

Don't listen to what I learned about hubmtors. A 10T direct drive hubmotor in 26" wheel run at 72v works really shitty. It fails to climb 20 degrees. Degrees bro, 20% is no problem.

Dogman that is a really confusing post, sorry. especially the last part. It fails to climb 20% and then it's no problem. Which one?

I am still researching and currently more locally for custom bike builders of concentric stuff that I can get them to tweak. I came across this guy just before.

https://www.facebook.com/photo.php?...98329978.70367.198431390224253&type=1&theater

My dream is to have something similar to a Lenz Milk Money 4" / pslope but with maximum suspension possible suited to a 20" rear and 24" front all single speed concentric design, with as much ground clearance as possible and battery box inside the frame.

I have one dumb question, how would the The crown in 20" compare to the 12T mac for strength and overheathing? I know the crown would be a monster (for more than climbing) and double the rear weight but would it handle the climbing at low speeds as well considering it's size?

On ebikes simulator which motor would be closest to the 12t mac for simulation purposes?

 

[John Bozi]

I have been searching for ages for concentric frames but only get the pstreet types which just have the wrong head angle and not enough suspension.

I am stoked to find something similar to what I want to either build or modify.

2004 DH9

The replacement to the older Mk1/Mk2/Mk3 moto-link bikes produced by the orginial owners of Rotec (EC era)

This version was the last of Rotecs low mono pivot single swingers

I really don't like that bar holding the brake. Does the brake caliper pivot? could that part not be solid welded to the swing arm?

Hold on here's an even tidier older design:

1997-1999 Mk1 Rotec Pro DH Moto-Link bike

Even better with tons of battery space!

Anyway I am saving these here for reference if I ever go custom frame.

 

[Chalo]

Definitely a different critter there in the pic. Once you go non hub, you get to pick your gearing.

Don't listen to what I learned about hubmtors. A 10T direct drive hubmotor in 26" wheel run at 72v works really shitty. It fails to climb 20 degrees. Degrees bro, 20% is no problem.

Dogman that is a really confusing post, sorry. especially the last part. It fails to climb 20% and then it's no problem. Which one?

20% grade is not equal to 20 degrees.

100% grade = 45 degrees

20% grade = 11.3 degrees