Hill conquering motor advice

[Michall2008]

Hi ES,

This will be my second ebike build,
my good friend asked me if I can build him an ebike to get him from
home to school, I asked him for the distance, he replied 5.5 - 6 Km,
i said no problem it will be done
(he just did not mention it is a 450m elevation in does 5.5 Km )

So this is the challenge:

I need help for deciding on what motor/motors will be best for this task,
I have access to Mac motors and 250w bafang,
drivers weight is 85k (187 lbs).

I have 4 options on mind:

1. Rear Mac T12 in a 24" or 26" rim
2. Rear Mac T12 in a 24" or 26" rim + 250w front bafang
3. Dual 250w bafangs system
4. Mid drive bafang/Mac or other mid drive system (i'm guessing it will be the best option for me but i would like to avoid that).

Speed should be 25 - 30 Kph (15 - 18 Mph) when climbing, I can go with 36v (12s LifePo4) or 48v (16s) system.

Another challenge will be stopping the bike when going downhill, will mechanical/hydraulic disc brakes do the job ?

Michael

 

[r3volved]

I'd love to see how the new 750w bafang or the 60V gng would handle that.

 

[dogman dan]

Definitely a 12t mac for starting point. It will handle the 15% with no big problems I think. But that steep bit at the end will come when the motor is getting good and toasty.

Definitely a second motor will help a lot.

Or, am I reading that chart right? If 90% of it is only 8%, then you might be fine with just a single 10t.

 

[Michall2008]

Thanx Dogman,

After more detailed examination of the section I found
out only 1500 meters of the 5.85 Km is over 10% grade,

Should I still go with the T12 ?

How can I estamate the power consumption for this section

Michael

 

[cal3thousand]

You're right that option #4 will be the best for hill climbing, but worst for the builder.

 

[e-beach]

Another challenge will be stopping the bike when going downhill, will mechanical/hydraulic disc brakes do the job?
Michael

What about regenerative braking for that nice long downhill?

 

[ddk]

option 2 would be my choice, because there's no such thing as 'overbuilt' when tackling long hills.
-except for the braking part-
I always had* to stop and wait 15-30 minutes about 3/4 down my local 7-mile (average 7%) hill to let the mechanical brakes cool down. (that burnt rubber scent from the brake pads)
AFAIK disc brakes wouldn't be that much better than my combination rim brakes... (tested mechanical disc - no difference)
Unfortunately, you don't list a DD in your 'access'

*Just yesterday I installed a DD hub motor on the front wheel, specifically to tame downhill runs. It works the charm.

 

[dogman dan]

I would say the 12t would still be a good choice. But as for the braking, a dd motor will definitely tame the descents.

The slower the wind, the better a dd motor controls your maximum speed when coasting downhill, greatly reducing the need to brake hard. It's another of the reasons I'm such a big fan of slow dd motors. It works without having regen enabled. As you reach about 20 mph with a slow wind dd motor, it starts to resist a lot. Very hard for me to exceed 30 mph down even the steepest hills with my 2810 motors.

So you might consider EM3ev's slowest rpm dd motor. I'm positive it can tackle that climb with no second motor. Run it on 48v 40 amps controller, or 72v 30 amps, and it will get up that hill no problems.

I have not done it yet, but I have always thought a rear dd and a front gearmotor would be a great way to go, if you are doing two motors. That way you get to freewheel one motor most of the time, have two motors when needed, and still get one motor helping you control your descent speeds.

 

[TheBeastie]

Also you want to think about your battery a bit since your probably going to constantly suck 30A out of it all the way up the hill non stop you will need a quality battery or lipo.

 

[Michall2008]

Hi,
Thank you evrybody,

Dogman, You are saying that the em3ev DD 275 rpm motor will take that hill, this is great.
The DD motor is 130$ cheaper than the guard, and i will have regen braking
I will definitely go with the DD.

The battery is OSN's 16s 20a Lifepo4 (a12320ahM1 cells)

Michael

 

[spinningmagnets]

For every configuration, there are plusses and minuses to each. I have long considered the rare application where having two hub motors might be a useful option. Just now, I was wondering about the possible benefits/drawbacks of dogmans suggestion of a front geared hub and read DD hub. I don't see any benefit to double DD hubs. Dual geared hubs are a possibility, and geared-hub coupled with a DD hub allows DD to be the faster winding (low RPMs on an uphill are the weak-spot for a DD hub), but having one of the motors be a DD allows for regen braking to keep the brakes cool and functioning at their max capabilities.

So, in a paired DD/geared-hub motor set-up, should the DD be on the front or the back? If the freewheeling geared hub is on the front, all fork drop-out issues resulting from high-power and a strong back-and-forth regen are completely avoided.

Dual motors are most appropriate on steep hills where a single conventional, affordable, and available motor doesn't have the best copper mass or heat-shedding for that job. Dual motors will add copper mass to the system and doubles the heat-shedding. Steep uphills have steep downhills on the other side, and regen braking is an appropriate feature for that scenario.

Score one more for dogman. Rear 9C and front MAC/BPM is now my new dual motor suggestion.