Power and Torque

[woodyvt]

Questions:

I have been looking at the setup for two different electric motorized bike kits and I have a couple questions regarding the benefits and drawbacks of each.

Kit # 1: http://www.gngebike.com/48v900wmiddrivekit.htm

Kit # 2: http://www.gngebike.com/ebikecargolfcart950w.htm

I am building a chopper style trike with 20" x 4.25" rear tires. It's not real heavy but obviously more than a standard steel frame two wheel bike.
Also I live in Vermont, USA, a somewhat hilly area. I intend to run whichever setup I build through an 8 speed mid-drive hub and derailleur just in front of my differential drive axle with a freewheel on the front bottom bracket. I went with an 8 speed drive hub to compensate for my hilly local terrain.

Question 1: Will the setup with two geared 450w brushed motors in tandem give me more torque or will the single 950w brushless motor?

Question 2: Will going for more torque to get up the hills significantly effect my top speed? I would like to achieve a top speed of 30 mph.


Question 3: I will be using 4 lead acid batteries due to their lower cost which will also add their own weight to the equation. What amp/hour battery rating should I choose to achieve a 50 mile range on flat ground?

Question 4: Which of the two setups will use battery power more efficiently?

I am on an extremely limited budget and I'm trying to do this in the most cost effective way. I do not intend to purchase the assembled kits but build my own setup with only the essential parts that are needed.

I am asking you folks for advice because my earlier attempt at building an electric bike was way under powered. I reluctantly put a gas motor on that bike and sold it. I accept my inexperience/ignorance regarding the realm of electric powered bikes and humbly ask for your expertise and experience in guiding me in this new adventure.

Thank you in advance.

 

[Brentis]

Questions:

I have been looking at the setup for two different electric motorized bike kits and I have a couple questions regarding the benefits and drawbacks of each.

Kit # 1: http://www.gngebike.com/48v900wmiddrivekit.htm

Kit # 2: http://www.gngebike.com/ebikecargolfcart950w.htm

I am building a chopper style trike with 20" x 4.25" rear tires. It's not real heavy but obviously more than a standard steel frame two wheel bike.
Also I live in Vermont, USA, a somewhat hilly area. I intend to run whichever setup I build through an 8 speed mid-drive hub and derailleur just in front of my differential drive axle with a freewheel on the front bottom bracket. I went with an 8 speed drive hub to compensate for my hilly local terrain.

Question 1: Will the setup with two geared 450w brushed motors in tandem give me more torque or will the single 950w brushless motor?

Question 2: Will going for more torque to get up the hills significantly effect my top speed? I would like to achieve a top speed of 30 mph.


Question 3: I will be using 4 lead acid batteries due to their lower cost which will also add their own weight to the equation. What amp/hour battery rating should I choose to achieve a 50 mile range on flat ground?

Question 4: Which of the two setups will use battery power more efficiently?

I am on an extremely limited budget and I'm trying to do this in the most cost effective way. I do not intend to purchase the assembled kits but build my own setup with only the essential parts that are needed.

I am asking you folks for advice because my earlier attempt at building an electric bike was way under powered. I reluctantly put a gas motor on that bike and sold it. I accept my inexperience/ignorance regarding the realm of electric powered bikes and humbly ask for your expertise and experience in guiding me in this new adventure.

Thank you in advance.

Question 1: Will the setup with two geared 450w brushed motors in tandem give me more torque or will the single 950w brushless motor?

I think you should opt for the brushless. It will likely be more efficient than those brushed pair.
I have seen dual motor setups work, but the are often alignment nightmares, chain jumping.

Question 2: Will going for more torque to get up the hills significantly effect my top speed? I would like to achieve a top speed of 30 mph.

Yes, the more you gear for torque the lower your high speed will go. Running a geared mid drive allows you lots of gearing options though.
Running the motor through a mid drive will be ideal for hilly Vermont.
You can gear down for monster hills or up on the flats for 30mph. 1000w should do around 30mph geared right on the flats.
Not up a hill though. If you want 30mph up a hill you will need much more power.

Question 3: I will be using 4 lead acid batteries due to their lower cost which will also add their own weight to the equation. What amp/hour battery rating should I choose to achieve a 50 mile range on flat ground?

I dont even want to touch that.
Some will suggest you can do it, but the bike you create will be closer to a motorcycle than a bike in weight.
48v Sla for 50miles wheeeew. your talking a couple hundred pounds.
Forget it.

Question 4: Which of the two setups will use battery power more efficiently?

See answer 2.

If you are handy and can assemble things/follow instructions you can get 30mph for 50miles.
Those motors are not the answer.
I would suggest you read/search up "hub motor mid drive".
You can buy many of the needed parts from SBP
http://www.sickbikeparts.com/catalog/index.php?osCsid=0f9e2a78cd90200c4e6496ff4d07826a
then run a hub motor capable of more power than those listed. Hub motors having the advantage of low kv. Easy to gear down.
There are quite a few stunning examples of this concept here. this is the latest.
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=37489&hilit=Tench

The battery issue is a tough one.
Good batteries cost more money up front but have many more cycles in them, weigh a fraction of lead, & hardly sag in voltage.
SLA is cheaper to get into, but its a trap that will cost you more in the long run.

I hope I didnt discourage you. I wish you the best on your build. You are in the right place.
Ask lots of ?'s before buying. You'll get 20 different ways to achieve what you want. Start reading build logs.

 

[MadRhino]

+1 for a mid drive built with a hub motor. It will be cheap, silent and reliable. I would consider a geared hub motor with fast winding, for they are small, cheap and efficient. You can see with cell-man Mac kit.

Doing 50 miles range without excessive weight on a low budget, you'd have to go for HK Lipo. You need to read about them and understand their safety and charging requirements. They need more care, but they will give you power and range with little weight, and can be charged fast.

 

[dogman dan]

The brushed motors in that kit are known workhorses, and we've seen double motor frankenbikes here using those. But it's not a great route to 30mph. Those currie motors are well known to be great for the cheapest possible ebike. One motor driving the rear wheel is quite torquey, but slow as hell and very noisy.

The other kit with the single brushless motor looks pretty promising. Be ready for the doesn't quite bolt on and work perfect approach with this sort of thing. But if the mounts don't exactly work on your bike, it does look like most of the basic components are there. Your bike is likely to need something the kit doesn't exactly supply. Part of the fun, to invent what you may need.

In the right gear, 1000w will typicaly get you 30 mph on the flat, with no headwind. The same wattage will also get you about 15 mph up 5-6% grade hills. Steeper hills will mean shifting down and going much slower. Trying to climb a hill in too big a gear stalls the electirc motor, causing it to make excess heat. Climb those hills in too steep a gear and it's a proven way to cook motors and controllers.

As for the battery. You'd just be that dumb to try for really long range with lead. Particularly on steeper hills, you reach a point where carrying more lead actually shortens your range. You can get your bike up and running with lead, smaller slas on the cheap, but range will be sub 10 miles at 30 mph. Quite possibly sub 5 miles at that speed.

Well, there went your budget, big time. The best approach for you will very likely be a 48v 15 ah lifepo4 battery from Pingbattery.com This would get you about half the range you want, and be large enough to supply your motor with 1000-1500w. With one of those, you should see about 20 miles at 30 mph, 25 miles at 25 mph, and 30 miles at 20 mph. At some time in the future you could purchase a second 15 ah battery, and then you would have true 50 mile range, while carrying about 30 pounds of battery.

As for riding 50 miles on a no suspension chopper bike? Ai yi yi! not me. That would be horribly uncomfortable for me by mile 20. My long range bikes are all full suspension, even my longtail cargo bike is a bouncer.

 

[LegendLength]

I am on an extremely limited budget and I'm trying to do this in the most cost effective way. I do not intend to purchase the assembled kits but build my own setup with only the essential parts that are needed.

Just one thing if budget is the main concern: Check if you'll need a better quality freewheel on your pedal system. The cyclone systems (similar to the brushless one you linked to) nearly always needed a new freewheel ($50 - $80 i think). So might be worth checking for this specific kit so you can factor that small amount of money in as well.

In fact make sure you're aware of all those little possible issues so you can budget for them (e.g. chain strength, motor freewheel, gearing, controller limitations, chain guards etc.). I'm not trying to steer you towards direct drive hubs (I like mid-drives better personally), but when you look at the cost of one of those systems, even something like the cromotor, there aren't as many gotchas. Basically just motor, controller, batteries and you're costed. So even though it may be cheaper in the end it's worth trying to cost all the little details when doing a mid-drive IMO.

 

[woodyvt]

Thank you all for your input and suggestions. The project is temporarily on hold till I get some work done on a motorhome I recently purchased.

I did find a Worksman PAV-3 with a 700 watt hub-motor for $100 and I'm using that to get around for now. It was a great deal... No charger but I just charge my 12v batteries individually with a 12v charger for now. I've ordered a replacement charger and it should be in a couple days.