Want to build a hunting bike with a hub motor

[1263]

I am building a hunting fat bike. 20" x 4" wheels. Don't care about weight. I want it to be able to pull a trailer. Total combined weight of 500 lbs. Grades between 20 and 40 percent. I would prefer to stay with a gearless, direct drive hub motor. I am designing it with one motor in the back but may have to upgrade to one in the front as well for more traction, torque, and balance, but will try it with one motor to start with. I don't care about how large the hub motor has to be to accomplish my goals. I am starting my calculations with a small 5000 watt gearless hub motor, 960 winding, 190 nm, 72 volts 60 ah, Peake phase current 300 amp, and a 150 amp controller. I will be running a hot rod cooling system. I know this isn't enough information to get a very accurate calculation but I am just looking at an approximate one. I would like to use zero rider power input into the system to start with.
Is this feasable, do I need more power or two motors, or is it impossible?

 

[1263]

I am building it because I can't seem to find a bike that has everything I want. The weight would be 500 lbs total with Rider, bike, and trailer. I realize it's large but I feel it has to be large to get enough torque, strength, durability, and for heat dissipation.

 

[Mike_V]

500#@$20=estimate $10K

Why not buy a dependable vehicle?

Like Elmer Fudd, If you go hunting where it's cold with an eBike, then prepare to fail.

 

[1263]

500#@$20=estimate $10K

Why not buy a dependable vehicle?

Like Elmer Fudd, If you go hunting where it's cold with an eBike, then prepare to fail.

A lot of the trails are single track, winding, steep and cannot be traversed by a vehicle.

 

[indianajo]

I carry 60 to 136 lb cargo on the bike left. Gross weight 320 lb to 400 lb. With tools panniers motor battery & 36" rack bike weighs 94 lb light. I climb 77 hills on my 30 mile commute to summer camp, 3 of them 15% about 100' long. I had a 1000 W DD hub motor in the beginning, but I was always running out of electricity from a 17.5 ah battery. Now I have a 1200 W geared hub motor and I can get to destination before the controller drops out, usually. DD hub motors are highly inefficient at low speed due to the slip. More suited to 25 mph commutes on flat ground & good pavement.
Geared hub motors cannot run full power for more than 15 minutes uphill without burning the windings. Do not cool well. My grades are short. My tires are 2.1" x 26", not 4" fat tires.
I feel your vehicle is doomed to failure. 20% to 40% grades are outside the envelope of bicycle performance.
Mid drive cools better but you'll be putting in at least half the power yourself. With those kind of loads, chain life will be in hundreds of miles, not thousands.
Sources for super power motors has dried up, They are illegal on road in US, Canada, Aus, EU, so nobody wants to import them anymore. If you feel confident on alibaba, you might find something but you might get some real garbage, too. I'd use a throw away debit card if I bought on ali, the FBI won't protect you if your card gets hacked.

 

[Bruce Arnold]

This is from an article about physics and road bikes: "Let's just put in some values here. Suppose the bike plus rider has a mass of 75 kg with an average speed of 2 m/s. If the grade was 30, this would require a power of 441 Watts." 441 Watts is a lot for a human-powered bike. Not so much for an ebike. Still, the motor will be working hard to get all that mass up this kind of slope.

That's for a 30 percent grade, 150 lbs, and does not figure air resistance or friction. You're talking about 500 lbs (and I don't get why it has to be that heavy but I'm not second-guessing you, I assume you have your reasons.)

The next issue I wonder about is center-of-mass. Seems like you'd be leaning out over your handlebars. I haven't graphed it so I might be wrong.

With a little back-of-the-envelope calculation, I don't think what you want to do is possible. But dang, if you pull it off, please post videos!

 

[indianajo]

My ebikeling 1200 W geared hub motor is 1200 W input. If I start it on a 15% grade it tops out at 6 mph. So gross weight 320 lb, calculates out to about 340 W on the ground.
I can pedal it up that grade in 32:28 without power, but that is at 1.5 mph. About 80 watts? not bad for a 69 year old.

 

[FlatSix911]

Tern advertises it can carry 400 lbs of cargo.
It comes with a Bosch mid drive, not some crazy 5000W motor x 2.

Hipster hunter... a true oxymoron.

 

[FlatSix911]

I am building a hunting fat bike. 20" x 4" wheels. Don't care about weight. I want it to be able to pull a trailer. Total combined weight of 500 lbs. Grades between 20 and 40 percent. I would prefer to stay with a gearless, direct drive hub motor. I am designing it with one motor in the back but may have to upgrade to one in the front as well for more traction, torque, and balance, but will try it with one motor to start with. I don't care about how large the hub motor has to be to accomplish my goals. I am starting my calculations with a small 5000 watt gearless hub motor, 960 winding, 190 nm, 72 volts 60 ah, Peake phase current 300 amp, and a 150 amp controller. I will be running a hot rod cooling system. I know this isn't enough information to get a very accurate calculation but I am just looking at an approximate one. I would like to use zero rider power input into the system to start with.
Is this feasable, do I need more power or two motors, or is it impossible?

Probably a better bet to just buy a purpose-built machine... what is your budget? YMMV

(Link Removed - No Longer Exists)

(Link Removed - No Longer Exists)

2020 Bintelli Fusion Hybrid Electric Bike | Bintelli Fusion | Bintelli Hybrid

The 2020 Bintelli Fusion is a hybrid electric bike combining the ease of owning an electric bicyclenwith all of the features of a scooter.

www.crazylennysebikes.com

 

[ruffruff]

I use my bike for hunting. NO way would I want to traverse some of the stuff I go over in the woods with 20" tires.
Motor strikes, derailuer rip offs. More junk in the chain ring, etc. etc.

 

[FlatSix911]

I use my bike for hunting. NO way would I want to traverse some of the stuff I go over in the woods with 20" tires.
Motor strikes, derailuer rip offs. More junk in the chain ring, etc. etc.

I agree, however, the OP specifically requested 20" wheels... 26" would be a much better alternative

 

[ruffruff]

I agree, however, the OP specifically requested 20" wheels... 26" would be a much better alternative

I feel he's on a unicorn hunt.

 

[1263]

what motor did you have? Crystalyte?

Qsv3 Cromotor

 

[1263]

wait I just realized that you sad 20" x 4" wheels? (NOT 26" x 4"? )

So you want something like Rad Mini??

Yes,. Of course highly reinforced to handle this scenario.

 

[1263]

Probably a better bet to just buy a purpose-built machine... what is your budget? YMMV

(Link Removed - No Longer Exists)

(Link Removed - No Longer Exists)View attachment 52530

2020 Bintelli Fusion Hybrid Electric Bike | Bintelli Fusion | Bintelli Hybrid

The 2020 Bintelli Fusion is a hybrid electric bike combining the ease of owning an electric bicyclenwith all of the features of a scooter.

www.crazylennysebikes.com

View attachment 52531

My budget is under 5k. But these bikes don't have enough power or strength to handle what I am proposing. But I feel I can build it. The question is will it perform as I envisioned it.

 

[1263]

This is from an article about physics and road bikes: "Let's just put in some values here. Suppose the bike plus rider has a mass of 75 kg with an average speed of 2 m/s. If the grade was 30, this would require a power of 441 Watts." 441 Watts is a lot for a human-powered bike. Not so much for an ebike. Still, the motor will be working hard to get all that mass up this kind of slope.

That's for a 30 percent grade, 150 lbs, and does not figure air resistance or friction. You're talking about 500 lbs (and I don't get why it has to be that heavy but I'm not second-guessing you, I assume you have your reasons.)

The next issue I wonder about is center-of-mass. Seems like you'd be leaning out over your handlebars. I haven't graphed it so I might be wrong.

With a little back-of-the-envelope calculation, I don't think what you want to do is possible. But dang, if you pull it off, please post videos!

The 500 lbs is with gear, bike, me, and game weight. You are right riding up a hill at 30 is much different then 40. I have done in granny gear leaned over and driving as hard as I can with 50 lbs and it just about killed me. That's why I think a second motor in the front might be needed to balance the load at 40 degrees. I spend most of my time at the 20 to 30 range which I feel I can engineer. Of course there is a winch to tackle the steepest, if necessary.

 

[1263]

My ebikeling 1200 W geared hub motor is 1200 W input. If I start it on a 15% grade it tops out at 6 mph. So gross weight 320 lb, calculates out to about 340 W on the ground.
I can pedal it up that grade in 32:28 without power, but that is at 1.5 mph. About 80 watts? not bad for a 69 year old.

I hope I am that strong!

 

[1263]

I use my bike for hunting. NO way would I want to traverse some of the stuff I go over in the woods with 20" tires.
Motor strikes, derailuer rip offs. More junk in the chain ring, etc. etc.

I have never had those types of problems with 20" tires. I prefer the weight distribution for climbing and the wheels have proven much stronger then the 26".

 

[1263]

wait I just realized that you sad 20" x 4" wheels? (NOT 26" x 4"? )

So you want something like Rad Mini??

wait I just realized that you sad 20" x 4" wheels? (NOT 26" x 4"? )

So you want something like Rad Mini??

But much stronger or reinforced to handle the weight and power needed to climb

 

[FlatSix911]

My budget is under 5k. But these bikes don't have enough power or strength to handle what I am proposing. But I feel I can build it. The question is will it perform as I envisioned it.

If you can stretch your budget, WattWagon builds a powerful machine available with a Bafang 3000W motor and dual batteries.

The Cross Tour is well equipped with the powerful Bafang Ultra motor, the Rohloff Hub, Carbon Gates belt drive train,
custom Miranda cranks, stopping power of the Hayes Dominion A4 brakes, with a 203mm front / 180mm rear rotor.

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