Want to build a hunting bike with a hub motor

1263

New Member
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

New Member
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

New Member
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".
 

FlatSix911

Well-Known Member
Region
USA
City
Silicon Valley
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.



1589657472643.png
 

1263

New Member
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.



View attachment 52611
This is out of my budget. It is yet to be seen but I am hoping to build something much stronger for less money. I have seen the independent testing on Bafang motors and they are not living up to their claimed torque numbers. Of course I realize we should be looking at the whole bike and I am sure overall this is a great bike but I think I can build something more suitable for my situation for a lot less.
 

Timpo

Well-Known Member
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".
I don't know why you think 20" bikes (such as Rad Mini) are more stronger than 26" bikes like Rad Wagon.

The payload capacity for Rad Mini is 275 lbs, and Rad Wagon is 350 lbs.
The Rad Rover (26" fat bike) is 275 lbs as well.

My point is, it depends.. just because bike is small, doesn't mean it's strong.

If that's the case, children's bicycles are the strongest bikes on the market.
 

1263

New Member
I don't know why you think 20" bikes (such as Rad Mini) are more stronger than 26" bikes like Rad Wagon.

The payload capacity for Rad Mini is 275 lbs, and Rad Wagon is 350 lbs.
The Rad Rover (26" fat bike) is 275 lbs as well.

My point is, it depends.. just because bike is small, doesn't mean it's strong.

If that's the case, children's bicycles are the strongest bikes on the market.
The reasons I chose a 20 over a 26 is as follows:
1)I am going to use a nongeared hub motor and the 20 will spin faster which will make the motor more efficient. When climbing steep hills every bit of mechanical advantage helps!
2)The 20 will make the overall bike smaller which provides a sturdier platform.
3)the 20 has a lower moment of inertia which aids climbing a lot.
4)the 20 allows me to maneuver better in tight turns.
5)20s can hold up better to the tremendous torque I am going to be putting in them with a larger hub motor. The tangential force applyed to an extra six inches of torque arm is tremendous. Of course anything can be mitigated with stronger spokes, frames etc.
And lastly, a lower center if gravity prevents less opportunity for tipping over backwards in a steep hill. I have tried both 20 and 26 on hill climbing and the 20 performed much better for me. I also find them much more manageable when I am hunting.
 

Timpo

Well-Known Member
The reasons I chose a 20 over a 26 is as follows:
1)I am going to use a nongeared hub motor and the 20 will spin faster which will make the motor more efficient. When climbing steep hills every bit of mechanical advantage helps!
2)The 20 will make the overall bike smaller which provides a sturdier platform.
3)the 20 has a lower moment of inertia which aids climbing a lot.
4)the 20 allows me to maneuver better in tight turns.
5)20s can hold up better to the tremendous torque I am going to be putting in them with a larger hub motor. The tangential force applyed to an extra six inches of torque arm is tremendous. Of course anything can be mitigated with stronger spokes, frames etc.
And lastly, a lower center if gravity prevents less opportunity for tipping over backwards in a steep hill. I have tried both 20 and 26 on hill climbing and the 20 performed much better for me. I also find them much more manageable when I am hunting.
I'm not a hunter, so I may be missing something but..

I'm not convinced that you need such HEAVY bike, minibike or not... for hunting.
A big gearless hub motor, perhaps twin motors, and with a big 72V 60Ah battery you're talking about... how much is your bike going to weigh? Like 100-120 lbs?

Is this more desirable for hunting than a 60 lbs or so fat bike?
 

1263

New Member
I'm not a hunter, so I may be missing something but..

I'm not convinced that you need such HEAVY bike, minibike or not... for hunting.
A big gearless hub motor, perhaps twin motors, and with a big 72V 60Ah battery you're talking about... how much is your bike going to weigh? Like 100-120 lbs?

Is this more desirable for hunting than a 60 lbs or so fat bike?
Yes, it's going to weigh a lot! But, in my opinion, it's going to maximize weight to torque, heat, reliability/longevity while still being able to pack a deer, the bike, and equipment up a steep hill in the middle of nowhere, on a limited budget! I am, of course, brainstorming, at this point and nothing is set in stone. And I am looking at ways to reduce weight. I realize that what I am asking for 500 lbs at 40 degrees may not be physically possible but it probably is at 30 and I will figure out what to do with the few short areas over that.