Minimalist engineering for bicycles

[johnrobholmes]

No, we just banned you, safe.




I am not familiar with your gear inches formulation. What are you using for the inputs? In simple terms the motor size determines your power. The slower you want to go, the less power you need. If you want a very small motor you will need much geardown to take advantage of high motor RPM.

 

[jawnn]

What gear ratio for half hp?

Can any one tell me what gear ratio it would take to drive 450lbs up a 16% grade 3 to 5 mph with a 24v half hp electric motor???

I assume that a higher voltage motor would have more torque. So it may be necessary.

Some one told me 45 to one at 5000 rpm for a gasoline motor, but don’t electric motors need to run faster?

The show me the formula that you used???

 

[safe]

It's best to start with a Bicycle Calculator:

http://www.me.psu.edu/lamancusa/ProdDiss/Bicycle/bikecalc.htm

...from this you can get a general idea about how much power is needed to achieve various results.

This other Bicycle Calculator is really good at figuring out the gear ratio you will need:

http://www.arachnoid.com/bike/index.html

...with these two you should be able to arrive at an exact gearing.

Example:

Motor Rpm (pedal cadence) - 4000 rpm
Front Gear - 10 tooth
Rear Gear - 450 tooth

Resulting Speed - 6.9 mph (11.1 kph)

About 45 to 1 is probably a pretty good guess. It's hard to take a motor that spins at 3000 - 5000 rpm and gear it down to something usable for an ebike. In most cases a multiple stage geardown is required to get anything usable.

This is (in part) why I'm looking at the experimental usage of AC Induction motors for ebikes because they can be run at as low as 1800 rpm and actually behave well at speeds below that for the 4 pole design.

Anyway... those calculators should do the trick... if you still feel frustrated let me know and I'll manually help you through it.

 

[jawnn]

good thinking,but.....

These calculators are great, but they dont tell me how to get the data I want. Maybe I have play with it a few days.

The idea of using an AC motor is very good, just the kind of thinking we all need.

It's best to start with a Bicycle Calculator:

http://www.me.psu.edu/lamancusa/ProdDiss/Bicycle/bikecalc.htm

...from this you can get a general idea about how much power is needed to achieve various results.

This other Bicycle Calculator is really good at figuring out the gear ratio you will need:

http://www.arachnoid.com/bike/index.html

...with these two you should be able to arrive at an exact gearing.

Example:

Motor Rpm (pedal cadence) - 4000 rpm
Front Gear - 10 tooth
Rear Gear - 450 tooth

Resulting Speed - 6.9 mph (11.1 kph)

About 45 to 1 is probably a pretty good guess. It's hard to take a motor that spins at 3000 - 5000 rpm and gear it down to something usable for an ebike. In most cases a multiple stage geardown is required to get anything usable.

This is (in part) why I'm looking at the experimental usage of AC Induction motors for ebikes because they can be run at as low as 1800 rpm and actually behave well at speeds below that for the 4 pole design.

Anyway... those calculators should do the trick... if you still feel frustrated let me know and I'll manually help you through it.

 

[safe]

These calculators are great, but they dont tell me how to get the data I want. Maybe I have play with it a few days.

The idea of using an AC motor is very good, just the kind of thinking we all need.

I try many often bold and somewhat crazy ideas at times and sometimes they work well and other times they don't. I do learn with each mistake and have incremetally improved my bikes so that they now perfrom really well. (I just managed to pull 58 mph downhill starting with a simple 600 watt motor)

As for AC Induction motors applied to ebikes... well... it's a pretty wild idea, but I can see that if it does work it could really spark a totally new way of building these bikes. (chain driven, but without complex geardown units)

About those calculators...

You just need to think about what you want to do. Insert the weight that you are going to be using. Select the slope you want to climb. Decide how fast you need to climb. From these starting conditions you can get a result about how much power you need to achieve those conditions.

...the calculator can't read your mind. And as they say:

"garbage in, garbage out"

...so your results are only as good as how well you define the question.

 

[jawnn]

Minimum RPM's?

The only problem I see with the calculators is that they do not let me add the sprockets I think will work, ie: 17 front and 34 rear, twice. Well I don't see the formula even on the "scource".

So just keep us informed how the experiments go, and I want to know how much power they produce at minimum rpm, and what that minimum rpm is.

I realy think I finnaly asked the most simple question possible. Not that I understand any of this. But I do know that I do not want to use a motor large than half hp and volts more than 24, because it just adds too much weight. That also why I dont mind not driveing fast, I just want to get up the hills with out a major strain on my legs...even at 10.5 gearinches.

 

[jawnn]

Missing Link

This is the missing link that I needed for calulating the power needed:
=
Figure out how fast you move with the weight and grade you need and then calculate the power you need.
=
Speed calculation:
18 front / 34 rear sprockets = 1 to .53 ratio .............
60 rpm’s at the crank x (.53) = 31.76wheel rpm's..............
62.8” circumference x 31.76 rpm's = 1994.82 ipm ..............
Divided by 12 = 166.235 fpm ..........
166.235 x 60 minutes = 9974.117 fph ............
Divided by 5280 = 1.889 mph.........
=


My second gear, with 28 sprockets on the crank, is 3 mph.


All I need now is a geared hub motor with a 50 to one gear ratio.