I have a bike and I want to add a small model airplane gas engine 3.5 cc. Engine speed is 15k. If I gear this down to 60RPM it would give me say 5lbft of T. This should be enough to give me a push on steep slopes. I just want a push for say 10 secs as I want to pedal for exercise. Is this feasible or am I missing something?

 

I have a bike and I want to add a small model airplane gas engine 3.5 cc. Engine speed is 15k. If I gear this down to 60RPM it would give me say 5lbft of T. This should be enough to give me a push on steep slopes. I just want a push for say 10 secs as I want to pedal for exercise. Is this feasible or am I missing something?

Your missing the friction of the gears and inertia that needs to be overcome to accelerate them up to speed and a clutch mechanism to engage the motor to the gears (unless you are using the moving gears to start the motor). And the noise of an RC motor. Oh, also, a gas motor has a power curve to deal with that requires significant RPMs before reaching maximum torque.

An electric motor would be much easier to work with. Maximum torque is at zero RPM.

watch this
https://www.cbsnews.com/news/60-minutes-investigates-hidden-motors-and-pro-cycling-2/

 

Your missing the friction of the gears and inertia that needs to be overcome to accelerate them up to speed and a clutch mechanism to engage the motor to the gears (unless you are using the moving gears to start the motor). And the noise of an RC motor. Oh, also, a gas motor has a power curve to deal with that requires significant RPMs before reaching maximum torque.

An electric motor would be much easier to work with. Maximum torque is at zero RPM.

watch this
https://www.cbsnews.com/news/60-minutes-investigates-hidden-motors-and-pro-cycling-2/

Fascinating! Looks like the motor can be mounted on the rear wheel or directly on the drive crank shaft.

 

Fascinating! Looks like the motor can be mounted on the rear wheel or directly on the drive crank shaft.

Getting it to fit in the down-tube or seat tube without other obvious wires or gears is an engineering feat. I would go with the rear wheel. A powered skateboard wheel that you can press onto the rear wheel is pretty easy. I did thst with a 2-cycle gas powered weedwacker motor with my son in a junkyard wars style competition. The spinning skateboard wheel spun by a weedwacker motor tore the heck out of the bicycle tire. Being able to control it with an electric motor makes life easy. We used a standard bicycle brake lever snd cable to raise/lower the spinning skateboard wheel to the bicycle tire. A return spring pulled the powered wheel away from the bicycle tire as a deadman safety mechanism. Good luck.

 

A sketch would be nice!

 

Looks like you've already started addressing this issue some years ago.
https://forum.allaboutcircuits.com/threads/bike-motor.172882/

 

I am 76 years old and I ride my bicycle and run with my dog around my neighborhood. Sure there are hills but I am still in good shape with the same muscles I had 60 years ago when the engine and propeller on my model airplane could not pull my bicycle.
I might think about getting an ebike when I am 100 years old.

 

So you did try with a airplane engine; this is what I am trying so kindly let me know how it went.

 

I am 76 years old and I ride my bicycle and run with my dog around my neighborhood. Sure there are hills but I am still in good shape with the same muscles I had 60 years ago when the engine and propeller on my model airplane could not pull my bicycle.
I might think about getting an ebike when I am 100 years old.

"Sure there are hills" is fun to claim when one lives in central Ohio or on he north shore of Lake Erie but I have a lot of respect for people riding bikes in Pittsburgh or other cities built in truly hilly areas.

Here is Mississauga, Ontario vs Pittsburgh, PA

 

When I was in my 40's (decades ago) the company I worked for had a two week shutdown, last week of July, first week of August. I'd take off on my bike (Connecticut) and ride a long (overall) down hill ride from Waterbury to New Haven. Then I'd turn east and ride to New London. That'd take a few days. But the payback was the ride home, which took me four days because (overall) it was up hill. UP A MOUNTAIN.

Today I get winded climbing into bed.

Back then they didn't have eBikes. They DID have a gasoline engine you mounted on your front wheel such as this.

You've seen something similar on post #57 on your thread of two years ago. Best review all the advice you've gotten there. That'll save us a bunch of time rehashing this subject.

 

So you did try with a airplane engine; this is what I am trying so kindly let me know how it went.

My airplane engine was 0.35 cubic inches which is 5.74cc. I assume that the thrust from its propeller was 1 pound at full power.
The thrust was so small that I did not notice it pulling me on my bicycle.
If you gear it down then the fast RPM will quickly will the gears and the resulting speed will be extremely slow.

 

the fast RPM will quickly will the gears???

 

I fixed my typo then I thought about the engine piston, connecting rod and bearings are also wearing out.
My older electric motors on model airplanes have their brushes wearing out and burning out very soon but the brushless motors on my newer model airplanes last forever.

 

Thanks. Question still is - Did you gear down the engine and did it make a difference to the bike i.e. did it give noticable help when pedalling?

 

I used the propeller that the engine normally drives with no gearing.
That was 60 years ago. Today brushless electric motors are used without gearing.

 

Your missing the friction of the gears and inertia that needs to be overcome to accelerate them up to speed and a clutch mechanism to engage the motor to the gears (unless you are using the moving gears to start the motor). And the noise of an RC motor. Oh, also, a gas motor has a power curve to deal with that requires significant RPMs before reaching maximum torque.

An electric motor would be much easier to work with. Maximum torque is at zero RPM.

watch this
https://www.cbsnews.com/news/60-minutes-investigates-hidden-motors-and-pro-cycling-2/

The motor looks small; wonder if it is easily available or a special design?

 

It was a special design but there is a member here that can make a motor for you. See the OP of this thread... he may have recommendations for you. Or he may build one for you.
https://forum.allaboutcircuits.com/threads/most-electronics-engineers-are-funny.185789/#post-1719565