Changing the direction of force

[Desertprep]

How much loss in efficiency will occur if the direction of the work done by a motor is change? suppose a motor is mounted on a bike so that the motion is parallel to the hub instead of perpendicular - so that the force needs to be change 90 degrees?

 

[amberwolf]

Depends on the method you use to change the direction, and the details of that method, lubrication, friction in any bearings, etc. You'd have to work it out based on those things.

 

[bobc]

bevel gears are pretty inefficient & bulky; you might prefer a couple of hooke joints (UJ's) at 45degrees each. If you line up the yokes on the intermediate 45degree shaft the angular velocity non-linearities cancel out.

 

[mat h physics]

Worm gears are great for high torque/speed reduction.

 

[fizzit]

Worm gears are great for high torque/speed reduction.

But aren't they ridiculously inefficient?

 

[Joe Perez]

In terms of friction losses, yeah, worm gears are not terribly efficient due to the inherent sliding action between the teeth.

A non-hypoid bevel gear (like an automotive diff or a motorcycle shaft-drive) is just about the most efficient way I know of to make a 90 degree turn in a drive system.

Curious about the application here. I'm having a hard time visualizing a situation where it would be advantageous to mount the motor in such an orientation.

 

[TylerDurden]

I'm having a hard time visualizing a situation where it would be advantageous to mount the motor in such an orientation.

http://endless-sphere.com/forums/viewtopic.php?f=28&t=26699

 

[REdiculous]

I'm having a hard time visualizing a situation where it would be advantageous to mount the motor in such an orientation.

Some motors are pretty long - mine is about 7.5" plus the shaft sticks out about an inch.

 

[boostjuice]

Bevel helical gearing is an efficient (94% for the below example) solution to inline mounting big, low-rpm, long barreled motors to bikes in an ergonomic/aesthetically pleasing manner, but not worth the expense/hassle/weight in the end....as i learned the hard way. Better to just go a transverse mounted RC motor thats narrow enough to fit between the cranks and waaaaaay easier to put together.

+

=

But much precision fab needed.....

 

[boostjuice]

Another interesting project....Catic/Tonaro gearbox mated to Astro 3220, but which never seemed to be integrated successfully onto a bike.

 

[mat h physics]

Yes, fizzit, they can be as ineff as the person making the selection wants them to be (like perez who must be a mech eng).
But use some common sense and some basic info like here: http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html

You will come to find out they can be designed close to 98% eff.

The problem lies w/ ppl who want the RPM, opting for the 5:1 rather than the slower 75:1 ratio. Children equate RPM w/ speed, and think it is critical. Can U imagine an output of 10,000 RPM in direct drive w/ the hub . No not practical, esp when the torque is measured in inch pounds.

Please give me more put downs, I like showing how energy REALLY works to the laymen. My favorite thing to do is learn, but usually wind up having to teach (which is actually the best way to learn).

PS Look @ this Mongoose, U got a gear reduction then the 90deg gear then a chain, then another chain. How eff do u think the energy is getting from the bat? Being they are in series U multiply the eff of each in series. I will say each is 95% eff, most will be higher, but the motor (the 1st component) is likely lower. So: .95(bat2motor)x.95(int gear reduction)x.95(90angle)x.95(chain2pedal)x.95(pedal2tire)= .773 So if a direct drive worm gear is 78% eff or better, U get more energy to the pavement than A SYSTEM W/ THESE PARAMETERS. 99% eff is not easy to achieve w/o high maintenance, chains can be as low as 80% eff. KISS (keep it simple stupid)

 

[Miles]

The problem lies w/ ppl who want the RPM, opting for the 5:1 rather than the slower 75:1 ratio.

Hi mat,

Perhaps you're confusing what they mean on the Roy Mech site by "high ratio"?

http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html

The efficiency of a worm gear ranges from 98% for the lowest ratios to 20% for the highest ratios.

 

[fizzit]

Yes, fizzit, they can be as ineff as the person making the selection wants them to be (like perez who must be a mech eng).
But use some common sense and some basic info like here: http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html

You will come to find out they can be designed close to 98% eff.

The problem lies w/ ppl who want the RPM, opting for the 5:1 rather than the slower 75:1 ratio. Children equate RPM w/ speed, and think it is critical. Can U imagine an output of 10,000 RPM in direct drive w/ the hub . No not practical, esp when the torque is measured in inch pounds.

Please give me more put downs, I like showing how energy REALLY works to the laymen. My favorite thing to do is learn, but usually wind up having to teach (which is actually the best way to learn).

PS Look @ this Mongoose, U got a gear reduction then the 90deg gear then a chain, then another chain. How eff do u think the energy is getting from the bat? Being they are in series U multiply the eff of each in series. I will say each is 95% eff, most will be higher, but the motor (the 1st component) is likely lower. So: .95(bat2motor)x.95(int gear reduction)x.95(90angle)x.95(chain2pedal)x.95(pedal2tire)= .773 So if a direct drive worm gear is 78% eff or better, U get more energy to the pavement than A SYSTEM W/ THESE PARAMETERS. 99% eff is not easy to achieve w/o high maintenance, chains can be as low as 80% eff. KISS (keep it simple stupid)

Sorry, I didn't intend it as a put down. I was just wondering about something that I thought I heard.

 

[Desertprep]

Thanks for the input! My main concern with anything I do on an ebike is efficiency because, in my mind, a loss of efficiency means a loss in range.

I am going to buy an ebike that has a frame similar to a motorcycle - even uses motorcycle tires and rims. It is a relatively narrow bike, not at all like the escooters sold here. I am looking at a turnigy 80-100, or something similar. One will fit within the width of the bicycle but I am thinking of ultimately installing two to help push this puppy over 50 mph comfortably. I read a post on this forum of someone connecting the shafts of two of these motors, making a rather long motor. I am not sure if I will go there at first, but want to know what my options are. It sounds to me, from your dialogs, that the best/most efficient way would be to use some kind of motorcycle driveshaft. What is the loss involved in a driveshaft? If i want i mount both motors parallel to each other, rather than in line, I could connect each by chain to a central pulley, and then connect that pulley to the back wheel, without having to change directions of the force.

 

[boostjuice]

If i want i mount both motors parallel to each other, rather than in line, I could connect each by chain to a central pulley, and then connect that pulley to the back wheel, without having to change directions of the force.

 

[Desertprep]

Wow! You are awesome! Can you tell me what is going on in the top picture, with the 2 motors connected by chain? I cannot see where the motion is being siphoned off to another use. Are those colussus motors? It looks like they have a shaft at each end, and the visible chain is holding the motors together for balance, while the shaft not visible to us is connected to some kind of reduction setup.

If i want i mount both motors parallel to each other, rather than in line, I could connect each by chain to a central pulley, and then connect that pulley to the back wheel, without having to change directions of the force.

 

[amberwolf]

I cannot see where the motion is being siphoned off to another use.

It looks like they have a shaft at each end, and the visible chain is holding the motors together for balance, while the shaft not visible to us is connected to some kind of reduction setup.

And then from that setup there is a chain going back to the rear wheel, on the far right.

 

[Desertprep]

What is the weight of each of the 2 motors? and what is the weight of the frame and reduction unit (not including the motors)? Doesn't have to be exact but if your guesstimate is close to the nearest half pound would be nice

...and what kind of motors do you have in the second setup? with what kind of reduction unit?

 

[boostjuice]

The RC stuff is not my gear. 1st photo is by 'Thud', the 2nd photo is a drive for 'rodgah' by 'recumpence'. Do some forum searching and you will find your answers.