90 degree transmission with belts only- possible?

leviterande

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Hi, I dont have a 3d model of what I want to do but for now tell me what you think of this:

I want to build a coaxial drive, since it is hard to find a "cogged gear" coaxial drive I thought about using belts only to build a 90 degree transmission.

The thing is that the belts are going to be flexed 90 degrees. My concerns if this is possible or will the load be too heavy and the belts wont make it? Furhtermore will the transmission efficiency be extraordinary low due to the 90 degree flexing?

the load on the two 90 degree belts are a total of 20 hp rotating around 150-200 rpm.

I hope I can model the belt in the 3d software I havent used in ages:typing: so you can see better
Kalle
 
I have seen a drive similar to what you are describing but it was used on a 48 inch riding lawnmower. The engine was a horizontal shaft 18 hp kohler (I think) with a single pulley on the crankshaft. The belt went from the engine to a horizontal jackshaft just below the engine with two pullies in line with the belt on the engine pulley. This allowed the engine power to be transferred from horizontal rotation to vertical. If I can find a picture of it online I will post it.

Could you possibly use a 2 stroke engine and just orient the crankshaft vertically?
 
I found this drive on the exmark website. It is from a 25 hp diesel exmark mower.

I am not saying that you should trust a drive like this with your life. I just wanted you to know that it is a design that is used.
 

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Success also depends on the radius of bend, the smaller the radius the more the belt needs to flex and that takes energy producing heat, same is true of a tire run on low air pressure.

.
 
It was a long time ago, in a galaxy far far away that I made 3d cartoons, here is a crude model of the drive that I hope you can grasp.

OBS! I wrote a half page of info but it all got deleted by some forum error??

The brown thingy is the engine, the black thingys are the belts . There are as you see 4 belts in total.

As you can see it is a coaxial (shaft inside a shaft). Any questions? please you are more than welcome to ask :phone:
The engine drives the two vertical rollers, the two vertical rollers drive the "coaxial shafts" by the 90 degree belts. It seems obvious that the distance between the horisontal and blue rollers should be big enough or one would use larger rollers so the belt is not "touching it self" at the place it twists.

So, will there be huge losses? what kind of obvious problem can you see here?
 

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Try the attached document from Gates.
Mike G
 

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The way you have it in your drawing will not work, because of the angle of the belt riding on the edge of the pulley. It will chew it apart. Also, the loss of power from a v-belt system will be unacceptable, because you will need to keep it so tight not to slip and overheat.
 
This is a quick and dirty drawing showing one way to counter-rotate two shafts using one quarter turn belt and two idler pulleys. You can use Mike's attachment to help with belt parameters. I would think that gears would be a better option for this use....
 
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Dennis, yes these are my concerns too, friction is gonna be obviously huge that the belt will rip apart and efficiency will be too low??!

rotoplane, I am not sure wether I understand your drawing?

How will the shafts counterrotate? a "cogged gear" between the vertical pulleys is missing from the your drawing maybe?
 
No gear required Kalle. The dotted lines and arrows show the pulley pitch diameter (P.D.) and path of the belt.
The horizontal distance between the two idler centers is the same as the two shaft pulley's P.D.
The two idlers P.D. are the same as the vertical center distance between the two shaft pulleys.
If you trace the belt path with your finger, you will find that the two shaft pulleys will counter-rotate.

As Dennis said, the way you arranged your pulleys (in the drawing) would quickly shred the belts....because the pulley grooves cannot be aligned.
 
Rotoplane, Aha, now I see, I missunderstood first . Thanx for the help .

hillberg, I just found that KISS is the hardest thing to do... But yeah it is true that a gear box is by far the most compact smallest, lightest and most simple drive for a coaxial. I actually really want to have a gearbox. The problem is where to find or scavange such a coaxial drive? a car transmission maybe?
 
Didn't the Chevy Corvair have a belt driven cooling fan that required a 90 degrees bend. The belt was drvien by the accessory pulley vertically to two idler pullies that turned the belts horizontally. Maybe, the answer is idler pullies to properly align your belts as Ed said. I think the belts were V belts.
 
The tail rotor of the switzow Bee helicopter was driven by a 90 deg belt, The video is some where on this site,C.Beady posted it.
 
90 degree transmission with belts

90 degree transmission with belts

some outboard motors have a ready made coaxial drive that looks like it would work for helicopter use.
Norm
 
There use to be some belt manufacturing companies that made round section belts for the lower hp applications.

The standard "V" gripbelts can be used with a 90° twist (called quarter-turn application) but the hp may need to be reduced by a correction factor (due to extra heat buildup).

Belt manufacturers have special design engineers that can help you pick the correct belt(s), if they know the center distance between pulleys, pulley diameters, torque and rpm. Note that the distance between pulley centers must be greater than normal due to the belt twist.

Normally however, belts are not used with high torque, low speed applications, but perhaps 25 hp won't be too much of an obstacle.
 
I use this aplication in my hovercraft. It's an A section belt handling 25 hp. The distance from centres is approx 700 mm. I have to use 2 idlers on the rear of the belt to stop vibration. Multi v belts were to difficult.
 
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