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Yamaha Apex internal gear reduction.

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Ally Wilke

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Is there enough room in the gear reduction case of the Apex motor for me to machine some gears to get the out put shaft speed down for prop use?Or would I have to machine a case and gear set?It does not make sense to me to use 2 gear boxes on a motor.Lots of mechanical loss and more moveing parts to fail.All advise is welcomed.Thx.
 

Jay Kempf

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There is a marine version of the engine that has no gear box. MR-1? It was mentioned in the main Apex thread.
 

rv7charlie

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I understand the premise, but it's become worthwhile to think in broader terms. For example, the old Kettering ignitions had 2 moving parts, and a carb has only one. Modern electronic engine control systems have electrical dependency, hundreds of electronic components, at least one (sometimes two) moving parts (injectors) for each cylinder, another two or three moving parts in the throttle body, moving parts in the fuel pressure regulator, etc etc. Yet modern engine control is several orders of magnitude more reliable, and efficient, than old school stuff. I haven't seen any info online indicating Yamaha powered a/c reliability issues, so maybe it isn't as big an issue as one might think.

My understanding is that Yamaha included the internal reduction to allow an efficient final reduction (the transmission system). The high crank rpm apparently precludes a single stage reduction to final drive rpm in the sled. In an a/c, I expect you'd face the same issue; either accept lower max engine rpm (and lower power), or accept the extra reduction stage.

Charlie
 
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Marc W

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In a word, NO! There is also a rubber damper built into the output gear to reduce torsional vibration. These engines turn 10,000 to 11,000 RPM. The internal gear reduction is there so the clutch and primary drive belt survive.
 

Ally Wilke

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The gear reduction in the Apex was intended to get the centrifical clutch to work more efficiently.Belts don't like high rpms.To me it is like chaseing your tail putting 2 PSRU's on an engine.The mechanical drag has to be in the insane area.
 

Ally Wilke

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In a word, NO! There is also a rubber damper built into the output gear to reduce torsional vibration. These engines turn 10,000 to 11,000 RPM. The internal gear reduction is there so the clutch and primary drive belt survive.
But we are not useing a centrifical belt clutch any more.They already make after market gears for these engines,but the drop in rpms is only about 1500.I am wondering if there is enough room to put gears into the existing case to get them into prop rpm range or do I have to machine a bigger case to fit gears.I do not have one of these engines to play with so if some one could take some messurements for me that would be awesome.
 

Ally Wilke

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There is a marine version of the engine that has no gear box. MR-1? It was mentioned in the main Apex thread.
I would rather have the internal gear reduction and swap out the gears and get the output shaft into the right range.The Skytrax PSRU is like $3,500.I can make a lot of gears for that money.
 

Jay Kempf

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I don't think there is room for that sort of gear reduction in that case. I looked up the MR-1. Nice engine but replaced by the 3 cyl TR-1. Both no gear box at all.

You cannot just use the direct drive gear box as is. The Skytrax deals with the prop loads and has isolation from the primary. It is a system.

Like what is going on in the Yamaha experimental world. But still would like a largely extended prop/psru system for pushers.
 

Ally Wilke

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Thx for the reply.I was just thinking about the prop loads.That settles it for me.I will machine a case with a thrust bearing that can handle the pull of the prop and make the gears fit.
 

Ally Wilke

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Anyone have cad files or any type of images that I can get measurments from?
 

Jay Kempf

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If you can get them I would like them as well. I assume all the Yamaha engines have the same bolt pattern at the front of the block where the reduction drive is attached. Maybe not. That is what I would like to find out. Happy to be involved in a reduction drive design experiment.
 

Marc W

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The various Yamaha engines do not have the same bolt pattern on the front of the block. That would be nice but all four of the current crop of conversions, the RX-1, the Apex, the 3 cylinder Nytro and the Phazer are different.

The internal gear reduction is inside the block so you would have to machine a new block to hold larger gears. Lookup Skytrax on YouTube to find gearbox installation videos. You should be able to see the inside of the block where the gears are if you watch closely.
 

wsimpso1

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Thx for the reply.I was just thinking about the prop loads.That settles it for me.I will machine a case with a thrust bearing that can handle the pull of the prop and make the gears fit.
More to it than just thrust. The prop is a big gyroscope, and we have rotation about the yaw and pitch axes.

Mgyro = MMOIp*thet1*thet2

Where MMOIp is mass moment of inertia of the prop; thet1 is rotation rate of the shaft in rad/s; thet2 is combined rotation rate in pitch and yaw in rad/s.
Trying to do this in British units tangles me up in my undershorts, doing MMOI in kg*m^2 works for me, then I calc back to in-lb. YMMV. You will need some idea what you are dealing with for rotation rates... Gyroscopic moment with an airscrew will likely drive the design of your prop shaft and its bearings, while it is much smaller with waterscrews...

Billski
 

Ally Wilke

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The various Yamaha engines do not have the same bolt pattern on the front of the block. That would be nice but all four of the current crop of conversions, the RX-1, the Apex, the 3 cylinder Nytro and the Phazer are different.

The internal gear reduction is inside the block so you would have to machine a new block to hold larger gears. Lookup Skytrax on YouTube to find gearbox installation videos. You should be able to see the inside of the block where the gears are if you watch closely.
Awesome!Thank you for the reply.This is the stuff I am looking for.O saw some pictures of the block and it looks like the case was the problem with
More to it than just thrust. The prop is a big gyroscope, and we have rotation about the yaw and pitch axes.

Mgyro = MMOIp*thet1*thet2

Where MMOIp is mass moment of inertia of the prop; thet1 is rotation rate of the shaft in rad/s; thet2 is combined rotation rate in pitch and yaw in rad/s.
Trying to do this in British units tangles me up in my undershorts, doing MMOI in kg*m^2 works for me, then I calc back to in-lb. YMMV. You will need some idea what you are dealing with for rotation rates... Gyroscopic moment with an airscrew will likely drive the design of your prop shaft and its bearings, while it is much smaller with waterscrews...

Billski
I have been looking at some bearings that are designed to handle those multidirectional loads.I am thinking this can be done cost effectively with the block being the deciding factor.If money was no issue a lot of people have made these blocks for racing applications.If the block does not have enough meat on it to machine it for the gears and it is too expensive to cast one or CNC one it wil probably not meet the cost effectiveness for the average builder.Thank you for your reply.
 

Ally Wilke

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I was just talking to my brother about this.He said his BMW 1000 RR is 130lbs at over 200 hp.I will never look at an engine again without wondering if it will be a viable aircraft engine.I just remembered The Wright Brothers had the same problem😃
 

Marc W

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You should look at the Yamaha 3 cylinder Nytro engine, also used by Arctic Cat. I don't believe it has the internal gear reduction. It is about the same displacement as the Apex and similar hp. Slightly lighter and a little shorter.
 

slociviccoupe

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The marine version also has a gear reduction. The mr1 turns 10,500 rpm's its almost a 2:1 reduction. There is no clutch or damper inside. But the output from the engine to the jet drive is a 5 finger type coupler.
 

Ally Wilke

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There maybbe issues
The marine version also has a gear reduction. The mr1 turns 10,500 rpm's its almost a 2:1 reduction. There is no clutch or damper inside. But the output from the engine to the jet drive is a 5 finger type coupler.
I am not familiar with jet drives,but I know they can only be spun so fast before the point of diminishing returns.It makes sense they would have one in there.Do you know the rpm of the output shaft?
 

Ally Wilke

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At 8000rpm max stock the impeller runs at 5442 rpm.Looks like it is at 1.47 to 1 ratio?I would probably need to get 3-1 to get the output shaft rpm down to 2500 rpms?I wish I knew if there was room in the gear case on the block side to do it.
 
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