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HelicopterCentury Radikal G20-30 N640 Hawk Predator › Torque Dampening Hub Prototype!
08-25-2014 12:03 AM  3 years agoPost 1
RM3

rrElite Veteran

Killeen, Texas - USA

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Finally finished it!

this is my prototype torque dampening hub for my gassers. all engine torque is transmitted from the main gear thru the springs to the center hub. This works on the same principal as the spring loaded pull starts on weed eaters that smooths out the the pulling force between the pull cord pully and the engine shaft. just a different design to suit this appliation. Its not intented to dampen an out of balance engine, rather just smooth its output before it reaches the main rotor and tail drives, in particular with engine that tend to "hammer".

It has a total of 6 mounting points to allow any even combination of 2 to 6 springs. It is shown here with two heavy springs (all I had BTW) mounted to a 41L40 steel alloy hub (very strong). The main gear is pancaked between to polished plates with a thin section bearing in the center. since the gear is made from delrin a naturally slippery and strong plastic the polished surface of the plates work very smoothly and should wear very little over time (remember that delrin gears wear against each other and last a lomg time in other applications).

I plan on testing this hopefully this week or next and experiment with different combinations of spring tensions and counts. I hope to post a before and after vid of the results.

hopefully this will solve the vibration issue that is transmitted from the engine via torque to the rotor.

It was a PITA to make as the machining tolerances have to be tight and is not as simple as it looks...

wish me luck!

showing a preference will only get you into trouble, 90% of everything is crap...

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08-25-2014 12:22 AM  3 years agoPost 2
JKos

rrProfessor

Redondo Beach, CA

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I wish you luck! I would think a design that compresses springs rather than extend them would be better. The failure mode would be quite different. The failure mode of your current design is an unloaded engine at a high torque (i.e. high throttle) moment leading to perhaps catastrophic engine overspeed.

I predict two springs like that will be torn apart quite quickly.

- John

RR rules!

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08-25-2014 01:05 AM  3 years agoPost 3
RM3

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Killeen, Texas - USA

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each spring is rated at 20Lbs... combined they exceed the torque available from a stock engine and is just below the torque limit of the delrin gear train itself over time. additional springs would further exceed this. consider that the clutch bell uses "soft" 6061 aluminum threaded onto a pinion with fine metric threads... its weak, and the engine torque does not rip it out...

honestly a design that uses compression springs would weigh more and be alot more difficult to incorporate into the cramped space as well as not allow for adjustment without complete disassembly. remember it has to work in both directions, compression springs don't allow for this with out a complex assembly.

Most importantly this design minimizes the modification required to the main gear.

besides engine over speed is a thing of the past with a gov installed. if it did fail it would simply over extend the springs and wrap them around the hub.
The failure mode would be quite different. The failure mode of your current design is an unloaded engine at a high torque (i.e. high throttle) moment leading to perhaps catastrophic engine overspeed.
I predict two springs like that will be torn apart quite quickly.
- John
alot of us that fly and loose drive in mid air from the engine to the main rotor don't end up with catastrophic engine overspeed, remember the gov control limits that and the fact that these engines have a throttle return spring as well in case the RX system dies would return it to idle or off.

as I recall I had similar comments about my prototype clutch not engaging or working properly... a vid proved that wrong.

showing a preference will only get you into trouble, 90% of everything is crap...

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08-25-2014 02:15 AM  3 years agoPost 4
Triggr Happy

rrApprentice

Ontario, Canada

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that looks great! before long I would hope to see Century releasing this type of upgrade.

Just my two cents though.

The springs may be exceeding the torque available from the engine...but maybe not the shock they will receive. Personally, I would choose maybe slightly lighter springs and mount to all 6 points, mainly for redundancy if a spring gives. Also to spread the load across the entire gear.

Could run it with the two springs for proof of concept and from there tweak it with a full set of 6 springs.

Would be nice if there was a way to measure the vibrations before and after each adjustment...dont some FBL systems measure vibration?

I am interested to see how well this works, keep us updated!

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08-25-2014 02:55 AM  3 years agoPost 5
RM3

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Killeen, Texas - USA

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Could run it with the two springs for proof of concept and from there tweak it with a full set of 6 springs
yes the testing will be with all 6 positions... these are the only two I had on hand so I used them for bench fit testing and pics. And they are just to damn stiff as they are 0.037 dia wire. so I had to order several tension ranges in the same length and diameter. so I'm stuck waiting on an order to proceed with flight testing.
its going to take some time but at least this design allows for simply pulling the main gear out and un boltng and re bolting different tension values.
Also to spread the load across the entire gear.
+++ agree, even though the hub is made from 4140 and the bolts are grade 8, the more points used the less beating each will have to endure.
Would be nice if there was a way to measure the vibrations before and after each adjustment...dont some FBL systems measure vibration?
I have the CGY750, but it does not have that capability to log the data, the V-bar does as far as I know.

just waiting on parts and time available.

showing a preference will only get you into trouble, 90% of everything is crap...

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08-25-2014 03:12 AM  3 years agoPost 6
Gearhead

rrMaster

Vt

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I was thinking a while ago, how about drilling and taping 6 more mounting screw holes in the Hub, then drill 6 extra screw holes in the Gear, but drill-out all 12 holes larger in the Gear and push in Dampeners for the screws, dampeners much like the ones used on the Spindle but smaller,, the extra 6 screws will stabilize the Hub from rocking much better than just 6 screws.

I have seen an old dirt bike's rear sprocket use dampeners like that

another thing that will help, "some", is to use much higher quality Main Shaft Bearings with tighter tolerances, this will tighten up the side to side slop in the main Shaft, it will also put more power to the head because higher quality bearings are smoother

Jim
Buzz Buzz Buzz

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08-25-2014 04:41 AM  3 years agoPost 7
RM3

rrElite Veteran

Killeen, Texas - USA

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how about drilling and taping 6 more mounting screw holes in the Hub, then drill 6 extra screw holes in the Gear, but drill-out all 12 holes larger in the Gear and push in Dampeners for the screws,
thats actually a good idea and had also thought about it initially.

the issue came with how much "meat" is left to work with on the main gear. To get something like that to work best would mean machining a new gear that would then allow me to cut the mounting holes where I needed them. But cutting a new gear from scratch is a pain especially a slant tooth gear.

I went with the springs cause they can have more "give" than a rubber bushing, and are more readily available and in more sizes and types.

Part of the problm is that I'm very limited to the size of spring that can fit in not only the length from the center to the inner edge but also the diameter of the spring... So testing may reveal that I may have to add an additional 6 mounts to the center hub as you suggest and then double them up to the outter mounting points. but just to early to know yet until I actually get it in the air.

funny thing is I actually also had an idea to use a bunch of rubber bands... but that would have looked like $hit

showing a preference will only get you into trouble, 90% of everything is crap...

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08-25-2014 11:51 AM  3 years agoPost 8
Pistol Pete

rrProfessor

Seffner, FL

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Will you be testing on the stock or modified engine?

This would cure your wagging tail or drift?

Very interesting.

~~Enjoying the hobby one flight at a time~~

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08-25-2014 01:27 PM  3 years agoPost 9
RM3

rrElite Veteran

Killeen, Texas - USA

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I will start with the stock engine in my stock G20, since it does not have the side frame braces it makes installing and removal easier for initial testing, then proceed to the modded G20 with the stroker motor, which does have the frame braces. The frame braces make removal and re installation a pain. Add to the fact that my RPM sensor is mounted to read the magnets on the main gear, so to test in the modded G20 I have to find an alternate method of getting the RPM to the CGY750 or just purchase another stator gator and mod that too to get it to work woith the CGY750 (I honestly don't know why that has not been fixed by now).
This would cure your wagging tail or drift?
not sure as a drift or tail wag can have more than one cause. My hope is to reduce vibration caused by engine torque being transmitted thru to the rotors via the drive train.

showing a preference will only get you into trouble, 90% of everything is crap...

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