Prerotator help

JAVA C

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Hey everyone's

I am preparing to start building my first gyrocoptor. My question is in regards to prerotator systems. From what I can tell there are three systems.

1) Flexible cable systems
2) Hydraulic systems
3) Electric motor systems

I am looking for easy to source and make parts and reliable.

I welcome any discussion or advice, if you could provide part numbers for design help, I would be very appreciative.

Please and thank you.

Shawn Schick
 

Tyger

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Since no one smarter has answered you...
From what I've gathered here, certain car starters (electric) are the simplest solution, and with easy-to-find parts. But they evidently need to be replaced more often. I believe Vance uses one on his machine.
 

Resasi

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1) Flexible cable systems
2) Hydraulic systems
3) Electric motor systems
...and a direct drive system via a shaft to the rotor.

I have flown gyros with the Armstrong starter, with the flexible cable, and the electric. No experience with hydraulic and the build underway is direct drive via a shaft.

Gyro Technic does have systems if you wish to buy.

Not sure what engine but they will be able to assist

Office: 507-243-3991
Cell: 507-420-7998

Email: [email protected]
Hours: 9:00am - 5:00pm
 

Vance

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Thank you, how long can a starter run for before it burns out?
An automobile starter has an expected duty cycle of about ten percent.

In other words if you use it for thirty seconds it needs to cool for five minutes.

Using an automobile starter for a pre-rotator is a particularly challenging application because it is near stall for much longer than in an automobile application.

Different starters have different tolerances for heat so there is not a fixed number.

A soft start system may reduce the thermal challenges.

On the gyroplane I fly (The Predator) with a thirty foot eight and a half chord rotor I have had a starter last over a thousand hours and I do not have a soft start.

Using an automobile starter on such a large rotor is probably not a good application.

I typically see a little over a hundred rotor rpm in no wind conditions.

It is a geared Denso starter that is no longer made so I have to have it rebuilt.

My recollection is I am on starter number five at over 2,200 hours of flight time. I am a flight instructor so I have more takeoffs than hours.

Some of my clients are hard on the starter.

The only advantage of an automobile starter is they are cheap and easy.

I like a flexible shaft because I can continue to pre-rotate with the disk back.

Rotor management is an important part of learning to fly a gyroplane.
 

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okaneco1

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I use a softstart and a Cadillac starter motor. The softstart had to be reverse engineered to repair it 2 years ago. All the part numbers were erased and made it almost impossible to repair after the designer pass away. There is an ex Delco radio employee from the EAA chapter I am a member that was very good with this repair. It cost about $25 with new parts
and two weeks of downtime. I don't have as many starts as Vance but I have been happy with my prerotation. I start with the blades flat until I get to 50 RPM and then bring the blades back as I start my roll. When I hit 100-110 RPM, I let go of the button and gradually build up enough ground speed to take off. I wouldn't know how the handle 200+ rotor RPM. I like the gentle increase in speed and take off.
 

ultracruiser41

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I’ve used Toyota geared starter motors on almost all of my gyros and have no issues at all. I do not run a soft start system and they usually last a year or two before I replace them. Last time I bought them they were $50 each. I think they’re a little higher now. I always keep several on the shelf and I also take one with me to all fly in’s just in case I have a problem with a prerotator I just change it out keep going
simple is reliable. Oh…. And I always turn 27 foot rotors.
 

JETLAG03

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I have used a high torque car starter and achieved 180rrpm 8.3m rotor resin.

High torque starter motor

The unit I am presently using is a 2Kw starter they have starters up to 2.3Kw

I have created a "soft start" system using 2mm TIG welding filler wire (adapted from original idea of Bobby Munroe)
TIG welding filler rods

I have discovered by trail and error that 5 pieces 1 metre long create a resistor that allows for a soft start, this runs for about 7 seconds then using a relay I bypass the resistor to supply full power to the starter. These I have mounted in ceramic connectors and used copper pipe 6mm at the ends to create the contacts.

Ceramic terminal blocks



RELAY.


I use two 12v batteries to provide enough "umph" for the starter.

Batteries.
 

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Brian Jackson

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Great thread. I'm hoping to do an electric PR on my build soon. I recall there were several University projects that John Roundtree was trying to get developed, one being an electric PR. Covid may have sidelined that. Was hoping for a plug-n-play system but it appears the engineering challenge is more involved than the basic concept would suggest.

I do have a structural question for those familiar with the issue. A high-torque motor might seem attractive at first, but since it must necessarily twist the mast (if mounted @ rotor head), is there a formula that other builders use to determine if a motor/controller is too powerful for a particular mast tube size? I can run an FEA in SolidWorks but that doesn't mean I know anything about the equal & opposite (pulsed) forces the PR motor will apply to the mast. Thanks.
 

JETLAG03

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Hi @Brian Jackson that is why I created my soft start. Originally, I had a 0.9Kw car starter motor which, when the pinion engaged (pre-engaged starter) the snatch was impressive, to use the same basic system with a 2.0Kw would create a huge, and unknown (to me) force.

With the soft start the start up is probably smoother and less aggressive than the flexible shaft.

I am hoping to get to the airfield this next week and should be able to provide video of my system in action.
 

Brian Jackson

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Hi @Brian Jackson that is why I created my soft start. Originally, I had a 0.9Kw car starter motor which, when the pinion engaged (pre-engaged starter) the snatch was impressive, to use the same basic system with a 2.0Kw would create a huge, and unknown (to me) force.

With the soft start the start up is probably smoother and less aggressive than the flexible shaft.

I am hoping to get to the airfield this next week and should be able to provide video of my system in action.
Hi Jetlag. I'm looking forward to seeing your video. Very interested to know more about your PR system and the associated batteries & controller. Thanks for the update. Cheers.
 

Vance

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I forgot to mention that I use an twelve volt Odyssey PC 680 battery for both the pre-rotator and starting my 160 horsepower Lycoming IO-320 engine.

Every couple of years the magic seems to leak out of the battery and I have to replace it.

I have a special charger for it.

I start my pre-rotation at the hold short line and usually see 100 rotor rpm by the time I reach the centerline and come half back with the cyclic.

Shortly I see 120 rotor rpm and come full back still at taxi speed and release the pre-rotator button.

At 180 rotor rpm I add full power, balance on the mains and she waddles into the air when she is ready; usually around 45kts indicated air speed and a little over 300 rotor rpm depending on takeoff weight.

My takeoff roll is around five hundred feet in no wind conditions.
 

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All_In

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PRA sponsored 2 state-of-the-art prerotators projects for 29-foot blades with S.D.S.U engineering students both using lightweight motors and lithium batteries.
One tried using a two-speed transmission that could be attached to a standard flex cable replacing the engine PTO.
The other uses a lightweight powerful motor mounted on the rotor head.

When I first came to this forum someone asked the same question regarding using a car starter motor.
I designed this slow start for the forum way back then. We just used a coat hanger for the resistor.
It uses 24 volts but can be scaled down to 12V just remove the battery and make it a two-position switch.
PreRotatorSchmatic2.jpg
 

gyrojake

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I could never understand why anyone would want an electric prerotator.
Vance's machine is a good candidate for one because of the convenience.
Most single seat gyro's have gobs of horse power to convert to prerotation.
Electric has to be the heaviest system compared to most.
starter, solenoid, two batteries, soft start and all the wires.
I would hand prop before I'd use one.
Back in the day hand starting is how us Appalachian Americans did it.
 

JohnS

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Flew a Bensen "ultralight" for several years, hand-starting my 23ft Dragonwings. Stand on the seat, choose one blade and spin it to come around once each second, slide into the seat-unlock the brake-start slow taxi with stick against the rear stop while latching my seatbelt, and nurse 'em up to speed. You really learn rotor management that way. Finishing up a Sparrowhawk these days, pretty sure I won't be hand starting the rotors on that one!
P.S. I've only used flex shaft prerotators, and usually gently. Just enough prerotation to catch the air without flapping. I think any prerotator will do well if you don't do performance takeoffs all the time. That is, 250 rpm prerotation and full throttle!
 
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okaneco1

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I could never understand why anyone would want an electric prerotator.
Vance's machine is a good candidate for one because of the convenience.
Most single seat gyro's have gobs of horse power to convert to prerotation.
Electric has to be the heaviest system compared to most.
starter, solenoid, two batteries, soft start and all the wires.
I would hand prop before I'd use one.
Back in the day hand starting is how us Appalachian Americans did it.
Jake, When I bought my TwinStarr from Gary it had an electric prerotator on it. It is working great. I did replace the lead batteries with lithium and saved about 50 lbs. I can't imagine hand propping my 28' blades, at least not on camera
 

Chuck Roberg

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29' Sport Rotors, Subaru 2.2 engine. Flex shaft. Originally had the 4" wheel contacting the drum on the reducer. But way too much torque. So I switched to a 5" wheel. Normally pre rotate to about 130 rpm before takeoff roll.

I tried the suggestion of leaving the prerotor engaged thru the takeoff roll. But with it engaged it wants to really pull the stick to the side. Then I have to apply a lot of force to keep the stick centered. So with a 5,500 ft runway I figure I'll just go back to the way I've always done it .
 

Smack

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Jake, When I bought my TwinStarr from Gary it had an electric prerotator on it. It is working great. I did replace the lead batteries with lithium and saved about 50 lbs. I can't imagine hand propping my 28' blades, at least not on camera
James, what happens if you leave your electric pre-rotator engaged during the take-off roll ?
 

okaneco1

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James, what happens if you leave your electric pre-rotator engaged during the take-off roll ?
I don't know, it has not happened. I have a check list of the take off procedures. I have a toggle switch to turn on the system and a push button on the throttle to engage the motor. I watch the rotor tach and when it reaches 100RMP I release the button and reverse the toggle switch and close the cover. Sometimes, I start rolling during the pre-rotation to get more RPM out of the rotors.
 

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Rene Genest

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I also have a Toyota electric starter on my Bensen with a sofststart which pulse the currrent at a frequency of about 1 Khz, starting with a
low duty cycle getting greather over the time.
 
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