Electric Pre-Rotator

Jean Claude

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The DC motor controller needs a speed setpoint that will be delivered by your Arduino
This setpoint must be initialized at 0 rpm at each power-up.
Then have it increment this set point by 0.5 rpm, each 50 milliseconds (for example) as long as the intensity obtained is less than the value entered (130 Amp for example) ), and do not increment it if this is not the case.
Thus, the acceleration obtained will be just that which will keep the current constant, better as if you were gradually turning the speed potentiometer while observing the amperemeter.
 

Jean Claude

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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
I get it.
Below is my rough comparison between the amperage controlled method and the constant acceleration method.
The latter introduces a final rpm loss, despite a longer duration.
Of course, a programmed acceleration with several slopes can improve efficiency.

Sans titre.png
 
Last edited:

NoWingsAttached

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I use a geared Denso starter off of a Toyota for a pre-rotator on The Predator with her thirty foot eight and a half inch chord Sport Rotors.

I do not have a soft start or a speed control.

Typically I see a little over a hundred rotor rpm in no wind conditions and I have been through four starters in over 2,000 takeoffs.

… in one very busy day I started the … the rotor 45 times.
I do not recommend a car starter for a pre-rotator. It is my understanding their duty cycle is six seconds and they make a lot of heat.

Maximum torque is at stall so a car starter is hard on the mast.

Godzilla reports just having fried her geared pre-ro starter motor yesterday. I sure hope Geoff can get it fixed before the Mentone Convention.

Vance, you thought from a photo I posted elsewhere it is the same motor you mentioned above, when I was posting that I didn't understand why it was wired with a switch marked "SOFT START" yet I could not get it to actually do a soft start. You replied that I "obviously needed to study to understand the basic principals of electricity and wiring" in a rather arrogant, dismissive way. I replied that I actually do know quite a bit about the topic, having studied electric physics at the University of Michigan, etc.

Some folks who have electric pro-ro's swear by them, like Barry Kroplin - whom we all had a good laugh at, at his expense, at Wrens one year watching as he tried in desperation to hand-start a set of Dragon Wings on a Wind Ryder after his electric starter burned out. He was done for the day, needless to say. I was saddened, I wanted to see that fancy gyrocopter fly!

I don't understand the love people have for these fussy electric motor pre-ro's. They are heavy and create a lot of weight on one side of the rotor head unnecessarily, for which you must add a trim spring opposite, and are far more time, trouble, maintenance, etc. They require a FAR heavier battery, many feet of very heavy copper cables, additional solenoid so you dont' have 600 amps of power running up the mast when not spinning up, and those darn solenoids burn out to - just like the motor will, which is a matter of when, not if.

You write that you expect to replace one every 500 starts, and that on one busy day you used it 47 times. So in 11 busy days you will be replacing the starter motor.

That's a lot of time, down time, and cash down the toidy.

Mechanical pro-ros are far less maintenance, very little side-heavy head weight, no worry and in the end far less expense. Oh, well. Good to know they can spin up your 30" rotor to 100 or 120 RRPMs. I mean, that's it?

The mechanical pre-ro's I've had experience spin up even heavy Sky Wheels, 28", to 180 RRPM using a somewhat poor-efficiency Wunderlich flex shaft and a flat belt PTO. After that, the belt slips and creates heat, causing the belt to warp as it cools after spin up. With a wider PTO belt I'm sure I could easily hit 200 RRPM, which is what MTO and other far more efficient shaft PTO's see routinely.

The electric PTO seems such a dumb system.

I see absolutely no advantage - and in fact many disadvantages - to electric pre-ro.

You literally could not give me one, much as the nice fellow in FLA who tried to give me a good Subaru with redrive, all in excellent condition. I humbly and kindly refused his offer. To me it is a waste of time and hanger space, just so much junk that I wouldn't even want to be bothered with trying to sell it.

That's just my opinion, formed after much observation and some personal experience over the past 15 years, a rather short time actually.

But to each his own, I say. "Whatever floats yer boat" - or in our case, gets you in the air.
 

Vance

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Godzilla reports just having fried her geared pre-ro starter motor yesterday. I sure hope Geoff can get it fixed before the Mentone Convention.

Vance, you thought from a photo I posted elsewhere it is the same motor you mentioned above, when I was posting that I didn't understand why it was wired with a switch marked "SOFT START" yet I could not get it to actually do a soft start. You replied that I "obviously needed to study to understand the basic principals of electricity and wiring" in a rather arrogant, dismissive way. I replied that I actually do know quite a bit about the topic, having studied electric physics at the University of Michigan, etc.

Some folks who have electric pro-ro's swear by them, like Barry Kroplin - whom we all had a good laugh at, at his expense, at Wrens one year watching as he tried in desperation to hand-start a set of Dragon Wings on a Wind Ryder after his electric starter burned out. He was done for the day, needless to say. I was saddened, I wanted to see that fancy gyrocopter fly!

I don't understand the love people have for these fussy electric motor pre-ro's. They are heavy and create a lot of weight on one side of the rotor head unnecessarily, for which you must add a trim spring opposite, and are far more time, trouble, maintenance, etc. They require a FAR heavier battery, many feet of very heavy copper cables, additional solenoid so you dont' have 600 amps of power running up the mast when not spinning up, and those darn solenoids burn out to - just like the motor will, which is a matter of when, not if.

You write that you expect to replace one every 500 starts, and that on one busy day you used it 47 times. So in 11 busy days you will be replacing the starter motor.

That's a lot of time, down time, and cash down the toidy.

Mechanical pro-ros are far less maintenance, very little side-heavy head weight, no worry and in the end far less expense. Oh, well. Good to know they can spin up your 30" rotor to 100 or 120 RRPMs. I mean, that's it?

The mechanical pre-ro's I've had experience spin up even heavy Sky Wheels, 28", to 180 RRPM using a somewhat poor-efficiency Wunderlich flex shaft and a flat belt PTO. After that, the belt slips and creates heat, causing the belt to warp as it cools after spin up. With a wider PTO belt I'm sure I could easily hit 200 RRPM, which is what MTO and other far more efficient shaft PTO's see routinely.

The electric PTO seems such a dumb system.

I see absolutely no advantage - and in fact many disadvantages - to electric pre-ro.

You literally could not give me one, much as the nice fellow in FLA who tried to give me a good Subaru with redrive, all in excellent condition. I humbly and kindly refused his offer. To me it is a waste of time and hanger space, just so much junk that I wouldn't even want to be bothered with trying to sell it.

That's just my opinion, formed after much observation and some personal experience over the past 15 years, a rather short time actually.

But to each his own, I say. "Whatever floats yer boat" - or in our case, gets you in the air.

I have a spare at the hangar and take it with me to air shows.

A pre-rotator automobile starter can be changed out in about ten minutes and costs around $75. Some auto parts stores have a life time guarantee so the cost is nothing after the first one.

I have no expectation for how long the starter will last.

My starter weighs seven pounds and with the mount, wiring, ring gear, brackets and attendant hardware it is under eleven pounds total weight.

My battery weighs just over 12 pounds.

I do not have a trim spring to deal with the starter weight.

I do not recommend using an automobile starter for a gyroplane pre-rotator with 30 foot blades.

Without a soft start an automobile starter is hard on the mast.

Most automobile starters drop the voltage below the threshold for the radio to work.

Although your reasoning appears flawed to me Greg; I have no love for an automobile starter for a pre-rotator either.

I have not had a pre-rotator of any kind on any gyroplane I have flown for more than a few hours that was trouble free.
 

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Jean Claude

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Location
Centre FRANCE
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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
If the manufacturer gives a limit of 42 volts, do not exceed this value. He knows better than you do what is tolerable.
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
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Location
Centre FRANCE
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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
You just have to ask yourself why the manufacturer has limited the voltage to 42 volts instead of 52 volts.
Read the technical specifications of this breaker carefully.
 

JETLAG03

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@Gyeric805, my solution was to rewire the live feed to the starter and create a direct earth return from the starter to the battery. Not sure how much it did help but considering the high amperage involved is seemed wise.
 

Vance

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Nipomo,California
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@Gyeric805, my solution was to rewire the live feed to the starter and create a direct earth return from the starter to the battery. Not sure how much it did help but considering the high amperage involved is seemed wise.

I did the same thing on The Predator.

On The Predator the ground went through the roll and pitch pivots.

I felt the large amperage might damage the bushings and it seemed there was a lot of resistance there, I don't remember the number.

She has a slider head with nonmetallic bushings.

Because of the constant bending of the wires I went to welding cable (woven fine copper strands) for both the power and ground. The cable has held up well for around 1,800 flight hours with perhaps 2,000 pre-rotation cycles.
 

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Gyeric805

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@Gyeric805, my solution was to rewire the live feed to the starter and create a direct earth return from the starter to the battery. Not sure how much it did help but considering the high amperage involved is seemed wise.
The problem in those old starter motors was in the starter motor it self and was caused by the resistance build up between the brush holder where it was riveted to the end mounting plate of the starter motor, don,t know brand of starter motors but were in original Holdens built in Australia 1950,s, I think they were a 6 volt system , 6 volts being half the electrical pressure of modern day 12 volt systems
 

Jazzenjohn

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Looks great JM! What size blades are you going to run on that setup? I chose to go with 7 or 8 plateaus instead of a more constant acceleration as you have done. I also set mine up with 1 button to go from 0-65 RRPM and the second from 65 to full. I did that because I always taxi with my blades turning and the first button ramps the blades up while I taxi and holds it at 65 (or whatever I set) RRPM. The second button goes to full when I call that I'm taking off. I chose 65 because it ramped up pretty quickly from there and it didn't take much power to hold that RRPM. What I have found out is that while it works great for me at my airport where I'm equally distant from either end of the runway, it isn't the best at other places. Like when I go to the Carolina Barnstormers fly-in or Mentone, where they are very close to one end of the runway and very far from the other. I still like the 2 button way because I can begin to prerotate while I'm warming the engine and it reduces the time to full RRPM after I taxi onto the runway.
 

XXavier

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Hi,

My rotor is a 8.6 m in diameter (28.3 ft) and 85 inches in cord, those rotors have untwisted heavy blades ... not a piece of cake to prespin

you ideas of making 8 plateaus if fine, in my case acceleration in exponential and the curve if more or less flat according to the delays chosen btw each incrementation .

nothing perfect

I can program change :

- the delay btw each throttle incrementation order sent by the arduino to the ESC
- the max throttle
- the time at max throttle before cutting power .


nothing scientific for the uneducated man I am

- I am going to install the 150 Amp breaker
- then I will program a long delay btw orders
- then I will start the process monitoring all long
- then I will reduce the delays and see what happens

when I find an acceptable balance I will do several tests from 100% batt charge to 30 % batt charge knowing that when the voltage goes down the current goes up ... it will be a nice testing day I think ..

I will keep folks aware if it is of any interest .. after all it is only a matter of using a brushless motor ... nothing really captivating


It's interesting... Pls keep us informed...
How much does your rotor weigh...? It's probably an Averso Stella. Quite heavy...
 

DaveJaksha

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Well done, JM. PLease keep us informed on further progress. I am not ready to implement the electric rotator yet,
but maybe in a couple of months. Dave
 

Resasi

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Hoping it all goes well JM good luck with that.

Didn’t have the best of luck with the electric prerotator we went for, but it was a prototype and entered into with that in mind.

It did however decide me on a mechanical one for this project. Lets hope we both have success.
 
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