Electric pre rotor Soft Start

pdclay

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This is my first post so any help will be appreciated. While at Ken Brock Fly-in with my Benson 12 volt electric pre-rotor, I had several suggestions to put on a soft start. I researched but I am not sure what I need. What do I need and where can I purchase? I found a 12 volt pulse width modulator that handles up to 100 amps but a starter can draw more than that? I am not an expert so please explain what I need? Thanks, pdclay
 

Mike Hook

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Go old school with the keep it simple thought. Use two solenoids, one with a resistor to soften the initial start and a second selonid to go across the line on the starter to full speed. You could use two buttons or switches to control each solenoid and use your own judgment as to when to switch to step off resistance, or install a timer to make the switch. As I said keep it simple, use one single pole, double throw switch with momentary contacts with center off.


Mike

They has been others here that have used resistance to prerotate, do a search.
 

Mike484

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I was there too, which Bensen (make note of spelling) was yours? Got a pic?
 

Alan_Cheatham

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In addition to what ever you have to turn on and off the current flow to the starter.



A simple soft start is just a coil of heavy uninsulated wire to act as a resistor wired between
the posts of a starter solenoid, that solenoid then being wired in series with the positive line to the starter.
When the prerotator is activated the current will flow through the coil resistor and this will reduce it's voltage
giving you reduced power at the starter, then when some rpms are built up the solenoid is activated which shorts across
the coil resistor bypassing it allowing full voltage and current to the starter.

One coil wire
One starter solenoid
One control switch for solenoid
Associated wires and lugs

.
 

RayPierce

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This is my first post so any help will be appreciated. While at Ken Brock Fly-in with my Benson 12 volt electric pre-rotor, I had several suggestions to put on a soft start. I researched but I am not sure what I need. What do I need and where can I purchase? I found a 12 volt pulse width modulator that handles up to 100 amps but a starter can draw more than that? I am not an expert so please explain what I need? Thanks, pdclay
Has anyone thought about using an electric golf cart controller? Say a Curtis PMC model 1204-001 (275 amp)
I imagine it would take separating the bendix solenoid from the starter motor via a switch then infinite control through a potentiometer to control the speed of the motor. Looks to me a setup like that would avoid over torguing the mast.
 

vickijohnk

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I would make sure that you have a heavy grounding conductor from the starter motor to the mast so that 100 amps+ is not running through the pivot point bearings. John K.
 

pdclay

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Hey thanks for all the help. I looked through all the 500 treads that came up on soft start search found a couple schematics. I was with the arizona group. Enclosed is a picture . I forgot my camera at the fly-in but I think Mary took a bunch of pictures.
Thanks Again.
 

themonarch

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soft starts

soft starts

Dear Alan,

Thank you for your post explaining what a simple soft start consists of. A short then a bypass direct to solenoid. My Butterfly uses this setup and I have operated it several times. Until your post I had not bothered to understand how it worked. Now I know.
Keeping it simple, now thats for me! Joe.
 

Mike Hook

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Why would you use a short ,that is a waste of energy. Just throtle the flow of current thru the resisantce of the wire used as a resistor. That is simple ohms law. You dont need to take it to ground parallel the load. Use it in series then by pass the resistor. Same start just less energy loss.

Mike
 

okikuma

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Clay,

Britta Penca has a soft start system using a piece of steel coat hanger wire wound into a coil (how many turns I don't know) and used as a resistor on her two place Air Command gyro.

After searching the net for previous posts on soft start pre-rotators, I've come up with the following schematic and thread.

Wayne

http://www.rotaryforum.com/forum/showthread.php?t=9294
 

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chris1961

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soft start

soft start

Couldn't you use a simple rheostat switch to gradually increase the voltage?
I have electric PR too. I wondered about that.
 

Mike Hook

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Reostat would hold up to the current. It would have to be very large.
Mike

I have worked on undergound mining equipment all my life and old school speed control was using stepped resistors to bring a load up with controlled current. We use Curtiss controlers also on on rubber tired mantrips but again weight is an issue. As shown in earlier post the wire acts as a resistor controlling the current flow. The number of turns changes the amount of current that will flow thru the wire. You will have to experiment on that resistor because you dont know the current that your starter draws.
 
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madwinger

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Starter Motor Hardware

Starter Motor Hardware

So what hardware does one need to hold the motor in place and actuate the rotor head to spin? I have and old wonderlich on my mid 90's Air Command and want to switch to electric. I understand the the wiring circuit but don't know how to hang the motor and make it actuate the rotor head.

Can anyone explain whats needed from the top of the motor up? Any drawings or pictures would help.

Can I use what is already there?

Attached some pictures of what I have. WOW seeing these old parts in this light....they really look hammered!

Thanks

Mark
 

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madwinger

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...............................................

.
Alan, thanks for this picture. If you could answer a few questions for me I would appreciate it.

1. Did you have to make the bracket that holds the starter or are these available and if so where?

2. Do the starter gears on all motors just mesh up with the ring gear on the rotor or do they have to be changed?

3. I assume that the Bendix in the starter pops up just like it would in a car?

4. I dont think my has a larger enough gap between for the adapter plate. did you have to do something to raise the rotor head?

5. I have 24' Dragon Wings. I read a lot about a Toyota Starter. Is that the starter I want?

6. Not related to the per-rotator but what does the spring assembly the top of your push rods do or prevent? I have never seen that and as curious.

Thanks again.

Mark
 
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GA Rotor Guy

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Alan, thanks for this picture. If you could answer a few questions for me I would appreciate it.

1. Did you have to make the bracket that holds the starter or are these available and if so where?

2. Do the starter gears on all motors just mesh up with the ring gear on the rotor or do they have to be changed?

3. I assume that the Bendix in the starter pops up just like it would in a car?

4. I dont think my has a larger enough gap between for the adapter plate. did you have to do something to raise the rotor head?

5. I have 24' Dragon Wings. I read a lot about a Toyota Starter. Is that the starter I want?

6. Not related to the per-rotator but what does the spring assembly the top of your push rods do or prevent? I have never seen that and as curious.

Thanks again.

Mark
X2...

I saw the picture and was wondering about the springs in the controls... is this to dampen vibs? Or to soften control inputs?
 

Big Dawg

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Hi PDCLAY,
I have made quite a few of these pre-rotators of which you mentioned.My design was featured in the Homebuilt Rotorcraft mag.(which no longer exists),a few years back.Don Parham did an article about my soft-start system. I am a 30-year expert on this matter.My
business is rebuilding starters,and alternators.
I was also the first one to design the small 100-amp Delco CS 121 alternator to fit on the Subaru EJ 25(Sparrow Hawk).Phone me @Straco Rebuilers 618-532 4846,and I will explain
how the soft-start works,and I will fax you simple instructions to do it yourself!
Big Dawg
 

Jean Claude

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About 500 h (FW + ultra light)
If I assume 3 hp (mechanical) to start the rotor, then the car starter requires about 6 hp (electric) from the battery. It is 500 amps / 8 Volts. To supply 500 A, the car battery (12 volts) will weigh almost 30 lbs. Or 36 lbs including the starter motor.
Usualy we need 50 Hp and 500 lbs of expensive technology to lift 180 lbs of pilot. So it is 10 hp and 100 lbs that really cost this launcher.
Sorry for the fly in the soup.



If the battery does not give 500 A, then needless to find a bigger launcher or better gear ratio.
 
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C. Beaty

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JC, don’t you believe that the most inefficient method of flight that is possible should also have the most inefficient method of rotor starting that is possible?:D
 
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