Mooney-fast, Automatic Electric Sidestep - Are you interested?

[FlyingDude]

Hello folks,

As a part of my liberation from the vacuum system, I will have to replace the sidestep retractor boot.  Currently it's tied up with ziplocks.  Although there is a good product for the electric sidestep conversion, I wanted to give it a shot and make my own.  My mechanic is doing the FSDO paperwork to make it legal.  He said that my design should pass with flying colors.

Here are the improvements I wanted to bring:

- fast.  2 seconds to retract, 2 seconds to extract the sidestep.

- automatic.  No user intervention.  Automatic just like the original sidestep.  No need to operate the beacon switch (mine is constantly on), no need for a separate sidestep switch.  

- one-bolt installation.  No need for the arm tied to the ceiling, no need to align the retractor with the sidestep.

- quick installation.  No need to remove the cable from the sidestep or fuselage ends, no need for a turnbuckle, no need for additional springs.

- motor-reductor consists of metal gears only and is rated at 2.9 ft-lb (35 in-lb) torque.  That's 25lb with the cam I used.

- The housing is 3D printed.  The videos show 85% filled PLA prototype (which still holds the weight), but I'll make the final product from PETG (70C - 15g impact force) or metal-grade polycarbonate (115C, higher impact force). 

The deadweight of the sidestep is 4.3lbs (1950g in the video).  As it starts moving it reaches 7.5lb momentarily until the speed levels.  As there is the pulley structure, the retractor needs to exert 2x the force: 15lb at start and 8.5lb while running.  The motor-reductor structure has a worm gear, so it holds its position with zero current draw.  There are 2 limit switches, for the top and bottom of the stroke.  Top of the stroke limit switch is activated by a marker on the wire, so once you adjust its location for your system, it will stop without tugging on the wire.  There is no need for a buffer spring and you will not need to adjust the cable length with a turnbuckle.  

I have 3 methods for the course reversal decision (up and down).  Here they are:

1) Mains connection from beacon supply or master relay output.  Once master switch is on, mains voltage powers the up stroke.  Once master is off, mains goes to 0V, so the onboard 9V battery powers the down stroke.  One average 9V battery is good for about ~100 down strokes.  I'll put 2 in parallel for longevity.  I think you should replace the battery at 50hr intervals when you should be lubricating the sidestep arm, although YMMV based on how many times you cycle your master switch rather than how long you fly. (Or you can just wait until the first time it fails to extract or the annual, whichever comes first).  I didn't want to use rechargeable batteries to avoid adding a recharging circuit, but I can switch to rechargeable batteries, if there is interest.  This is the solution I will install in my plane.

2) Mains connection from beacon supply or master relay output.  Mains connection powers both up and down strokes.  If the mains is 14V or above, then the engine must be on.  It pulls sidestep up.  If it is 13V or lower, then engine must be off, it extracts it.  Batteries are rated at 12.6V at their best shape, so 13V sounds like a good threshold.  Though, if your generator cannot reach 14V at <1500rpm (like mine), you may have extra up/down cycles during engine run-up and potentially at taxi, and the final retraction might happen at take-off run.

3) Just like the 9V battery solution, but instead of 9V batteries, I'll put sufficiently charged capacitors.  This is a cost adder, though, because ~36V caps that withstand -20C and +70C are not cheap.

I wanted to make a decent product.  If you guys have any ideas for improvement, please let me know...  

I would like to manufacture this, if there is enough interest from the community.  I'm going to price it as cost-effective as I can, though I've had plenty of expenses (patent attorney who made sure I'm not in breach of any existing IP and made me file a provisional patent; tons of material wasted during trial-and-error; my mechanic's time) and so far I have spent 250+ hrs on designing and testing it, which has sufficiently annoyed wife... 

Some videos:

Sidestep going up in 2 seconds: https://youtu.be/1WLryc9MxLs

Side step going down in 2 seconds: https://youtu.be/xC1EWTeuJOY

15lb test weight going up and down: https://youtu.be/AvVHJZZTifg  https://youtu.be/rTtK4cvWsmE

25lb test weight going up and down: https://youtu.be/nd-aCa_VuO0  https://youtu.be/snBcMaPE3Kk

Measurement of force to move the sidestep up: https://youtu.be/PB96DY08i10

One-bolt installation: (this is the prototype, so motor wires are sticking out)

 

Yeah, I'm eager to hear your comments.  

Thanks guys.

Cheers.

F

 

 

[RLCarter]

YouTube videos are not viewable...... no permission from owner

[FlyingDude]

6 minutes ago, RLCarter said:

YouTube videos are not viewable...... no permission from owner

Ok. Thanks for letting me know. My first time uploading on YouTube...

Just changed settings. Please let me know if it works now.

[aviatoreb]

I can see your video.  Nice work.

[EricJ]

A downside of using the system voltage to determine up/down is that if you're picking somebody up or dropping them off, or they wait for you to start engine before getting in, the step will be up.    This is a practical consideration.   I'd think the gear handle position would be a better indicator.

Stress test the operation of the system under expected temperature and humidity ranges.    It gets cold in the north and hot in the south.

Edit:   Also test what it does if somebody heavy steps on it while it is up.

 

Edited May 24, 2021 by EricJ

[FlyingDude]

14 minutes ago, bluehighwayflyer said:

I’m interested

Thank you. I certainly will keep you advised.

[carusoam]

Dude,

Great videos!  I can see what you are doing, clearly...  

 

From the plastics camp...

What is the softening temp of PLA and PETG that you are using?

The tail of a Mooney, outside in the summer... may get really hot... similar to automobiles... near the boiling point of water...

Polymers at the top of our fuel tanks don’t do very well over time... because of heat degradation...

 

Nylon sometimes gets used in some pretty hot places... gears inside of mags...

 

There should probably be some tensile strength vs. temp graphs for the materials you have tested so far...

Expect that you may see a 300+Lb foot stand on the step....  if it is partially down or up, does something not stand the human forces..?

Keep sharing your progress!

PP thoughts only not a polymer expert...

Best regards,

-a-

[FlyingDude]

@EricJ thank you for your feedback. First the easy stuff: I did leave it in the freezer at -20C overnight and heated it with heat gun up to 75C and it worked with the 25 lbs load drawing pretty much the same current as room temp and at the same speed.

Gear handle in Johnson bar systems is finicky. Sometimes it doesn't signal the gear down. Having said that, as a CFI of like to say that it's a bad idea to let pax on and off with the prop spinning. During my commercial and CFI training I was taught it's a no go. I can't honestly locate it in the CFRs. At any rate, in the current pneumatic system the sidestep stays up if you have a little bit of vacuum, so this is faithful with the original design.

As for the weight of passengers: once the sidestep is fully down, it's supported by the fuselage. When it's up, you can't step on it, because it's flush with the fuselage. If they choose to step on it while it's moving... Well, they need to move with Super Cat Speed (as in my kids' cartoon) to catch it during those 2 seconds... And if they do... Well, they break it. I don't honestly know what would happen to the pneumatic boot if you step on it while it's going up or down.

Thank you.

[hammdo]

Depending on the 3D plastic used, some have melted here in Texas. I'd verify the temp range...

I do have takair's unit too...

-Don

[FlyingDude]

@carusoam @hammdo

Polycarbonate melts at 115C. I'm used to designing electronics and mechatronics for automobiles cooked under the sun at my automotive job. We design for 80C-90C in the cabin, which has windows, and therefore greenhouse effect. Plus, if it gets 115C at the battery compartment, which has no windows, it'll be even warmer in the cabin. All electronics will be tortured and probably dead..  sidestep will be the least of one's concerns...

petg withstands up to 80C and that's analogous to the original boot design. Anyway, the incremental cost from petg to polycarbonate is not huge. No biggie there.. 

the system is not designed to withstand human weight. I don't even think that the metal connection point next to the portal where this thing is hooked up to could actually withstand a person's weight. When it releases the sidestep all the way down, it's fully supported by the fuselage. Well, if someone activates it while they were already stepping on it... It'll only blow the fuse. 

thank you for your time and feedback.

[carusoam]

I sensed you had some familiarity with this kind of development from somewhere...   

Unfortunately, my step doesn’t move... 

Best regards,

-a-

[FlyingDude]

This is the flange that supports occupant's weight. It rests on the square channel.

 

[1964-M20E]

Neat design.  However, what is driving the need to be fast with the step going up and down?

Are you going to work on and STC as well?

I guess you are using the gear position indicator switches to tell the step to go up or down as well.

[FlyingDude]

21 minutes ago, 1964-M20E said:

Neat design

Thank you John @1964-M20E

The original pneumatic boot extends very quickly once the engine stops which means no more vacuum is generated.  Some of my pax who are used to getting in&out of Mooneys and race cars are on the wing ready to get off in 5-10 seconds after engine shut down.  A slow system (like those taking 15+ seconds) will not be ready for use and there is the risk that the pax may step on the step before full it's fully extracted.  That would put their weight on the retraction system (and not on the built-in iron flange of the sidestep which rests on the fuselage).  I don't think that the top connection point of the retractor would withstand 100+ lbs human weight, so it's good to make sure that it's extended before anyone steps on it.  

As for the fast retraction: speed is cool, and that's why we fly Mooneys, right?

Yep. The paperwork is underway.  My plane is certified, so I need it even if I didn't make it available to others.

I "can" use the gear position indicator switch, if people want it.  It would be a quick rewiring of the internal relays.  However, the original design provides that the sidestep is retracted during take-off and landing.  Do people really want this extra drag during initial climb, before they haven't retracted the gear, and in the pattern?  I personally do not, so I won't wire it this way in my plane.  But if people want it, I can add it to the design and FSDO paperwork.

Actually, this system (with the automatic mode using onboard battery or capacitor) will be an improvement in case of an engine out: the original system would extract the sidestep as the vacuum pump also stops in case of engine out.  That would increase drag and jeopardize the glide ratio.  With my product, the sidestep would stay retracted during the entire engine-out glide, improving glide performance.  

Thank you for your time and feedback.

[carusoam]

Having the step up... can also improve the GU landing situation.... less damage without the step being down...

+1 regarding speed of operation... the vac step on my 65C was pretty quick getting down... until everyone on board was experienced at deplaning... 

Best regards,

-a-

[DCarlton]

First of all, great effort; nice description.  Here's a few thoughts.  

- I'm not crazy about the idea of 9V batteries.  More maintenance; more potential for battery leakage and corrosion; just something else to worry about.    

- Using the voltage as a trigger sounds good if it's reliable across all installations.  Using capacitors sounds OK if there are no safety or reliability implications; don't know how big they need to be to drive that motor (or if they're just tripping something that lets a spring do the work).  

- I like the idea of wiring at the beacon; simplifies installation; avoids another interior rip out; crawling around under the panel, etc.  

- I don't think I like the idea of using the gear position circuit.  Do you happen to know where those switches are relays are?  

- I haven't looked at the step in a while but I'm not clear on what drives your step down.  Is it using an existing spring?  My step is sticking on the down stroke; I usually have to pull it down; I'm planning to see if I can clean it up; I have some corrosion under the chrome.  If it's using the existing spring, perhaps you could offer parts to remove and replace the spring if needed (and recommendations for cleaning up and lubricating the step guides).  

- Do you happen to know where the step boot taps the pneumatic vacuum line?  Does it go all the way to the pilots side panel?  I'm planning to downsize my vacuum system but keep enough of it to drive my Brittain EVT turn coordinator and wing/rudder servos.  Would like to take the step out of the vacuum circuit in addition to the AI.  

- Please don't include a large format touch screen display.  :>  

 

Edited May 24, 2021 by DCarlton
Added gear position circuit comment.

[FlyingDude]

Hi @DCarlton,

Thank you for your feedback.  Here are my notes:

- 9V batteries are fine.  They are in garage door openers that sit outside all year long and never leak or corrode.  Well, the decent brands at least.  I never buy them from dirt cheap stores...  Li-Ion batteries require special care, like in shipping, storage, charging, etc. etc.  And it's not really worth it.  Based on my measurements and math, a single 300mAh 9V battery is good for 360 down strokes.  I'll put 9V batteries in parallel and make that 720.  Who logs 720 landings in a year (assuming 1 landing=1 engine on/off cycle)?  Anyway, FAA requires me to require battery replacement intervals for continued airworthiness.  I'll probably recommend 50hr lubrication intervals and make it mandatory at the annual at the latest.  You have to open that side portal and lubricate the sidestep arm at these maintenance points anyway.  Replacing the battery will add $6 and 5 minutes to your annual...  I've wasted enough trim screws that cost me a lot more than that...

- Voltage trigger is based on standard spec across all 14V systems (12.6V max battery voltage and min 14V generator/alternator voltage).  The only caveat is that some generators output this voltage at 1500rpm and above.  So, I assume people whose generators output the rated voltage at idle will opt for this model, and others won't...  As for caps, yeah they are safe.  Automotive grade caps are literally panzers...  The only issue is the cost.  They can get pricey, that's why I prefer the battery.

- I am not fan of the gear position switch either.  If there is demand, I will just leave a "switch input" and leave it to the installer to tap on any switch of their pick, which could be the gear switch or a dedicated sidestep switch; or power the sidestep from master relay and use the beacon as a switch.  Well, that's exactly what I tried to avoid when designing it as automatic, but if people want that, I can provide it.  It's in the service manual, but it would be wise to consult with an AP if one is not sure about where to tap.  Improper wiring is a fire hazard and must be avoided!  

- I'm not planning on modifying the existing system more than the bare minimum necessary.  So, I'll rely on the existing spring and gravity for the down pull.  Business-wise, stocking and selling spare springs would be a logistics, inventory and cost issue for me.  Plus, Lasar and other vendors carry these parts.  

Btw: I'd suggest you take care of your sticking sidestep.  Corrosion is a bad thing and it spreads... 

- The sidestep plumbing is in the service manual.  It T's behind the directional gyro, runs along the left cabin wall.  Removing the pneumatic boot will definitely offload your vacuum pump, potentially increasing its longevity (or delaying its premature death).

- You got me on the display  If I make it touch screen, will you change your mind?

Cheers

[Chocks]

Ok following this.

I've got the hand crank step that I would love to automate. Would be interested in either 9v internal or 12v direct to battery connection and I'm good with automated engagement (with indicator) or I can add a toggle switch to my panel.

Looks great! Can't wait to get my hands on one!

[FlyingDude]

@Chocks

Thank you!  I will definitely keep you posted.

[Fly Boomer]

On 5/23/2021 at 10:11 PM, carusoam said:

Unfortunately, my step doesn’t move...

Neither does mine.

 

[M20F]

Vacuum or death 

[chriscalandro]

That thing will turn to mush in Palm Springs or AZ. 
 

Ship power is the way to go. 
 

I don’t think you can get 3d printed parts approved. 

[FlyingDude]

Yeah... The project had a hiatus. It's on my todo list. I'll get there. 

[0TreeLemur]

The system developed and sold by @takair has FAA-PMA approval.  Why reinvent the wheel?

 

[hmasing]

On 5/24/2021 at 9:06 AM, FlyingDude said:

The original pneumatic boot extends very quickly once the engine stops which means no more vacuum is generated.  Some of my pax who are used to getting in&out of Mooneys and race cars are on the wing ready to get off in 5-10 seconds after engine shut down.  A slow system (like those taking 15+ seconds) will not be ready for use and there is the risk that the pax may step on the step before full it's fully extracted.

I have my electric step on a separate switch - was my top beacon, but I moved to a single LED beacon on the belly.   The default power-off position is down. While it takes 15-20 seconds to lower or retract, I find that if I put it on my pre-taxi checklist, then I have no issues with it being fully down by the time I get to the ramp. Retract is a non-factor, as everyone is inside my Mooney by the time I hit that item on the checklist  anyway.