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Hobby Lobby's Model Motors Brand EVP Pro Variable Pitch Prop on the Mini Hotrod 3D ARF

Former US National Freestyle Champion Mike Cross explores the Model Motors Brand EVP Pro variable pitch prop...and shares the joy of a very first nose down torque roll, and more!

Splash

Introduction

Model Motors' EVP Pro

Motor:Axi 2208-34 Hollow shaft
Available From:Hobby Lobby

Remember When....how about the first time you had a good landing?

There are several things that I remember as flying firsts...

  • First good landing
  • First loop (Done so high that I was the only one that could see it)
  • First roll (Done were people could see it but it started horizontal and ended vertical)
  • First Harrier landing (Ok the engine sputtered)
  • First tail touch.

These are all things I will remember clearly for the rest of my life. Very rarely does something else happen that is a first that I can say I will remember forever. Well, the first time I did a down line, put negative pitch into the prop and watched the plane stop and torque roll is another of these things I will remember forever....let's look at how we got there...

What IS EVP?

Electric variable pitch props started surfacing back in late 2004. Many setups were modified from helicopter setups, others were scratch built. Power and efficiency seemed to be marginal, with the main reason being the propellers. At the time many setups were using unsymmetrical propellers, which left negative pitch suffering for thrust.

Scott Foster brought his own version VPP unit to the E-TOC and rocked a lot of people's views of aerobatics...

Hobby-Lobby stepped up to the plate, importing Model Motors' Czech made electric variable pitch system. It contains symmetrical blades, and this hollow-shafted Axi motor is designed to accommodate the EVP system without modification. The Electric Variable Pitch system, EVP for short, was flown in the 2005 ETOC by Scott Foster. Scott placed first, with an incredible jaw dropping performance.

How does it work?

The EVP is operated by another servo, used to change the angle of the blades. Most people use helicopter-style programming with a throttle and pitch curve to operate the blade pitch. As a heli pilot this was pretty easy to understand the logic and setup; however, some aircraft pilots might not quite understand how this works.

One way to think about it is like an aileron-to-rudder mix designed to create coordinated turns off aileron inputs alone. Like how the rudder servo responds when aileron stick is given, when the throttle stick is moved, the curved mix tells the pitch servo to increase or decrease the pitch as required. Remember, for example, that a 100% mix would move the pitch servo full travel when the throttle servo is at full travel, and so on.

The second piece that is heli-normal but confusing to acro pilots -- we need to make a v-shaped throttle curve. At mid stick, the throttle is still half throttle; the upper half is normal; the lower half of the curve, however, mirrors the upper half, so that pulling the throttle stick down below half gradually INCREASES the throttle (the motor RPMs). In a helicopter, we then have to carefully match to the pitch curve so that there is then increasing power applied to the reverse direction prop. I found with the EVP that I didn't need to be quite so complex. If I simply set up a pitch curve that is two flat lines -- from half stick and above I have one normal positive pitch setting -- like a regular forward pitched prop. When I come below half pitch, I have a second pitch setting -- like the regular forward pitched prop, but pitched backwards. Then, by varying throttle alone, I was able to increase/decrease the model's acceleration or deceleration, without struggling with the added complexity of a true pitch curve.

Remember, we have to have negative pitch belowhalf stick to be able to allow the model to decelerate, torque roll nose down, and even back up. You can see the model backing up on the ground in the flight video below.

Remember, of course, that this mix MUST be on a switch (identical to a heli's idle up), so that a normal setup also exists for normal forward flight, take-offs, etc.

Electric Variable Pitch Contents

The EVP system comes with everything needed to complete the system, expect the motor. The setup comes with a detailed direction booklet, with tips, tricks, and throttle curves in the back.

Components needed to complete the EVP system:

  • Hollow Shaft Brushless motor
  • Different size hex wrenches
  • Micro Servo
  • A drop of Super Glue

Assembly

The instruction booklet was very complete, with step by step instructions. The assembly went very smoothly, every part fit perfect. The assembly uses set screws that use hex wrenches. A good set of wrenches with very small bite is required to attach the pitch slider to the motor.

While it's not mentioned in the instruction booklet, a dab of loctite would be very helpful here. If the pitch slider comes off the motor, you'll loose all thrust.

I had to mount the pitch servo as straight inline behind the motor as I could get it. It was a very simple linkage.

Nearly Ready to Fly...Creating the Curves

I began with heli-like curves, and worked hard to try to match the throttle to pitch curves, like I would on a precision helicopter. I had a classic V throttle curve and adjusted the pitch. Flying, however, I found that we're trying to do very different tasks than what a heli pilot needs, and I was doing a lot of difficult work for nothing. My resulting curves that worked for me are shown below....the throttle curve more of a U, and the pitch curve 2 flat lines with the required transition between them.

Throttle curve: I began with a simple V shaped curve, but I'm raelly never using zero pitch -- and I didn't want to overspeed the prop, so I flattened the throttle input there to avoid that.

Pitch Curve: I created the pitch curve by first setting the high pitch setting...with an amp meter in place, I went to full throttle, then decreased the last point of the pitch curve until I had eased the draw down to my max acceptable amperage. In this case, that was 8A. I then did the same on the negative side -- I'd already created the V-shaped throttle curve above. I gave full negative throttle, then adjusted the pitch curve point until I was agrain drawing 8A, but negative.

Note that, on my 9Z, my curves have 13 points, so it was pretty easy to get a long flat line, with a small step occuring around mid stick. In fact, with the 14MZ you could even adjust the point positions so that step would be almost invisible. However, don't spend too much time worrying about it. Whereas Futaba's setup for heli pilots have them hovering at half throttle so that the pitch curve at half throttle is critical, acro pilots are hovering at a much higher stick position and you've already passed through those points where the pitch is adjusting gradually.

Flying

Indoors or Out?

Assuming you're reading this because you've not flown EVP/VPP before, I strongly recommend beginning outdoors with zero wind. You'll run out of room very quickly as you work to learn the differences in flying with this, and walls will get in the way awefully fast! Heck, the ground got in my way a time or two even outside!

Backing Up On the Ground?

As you can see in the video, I set up a throttle curve with zero throttle at center stick, positive positive at top stick, positive negative at the bottom. I did this to get a feel of the model on the ground. What happened, though, is when i was taxiing and it felt it was moving a bit quick, my instinct pulled the throttle stick backwards. OOPS! Now we're rushin gbackwards! I ended up chasing the model on the groudnk -- too much forward, too much back...I don't really recommend this approach. Seemed like a good idea at the time...

Knowing the Airplane

Definitely get to know the aircraft in your normal flight condition before you start trying to play withthe pitch. Know how ti feels in a stall; know how it feels when you're hanging.

Oh, and heli pilots, in this idle up, when you go to do a roll in forward flight, DONT try to give negative pitch as your model is inverted!!! Just a helpful suggestion here!!! (I can't say how many times I did that!! Nearly every time I tried a roll I found myself trying to pull negative pitch.)

The First Time Trying The Pitch...

Once you think you're ready, put the model in the stunt mode, but then concentrate on trying to fly it with the stick above half and get its feel there. Then, on a full speed level line up high, ease the stick below half. Realize how quickly the model decelerates, and even stops!! Get used to this feeling...it might take you a few flights to feel you have control of it! Try to get the model down to stall speed, then accelerate back forward, keeping your straight line.

Once you're comfortable there, let's try a vertical down line. Point your model nose down with the throttle just above half. Now ease the stick below half, and watch your model fight gravity, decelerating on the down!!! Don't expect to be able to do an inverted torque roll your first attempt!

Because you are transitioning from airflow over the tail to no airflow over the tail, the only real control you have over whether or not you can hold it stationary is how well you handled the entry. Was the model perfectly vertical? If so, it will likely stay in that vertical position as that airflow disappears, and you'll start to head toward your first inverted torque roll!

From a Different Viewpoint

I'm AnnMarie Cross, Mike's wife. I have to tell you, Mike used to be a professional test pilot for a major industry player. He'd flown more planes than anybody wants to remember. And long ago, he'd stopped having any fun. There was nothing new, nothing interesting, nothing to catch his attention. Yep, fly another tailheavy this, or twisted wing that, diagnose what was wrong, fly it again. BOOO-RING.

When HL offered for RCGroups.com to review this product, I couldn't suppress a bit of a smile, and started nudging Mike to do it. Finally he said, "I guess I'll try it." I had to remind him of all the fun we had when 3D was young, when he invented bug on a windshield. I think the one that really got his attention was reminding him of the first time he showed Chip Hyde a high alfa tail touch.

"Remember how much fun it was back then, inventing new things? Experimenting with things that were outside the 'rules'?" He agreed to try it.

It has been such fun to see him just out flying on his own again! To come home from work, and find he's doing some patch work on the airplane again after another fun experimenting. I can't remember the last time he was out flying for fun.

"Where'd WHO Go?"

Aw come on, we've all seen Top Gun. You know the quote...."hit the brakes, he'll fly right by." This is the ultimate of that...slam on the brakes, and make it a u-turn...suddenly you're going the other way.

This manuever is covered on the video. It's as simple as flying along a bit nose high, slow throttle. Go to full negative throttle, full down stick (keeps the tail from flipping upward). The plane reverses direction, simply go back positive throttle and fly her out! What fun, that's all it takes.

I found I just was having a lot of fun applying negative and seeing what happens. Giving negative in a stall turn sometimes would give me a full cartweel! It was something new, something fun to play with.

Flight Video/Photo Gallery

Downloads

Conclusion

This unit has made flying fun again. If you're looking for a new challenge, this EVP Pro unit certainly can provide it. What a blast! The instructions are good, the unit arrives nearly comletely assembled and installs quickly. The throttle/pitch setup are not nearly as complex as setting up a heli, and on a small inexpensive foamie, there's little cost involved in getting to learn this fun new style of flying! The Mini Hot Rod was a perfect match.

Discussion

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Old Mar 22, 2006, 01:49 PM
AvroFan
Joined Mar 2006
1 Posts
Nice flying, too bad it's a typical video of a plane against a clear blue sky. It would have been nice to have a background reference(tall building or tree or something) to really see the plane's radical moves.
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Old Mar 22, 2006, 07:11 PM
Registered User
Joined Mar 2004
51 Posts
Hi Mike,

Great review and awesome flying! Planes aren't supposed to fly backwards nose down are they?

I thought the video was great. Keep up the good work.
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Old Jun 03, 2006, 03:35 PM
Hold my beer and watch this!
Jeremy Z's Avatar
Northern IL
Joined Oct 2005
2,380 Posts
Wow. It seems like that would upset the way your mind works for a good while, until you really get a chance to learn it. Good job with the review. One thing: the text is mixed up for the Jason Cole videos. (large--> small size & vice versa)

I look forward to more video footage of variable pitch 3D flying.
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Old Jan 31, 2007, 05:08 AM
Just Happy To Be Here!!!
harrymc's Avatar
United States, AL, Tuscaloosa
Joined Nov 2004
1,692 Posts
I loved that reverse direction move!
I've got a Shockie Yak with a Hacker VP setup. I'm going to try that with mine first good flying day!!! What a hoot!!!

Harry
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