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Electrifying a Vario R-22

hrbeta

Heliman

Boca Raton, FL. USA

I finally gave in... Placed my order for a Vario Robinson R-22 this afternoon, but I want to go electric, so no engine/engine parts were ordered. Now I am looking for some advice as to the best motor / ESC / batt combination for this heli. I have converted all my helis but I have nothing bigger than a .90 size and this R-22 is a monster, so any comments/advice/experiences from the group will be greatly appreciated.
Regards.

10-24-2009 Over year old.
darrens

Key Veteran

United Kingdom

A machine of that size will have to be 12s for sure. I recently built a large Robbe Alouette and converted it to electric (see here http://www.runryder.com/helicopter/t534439p1/) and I got asked by someone the other week how I chose a motor/battery set up for it. The response was a bit lengthy.....sorry, but in case it is of use to you, here it is;

ELECTRIC MOTOR CHOICE

KV as we use it refers to the rpm constant of a motor - it is the number of revolutions per minute that the motor will turn when 1V (one volt) is applied with no load attached to the motor. In summary, we call it revs per minute per volt, but do not think you will obtain those revs when you attach a motor to your heli drive train, as obviously the revs will be reduced because of the load unless you use an ESC in governor mode and you have enough reserve power for it to compensate with more throttle (more on this later).

So what does the KV tell us? Well it is related to the power out from a motor, or more usefully the torque level of a motor. It is determined by the number of winds on the armature (or turns as we sometimes call it) and the strength of the magnets so there are many possible variables. KV allows us to get a idea on the torque we can expect from a particular motor.

In summary, a low KV motor has more winds of thinner wire - it will carry more volts, but at less amps, produce higher torque and drive a higher gear ratio.

That may sound confusing, but compare it with a high KV motor which has less winds of thicker wire which will carry more amps at less volts and spin a lower gear ratio at high revs.

Let me give you an example:

A 6 turn is called a hot motor - it has only 6 winds of thick wire and is made to carry big amps at low volts.

For example, a 3025/6 motor has a KV rating of 1255, meaning that the motor will spin at 1,255 rpm per volt with no load (not recommended for brushless motors - never run them without a load - it is a theoretical value only). This motor is often used in medium sized fixed wing and will spin a 12 x 6 prop at 7,900 rpm on 7 cells and draw 48A - giving 350W. You might want to push the amps with this motor and fit an even bigger prop to give you more Watts for competition use because it will take more amps - it is able to take 65A for up to 60 seconds or 100A for up to 10 seconds, the manufacture specs sheet show this.

Compare this with a 3025/8 motor - that is the same size motor physically (armature 30mm diameter and magnets 25mm long), but it is wound with 8 turns of thinner wire. It has a KV rating of 985 - much lower than the hotter 3025/6. It will spin a 12 x 6 prop at 6,900 rpm on 7 cells and draw only 27A producing 249W. This motor has more torque and you might want to increase the voltage to take advantage of that characteristic, but watch the amps because this motor has an amps limit of 52A for 60 seconds as per the spec sheet.

These motors are quite close in specs, but you can see the difference. The point is that the higher KV motor would be used to give high power for short bursts in competition flying, but the lower KV motor has more torque and is better suited to a sports application or continuous power. So - you can see that the KV figure is useful in helping you choose a motor for a particular application/head speed target. It is particularly useful when considering two motors of exactly the same size but different windings.

When considering motors of different sizes, it is just another figure in the electric power jig-saw that allows you get a handle on a motor and its uses. You might come across a larger motor such as a 4035/10 and you will find the KV rating at 405. Now I know that seems like a low KV, but check the useful current range for that motor when considering it. Compare it with a 4035/14 and you will find that the 14 wind motor only has a KV of 299 - so you can see that bigger motors have a lower KV rating than smaller motors and operate at higher volt ranges for a different purpose. A 4035 motor will use 6S to 8S (higher voltage Lipo batteries) and comfortably fly a .60 size model weighing up to 8.0kg.

In essence, the KV figure allows you to compare similar motors and understand what gearing would be required for your application. You may have a limited gearing range available so therefore have to pick the motor to suit the gearing rather than the other way round.
If you take a high-KV motor and gear it down, you effectively make it in to a lower KV motor! For example, take a high 5000 KV motor, but gear it at 10:1. It is a 5000 KV motor when considered without the gearbox, but it is a 500 KV in effect when a 10:1 gear ratio is added to it. The motor is still doing 5000 rpm when one volt is applied to it, but the output shaft of the gearbox is doing 500 rpm. You can still see that this is a low voltage/ high current motor because if you apply 12 volts to the motor (circa 3s pack)it will do 60000 rpm without a load (not that we ever do that - we should not run brushless motors without a load) and that is a high revs level. Inner-runner motors like this will run at quite high revs, but Plettenberg for example say that there is a limit to the revs capability of their inner-runners and it is about 70,000 rpm!

Outer-runner motors on the other hand are low rev, high torque motors and are not intended to run at very high revs like some inner-runners are. Outer-runners are generally limited to more like 15,000 revs and this is reflected in the relative KV ratings.


So - there are horses for courses, and the KV rating of a motor is one factor that gives us an indication of the way it is meant to be used. You would not use a low KV motor in a Zagi because you need high revs with a little prop at 1:1 ratio. You would not use a really high KV motor in a large heli because you want to swing a large disc and obtain high torque at lower rpm when compared to something like a Trex 450 where you may run up to a 3500KV motor, a Trex 500 would be circa 1600KV and a Trex 600 would be 1200KV. Compare these to the size of a large scale heli and you will see why the KV is more likely to be around 400 - 600 max.


Take my recent Robbe Aouette conversion for example. My gear ratio is 11.12:1, my motor is 500KV and I am running 10s cells which are circa 40V, so my equation is giving 1438 at 80% esc......500KV x 40V divided by 11.12 gear ratio x 80% esc setting = 1438. Loading is not much of an issue as the esc I use is in gov mode, so the 80% off load dictates the "desired" head speed of 1438 and the esc is free to increase throttle up to 100% where required to maintain that.

He who dies with the most toys is the winner!

10-24-2009 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

Thank you darrens, your post was very informative to me.
I have put together a power system consisting of: an AXI 5330-18 motor, a Kontronic Jazz 63v ESC and still debating on the number of Lipo cells.
If I am to retain the stock pulley/clutch-bell on the motor's end (22T) I might have to run 3 x 5 S Lipos; if I want to use my many 6 s Lipos in series of two (and I wish I could), I need to go to 24T on that pulley, and then either adapt the clutch bell or dismiss it all together. I hear that a machine this size should keep its clutch, on the other hand, no clutch is a lot simpler. DTM in Belgium did it on his e-R22, but I have not heard from his experience.
I'm also waiting on Darrell to come back from vacations and showing me his motor base/ clutch adapter. Meanwhile I've been working on other areas of this project. (photos coming)
Cheers.

11-13-2009 Over year old.
darrens

Key Veteran

United Kingdom

Hi,

Glad it was useful.

The clutch or no clutch debate seems to be on-going, but I think it offers 2 benefits of you can include it. Firstly, it makes for a very scale spool up, but more inportantly, it gives a low cost (clutch lining is cheap) protection in your gear train. The motor produces the same torque at 1rpm as it would at 10,000rpm and if ever you had a problem, you would struggle to hold on to the head or would rip your gears entirely. Is it absolutely essential, I would guess no as the esc has a fantastic soft start, but on these big birds caution is the sensible route.
I'll look forward to seeing pictures as you post on the build.

Cheers
Darren

He who dies with the most toys is the winner!

11-13-2009 Over year old.
PETER ROB

Elite Veteran

Devon UK

This R22 was converted about 3 years ago by another Peter R, before electric heli's took off, can't say much about the specification, but the gearbox is scratch built
Peter R

11-13-2009 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

I have it ready to test fly now Too bad it is incredibly cold in South Florida right now We are talking freaking 35 deegres and 15 mph winds. Really crazy. So I'm going nuts inside playing with my sim...
I decided to forgo the clutch assembly and work with the Knotronics' soft start, which BTW seems to be very smooth and strong.
Mounted a 24 grooves pulley on the motor's side and that'll provide the R-22 with 800+ rpms, according to my calculations.
It's been great tp work on this thing, plenty of interior space for all the components and electronics.
As it is now, is about 90% completed, I'll leave the painting and afixing of doors, windshield, etc., until after the test flight.
Here are some pics. Enjoy.
Cheers and Happy New Year to all BTW

01-06-2010 Over year old.
PETER ROB

Elite Veteran

Devon UK

Helicommand

Can you say why you have fitted a head stabilisation unit?
The Vario R22 is probably the most stable scale helicopter on the market, straight out of the box built
I have owned nine, and still fly one, none have ever needed head stabilisation
Peter R

01-06-2010 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

For no particular reason Peter; I had the HC unit sitting in a drawer and I thought it'd be a nice match. I'm glad to learn the R-22 is a stable flyer on its own right.
Cheers.

01-06-2010 Over year old.
Etan30

Senior Heliman

The Netherlands (EUR)

I look forward to see your result on flying this machine electric. As i have almost finished my EC i would also like to start building an R22 with electro conversion.

Ed

01-06-2010 Over year old.
PETER ROB

Elite Veteran

Devon UK

Vario R22, New in box

Ed, I have a spare Vario kit and blades,surplus to requirements, if you are interested, send an e-mail
Peter R

01-06-2010 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

R-22 maiden video

Hi guys. The weather gave me a break today and I was finally able to maiden my e/R-22.
I was very pleased with the flight. No vibrations, no surprises, no weird noises, etc.
This heli is indeed very stable and predictable. In total, I put in about 10 minutes hovering time, which only drainned 3300 mAh out of my 5800 mAh batteries. I think solid 15 min flights could be attained.
The only thing I am not totally pleased with is the ESC's soft start. It's not very soft at all. I needed to carefully work the throttle stick to spool up the rotor. I guess I need to buy the programing card to fix this...
The R-22 has been taken apart now and the fuse will be off to the painter next Monday... Can't wait to have it finished!!!
Here is a link to the video http://www.youtube.com/user/hrbeta
Cheers.

01-15-2010 Over year old.
PETER ROB

Elite Veteran

Devon UK

R-22 maiden

With or without the Helicommand?
Peter R

01-15-2010 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

Helicommand was onboard just to take care of the tail gyro.

02-03-2010 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

OK it's complete now

I got the fuselage painted by fly-buddy Wayne Palz and proceeded to put the R-22 back together. Here are some pics, I hope you like them.
Cheers.

02-04-2010 Over year old.
buster1

Veteran

Manhattan, NY

extremely nice!!!
Love to see a flying video - how do you like it electrified?

02-04-2010 Over year old.
darrens

Key Veteran

United Kingdom

Looks sweet, we really do need a video!

He who dies with the most toys is the winner!

02-04-2010 Over year old.
PETER ROB

Elite Veteran

Devon UK

OK it's complete now

hrbeta, Nice paint finish
It's screaming out for some decals, with some it will come alive
Peter R

02-04-2010 Over year old.
spiacro

Senior Heliman

Athens, Greece

Very nice job!
Waiting for a video,too!


Spiros

Engine is the HEART of an r/c model, but THE PILOT is it's SOUL.

02-04-2010 Over year old.
ba board

Veteran

England

Love the colour.....great job.

02-04-2010 Over year old.
hrbeta

Heliman

Boca Raton, FL. USA

Video

Hi guys, here is the link to the video we shot this morning

http://www.youtube.com/watch?v=XHQCDYPytHM

Cheers.

02-08-2010 Over year old.
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