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Apr 19, 2007, 05:52 AM
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Micromum V7 - the trike


Basically, V7 is not much more than a V4 with the main landing gear mounted back to front, with the main booms angle of attack changed to get the front wheel under the boom and with the tail unit closer to the mast. Plus, it's got a rudder (without the rudder it's V6).

Specifications of V7:
- rotor diameter: 700 mm / 27.6"
- rotor blades: 1 " Aerobalsa rotor blades
- AUW: 230 g / 8.1 oz.
- motor: Potensky POT 50, 30 g with mount, turning a 7x4 APC SF prop at 8400 rpm/min, using 3.9 A from a 3s lipo battery
- battery: 3s Kokam lipo, 350 mAh, 34 g
- Rx: 4 channel, 9 g, roll, pitch, rudder, motor
- ESC: 9 A ESC with BEC, 10 g
- servos: three 6 g servos with metal gears

I've decided to try out a trike configuration, because I thought it might be helpful when doing ROGs. With old V3 I could do take-offs from the snow in winter, but when I tried to taxi on a grass surface, the gyro just did somersaults. Unfortunately the quality of our airfield with its wheel-devouring mouse holes and awe-inspiring bumps still doesn't permit ROGs, even with the trike. But on a flat surface, they should now be possible.

As always, the *.jpg files in the attachments are for looking at, the *.pdf files are for printing out - without any size adjustment - and building.

Since building V7 is pretty much the same as building V4, I'll just go over the differences. The main boom now has an angle of attack of 4, therefore the angle between the main boom and the rotor mast has increased from 82 to 86. Build the airframe as mentioned in the V4 instructions, with the axle of the main landing gear just behind the rotor mast. For the main landing gear I used slow-fly wheels with an O.D. of 64 mm / 2.5".

As the battery pod now serves as a holder for the front landing gear, I've swapped the 1 mm balsa strips glued to the cf reinforcements for 1 mm plywood strips. The outer grain of the plywood should be perpendicular to the grain of the main boom and the fibres of the cf reinforcements to keep those parts from splitting lengthwise under extreme loads. Cut the wheel holders from 1mm cf. Drill 2mm holes for the axle and the screws and drill the appropriate holes through the main boom. The front wheel is the usual slow-fly wheel with an O.D. of 43 mm / 1.7". Put the wheel on its axle and add two wheel collars - mine were 4 mm / 0.16" thick. Then slip the cf wheel holders over the ends of the axle and fix everything to the main boom with 2 mm screws. Adjust the wheel collars so that the front wheel runs free.

The motor mount has undergone a change, too. The motor position is now offset 8.5 mm / .34" to the right of the centre line of the gyro - seen from behind. The motor thrust line is parallel to the main boom, when seen from above. This offset position compensates the effects of the prop-wash on the rudder.
(See here: https://www.rcgroups.com/forums/showthread.php?t=656504)

Because of the added rudder, the tail unit now consists of four parts, cut from 3 mm Depron. Cover the bottom end of the rudder with thin plywood and drill a hole through it, big enough to take a piece of outer bowden cable tube with a length of 34 mm / 1.3". This tube will serve as a control arm. Join the rudder to the fin with thin plastic strips. Stabilize everything with the cf strips and rods and fix the tail unit into the tail booms slot with 2 mm screws. Glue the plywood triangle that serves as a holder for the rudder servo into the notch made by the cf reinforcements and the balsa of the boom and mast. Mount the servo - I've used removable double-sided tape (someting called 'Tesa Power Strips' over here). Thread some twine through the tube in the rudder and connect the ends to the servo. Then adjust the rudder position and drop a bit of ca glue into the tube.

Build the rotor and pilot according to V4 instructions.

Mount the rest of your radio equipment. Adjust positions for a hang angle of -8. Roll tilt should be about 15 to each side, pitch tilt should be about 8 front and back.To compensate coning effects, I adjusted the rotor to have a basic tilt to the left - seen from behind - of about 2. Then I've mixed a bit of throttle onto roll so that at full speed the basic rotor tilt is practically zero.

V7 needs little more than half speed to fly horizontal (less than 2.5 A) and flight times of 7 - 8 minutes are usual.

I hope this makes sense to you. If not, feel free to ask.

Jochen

Video: https://www.rcgroups.com/forums/showthread.php?t=669112
Last edited by JochenK; Sep 12, 2007 at 04:30 PM. Reason: addition
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Jun 02, 2007, 11:56 AM
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Micromum V8 - the two-blader


When I decided to build a two-bladed rotor with a delta 3 hub, my original intention was to use this rotor as a temporary replacement for the teetering head rotor until I got my problems with the V5 airframe solved. That done, I modified my original hub design to get a better control response. Since the modifications were quite successful, I went on and build a new trike airframe for the two-bladed rotor - the V8.

Specifications of V8:
- rotor diameter: 840 mm / 33"
- rotor blades: 1 " Aerobalsa rotor blades
- AUW: 217 g / 7.7 oz.
- motor: Potensky POT 50, 30 g with mount, turning a 7x4 APC SF prop at 8400 rpm/min, using 3.9 A from a 3s lipo battery
- battery: 3s Kokam lipo, 350 mAh, 34 g
- Rx: 4 channel, 9 g, roll, pitch, motor
- ESC: 9 A ESC with BEC, 10 g
- servos: two 6 g servos with metal gears

Changes against V7:
- no rudder again
- mast rake has increased from 8 to 12
- rotor mast is about 20 mm / 0.8" longer
- two-bladed rotor
- new locations for the Rx and battery
- reduced roll servo throws


Building instructions

Combine the instructions for building the V4 airframe (https://www.rcgroups.com/forums/show...9&postcount=69) with those for building the V7 airframe (https://www.rcgroups.com/forums/show...&postcount=76), leave out the parts that are dealing with the rudder and battery pod - this has been replaced by a simple balsa wedge -, and you've got the V8 building instructions. I'm not going to repeat all this again and move straight on to the new rotor.

Use the instructions in this post (https://www.rcgroups.com/forums/show...5&postcount=40) to build the pivot joint and control arm. Since this is a two-blader, I'm now using two four-armed servo levers (Multiplex USA part # M85202, european part # is just 85202) instead of the usual six-armed levers to hold the ball bearings.Trim off the little rim on the top side of the levers to get a flush surface and use a moulding cutter with an O.D. of 6 mm and a flat cutting surface to scrape out the teeth from the hole on the bottom of the servo lever. Slip two ball bearings with an I.D. of 3 mm and an O.D. of 6 mm into these holes. Enlarge the four servo arm holes marked in the drawing to an O.D. of 2 mm.

Cut the flapping hinge out of a 0.5 mm / 0.02" gf sheet using the drawing as a template. Drill the holes for the blades (2 mm) and the center hole (3.2 mm) and make sure that they are symmetrical and aligned. Cut out the two hub reinforcements from 1 mm cf or gf and drill the center hole (3.2 mm). Put some double-sided adhesive tape on the flapping hinge where the reinforcements are going to be and put a 3.2 mm drill through the center hole of the hinge. Use the drill to center the reinforcements and stick them to the hinge. Slip one of the servo arms onto the drill, adjust its position and use double-sided tape to hold it in place. Use the enlarged holes in the servo arm as guides for drilling four 2 mm holes through the hinge and the reinforcements. Remove the adhesive tape and bolt everything together with 2 mm srews - not forgetting the second servo arm. Cut the shims from 1.5 mm / 1/16" balsa and use double sided adhesive tape to stick them to the flapping hinge.

Here's some advice on how to treat your 1 1/2" Aerobalsa blades:
https://www.rcgroups.com/forums/show...53&postcount=1
After finishing the blades, use a 3.2 mm drill to drill the mounting holes into the blades. Glue some pieces of outer bowden cable tube (flexitube) into the holes and cut off flush with the blade holder's suface. Take two 2 mm screws to mount the blades on the flapping hinge, using the inner holes. Cut off two pieces (13 mm / 1/2" long) from an inner bowden cable tube and cut a 2 mm thread on their ends. Use 2 mm nuts and bolt them into the outer holes of the blades. These plastic pieces are used as shearing pins should your rotor come into contact with something it shouldn't. Slip the rotor on the pivot hinge and use a 3 mm self-locking nut to hold it in place. Use some small washers to adjust the distance from the upper ball bearing to the self-locking nut to avoid friction in the head or trim down the rim holding the upper ball bearing.

Balance your rotor, then take the gyro out into the wind and let the roror spin up and the blades settle in their positions. After that, re-balance the rotor.

Put in your RC equipment and adjust the hang angle to -4. Use a delta mixer in your Tx for the servos controlling the rotor head and adjust the maximum roll tilt of the rotor to 9 and its pitch tilt to about 8. Use 55% exponential on roll and 50% on pitch.

Flying the two-blader is a bit more anbitious than flying the three-blader, it's like moving on from a station wagon to a sports car (compare the max. roll tilt of V8 to that of V7). If you control yourself, nothing much will happen, but when you try something fancy, you ought to know what you're doing. The last few millimeters of your roll stick travel are not meant to be used in normal flight conditions, they only need to be used in emergency recovery operations. With previous gyro experience you won't have trouble flying this one.

The normal back tilt of the rotor is meant to be used in light breeze conditions. If you've got no wind at all, you can slow down the gyro by trimming in a bit more back tilt, if the wind steps up, you'll be more comfortable with the rotor trimmed slightly forward.

A video of the V8 for your entertainment:
https://www.rcgroups.com/forums/show...49#post7559451

Have fun,

Jochen
Jun 02, 2007, 12:46 PM
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Lovely work Jochen
Jun 02, 2007, 04:47 PM
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Outstanding results Jochan!
regards,
Al
Jun 03, 2007, 02:16 AM
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JochenK's Avatar
Thanks for all kind comments here and in the video thread.

Yes, I'm a bit proud of the two-blader, especially after stumbling across the following facts: after one of my last flights, which lasted 6:10 minutes, I recharged the battery with 208 mAh. Which means that the average current draw on a nomal flight, as shown in the video, is just above 2 A. I think that's quite amazing with an 840 mm / 33" rotor.

Jochen
Jun 08, 2007, 03:56 PM
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JochenK's Avatar
Today I was able to do a ROG with the V8. I'd had a good flight with a good landing and I was even able to taxi the gyro back for a bit through the freshly mown grass, before the influence of the missing rudder made itself known. Although a light breeze of 2 to 3 bft was blowing down the runway, the rotor would not spin up during the ground manoeuvres, and I decided to investigate a bit.

I put the V8's nose straight into the wind, gave the rotor a flick, tilted it fully back and waited. After a few seconds the rotor began to pick up speed, and I eased the gyro slowly forward with the prop. As the rotor speed increased even further, I gradually released the back tilt of the rotor, increasing the forward speed at the same time. V8 looked as if she was becoming lighter and lighter and started to veer to the left. That's when I decided to make a go for it and gave full speed - and airborne she was, leaning heavily to the left, but flying. The juice left in the battery was just sufficient to get her back to the landing strip unhurt. Take-off distance was about 6 m / 20".

I have to admit that I was not able to repeat this performance with a full battery as the gyro always veered to the left, and without a rudder I couldn't do much about it. But it looked as if the two-blader spun up better than the three-blader in my previous attempts, and I think I'll have to build V9 with a rudder.

Jochen
Jun 08, 2007, 04:36 PM
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Nutten like a V8 Jochen, my Van has a V6 and it won't get off the ground !!!

Sorry.
Jun 09, 2007, 03:11 AM
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Hehehe !
Good one Dave, LOL!
Al

Jochen,

Keep at it mate, you are doing marvelously!
regards
Al
Jun 09, 2007, 03:55 AM
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JochenK's Avatar


Jochen
Jun 09, 2007, 07:23 AM
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Jochen, I've read through this thread a few times. I admire your articulated presentation and attention to detail. Especially enjoy your craftsmanship. Instead of the silly V8 comment I should have said thank you.
Jun 09, 2007, 05:59 PM
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JochenK's Avatar
David,

your comment caused a big grin to appear on my face, therefore it can't have been silly. Remember, were in this for fun, aren't we. And I think I may have misinterpreted the meaning of that smiley.

Jochen
Jun 10, 2007, 08:40 AM
Registered User
Jochen, your smiley was not misinterpeted, but I thought I should add a respectful note too. You're right, it's about the fun!
Jun 10, 2007, 04:55 PM
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JochenK's Avatar
David,

when someone goes respectful on me, I get really worried.

Jochen


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