HIROBO EC 120
At the end of last year, I received an e-mail from Heli Proz offering some deals on scale helicopters. I had searched their site and could not find any scale helicopters so that explained why they were offering deals. No one was buying them as they could not find them on their site. I ended up buying a Hirobo EC 120 kit at about half the normal price.
This model was designed to be used with a 90 size glow engine and that was the first change that had to be made. I machined up a collett adaptor for the clutch and mounted an Actro motor to a metal baseplate. One problem I has was that I had no idea which motor it was so I didn't know what Kv it had. All I knew was it made enough power as it had similar power to an early 90 motor. I was going to use battery size to change the headspeed.
This is the mechanics with the motor mounted
In front of the mechanics is the Kontronik 55-10-18 ESC I used. Flight testing showed the model used 53 amp in the hover and the helicopter shut down after 4 minutes using 5800mAH batteries. I changed the ESC for another one which I found in my junk box which had better capacity and a built in fan
The beauty of the Hirobo kit is that the windows are all cut out for you and the woodwork is all glued in place. The all plastic fenestron runs at motor rpm so it will be doing 14500-15000 rpm. Once I had the mechanics fitted to the fuse I put 2 5S batteries in and checked the headspeed. With the throttle just cracked, it was dead on 1450 rpm, but if I opened it any more it was going to go way too high. I switched the 5S packs out for 3S packs and this time at full throttle I got 1400 rpm. I then tried some old 4S packs and at 80% throttle was on the nail at 1450. The current I measured was 53 amps so I decided I had better order a bunch of batteries and got a 5AH pack, a 5.8AH pack and an 8AH pack. They were all 30C packs from Hobby King so the price was pretty reasonable.
A quick paint job ensued. Actually I had big ambitions for the paint job but Joe told me to try something a bit simpler for my first multi mask job and I'm glad he did
I had made up one of my famous instrument panels
But when the doors are closed, the inside of the glazing panels are so rough, you can hardly tell there is a panel in there, never mind see all the detail.
Flight testing showed the model was superb to fly, but after 4 minutes it overheated the ESC. Fitting the power Jazz ESC improved the situation dramatically. At 9 minutes and still hovering, I got bored and gave up, and that was on the 5800 mAH batteries.
A 3 blade head system is now ordered and a new Stabilization system will find its way inside. More to follow