JR DS 8915 servos

Written by Trev Burley Friday, 14 August 2009 13:15

I bought these from Midland Helicopters a few days back for use in my T-Rex 600e, they weren't in stock so took 2 days to arrive at my work rather than the next day delivery which is pretty fast considering they had to be ordered in. The cost of each servo was £125.99.

Installation:

Installing the servos on my cyclics required a little hollowing out of the frames since the servos are a little wider than standard servos and also a fair bit deeper. The length was the same so I had no trouble with locating the screw holes. My 9255's were already spaced away from the frames to improve the geometry so there was no issue with the depth of the servos on my machine. I used a single Quick UK servo plate as a spacer - I believe the Align kit is supplied with plastic versions.

When setting up it's very noticable how accurate these servos are. For the first time I was able to set up a heli without _any_ subtrim on the transmitter or CSM Cyclock. All my end points were also perfectly matched which is very unusual. So far so good...

I copied my old 9255 pitch ranges so the comparison would be accurate:

• Collective: 12 degrees
• Cyclic: 9 degrees

In Flight:

I've put a few flights on these and they are justifying the price to me. I am running them on 6v using a 5A regulator in my 600e. They've replaced some fairly old 9255's which are still in good working condition. First impressions were that there was no _major_ difference in noticable speed from my 9255's which I was also running on 6v. This doesn't worry me as in the past I have noticed that there is an optimum balance of torque / speed that will make the servo 'feel' fast. Not enough torque and the servo won't get up to speed too easily.

The model sat happier in the hover indicating that either there was less play in the servos or that they were more accurate at updating the servo position (possibly due to the amount of torque). The 9255's used to fidget on the cyclics and pitch during the hover and pirouetting hover quite a bit - the 8915's seemed to have a simulator (Phoenix) type feel to them.

When doing crack moves I always believed that I couldn't actually do it (I could on the sim, just not a real model). My heli just wobbled rather than doing crack. With the 8915's it's a piece of cake, it will do it without much effort at all. I believe this is the torque at work here...

The whole in flight precision improved dramatically, I found that counteracting for wind was a lot easier and also my moves became a lot more controlled without any changes in my ability. Moves like the singapore sling just became effortless whereas before they had a bit of a sideways weave to them.

Pros:

• Incredibly accurate
• Good amount of speed and torque
• Very little slop
• Good quality parts

Cons:

• Price, a little expensive when you have to buy 3 of them, about £90-£100 maybe a little more realistic
• Large size means dremelling frames and spacing out the servos.

Conclusion:

These are very nice servos to fly with and setup. I believe my setup time was halved compared to my 9255's. A little bit disappointed with the price but not the product. Overall I would recommend these a a good buy if you are wanting of more accuracy and performance. Thumbs up from me.

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