Sm Tall alk
by pat tritle You can reach Pat Tritle at 10313 Snowheights NE, Albuquerque, NM 87112 or via e-mail at
patscustommodels@aol.com
Mark Hadfield did a wonderful job building his 55-inch span Gull II. The model flies beautifully, and still shows strong signs of its free flight lineage in its stable flight characteristics. Model storage and transport is always a challenge, but Pat Ryan solved his problem with nothing more than a cardboard box (at right). Sometimes, you just can’t beat good old fashioned simplicity.
S
pring has sprung in our neck of the woods and the morning temps are becoming increasingly more tolera- ble for those of us who fly at the crack of dawn. Windy season hasn’t been all that bad so far and with that it’s shaping up to be a great start on the flying season. Now for those of you who haven’t quite fin-
ished setting up your latest creations, I thought we would look at a bit of wisdom along those lines from local modeler Greg Rullman. The whole concept here is to get the best mechanical advantage and most ac- curate centering possible from the servos.
Servo tips to fly by
Assuming that most of us are using com- puter radios now, the idea is to set up the servos so that, with the sub-trim in your transmitter zeroed, the servo arm is as close to neutral as possible with the pushrod per- pendicular to the servo arm. By using as lit- tle sub-trim as possible, the centering will be the most accurate.
Equally as important, your controls should be as close to the desired maximum throws
as possible with the end points at 100 per- cent. Now for those not using computer ra- dios, all this is a given and the same proce- dures will be followed to achieve those throws either way.
To get the throws you’re after with the least amount of load on the servo, the idea is to keep the pushrod on the servo arm as close to the inboard hole on the arm as pos- sible, while on the control horn, keeping it as close to the outboard hole as possible. There are two reasons to do it this way; one is the mechanical advantage, the other is accuracy in centering.
In terms of mechanical advantage, it’s all about leverage. The longer the servo arm, the harder the servo will have to work to move the control surface. On the other end, by us- ing a longer control horn, the surface will be easier to move through simple leverage. Where accuracy is concerned, a shorter servo arm is the best bet, as is a longer con- trol horn on the flying surface. The reason is that not all servos are created equal. Some definitely do center more accurately than others and the longer the servo arm, the
greater the inaccuracy will be. It’s all about angles; the shorter the arc, the less deflec- tion that inaccuracy will cause.
On the control horn end it’s just the opposite; the shorter the arm, the greater the inaccura- cy. That being the case, if you set up a long ser- vo arm and a short control horn to achieve your desired throws, the centering will be the least accurate and the control deflection will require the most mechanical effort.
Now getting back to computer radios: great stuff, but the sub-trim and end point adjustments should only be used for fine tuning, not to make up for sloppy or improp- er installations. The closer to zero sub-trim and 100 percent deflection you can get, the more accurately your system will function. These radios will also allow you to set up travel values greater than 100 percent. Be careful there, if you set up too much “over- travel” there is a chance that the servo will bind up and stick at full deflection, which in my personal experience has never turned out well.
One final word on centering accuracy. En- sure that your control surface installation is
John Patton spent a year building his Cessna Ag Truck (above). The model is set up with a brushless outrunner motor and 5-channel RC for some very scale “dusting.” John trimmed his model (at right) using custom graphics from Callie Graphics and from it has created a very striking color scheme for the Ag Truck.
44 JUNE 2014
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68