Exponential for beginners?

[Steve Hill 5]

.,I have driven most means of transport available, from tanks to light aircraft, and there is one thing they have all had in common. Their controls were always linear. Doesn’t matter whether it was a push bike or a racing yacht, equal inputs always resulted in equal outputs. The only time that was not true is right on the ragged edge when a small input could have a major, often unwanted, effect. The reason is obvious, predictability. Your body’s muscle memory knew that this input always produced that result.

Which is a long winded way of asking why we teach new modellers to use exponential, where the same thumb movement can produce wildly differing results, at a stage in their development when above all else they need stability and predictability.

[john stones 1 - Moderator]

I don't teach learners to use expo, I teach then to fly and develop ability to control safely, reduced movement mechanically after test flys, if needed, movement is set up to suit them, not me.

Later in their development, if they require expo to suit their style or needs, the choice is there.

[Denis Watkins]

As John says, don't add to the workload of the novice

A suitable stable trainer, set up and trimmed is enough

As skills progress, then give them the option to use other features

Expo is really the last on a long list of useful information for the novice

[Jon H]

Agreed. A trainer should be set up so that it is sufficiently docile to not frighten the learner but should also be representative of something they will fly later. I dont believe in making learning to fly artificially easy as the student will only have to learn it all again later when they fly something else. Its better to get the basics right from the start and there are certain things that they just have to knuckle down and learn. Expo is a useful tool when used correctly but i would say that in probably 90% of cases it is used incorrectly to cover up a different issue (usually excessive rates) and in many cases it can make models virtually uncontrollable.

[Gary Manuel]

Posted by Steve Hill 5 on 29/04/2019 15:59:11:

.,I have driven most means of transport available, from tanks to light aircraft, and there is one thing they have all had in common. Their controls were always linear. Doesn’t matter whether it was a push bike or a racing yacht, equal inputs always resulted in equal outputs. The only time that was not true is right on the ragged edge when a small input could have a major, often unwanted, effect. The reason is obvious, predictability. Your body’s muscle memory knew that this input always produced that result.

Which is a long winded way of asking why we teach new modellers to use exponential, where the same thumb movement can produce wildly differing results, at a stage in their development when above all else they need stability and predictability.

I would argue the other way (because I'm in an argumentative mood) that expo IS needed in order to make the controls feel linear. A rotary servo with no expo applied will always be more sensitive around the centre (with the arm at 90 degrees to control) purely due to geometry. Expo is needed to compensate for the geometry if one is after a linear feel.

Whether we should be teaching newcomers to use expo is another matter. They have enough on their plate just keeping a model in the air.

[Frank Skilbeck]

Expo maybe required to give a linear response from a model. Back in the day before computerised radios, trainers would be set up with small control surface movements so they were not overly responsive (like Jon notes above)

On one of my trainers, I have the buddy switch set to bring in low rates when the control is passed to the student, but high rates back to me so if I need it to avoid a ground/tree incident it's there

[john stones 1 - Moderator]

Well I'm never argumentative as you well know.

Every servo needing expo to deliver linear movement, hours spent on the task achieving said wotnot and graphs to prove said thingy, or fly and develop your own custom built link, between your grey matter and the two opposing doodahs on your hands, I'll take the later please.

[Gary Manuel]

Don't disagree John.

Just answering the question asked by the OP.

[john stones 1 - Moderator]

Posted by Gary Manuel on 29/04/2019 16:56:59:

Don't disagree John.

Just answering the question asked by the OP.

I do apologise, I thought we where in the argument room.

[PatMc]

Posted by Gary Manuel on 29/04/2019 16:47:08:

. A rotary servo with no expo applied will always be more sensitive around the centre (with the arm at 90 degrees to control) purely due to geometry. Expo is needed to compensate for the geometry if one is after a linear feel.

The fact that the control surface horn is almost always sized to gear down the control surface's angular movement increases this centre biased sensitivity.

[Gary Manuel]

Posted by john stones 1 on 29/04/2019 17:00:18:

Posted by Gary Manuel on 29/04/2019 16:56:59:

Don't disagree John.

Just answering the question asked by the OP.

I do apologise, I thought we where in the argument room.

No you didn't...

[jrman]

Posted by john stones 1 on 29/04/2019 17:00:18:

Posted by Gary Manuel on 29/04/2019 16:56:59:

Don't disagree John.

Just answering the question asked by the OP.

I do apologise, I thought we where in the argument room.

No you didn't...

I'm sure he did.

[Steve Hill 5]

Thanks guys. You have helped clarify my own thoughts. Expo is fine if you need it, pointless or dangerous if you don’t. As John says, a learner needs a decent, stable trainer. When he/she gets more advanced, then the decision can be taken to use expo or not.

[Brian Cooper]

Expo is not sort of strange, dictatorial religion which needs to be slavishly worshipped. Nor is it to be rejected out- of- hand because "We didn't have it 50 years ago". . . If a model needs expo to make it fly more smoothly to control inputs, then it should have it regardless of whatever the model is, or whether the pilot is a world champion or a complete novice.

The technology is there to make life easier. . . . . . Use it.

B.C.

[john stones 1 - Moderator]

"50 years ago" Who you quoting Brian ? And who's dismissed anything out- of -hand ? ....people have given opinions and the reasons for holding them.

Others will post different opinions, the technology is there to do it.

[ASH.]

I am a firm believer in Expo... Not much, just 10-12%. It's almost negligible but it helps smooth out the centre ever so slightly. I would always recommend it to all. And newbies need not fear it. I don't fly 3D.

[SIMON CRAGG]

Posted by ASH. on 29/04/2019 22:56:43:

I am a firm believer in Expo... Not much, just 10-12%. It's almost negligible but it helps smooth out the centre ever so slightly. I would always recommend it to all. And newbies need not fear it. I don't fly 3D.

Me too. Usually teach with 30% dialled in. Especially helpful with a nervous FNG. Over many years, I have found that they progress much better with it, than without it. I always carefully explain what it is, and how / when it can be adjusted as the student progesses.

[Nigel R]

If your control surface moves 15 or 20 deg, whilst servo moves 45, you have non-linear.

Moderate expo brings it back a bit closer to linear.

It is a simple transmitter fix for a complex mechanical issue.

If you like having a model more twitchy at the centre than it is at the extremes, crack on without it.

Personally, I like expo.

PS I am not here for the argument room or disagreements, I am looking for the cheese shop.

[extra slim]

People I have taught struggled with left and right!!.. rates discussion blows their mind..expo is like rocket science!!.. I tend to look at how they are flying.. adjust rates and expo accordingly for them (without telling them), and have a separate setup for me when I take back control... only down the line do I start explaining... I just found it less hassle..

[Steve Hill 5]

Disagree, Nigel. If your servo moves 20 degrees while your output arm moves 10 degrees, you still have linear - and therefore predictable - movement, but at a reduced rate. My original post came after visiting another club where I saw a new flyer on his first flight being told he needed “at least 40% expo, and 50% may be better”. Not surprisingly he took his model home in a carrier bag

[Don Fry]

Arrrrrrrr Steve, but who told him? If you listen to to an idiot, that makes two idiots, when I learn maths.

[Denis Watkins]

Posted by Steve Hill 5 on 30/04/2019 13:53:13:

Disagree, Nigel. If your servo moves 20 degrees while your output arm moves 10 degrees, you still have linear - and therefore predictable - movement, but at a reduced rate. My original post came after visiting another club where I saw a new flyer on his first flight being told he needed “at least 40% expo, and 50% may be better”. Not surprisingly he took his model home in a carrier bag

Agree with you Steve, a novice with a trainer, no expo

Discuss expo when they get an extra 330

[Nigel R]

"Disagree, Nigel. If your servo moves 20 degrees while your output arm moves 10 degrees, you still have linear - and therefore predictable - movement"

That's not how geometry works.

For a control horn twice the length of the servo arm,

60 deg servo movement (i.e. absolutely full throw) equates to approx 25.6 deg control surface movement - under half the servo movement.

10 deg servo movement equates to 5 deg control surface movement. i.e exactly half the surface movement.

Granted, not far off linear, but, not linear. A mild dose of expo will bring things back to something very very close to linear. It will not make things unpredictable. Large expo will have an obvious effect on things and go beyond "back to linear".

Argue if you wish, the maths says otherwise.

[Former Member]

[This posting has been removed]

[SIMON CRAGG]

Posted by Andrew Ray on 30/04/2019 14:35:32:

This would have been a non argument when I learnt to fly, we didn't even know what rates were let alone expo because they hadn't been invented. The model was set up appropriately so we didn't worry about non linear movement as it was not noticeable.

Edited By Andrew Ray on 30/04/2019 14:36:15

Me too.

Just grateful that it went up.............and came down. Then we went to the pub.

Simple really.