Maiden flight lasted about 3 seconds

[Big A]

He is in Woking!!

[Optimist]

are you sure its not a tx setup problem using the right stick only does swash follow the stick? i.e push the stick forward the swash follows pull back swash tilts back etc.

swash definately moving correctly i.e. tilt forward towards nose when moving right stick up and towards tail when pulling right stick down.

[Boggy]

mmmmm strange one then!!

[scallybert]

Set the G5 up with 3d settings - which is Optimistic given that apart from Phoenix I have never flown anything except paper aeroplanes. Is one of the things I plan on changing now.

You didn't really give yourself a chance. So it may just be a smal hiccup put you in a situation you couldn't handle on those settings.

NB, with the basic setting, there are some issues around binding, but there's an easy workaround.

I have training gear which is why i could just bang it down when it was going pear shaped

Ok. Not sure how the damage got done, then. I reckon my training gear would save from quite a bad bang down.

question on the training gear is whether it is normal that the tail is a bit more twitchy when spooling up. Reason is i noticed that as i applied throttle the tail started wagging a fair amount - 1st time i shut it down thinking my gyro was reversed but after checking it was fine. My training gear is quite spring but presume that is the point.

I'd say not.

What mode is your gyro in, and what gain setting are you at ?

(Actually, what gyro ? You have an S9257 - how far out is the tail link on the servo arm ?)

This is doing my head in - don't mind the crashing (although more than 3 seconds would have been nice) its not being able to work out why which makes me more nervous.

I can relate to that.

I think we've found a coupe of clues so far.

[Optimist]

For the tail servo using the second ball (changed the push rod to a carbon fibre one to get better movement). Using a CSM 720 gyro. Not sure what you mean by gain setting. On my Dx7 i cannot see the setting. Could this be the problem?

[machasm]

What channel is the gain set to?
It should be channel 5.
Is channel 5 set to the gear channel?
If so change the ATVs of channel 5 to increase/decrease gain.

[scallybert]

For the tail servo using the second ball (changed the push rod to a carbon fibre one to get better movement). Using a CSM 720 gyro. Not sure what you mean by gain setting. On my Dx7 i cannot see the setting. Could this be the problem?

I use a DS760, so we can't directly compare settings.

However, (from memory) my gyro gain is 50%, and I have the linkage ~12mm from the servo shaft centre. This worked fine for gentle hovering.

In 'heading hold' or AVCS mode (the gyro keeps the heli pointing in the same direction), too high a gain setting will make the tail wag. Which may sound familiar.

On most (?) gyros, there are 2 inputs to the gyro. One is the rudder, the other is the gain. Gain sets mode (>0 HH, <0 rate), and the actual value affects the gyro responsiveness/sensitivity/etc.

There are various different ways of controlling the gain channel, but on a DX7 it's typically the 'gear' channel. The gear switch toggles this. The easiest way of setting the two values is to set the end-points via 'travel adjust'. You can see the values in 'monitor'.

HH mode is good, and was easy to set-up on a DS760. If the tail seem to be wagging winding down the gain might be a good idea.

However, I'm not sure that CSM gyros set up in this way.

[Optimist]

I use a DS760, so we can't directly compare settings.

However, (from memory) my gyro gain is 50%, and I have the linkage ~12mm from the servo shaft centre. This worked fine for gentle hovering.

In 'heading hold' or AVCS mode (the gyro keeps the heli pointing in the same direction), too high a gain setting will make the tail wag. Which may sound familiar.

On most (?) gyros, there are 2 inputs to the gyro. One is the rudder, the other is the gain. Gain sets mode (>0 HH, <0 rate), and the actual value affects the gyro responsiveness/sensitivity/etc.

There are various different ways of controlling the gain channel, but on a DX7 it's typically the 'gear' channel. The gear switch toggles this. The easiest way of setting the two values is to set the end-points via 'travel adjust'. You can see the values in 'monitor'.

HH mode is good, and was easy to set-up on a DS760. If the tail seem to be wagging winding down the gain might be a good idea.

However, I'm not sure that CSM gyros set up in this way.

Ok, read up about gain and now think i may have made a blunder earlier.

When i setup the CSM, the only way to enter setup was to set the gear channel in the DX7 (which is plugged into gain on gyro) as gear - thus allowing me to enter setup using the gear toggle switch.

When i set gear to gyro i cannot enter setup but i am now in heading hold which means that tail doesn't center after applying rudder and then returning to center but will center once i move the nose in the direction i applied rudder. Set the gain in Dx7 to 35 now.


Question is what is the impact of rudder not centering once you release the stick? Also, what is the difference between gain and rate mode?

Anyway, had a bit of luck with the 9257 in that only one of the mounting points was bust so by swing the servo around i can still use it. Will order a new case anyway i think.

thanks for the help.

[scallybert]

I've got no experience with CSM kit.

Also, what is the difference between gain and rate mode?

Rate mode vs heading hold mode ?

In rate mode, the pilot mainly controls the tail rotor pitch, but the gyro modifies your input to reduce the yaw rate at any time. Like velocity damping, or -ve velocity feedback.

In HH mode, the rudder input specifies the desired yaw rate (centre is zero), and hence the desired orientation. The gyro controls the tail rotor pitch to put the heli in that orientation.

I think with CSM gyros you can mix & match these values to create your own modes, whereas others tend to be one or the other. Maybe...

In rate mode, the 'gain' is likely to be the amount of -ve velocity feedback that's input to the rotor pitch.

HH mode is likely to be more complicated, but the gain is likely to relate tail rotor pitch to the 'error' between desired & actual orientation. There's likely to be -ve velocity fedback, plus other stuff as well.

[cjcj1949]

Heading hold and rate mode are very similar. Both reduce the effect of external forces. A rate gyro measures the rate in degrees/second caused by external forces and uses feedback to reduce that rate. Heading Hold does much the same except that it logs the angle that the heli has turned and in effect keeps a log of it.

It knows the rate of turn and if you know how long that turn has taken you can work out where you are. I.e. A turn rate of 5 degrees a second for 5 seconds means an error of 25 degrees.

It then uses feedback to reduce that error to zero. So it looks as though it knows where it is and somehow keeps that same heading. In reality it doesn't know where it is, only the heading error produced by external forces and by feedback it reduces that error to zero.

Only the cheaper heading hold gyros use centre trim as zero rate demand. The better ones set the zero rate demand to whatever it sees on powerup or reinitialisation.

On powerup all gyros have to calibrate the rate sensor, ie find the voltage that represent zero rotation. Unforunately this is very temperature sensitive and all gyros will have an error as temperature changes and the assumed zero rate voltage is no longer correct. Hence the advice to let the gyro reach ambient temperature before switching on,and then waiting a few minutes for the rate sensor to reach a stable temperature due to the heating effect of the gyro's electronics. Then you can command the servo to reinitialise or for more basic gyros you can power cycle.
If you move a heli with a gyro in HH mode, the gyro will see that as an external force and as soon as it takes off it will correct the error and go back to where it was pointing when it landed. This error can be removed by switching into rate and only going back to HH just before takeoff.

The SMM gyros have thier components on one slice of silicon and this allows the rate sensor output voltage to change less with temperature change.

The gyro gain is a measure of the amount of force used to feedback. Too high a gain is the noise you get when the volume is turned up to high on a mic

Sorry, I was trying to keep it simple.

Chris

[scallybert]

Training Gear

I knocked up a quick description of my training gear:
http://www.rcheliaddict.co.uk/f22/training-gear-19385/