I’m working my way through the Traditional Helicopter Swashplate Setup section in the Aruducopter web site, using MP, and need some help with the stabilised collective curve settings please.
I’ve set up H_COL_MAX, _MIN, and _MID to give +12 degrees, -3 degrees, and -1 degree, as suggested in the text. The values come out as 1706, 1520, and 1490.
When I move on to the stabilised collective curve section it shows a graph with _MIN, _MID, and _MAX on a straight line, which is not the case if one goes for the suggested -3 degrees to +12 degrees setup. So do I then set IM_STAB_COL_1 at 80% of the way between _MIN and _MID (i.e. 1514 using my data above), and then IM_STAB_COL_2, _3, and _4 at the 40%, 60% and 80% points between _MID and _MAX (i.e. 1594, 1631, and 1668 using my data)?
Edit: I’ve just realised that in MP the note for parameters IM_STAB_COL_n says they are “… a percent of the collective range given by H_COL_MAX minus H_COL_MIN”. In my case that would make IM_STAB_COL_1 greater than H_COL_MID, which can’t be right.
Allan, where are you seeing a graph? Is this in Mission Planner?
Also what version of code are you using? The names you are using for the Stabilize collective curve are pretty old. I’m thinking they are from version 3.6? Much of this has been updated in the latest version and the heli screen that has the graph of the curve have been removed and replaced with a new heli screen. There have been some significant improvements in the code.
Thanks Bill (again!). The graph I’m talking about is near the bottom of this page in the Ardupilot Traditional Helicopter setup guide. I’m using Arductopter v4.1.1 heli, and I did notice a slight difference between the web-based documentation and MP when it came to the names of some of the parameters (e.g. IM_STAB_COL vs IM_STB_COL).
No. You are using the most up to date info. I’ll have to get the graph fixed with the correct parameter names. Thanks for pointing that out.
Ok. Looking at that graph further, I see your confusion. Disregard the labeling for H_COL_MID on the graph. That is not correct. H_COL_MID is NOT used in the determination of collective stick input to collective swashplate position output. Sorry. I will get that corrected ASAP.
So I just set IM_STAB_COL_1 , _2, _3, and _4. to 40, 70, 80, and 90% and Arducopter will reference them to H_COL_MAX and _MIN, ignoring the _MID value?
When I go to the IM_STAB_COL parameters in MP the default value for _1 is 0, and for _2 is 40%. Can’t remember offhand what the other defaults are, but presumably I simply edit them to the above-mentioned values.
So I don’t understand. You set up the collective range with H_COL_MIN to H_COL_MAX as -3 to 12 deg. So that means with the set up you have for collective in stabilize flight mode, with your collective stick on the lower limits you would be at 3° of collective pitch on the blades.
I don’t think that’s what you intended. I think you would want zero as the value for the first stabilize collective parameter. You may want to modify the upper end of the stabilize collective parameters so that it doesn’t go all the way to 12°, but that’s up to you. The middle to stabilize collective parameters are designed to give the user the ability to flatten the collective curve near the midpoint of the stick.
My H_COL_MIN is -3 degrees (negative). I don’t understand why that wouldn’t be what I want, for that’s the minimum pitch I’ve always flown with this heli (and my others), and my understanding of the guide document is that’s what’s suggested there too.
I accept that something a bit less than 12 degrees could be good for the upper parameter, but I don’t understand why the lower one should be zero – wouldn’t that leave Arducopter unable to go to negative pitch and, hence, unable to counteract unexpected wind gusts creating lift?
I’m saying that the set up of your min and max collective values with the parameters H_COL_MIN and H_COL_MAX are fine. The problem is your stabilize collective curve as the values you’re using such as 40% for the H_STB_COL_1 value would result in your stabilize collective being at 3° of positive pitch. that’s what I’m concerned with.
The value of H_STB_COL_1 should be zero if you want your collective blade pitch at minimum collective stick in stabilize mode to be -3°. Value of H_STB_COL_4 should be 100 if you want collector blade pitch at maximum collective stick in stabilize mode to be 12°.
Thanks for your patience. So that’s why the default for H_STV_COL_1 is 0. I’m beginning to understand it now, so I’ll set H_STB_COL_4 to something less than 100% to give me maximum pitch a bit less than 12 degrees, and set the other two values at equal intervals inbetween.
Edit: In the paragraph before the graph, the guide says that H_COL_MID should set the blades to 0 degrees, or maybe -1 degree. That gives a straight line, like the blue line on the graph, only if upper and lower limits are the same number of + or - degrees, like the blue line on the graph. But my base curve is -3 to +12 degrees, so the H_COL_MID figure to give zero degrees is nowhere near mid way between _MIN and _MAX. I guess that what I’m trying to achieve with the IM_STB_COL figures is create a curve that looks like the red one on the graph, with hover pitch (probably +3 to +4 degrees) at mid stick on the Tx and H_COL_MID at 0 to -1 degrees. Is there any way to check the actual pitch on the bench, or do I just accept the default values for IM_COL_STB (0, 40, 60, and 100) and see how it flies?
Truthfully, if your min and max collective blade pitch is -3 and 12 deg respectively, just leave the H_STB_COL params at their default values. THat way our stabilize collective pitch curve will match the straight line from min to max. What is shown in the graph is more of a sport setup where the user would want -10 to 10 deg in acro mode (blue line) but then only -2 to 8 deg in stabilize (red line). The H_STB_COL_2 and H_STB_COL_3 are used to move the collective blade pitch so when your collective stick is centered, the blade pitch is around hover blade pitch. You could also use it to flatten the pitch curve around the hover blade pitch. This would only be for the Stabilize flight mode.
For you first flight, leave the stabilize curve at default and see what you think. You can play with it from there but you may have a better understanding at that point.
As far as checking blade pitch values, there is a parameter called H_SV_MAN which lets you set the swashplate at the H_COL_MIN, H_COL_MID, and H_COL_MAX positions so you can check your actual blade collective pitch without the controllers interfering or affecting the measurement. As for the H_STB_COL values, you can see approximately where they will be by switching into stabilize mode with the aircraft pitch and roll attitude at zero. having the pitch and roll at zero just minimizes the controller inputs affecting your measurements.
Thanks Bill. I’m leaving the HB_STB_COL values at default. I’ve already used H_SV_MAN to initially set the MAX, MIN, and MID pitches, but I thought that the FC might affect the values. So, once I get the motor running I’ll just see how it feels in Stab mode before changing anything.