Goblin Speed - Turn down the heat!

[Mikey69]

Ok,

So as some of you know i'm new to Speed flying, having only just got my Goblin Speed airworthy and flying well. (I'm currently going through 'shakedown' flights to optimize Spartan VX1N settings, wind headspeed up and increase +tive pitch range).

My question is regarding heat generated by the power system, whih obviously i'm trying to minimize. I've been reading up on PWM frequenies, power rippling effects generating excess heat, best power level to run ESCS at, etc.

It seems that most ESCS perform at their best around 85 - 90% power. Is that correct?

My current Speed is setup is as follows:
12s, 24T (8.9 ger ratio) motor pinion, 535KV motor, YGE 320HV ESC, which theoretically yields:

44.4v x 535kv = 23,754 (max rpm) /8.9 (g. ratio) = 2,668 max. headspeed.

I'm looking for a governed headspeed of 2,600 rpm for speed runs. There really doesn't seem to be much 'headroom', especially given the usual 'losses', etc.

I'm thinking that a need to change the motor pinion to 25T (8.6 gear ratio), which will yeild a max. headspeed of 2,762, this would give me more 'headroom' with rpms to spare.

Do you think this would be a good move? Is it likely to generate less heat? etc.

I'm planning to run the heli on 14s at some point in the future. With it's current setup it would yield the following:

51.8v x 535kv = 27,713 (max. rpm) /8.9 (g. ratio) = 3,113, max. headspeed.

This seems like waaay overkill, as there would be far too much 'headroom'. I initially thought the system would generate less heat because i wouldn't be anywhere near max throttle/power until i read about ESC PWM/switching rates, etc.

If i change the pinion to 22T it will yield the following:

51.8v x 535kv = 27,713 (max. rpm) /9.8 (g. ratio) = 2,827 max. headspeed. This leaves a good amount of 'headroom without being excessive.

Again, do you think this would be a good move? Is it likely to generate less heat? etc.

I hope this makes sense?

If anyone could advise i'd be very grateful :-)

Mike

[john2kx]

Mike,

Since no one has replied to your questions, I'll give a stab from what I learned during my 100 flights of speed flying with a gaui x5 last season.

First, I always run with governor operating.

All the math (as you spelled out the formulas already) get you in the ball park. But, review of flight logs after 4 passes really tell you what is going on. I got this all wrong in the beginning by making as many passes as possible until my mah consumption alarm tripped. If you are going to compete, 4 passes is all you be allowed to make AND that must be performed in less than 3.5 minutes (if memory serves me right). Flying by mah consumed can leave you high and dry depending on where in the course you are when it activates. You could be left with not enough power to get back to the pad as well as really stressing your battery packs.

I learned to pay attention to PWM (or duty cycle) and adjust pitch and head speed to be near 100% while in the speed run. While at the same time making sure HS does not drop more than 50 rpm or so.

Battery voltage: perhaps one of the most important pieces of data you can have. If you are dropping below 20 volts per pack (in a 12S system or 3.3 volts per cell) on your 1st, 2nd or 3rd pass, something is wrong. Too much pitch, bad batteries, wrong gear ratio could be the cause. As I mentioned in reply to one of your other posts, the batteries are the what I would call the weak link in a speed heli, not so much the heat of components.

Speaking of heat, I use a Kontronik Kosmik and they suggest using 100C as maximum operating temperature. This is the only measure of temperature I have a alarm setup for.

I have read in a few posts that batteries should be kept below 114-117F (again, from memory). Checked my packs after landing and pulling canopy off which required several minutes and my IR gun indicated I was always in that range.

Motor temps taken with IR gun seemed to be all over the place and not found to be useful at all by this method of measuring.

This all leads up to a point. Running on the edge as we do with speed helis requires the proper equipment to capture key parameters. One could rely on a esc that records flight data on a sd card which can be reviewed after flight but I'm a firm believer in live data being delivered to pilot while in flight. Example: after performing 50 or so flights with my R5, I decided to install a new more powerful motor. Several flights made and all was well. I started increasing HS and all was good. Then started going up in pitch from 13, then 14, then 15. I reached a point where I tripped main pack voltage <20 volts per cell on my first pass. Bad packs? I tried another set with the same results. With live data I believe I saved the machine and or the packs from permanent damage. Backing off the pitch one degree and reducing HS 200 rpm put me back where I could make 4 passes without tripping any alarms, and batteries appear to have not been damaged.

In closing, I would not focus so much on temperatures so much and focus more on maintaining rpm thru the run with battery voltage that does not drop out to dangerous levels. Same goes for a targeted HS. You will have to experiment to find out what works with your choice of equipment. Once you get that under control, you can focus on flying smooth and coming up with good entry/exit techniques and maximize your speed through the gates.

John

[Mikey69]

Hi John,

thank you very much for taking the time to compose such a detailled response. It's all very helpful. I did in fact visit your older post as you suggested. I saved it to my desktop for future use. I now have a much better understanding of the issues of power/torque/voltage sags/batteries, etc. I'm very grateful.

i a definitely going to invest it telemetry/data logging. Once again it's all new to me, so i need to wrap my brain around all of that. I'm currently running a Futaba 14MZ and i would like to stick with that, so i will need to find a system that is compatible.

Initial research has led me to Jeti, Powerbox, and Eagle Tree thus far. But i haven't had the time to really look into any of it as yet.

I'v now got my Goblin Speed running at a governed headspeed of 2,350 at 90% throttle on 12s at 12.5 deg. pitch, I don't really want to push the syatem any further until I've decided whether to change the motor pinion as discussed in my initial post. If i did it would yield higher headspeeds at lower throttle which would give me some throttle/power 'headroom', so there's some 'left over', which i wouldn't need. I'm definitely leaning towards the change. it seems to make sense to me.

So far all has gone very well with test flights with no concerns noted. But i'm not really pushing the system as yet.

My next plan is to run a series of test flights increasing the max pitch 1 degree at a time per flight until i reach 16 degrees.

Only then will i really know how the power system will hold up (especially the batteries),

Many thanks,

Mike

[john2kx]

Mike,

Understand that switching radio brands is a big deal as I flew JR for about 25 or so years before switching to Jeti. Telemetry was the true selling point for me. Nothing to do with speed helis but for so many years I launched my models with little more info than signal strength and tx voltage. Kind of like driving your car without any gauges. The introduction of live data (and lots of it) had me on the pre order list with jeti for a ds16.

You could keep your futaba and use a esc that creates flight logs to be reviewed after flight as a stepping stone to having critical points of data vs nothing at all.

I would be really nervous going above 14.5 degrees of pitch without some form of data recording. With my R5, things started to change at 15+ (the voltage drop on first pass described earlier) and I never tried 16 degrees.

Like yourself, I wanted to try 14S in hopes of more speed and less strain on the power train but could not get my hands on 7S packs of the right size and mah. You have much more room than I do with your machine and should have more choices to select from.

Funny in a way that your original focus was on heat. I had the same concern after installing my fuse and was really surprised at how warm things were compared to flying pod and boom helis. One of my first mods was to install naca ducts in the nose. Flight logs did not indicate much change in esc temp from memory.

You may find as you go up 2 or 3 degrees in pitch (from where you are now) that flight characteristics change. Hopefully, retreating blade stall followed by violent pitch ups have not found you.

I would take increasing pitch very slowly, meaning I would fly a half dozen or so flights, preferably in different wind conditions before increasing pitch again. More than likely, as you go faster you will need to tune your fbl unit to maintain steady flight through the pass.

For me, I use a jeti radio/rx, Kosmik esc, jlog 2.6 to translate telemetry data from esc to tx and a power box gps II for measuring speed. This system has worked flawlessly. I can have the tx announce when I'm out of the box (for example, gps knows when I'm 200 meters away from center stage as well as announcing when to pull vertical at the other end) .

John

[Raptorapture]

Originally Posted by john2kx

This system has worked flawlessly. I can have the tx announce when I'm out of the box (for example, gps knows when I'm 200 meters away from center stage as well as announcing when to pull vertical at the other end)

Now That is a nice feature!

[Mikey69]

Hi John,

It's very good to hear from you again :-)

Thank you for providing even more very useful information. I've saved every post you've written to my desktop for future use.

The reason i got caught up in the whole heat thing is because i was very surprised and concerned by just how hot the Xnova Speed motor got running a headspeed of only 1,700RPM, 12.5 pitch under 12s power, whilst merely hovering around. I was concerned that it was abnormal or something. But apprently it's not so i'm happy :-)

I flew the Speed again today so i could tweak the gyro. It's now up to a headspeed of 2,350rpm and I was actually flying, as opposed to hovering. So the shakedown flights are going well.

I'm going to change the motor pinion to give me the additional headspeed and i'm going to keep pitch as it is for now. I want to make sure i'm happy with how the heli/power system is performing before i start increasing the blade pitch.

I'm going to heed your advice and not go above 14.5 degrees for the time being. I will probably save going above that for when i'm running on 14s and have some kind of flight telemetry system inatalled.

My main concerns are to get the heli performing at it's best and then to get lots of flying practise in. Speed flying is a whole new ball game to 3D. But damn it's fun!