Author Topic: KR timer rpm setting advice please (Read 3139 times)

Electric George · « **on:** July 20, 2022, 03:46:46 AM »

Hi All,
I will hopefully maiden my Banshee sometime in the next few weeks and I am about to set up the KR timer and check everything with the Watt Meter and Tacho.
My electric set up is: Emax2820/07 919kv with 50amp esc, 4s 2200 lipo, APC E 11x5.5 prop.

What rpm should I set the KR timer to?

Should I start at gain 1 for first flights and then move up from there if required?
Many thanks.

Frank Donnelly · « **Reply #1 on:** July 20, 2022, 06:46:26 AM »

The optimal RPM depends on a lot of other variables such as the weight of the plane, line length, airfoil, wind conditions, etc. But I think we can get you in the ballpark. The Banshee has a relatively thin airfoil so it may have to carry a little more speed. I have 2 planes setup with a KR Timer. One of those is a Trophy Trainer with a Cobra2826/930KV motor, 61 ft lines, weighs 47.9oz, 11.5x6 prop. The RPM is set to 8,800 which gives a 5.2 sec lap, and good line tension overhead in up to about a 6mph wind.
I would suggest you start with more RPM than you need and work down. Say start at 9,200. Then keep working down until the overhead line tension starts to fall off. (Keep in mind that a lot of other factors influence overhead line tension).
I have a 14 pole motor so 1 button click on the programmer changes the RPM about 100. Yours may differ. On windy days I usually go up a few 100.
I think it’s fine to set the gain at 1 and work up from there. In my case I settled on 4.

John Rist · « **Reply #2 on:** July 20, 2022, 08:06:15 AM »

If it's a new KR timer the factory set default for gain is a good starting point. I think this may be 4. Starting point for RPMs should be around 9K rpm. Be careful when running the setup on the ground. When the airplane takes off the motor unloads and the current goes down. Extended ground runs can fry a motor. By the way you can use a smaller prop on the ground to set RPM. With the KR timer prop size has little effect on RPMs. A small props reduces load keeping the motor safe. For checking run times and startup times no prop works for me. Good luck. You will love the KR timer.

jerry v · « **Reply #3 on:** July 20, 2022, 10:29:14 AM »

With this prop set 10000 - 9600 RPM on the ground.
Gain can be anything in the middle - 4 or 5.

Jerry

Motorman · « **Reply #4 on:** July 20, 2022, 10:41:25 AM »

First flights should be short and slow. The 11-5.5 at 10K on a Banshee will be a rat racer. Set it at 8,000 for a 2 minute flight. You'll get two test flights per battery and quickly see where you need to go with the rpm. Don't over heat anything or stress your batteries trying to save time.

Motorman

John Rist · « **Reply #5 on:** July 20, 2022, 12:57:13 PM »

KV at 919 x 4 cell @ 14.4 = 13,000 max rpm. The 8k tp 9K suggested should be spot on. This will allow good head room for good RPM control.

Electric George · « **Reply #6 on:** July 21, 2022, 02:30:27 AM »

Thanks everyone for your replies and very useful information.
Reading through I realise I have made a mistake with the kv - it is actually 850kv. So 850x 14.4 = 12,240rpm.
I will set RPM in the suggested range of 8k-9k. I was thinking that a fox 35 has the spec of 9500rpm on a 10x6 and so I was going to set just below this for the first test run but thought best to check on here first.
I always test my set ups using the Watt Meter and Tacho and running no more that 10 seconds. I then ensure the readings are in range with no chance of burning up anything.
Before flying I will check I have the right ball park figure in terms of Watts for the suggested RPM range of 8k to 9k and as it is a new model I will keep the flight short.
I read that 11 watts per ounce is the figure to aim for? That would be 42.5 ounces x 11= 467.5 watts or 176 watts per pound which seems good power as my Flite Streak performs well at just under that.

Thanks again, I feel more confident to give it a short ground run and set it up now.

jerry v · « **Reply #7 on:** July 21, 2022, 06:16:16 AM »

George,
RPM is just a tool to make proper lap time. You didn’t specify the line length. If it’s 60 ft, then 11x5.5 prop will work 10k plus to make 5 seconds per lap.
Having 850 kv motor - it’s a bit low kv for this prop. ESC will run it on the extreme end of throttle . To make better settings it have to be bigger prop - 12x6 or even 13x 6.5 on 850 kv. Now, it will be too big for 42.5 oz model, and too much capacity consumption for 2200 mah battery.
The solution can be done by using higher kv motor. Good choice can be Cobra 2820 970 kv on 11x5.5 prop. Or Arrowind 1100 kv from Brodak on 10x5 or 9x5 prop. 2200 mah lipo is on the edge of limit for 5 min flight.

Jerry

Ken Culbertson · « **Reply #8 on:** July 21, 2022, 07:55:00 AM »

Quote from: jerry v on July 21, 2022, 06:16:16 AM

Good choice can be Cobra 2820 970 kv on 11x5.5 prop...... 2200 mah lipo is on the edge of limit for 5 min flight.
Jerry

I concur with this arrangement. I put 200+ flights on a Twister (Banshee's brother/sister?) on that motor and prop using a set of 4s 2200 batteries. It runs them down to around 16% and I cut my normal 5:40 run time to 5:30, but they lasted 50 cycles and still working. I do store my batteries in a refrigerator, and I did run them back up to 30% for storage. Better choice would be a 26-2800 battery. It has been a couple of years but, if I remember right, that model Cobra is not rated for 5s.

Ken

Electric George · « **Reply #9 on:** July 22, 2022, 09:57:56 AM »

Between the rain showers I had the opportunity to plug in the KR Timer and got some readings.
First thing I noticed is the default delay setting is lower than the stated 25 secs and is 10s. No problem as I will check the other settings and adjust anyway.
Using short motor runs I had the following readings:
26.29 amps
391.9 watts
Everything was cool to the touch.

The motor spools up to 9700 RPM for a second before dropping down and stabilising at 8880 RPM. Am I right that this happens with the KR Timer and that the 9700 is the top rpm before the Timer brings it down to 8800?
When it stops raining again I will try increasing the RPM settings in steps (to ensure nothing is stressed) to move towards the 10k.
I have read much about the Cobra motors and would like to try one but for now I am unable to get hold of one where I live. I am using the Banshee as an early stunt attempts trainer and so not too worried about shorter flying time. I will look at changing the motor out to a 950 kv, as per your recommendations, in the future if I get to the point of being able to fly a full pattern.
Thanks all.

jerry v · « **Reply #10 on:** July 22, 2022, 10:57:00 AM »

George,
You can go up to 29 - 30 amps by increasing RPM with 11x5.5 prop, or changing the prop to 12x6.
Minimal watts per ounce is 9 to fly CL. If the weight of the model is 42.5 oz, and power is 400 watts, it will be good start. Use all of the components you have, figure out all of the settings, and then decide next steps to change motor or other things.

Jerry

CircuitFlyer · « **Reply #11 on:** July 22, 2022, 02:50:38 PM »

Quote

The motor spools up to 9700 RPM for a second before dropping down and stabilising at 8880 RPM. Am I right that this happens with the KR Timer and that the 9700 is the top rpm before the Timer brings it down to 8800?

My KR timers do the same (sometimes). Programming wise, it's a bit tricky to get a bumpless transfer between an RPM thats increasing and the fixed RPM governing mode. You're just seeing a slight overshoot for a fraction of a second as the governor kicks in. Sometimes you'll hear it and sometimes you won't. BTW, make sure any soft start function in the ESC is turned OFF.

John Rist · « **Reply #12 on:** July 22, 2022, 05:40:12 PM »

A while back I posted a thread titled how my KR timer works. Might give it a read. Should help understand what is going on when you use a KR setup. Near the end of the thread Keith chimed in and gives some really good insight into his timer.

https://stunthanger.com/smf/gettin-all-amp'ed-up!/how-my-kr-timer-works/msg566404/#msg566404

Electric George · « **Reply #13 on:** July 23, 2022, 02:13:56 AM »

Thanks everyone for the replies.

I had another opportunity to try out the set up yesterday and tried increasing the RPM in steps. I got to 9660rpm, 29 amps and 412 watts which comes out to around 155 watts per pound.
I am becoming familiar with the programming process and will continue to check things out today if the weather allows.

Jerry.v - Thanks, You were spot on with these readings and I am happy to test fly with the 155 watts.

John Rist - Thanks, I have already read this excellent post of yours and will now give it another read to refresh my memory.

CircuitFlyer - Thanks, I will double check the soft start but it seems to be OK.

Electric George · « **Reply #14 on:** July 23, 2022, 05:40:12 AM »

At the end of testing yesterday I found that the lipo was at 27% and so as I always test with a fully charged lipo, I charged up this morning and waited an hour or two for an opportunity to run the motor and check. I have just done this and the Watt meter and tacho are showing:
10,000 rpm
32.42 Amps
480 Watts
Everything still cool to the touch after 30 seconds of running.
That works out at around 180 Watts per pound. I am guessing the amps will drop a little when the system is unloaded in the air and so I think I may fly it at that for the first 1 minute or so test flight and I can check amps consumption from there and increase flight time in steps.
Am I good to fly or should I back of the RPM a little?
Thanks all.

Motorman · « **Reply #15 on:** July 23, 2022, 09:25:25 AM »

When I run nitro engines the first flights are set rich so I don't hurt the engine. I do the same with electrics, set the rpm low and bump it up from there. You only have to do this 2-3 times then you're set.

Motorman

Ken Culbertson · « **Reply #16 on:** July 23, 2022, 10:13:39 AM »

Quote from: Motorman on July 23, 2022, 09:25:25 AM

When I run nitro engines the first flights are set rich so I don't hurt the engine. I do the same with electrics, set the rpm low and bump it up from there. You only have to do this 2-3 times then you're set.

Motorman

This is good advice. I worried about battery way too much at first. A very wise friend who has been at this as long as I have told me that the battery is simply the gas tank. Trim the plane then get a battery that fits. Please don't trim the plane to match the battery. Find the right prop, rpm, line length and lap speed that the plane wants to perform at it's best then go find a battery that will leave you at 20%+ after 5:40.

Ken

Electric George · « **Reply #17 on:** July 24, 2022, 01:00:10 AM »

Thanks for the replies.

I will back off the RPM today and reassess after the first flight which will hopefully happen in the next couple of weeks.

Thanks.

jerry v · « **Reply #18 on:** July 24, 2022, 05:19:59 AM »

George,
If you set the flight time to 1 minute, you can check the lap time and do simple loop or wingover and have the feeling about the model. After landing adjust the RPM and test fly again on the same battery. If you will be satisfied with results, put freshly charged battery and adjust flight time to 5 minutes. After landing check the remaining battery capacity. If it’s 3.7 -3.75 volts per cell, it’s a good setup.
For test flights it is better to start with faster model and good line tension. You can always slow it down. If motor will consume too much energy, - it’s not a big deal, the speed control have a low voltage cut off function, and it will save the battery at 3.7 volts per cell.
Your calculations are safe to have a confidence in a first flight.
Good luck!

Jerry

Electric George · « **Reply #19 on:** July 28, 2022, 01:18:50 AM »

Update: First flight went well. I set the Timer for 9660rpm at around 29 amps for a two minute run. Power/lap time felt good and good line tension throughout. System landed cool. A good place to start and from which things can be gradually adjusted.
Charger put in 642 milliamps. and so 642 divided by 2 ==321 per minute.
2200ma -20percent = 1760
1760 divided by 321= 5.4 minutes flight time. I will be very pleased if this is true. However, I plan to increase the flight time a little each flight until I know what the true flight time is.

Thanks everyone.

jerry v · « **Reply #20 on:** July 29, 2022, 08:13:00 AM »

George,

Congratulations!
20 % is very generous)) It can be around 14% if you really need it. Saving battery life will give you more flights in the future. If you will play with the timer gain from 1 to 7 you may have a different consumption of the battery capacity.

My personal experience with KR timer was good trough one season. But in the next season in the spring at the first flight motor went extra 1k RPM . Don’t know why)). I reset it to correct RPM, flew one more season. Now the model has Hubin/Brodak FM-9 timer.

Jerry.

Electric George · « **Reply #21 on:** July 29, 2022, 09:47:29 AM »

Quote from: jerry v on July 29, 2022, 08:13:00 AM

George,

Congratulations!
20 % is very generous)) It can be around 14% if you really need it. Saving battery life will give you more flights in the future. If you will play with the timer gain from 1 to 7 you may have a different consumption of the battery capacity.

My personal experience with KR timer was good trough one season. But in the next season in the spring at the first flight motor went extra 1k RPM . Don’t know why)). I reset it to correct RPM, flew one more season. Now the model has Hubin/Brodak FM-9 timer.

Jerry.

Thanks Jerry,
Bad luck regarding your KR timer. Fingers crossed mine will work ok.
I think you are right and I did think about the difference in consumption once the gain was adjusted but I may be able to save a little if I slow the lap time down a little. It will be plenty of motor run time for me at my stage of flying at this time I think and so looking forward to getting it in the air again!
George

Motorman · « **Reply #22 on:** July 29, 2022, 11:48:02 AM »

You can get your flight time down to 5:15 maybe less and have 2 laps after the pattern but you have to do the pattern with no extra laps. If you're stressing your battery, you can look at props, rpm and line length but you should fly at the speed your plane likes.

Motorman

Electric George · « **Reply #23 on:** July 30, 2022, 02:47:05 AM »

Quote from: Motorman on July 29, 2022, 11:48:02 AM

You can get your flight time down to 5:15 maybe less and have 2 laps after the pattern but you have to do the pattern with no extra laps. If you're stressing your battery, you can look at props, rpm and line length but you should fly at the speed your plane likes.

Motorman

Thanks Motorman, all good info for me to take forward.