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Old Jan 14, 2015, 06:27 PM
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Bench testing power train/ any value?

Pieces and parts are coming in for my 3.7M Volcano build and I had the idea that testing the power train on a stand would be a good idea vs. installing it all in the fuse and waiting for the maiden to finally do the run up.

Using Jeti Tx and esc, I can view amps, volts, watts, rpm, motor temp, etc. real time and felt like doing some bench testing might be warranted.

After reading some old threads tonight, I picked up that static numbers were not really worth much. Props stalling, etc.

Is it worth the effort?

John
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Old Jan 14, 2015, 07:17 PM
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I do bench test but not for benchmarking purposes. If I need very accurate results of amp draws/wattage/v.drop etc I use unilog and check after a flight. If I need a rough number quickly I use the onboard logger of the ESC (I generally fly castle).

I DO test my set ups prior to launch to make sure motor rotation is correct, brake is correct, programming is correct, etc.

On my first flight I generally do a couple of motor runs, check end points, dual rates, expo, crow/spoileron, etc and come down as soon as I'm comfortable. Then I check my motor logs (watts, motor run time, etc) and check temps to make sure everything is in line with what should be reasonable. I calculate my estimated mah usage per second and try not to pull my packs down more than 30% on LMR set-ups to preserve battery life. Yes, that means that when I'm done flying my motor pack is still 70% 'full.' 30% use is generally 15-30sec depending on the plane I fly (ie: 30% on my backfire is about 15sec motor run and 30% on my raketenwurm is about 25sec). My throttle switch counts down a timer to let me know when I've hit my last climb.

ymmv.
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Old Jan 15, 2015, 05:56 AM
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Other than a quick 2-3second burst to have a rough estimate where your drive is at powerwise, I would not recommend any static running of high performance setups. They are by definition close to the limit and may overheat motor or controller or kill your lipo by any prolonged bench testing.

Gerben
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Old Jan 15, 2015, 01:53 PM
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That's a good point I omitted. My bench tests do not involve any more than a blip of throttle (0.5sec or less in most cases) and I usually use a 3 cell test pack rather than my usual 6-12s flight pack. 400w on the bench is a lot more reasonable than 5,000w and it has given me all the information I need.
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Old Jan 16, 2015, 02:21 PM
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If the efficiency would be linear this might be an useful option.

Unfortunately it isnīt. So, you can get a hint for the direction but still with good chance for surprises in final configuration.
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Old Jan 16, 2015, 03:37 PM
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I do static runs to check performance of the motor, ESC and Lipo but mainly because these have been prototypes or odd combinations. Only a couple of bursts and usualy with a slightly smaller prop to reduce the load.

You will need a firm grip on the fuselageand be prepared for the fuselage to want to twist out of your hand due to the huge torque. There is a huge risk here of things going horribly wrong.

It is probably best to check direction and fuction with a lower voltage pack (check lowest cell count of your ESC) and then simply go flying.
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Old Jan 16, 2015, 04:08 PM
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Just DO NOT do like this dude did his testing.....
Warning: What NOT to do (0 min 56 sec)


Still hurts to watch this.....
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Old Jan 16, 2015, 05:13 PM
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Quote:
Originally Posted by Arcteryxxx View Post
Just DO NOT do like this dude did his testing.....
http://youtu.be/Zzo7F7pmbok

Still hurts to watch this.....
What an idiot...... wait that was me
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Old Jan 17, 2015, 01:52 AM
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Quote:
What an idiot...... wait that was me
Just the best quote I've ever seen
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Old Jan 17, 2015, 03:41 AM
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Haha!
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Old Jan 17, 2015, 08:45 AM
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Thanks for your opinions guys. I guess coming from several decades of running nitro motors, where bench testing was worth the effort, I'm seeing most don't have that same value with electric setups.

I assumed doing 3 second run ups (1 or 2) with verification of not over heating between runs and using a mezon 165 opto, I have instant view of amps, volts, rpm, motor temp etc. from the Tx. Since I expect to see about 3-3.5Kv, a stand was going to be made to mount motor to, no hand holding like in the video (Yikes!!!) or attached to fuselage but attached in a way much stronger than needed.

I wanted to test the system on 6S and then with 8S with two different props. Again, only for 3 second run up to see where the different props pull the batteries to and obtain watt/ amp figures.

I get it that static numbers are somewhat misleading. With my current model, I see 145 amps static and the same amps during initial launch as I go to full power in a pretty steep angle (about 70-80 degrees). But 1-2 seconds after that, amps level out to 120 until I turn the power off. In straight and level flight (at full power) I see about 60 amps.

I'd really like to know if I'm going 6S or 8S so I only have to do the radio tray layout once. All my 6S packs are a single cell, I'll have to run 2 4S packs if I go the 8S route. Another reason I was thinking about bench testing.

I'm a couple of weeks from any actually testing. Again, thanks for your input.
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Old Jan 17, 2015, 12:13 PM
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Which setup do you have?
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Old Jan 17, 2015, 12:32 PM
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You won't get useful numbers from static tests, as you have already discovered the amps go down a lot when the model gains speed. There are enough people here who can advise you on what you will get out of a given setup. Ultimately it is up to you how much power you want, you may find 6S boring. Or you may find that 8S is to much and gives to little run time. That is a personal thing a static test also won't give you much information on. If you are not scared, go 8S. Otherwise try 6S first until you get bored.

I wish anyone good luck designing and making a static rig to hold these power systems. It's possible but needs some serious thought put into. Unlike the video above.

Note, any prop that has some twist in the centre piece (specially the ones with 17.5-20 degrees) will want to fold back firmly when the brake is applied. Another reason why you don't want to be anywhere near the motor with your hands.
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Old Jan 17, 2015, 07:11 PM
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Quote:
Originally Posted by combatflier View Post
I do bench test but not for benchmarking purposes. If I need very accurate results of amp draws/wattage/v.drop etc I use unilog and check after a flight. If I need a rough number quickly I use the onboard logger of the ESC (I generally fly castle).

I DO test my set ups prior to launch to make sure motor rotation is correct, brake is correct, programming is correct, etc.

On my first flight I generally do a couple of motor runs, check end points, dual rates, expo, crow/spoileron, etc and come down as soon as I'm comfortable. Then I check my motor logs (watts, motor run time, etc) and check temps to make sure everything is in line with what should be reasonable. I calculate my estimated mah usage per second and try not to pull my packs down more than 30% on LMR set-ups to preserve battery life. Yes, that means that when I'm done flying my motor pack is still 70% 'full.' 30% use is generally 15-30sec depending on the plane I fly (ie: 30% on my backfire is about 15sec motor run and 30% on my raketenwurm is about 25sec). My throttle switch counts down a timer to let me know when I've hit my last climb.

ymmv.
Combat,

I've viewed your reply all week and have just had time to respond. You bring up a good point about the batteries.....for me, anyway. I've been running my glider batteries down just like I do all my helis and other sport type aircraft (to 30% charge left and thought I was being conservative by not dipping to 80% very often. I'm not going to say I've never had any battery issues with the 25 or so I have assigned for heli use (estimate 6 of those have been placed out of service in the last 24 months. I have not had a glider long enough at this point to have my new batteries show any sign of having issues. Have had 4 different gliders and they all used different batteries (so most of those are gone) or I was continuing to upgrade from 4 to 5S etc and have several packs laying around with 3-5 cycles through them.

I'm not running a switch on throttle and prefer to keep it this way, nor have I thought 2-3.5 kW was crossing into hotliner category where I had to abide by special rules like throttle on a switch and 30% battery use.

I'm tracking mah consumption via jeti telemetry and have mah data updated by voice throughout my flight and with alarm set at 70% consumption and additional alarm at 80% consumption. These numbers agree with the data displayed on my ichargers.

With my current 2.5M Spider setup, I'm seeing 2500 watts in a climb on 5S at 160 amp spike for less than a second, then settle down to 123 amps going straight up until out of site if you want. A dozen flights now and the 5S 70C TP 3300 is giving the same input/output mah figures I used after first giving the battereies a charge/storage/charge cycle four times.
Would you say I should use the 30% consumption method with this plane?

I'll list the specs of my current build and motor setup on another question asked about the setup.
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Old Jan 17, 2015, 10:13 PM
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John,

It really depends on the the pack size and quality versus the current pulled.
F5B models are at the extreme end of the spectrum, pulling 100-120C from the battery. The packs are typically discharged about 50% and hold up fairly well.
Low powered sport models would be at the other end of the spectrum. With low battery loads it is reasonable to discharge the battery 80% without harm.
Most other models are somewhere in between, so I would plan for a battery discharge somewhere between 50 and 80%.

160A peak current on a good 3300mah pack isn't that extreme. I would probably plan for a battery discharge about 60-70%.

Good luck,
Lenny
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