First Logo (550SX). Maintenance questions

[hemp]

Originally Posted by Crowbar

How did you know that you shorted the motor?

You can generally detect a motor short with an ohmmeter or multimeter. Connect it across any two plugs or between any plug and the pinion - if you get continuity then there's a definite short.

[crashjack]

I say it shorted the motor, because I got no motor beeps or motor response but everything else seemed ok. Also after I pulled the wires away form the motor, the motor beeped and fired-up. However, I didn't fly until I made the corrections I stated in an earlier post.

"Shorted the motor" was probably a poor choice of words. Probably a better description would be that it appears a hot wire got grounded or a wire got improperly grounded, thereby causing the motor not to work.

[Crowbar]

Originally Posted by hemp

You can generally detect a motor short with an ohmmeter or multimeter. Connect it across any two plugs or between any plug and the pinion - if you get continuity then there's a definite short.

I don't have continuity beween the plugs and the pinion. If I understand this (http://www.justgofly.com/techfaq.htm#MotorShort) correctly, my motor is not shorted.

However I do have 0 Ohms (that's what you call continuity, right?) between any of the motor plugs.

It appears to run fine on 3S with another ESC.
I shall try making a video tonight. Would be a bummer if I destroyed another ESC because it's actually the motor.

[rumo]

With the 550SX you got a hassle free helicopter with a maintenance effort near 0 - at least for sport and mild 3D pilots like me.
My 550SX is more than one year old and has about 250 or 300 flights on it. I did't lube the gears, didn't oil the motor bearings a single time or spent a single minute with maintenance. The gears are showing no sign of wear, and the motor runs, and runs....
The only thing I will do next month is to change the wear and tear parts of the head.

My answers in blue.

Originally Posted by Crowbar

I

- Bundled (Combo) Scorpion motor: Do I really need to oil the bearings regularly? How often and with what?
The Scorpion motor I'm using in my 550SX comes from a four year old 500SE combo. About 1000 flights and around 15 crashes survived. At the very beginning I used the Scorpion oil from time to time, but not since I'm flying the 550SX. I will try to change the shaft and bearings in the winter to come, but will probably "forget" it as happend for the last three ones.
By the way. The bearings of my motor looks like they are sealed. If that's true then using oli makes not that much sense - and that would also be a good explanation why the motor is still running.

- Do I need to worry about the belt coming off at the back? I read a lot about people using an aftermarket belt tensioner. Couldn't find out whether this issue was fixed with the v2 or not.
I'm also using the belt tensioner from Spedix on my 550SX. Reason was that the the belt jumped of several times on my 500SE. Mikado has changed this part, so I wouldn't see the need to buy it anymore.

- Antistatic kit. Best places to connect both ends?
There is a manual coming with the one of Mikado, best thing is to do as described. Short version: Belt tensioner must be connected to the motor. Use a multi-meter to check!

- Anything else I should know that is not written in the manual? This is my first belt-driven heli. Only built T-Rex helis so far.
1. I rarely have to correct the tension of the belt, because I'm using a self tapping screw to secure the tail boom from slowly sliding back into the chassis. The right half of the chassis is already prepared for doing so. Be careful that the screw isn't too long, it only has to make a small dent into the tube.
If I remember right I didn't have to re-adjust the belt tension of my 550SX since I finished the building more than 1 year ago. Nevertheless belt tension is a thing I check at least before the first flight of a day. Also after I had a hard landing.

2. Be careful that the plates from the tail rotor are in parallel. Check the temperatures of the tail shaft bearings after your first test run on the bench. They shouldn't be hot, if so then probably the the plates are not in parallel. Besides the increased wearing, this can also cause the belt to jump.

[rumo]

This topic is also covered by a video from Mikado:

http://www.vstabi.info/en/node/1846

Originally Posted by hemp

You can generally detect a motor short with an ohmmeter or multimeter. Connect it across any two plugs or between any plug and the pinion - if you get continuity then there's a definite short.

[Crowbar]

Looks like my motor is alright, it spins well with the YEP45 on 3S. Can't put high voltage through like in the Mikado Video but I guess it's fine.

My replacement ESC (YEP120LV with 12A BEC) is still underway but I'm hoping I can actually use its BEC. The YEP100 reliably dropped voltage below 3.5V after 3 seconds of wiggling the sticks. I got a big buffer pack and telemetry so I don't really care if the ESC dies in flight so I'm going the cheapo route for now.

My dealer replaced the bent main shaft no questions asked (commendable, another dealer wouldn't even exchange obviously badly molded tail drive gears on a T-Rex).

I only have a few minor questions left:
There's a brass shim in the kit that is 2 or 3 millimeters thick and fits the main shaft. Where does it go? Couldn't find it in the manual which is very vague about the number of shims.

One of my fellow club members has a Logo 500 that looks pretty similar and his main gear has close to 2 millimeters of up-and-down play along the main shaft. He explained that this was intentional so that the gear could center itself on the double-slanted pinion. Kinda makes sense that the gears or frame could flex a bit under high loads and the gears get out of alignment. I built mine so the main gear has 1.2mm of room to go up and down the main shaft, pinion inholding it right in the middle. Anything wrong with having it like that?

Is it a good idea to turn active free-wheeling off on super slow bench testing (about one full head rotation per second)? I feel like that could have damaged my old ESC during bench testing. That or the bent main shaft requiring lots of torque on some spots.

Thank you all!

[hemp]

Originally Posted by Crowbar

There's a brass shim in the kit that is 2 or 3 millimeters thick and fits the main shaft. Where does it go? Couldn't find it in the manual which is very vague about the number of shims.

These would go above and below the one-way bearing inside the one-way hub. However, they're supposed to be press-fit and shouldn't be loose in a bag. May just have been a vagrant part.

Originally Posted by Crowbar

I built mine so the main gear has 1.2mm of room to go up and down the main shaft

That'll be fine.

[Crowbar]

Originally Posted by hemp

These would go above and below the one-way bearing inside the one-way hub. However, they're supposed to be press-fit and shouldn't be loose in a bag.

Interesting, I guess I'll have to tear it all down again and have a look inside the OWB. Thanks for the tip, don't think I'd have figured that out by myself without trashing my OWB in flight first.
I did have to wiggle out the main shaft out of the OWB because the one that came in the kit turned out to be bent. So that shim might just have popped out then.

[Crowbar]

The brass washer did indeed come out from the OWB sleeve. Thanks so much, I'd never would have figured that out by myself.

Got the airframe all built now, Main gear can go up and down half a millimeter, pinion hold it right in the middle of that range so that is perfect now.

Got my 120A ESC as well now, built-in BEC is a bit weak but with the buffer caps it's decent.

Does anyone have the combo with the coreless Savöx servos? BEC can do 5.7V, 7.4V and 8.2V, servos are officially rated for 6V.

[Crowbar]

Shouldn't the kit come with bolts and nuts for the tail blades? It came with bolts for the main blades but nothing for the tail blades.

Gotta be honest, this has been the most frustrating build ever.

[mkovalcson]

Originally Posted by Crowbar

Shouldn't the kit come with bolts and nuts for the tail blades? It came with bolts for the main blades but nothing for the tail blades.

Gotta be honest, this has been the most frustrating build ever.

It should come with all the bolts needed. Mine did.

[hemp]

Yes, the kit comes with grip bolts and nuts for main and tail rotor. I've never heard of those missing. Anything is possible, of course, but given the number of problems you've had, I have to wonder if your kit was messed with at some point between Mikado sending it out and you receiving it.

[Crowbar]

Update: got the parts, put off the maiden a lot because I had little enthousiasm to get it flying with the 700 flying perfectly. Finally maddened it yesterday. 5 flights total, still cranking up the gains slowly, feeling things out.

Belt loosened up quite a bit, it's occasionally touching the boom now when spinning by hand, gotta tighten it up a bit. Not happy with the head speed yet but I'm still figuring out the gov settings for that thing. If someone got good settings for the 120LV ESC, lemme know. PWM, I-gain and P-gain is kinda what I'm looking for. 15T pinion and about 2200 rpm is what I'm aiming for.

[hemp]

Originally Posted by Crowbar

15T pinion and about 2200 rpm is what I'm aiming for.

You may have some trouble holding that headspeed with a 15t pinion. Increasing the gains won't help if the PWM is maxed out to start with; what throttle percentage are you using to get 2200 in a hover?

I recommend auto-timing unless you find it doesn't run well. If this is the Mikado edition 1100Kv scorpion motor, auto should work for you.

[Crowbar]

Originally Posted by hemp

You may have some trouble holding that headspeed with a 15t pinion. Increasing the gains won't help if the PWM is maxed out to start with; what throttle percentage are you using to get 2200 in a hover?

I recommend auto-timing unless you find it doesn't run well. If this is the Mikado edition 1100Kv scorpion motor, auto should work for you.

I got timing at 18° which I hear is the norm for that Scorpion motor. Does auto-timing actually adjust it continually depending on what the motor is doing?

PWM is by no means maxed out, I can still go up, just working my way up there, if I understand it correctly, increasing PWM gives me more motor power but less efficiency.

Dunno about the throttle percentage for 2200 rpm in a hover. I'd need someone to look at my Tx while I hover. I got telemetry for the rpm but as soon as I demand some power (quick collective move) it displays rpm numbers above 10.000. Guess the Spektrum rpm sensor can't handle the high currents. The same never worked on my 700 either but fine on the older and weaker T-Rex 550.

[hemp]

Originally Posted by Crowbar

Does auto-timing actually adjust it continually depending on what the motor is doing?

That's correct.

Originally Posted by Crowbar

if I understand it correctly, increasing PWM gives me more motor power but less efficiency.

Depending on the motor and where it's at, more PWM will likely give you more efficiency (up to a point). What you lose with PWM is headroom. If the PWM is high to begin with, then putting the disc under load will cause the headspeed to drop because there isn't room to apply additional power.

[jmackey]

Originally Posted by hemp

That's correct.

Depending on the motor and where it's at, more PWM will likely give you more efficiency (up to a point). What you lose with PWM is headroom. If the PWM is high to begin with, then putting the disc under load will cause the headspeed to drop because there isn't room to apply additional power.

Thinking you guys are discussing different definitions of PWM

Sounds like hemp is talking about PWM as Kontronik defines it. Actual throttle % that the ESC is sending the motor at any given moment in governor mode. In example, 80% flat throttle curve from transmitter (Kosmik/JivePro series) yields very close to 80% actual throttle to motor (PWM) at first spoolup on a fresh pack with no load (maybe 81%-83% actual). Introduce a lot of load in hard flight and this number goes up to 100%. You need to make sure you have enough overhead for the governor to work. If it's flat-lining at 100%, there is no way it can hold headspeed, since it can't give more than 100%.

Sounds like Crowbar is thinking about PWM in the more traditional sense as Pulse Width Modulation (frequency that ESC bumps the "paddles" (motor coils) at). Like whether to use 8, 12 or 16KHz setting for PWM on his YEP 120 ESC. MrMel did a pretty cool demo of that a while back, but I can't find it anymore to share.

[hemp]

Originally Posted by jmackey

Thinking you guys are discussing different definitions of PWM

Good catch.

[Crowbar]

Hmm, haven't tried auto-timing yet but played around with P and I gain today. It's close to perfect at 2200 rpm, only minor bobbles when I come down at full pitch and to a hard stop. When I do a climb out again I feel and hear no bogging whatsoever. Tic tocs are very solid.

On 1900 rpm however punch-outs have a noticeable delay until the gov suddenly kicks in and gives it more power. Same on hard stops, it bogs and wobbles and then it kicks back into gear.

ESC, LiPo and motor don't really get any warm even if I try, I know I can get some more power out of the system but I don't really know how.
P and I gain are currently both one step from maximum (using the little YGE programming card), PWM is currently on "9" (the second lowest setting).

The programming card (v2) says the following about PWM:

PWM Frequency is the switching rate used for partial load operation. With low frequencies the losses are reduced, but the motors run slightly rougher. With high frequencies, it is the opposite. The optimum frequency may be found in the user manual of your motor.

[Crowbar]

I found this formula on another post and I remember it from a video about the YGE programming:

Kv x Volts (nominal you are using) x Pole count / 20

So for my Scorpion 4025 III 1100kV, that would be:
1100 x 3.7 * 6 * 10 / 20
= 1100 * 22.2 / 2
= 12210
So shouldn't my PWM be 12 kHz instead of the scorpion recommended 8?

This thread here (https://www.helifreak.com/showthread...08#post6540408) about the same ESC and motor combo suggests a PWM of 10. I asked in there as this is a bit off-topic for this thread.

Gotta say I'm quite impressed with that heli so far, it sorta out-files my 12S T-Rex 700 (IKON) already. Just wish it had a little bit more power so it doesn't bog if I mess up or need to use the FBL rescue.