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Old Mar 18, 2008, 09:19 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Germantown, MD
Joined Mar 2006
3,376 Posts
Quote:
Originally Posted by swwesq
As far as that pic above goes, it doesn't show you that it was a train that hit the hummer and the other car just hit the curb. LOL
I found that pic on the internet a long time ago. I have no other information other than what you see. Could be you're right, but I don't know for sure. I do know that there is no way that other car (it's a truck actually) JUST hit a curb. Unless that curb was 5 feet tall. If it had hit a normal curb, it would have taken out the wheel possibly and that's it. But you can clearly see the front end pushed in and the hood (which probably sits 4 to 5 feet high) buckled.
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Old Mar 19, 2008, 12:14 AM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Germantown, MD
Joined Mar 2006
3,376 Posts
Check it out:

http://www.vimeo.com/800485

What do you guys think? I sent this to Vova also. I'm hoping he will respond soon. If this is normal behavior, well I guess I just have to make sure I mount the Tx as far from servos as possible. If it's NOT normal behavior though, well I don't know...

It's interesting that the RC receiver does not seem to be bothered by the video Tx. Even holding it right up against the receivers antenna does not do much. It's only when the Tx is held close to the servos or the servo wires that I see strange behavior. BTW, I do have ferrite rings installed, and the servo wires are twisted.
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Old Mar 19, 2008, 12:37 AM
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JMSTECH's Avatar
Canada, BC, Duncan
Joined Dec 2006
3,621 Posts
Quote:
Originally Posted by Crash9
Not to get off topic here (lol ) but I saw this video on RCU of some boat racing. It's got some onboard video that makes me want a boat for some FPV driving. It's funny that I don't have one yet and I live 2 blocks from a large lake, humm maybe it's because I have a full-size one .

The Traxxas electric w/Twin motors looks good.


http://rcuvideos.com/item/B58Y92DH3D9M9Y7F
Actually what a rush!!! How about a little slower paced, more relaxed...like this?
MBG June 2003 Video (3 min 27 sec)
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Old Mar 19, 2008, 07:01 AM
Mr.Pibb's Avatar
Lewis Center, OH
Joined Jun 2006
2,275 Posts
Quote:
Originally Posted by twinturbostang
Check it out:

http://www.vimeo.com/800485

What do you guys think? I sent this to Vova also. I'm hoping he will respond soon. If this is normal behavior, well I guess I just have to make sure I mount the Tx as far from servos as possible. If it's NOT normal behavior though, well I don't know...

It's interesting that the RC receiver does not seem to be bothered by the video Tx. Even holding it right up against the receivers antenna does not do much. It's only when the Tx is held close to the servos or the servo wires that I see strange behavior. BTW, I do have ferrite rings installed, and the servo wires are twisted.
I've seen similar effects with the smaller HXT 9G servos. It seems that some servos are more sensitive to the 900MHz signal. The high power RF is probably generating a "charge" in the circuit in the servo that makes it think that it is at a different position than it actually really is. Regarding smaller servos, I've seen some reports that JR S75 don't seem to have this problem. It may just be that the particular servos you have don't play nice with the 900MHz signal. I don't know that I've seen folks report on full sized servos that work well with the higher powered video TX's.
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Old Mar 19, 2008, 02:03 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Germantown, MD
Joined Mar 2006
3,376 Posts
Hmm, yeah that could be. That would explain why the receiver didn't seem to care too much about it, which btw was an FMA 8 channel (Quantum 8 I think). So, in terms of "deflection" of the servo when the Tx is close, here is what I've seen so far...

HS-325HB - not much deflection/interference
HS-65HB - considerable deflection but only when Tx antenna touches servo or wires
HS-55 - pretty good actually! not much deflection/interference
GWS naro - These go nuts when the Tx is moved real close
Ko Propo (JR??) PS-701 - This is the REALLY old servo on my car steering. DITCH IT!!! It sucks!! lol
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Old Mar 19, 2008, 03:33 PM
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United States, IN, Carmel
Joined Jan 2008
2,573 Posts
Yes it true! IF an 18 wheeler runs over a much smaller vehicle apparently the truck won't sustain much damage and the smaller vehicle will be crashed flat to the ground.
Fortunately though that doesn't usually happen in real life. Cars just hit on each other, deform (while they are absorbing kinetic energy - theirs and the other car's) and bounce off.

I still hear some guys - this goes to you swwesq ;-) - proudly announcing how their bumber hardly sustained any damage while the other car "split in half" and I can't help remembering my grandfather (see my post above - thank you for that by the way!)
This way of thinking can not be more wrong.... stop for a while and try to imagine what would happen if the car that rearended you had the same RIGID construction quality like your has?
Well... all this kinetic energy would have to be absorbed in a distance of a few inches, instead of a few feet and subsequently gone straight to the occupants and cargo of BOTH cars. This rapid deceleration forces are that mostly kill the passengers nowdays in modern cars and not the traumas due to direct hit to dashboards, windshields, etc. Surprisingly people are daily removed for damaged cars with no obvious external traumas and they pass away from internal bleeding due to aortic arch rupture (typical deceleration damage), epidural haematomas, etc. Mnimising the decelaration is a very tricky business and a lot of R&D is directed that way.
So, the fact that this unlucky (or stupid, call him however you want) bastard was driving a well designed BMW that "spilt in half", saved you from a nasty whiplash injury in the best case senario (yes people die from that too)!

The cars nowdays are being tested in many different crash tests that simulate different accident scenarios but the most important one is still the classic one that a single car (the test subject) collides with half it's frontal surface against an imobile object (a huge block of concrete usually) at a certain speed. This object for all the formulas of physics that are involved in describing the collision pheomenon can be considered of infinite mass. Obviously much more than a Expedition or an H2 or H1 or an 18 wheeler for that matter!
And still at these tests small cars like Smart make better scores than other bigger ones and the acceleration sensors record less Gs!

Can you guys imagine if everybody was driving and crashing at each other in tanks that have a 5" armour all around. No too much job for the body shop but a shitload for the hospitals (and the undertakers... :-(
Yes common sense might elude you to think otherwise, but in this case it's not Big fish eats small fish! Big mass and big inertia is a bad think both for the active (acceleration, braking, handling, grip) and the passive safety of the one who has it on board. That's why every single car, aircraft, boat, spaceship designer that wants to design a good vehicle (and not one that satisfies a misinformed customer target group or a trend for ever bigger SUVs) tries to shed off as much weight as possible.

Dimitris

PS Sorry for getting totally out of the FPV subject here but I think it's important. I am not trying to lecture here, just trying to share some facts I know, due to my profession (I am surgeon here in Sweden). I have seen my share of traffic accidents and their victims and I also took some courses recently in that. DS
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Old Mar 19, 2008, 04:28 PM
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JMSTECH's Avatar
Canada, BC, Duncan
Joined Dec 2006
3,621 Posts
Quote:
Originally Posted by Mr.Pibb
I've seen similar effects with the smaller HXT 9G servos. It seems that some servos are more sensitive to the 900MHz signal. The high power RF is probably generating a "charge" in the circuit in the servo that makes it think that it is at a different position than it actually really is. Regarding smaller servos, I've seen some reports that JR S75 don't seem to have this problem. It may just be that the particular servos you have don't play nice with the 900MHz signal. I don't know that I've seen folks report on full sized servos that work well with the higher powered video TX's.
VERY INTERESTING Mr. Pibb! Thank god that it didn't affect his throttle! DID YOU SEE WHERE HIS CAR WAS AIMING?


Oh Dimitris, I guess it's ok to buy a Smart Cart?
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Old Mar 19, 2008, 07:32 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Germantown, MD
Joined Mar 2006
3,376 Posts
Quote:
Originally Posted by JMSTECH
VERY INTERESTING Mr. Pibb! Thank god that it didn't affect his throttle! DID YOU SEE WHERE HIS CAR WAS AIMING?
It's ok. I don't need anymore kids. Number four is cooking right now, and should be done soon.
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Old Mar 19, 2008, 08:09 PM
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JMSTECH's Avatar
Canada, BC, Duncan
Joined Dec 2006
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HA HA HA... ok Brian.. I crown you king of fast come backs!
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Old Mar 19, 2008, 10:23 PM
No guts no glory
pratorian's Avatar
Quebec, Canada
Joined Sep 2007
1,677 Posts
I have the same problem on my easystar, when I turn on my 900mhz 500mw tx the hxt 9g servos glitch and go out of control, one thing is weird tho if I hold the tx with my bare fingers, the glitches go away and servos respond ok... Any of you guys using 900mhz 500mw tx with the easypod ? those are the stock servos that came with the easypod so I guess that some people managed to get them to coexist with the 900mhz nearby.

All my servo wires are twisted, ferite rings etc.. nothing helps, I tried different receivers 2.4ghz and 72mhz same story

Quote:
Originally Posted by twinturbostang
Check it out:

http://www.vimeo.com/800485

What do you guys think? I sent this to Vova also. I'm hoping he will respond soon. If this is normal behavior, well I guess I just have to make sure I mount the Tx as far from servos as possible. If it's NOT normal behavior though, well I don't know...

It's interesting that the RC receiver does not seem to be bothered by the video Tx. Even holding it right up against the receivers antenna does not do much. It's only when the Tx is held close to the servos or the servo wires that I see strange behavior. BTW, I do have ferrite rings installed, and the servo wires are twisted.
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Old Mar 19, 2008, 11:14 PM
Cameras are EVERYWHERE...
tvdude310's Avatar
Los Angeles
Joined Jan 2008
1,879 Posts
Leakage

Quote:
Originally Posted by pratorian
I have the same problem on my easystar, when I turn on my 900mhz 500mw tx the hxt 9g servos glitch and go out of control, one thing is weird tho if I hold the tx with my bare fingers, the glitches go away and servos respond ok... Any of you guys using 900mhz 500mw tx with the easypod ? those are the stock servos that came with the easypod so I guess that some people managed to get them to coexist with the 900mhz nearby.

All my servo wires are twisted, ferite rings etc.. nothing helps, I tried different receivers 2.4ghz and 72mhz same story
It sounds like the Tx has a lot of RF leakage. I say this because you mentioned that when held in your bare fingers, the problem seems to go away. To me it sounds like the leakage has found a nice path to ground when you're holding it. I'll bet the glitching is worse when the BODY of the Tx is held close to the servos. If this is indeed the case, you might want to try shielding the Tx with something, maybe foil. Don't block it from cooling, but try to separate the servos and Tx with foil, preferably grounded if possible. If you see improvement you might want to look into metal that is made specifically for shielding (it's called "mew" metal, mew being the greek symbol for "micro" but I don't seem to find it on a keyboard ).
Also, if the cover on the Tx is easily removed, you may have better luck with a smaller piece of shielding at the point where the RF leaves the board on its way to the antenna. This is usually where most leakage occurs, and will be much easier to ground the shield to the proper ground within the Tx. Just be sure not to short anything with the metal (it's easy to do). By the way, I have ZERO hands on experience with 900mhz video transmission, all of this is old military RF experience. So don't kill me if it doesn't work! Good luck either way, I'm about to take the plunge and buy an FPV system so your experiences are valuable...
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Old Mar 20, 2008, 01:18 AM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Germantown, MD
Joined Mar 2006
3,376 Posts
tvdude: that definitely sounds plausible, and in some cases it probably could be the source of interference. Just for giggles, I wrapped my Tx in aluminum foil to see if it made any difference. Nope. Still the same type and magnitude of glitching/interference. So for me at least, it didn't help.
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Old Mar 20, 2008, 09:34 AM
No guts no glory
pratorian's Avatar
Quebec, Canada
Joined Sep 2007
1,677 Posts
thanks for the idea tvdude I'll try it as soon as I have some free time
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Old Mar 20, 2008, 03:43 PM
Cameras are EVERYWHERE...
tvdude310's Avatar
Los Angeles
Joined Jan 2008
1,879 Posts
Vswr?

TTStang and Pratorian-
It sounds like the case may be a bad VSWR (standing waves). This is usually caused by an antenna length that is a little bit wrong, either too short or too long. You end up with standing waves on the antenna that spray RF all over the place. Basically, the antenna needs to be a length that is an even division of the physical wavelength of the signal (i.e. half-wave, quarter-wave, etc.). If the length isn't exactly right, you get standing waves and poor transmission quality. There are formulas for determining all of this stuff, and since you can't put an antenna matcher and VSWR meter in the antenna path, the only solution is to make it the correct length. It's probably only off by a little bit, but enough to cause problems.
One thing you might want to check is the solder connection to the antenna. If it's even a little bit cruddy, it will add electrical length (in the form of resistance) to the antenna, causing this problem. I would try to re-flow this connection or completely resolder it and see if this helps. If you have good soldering skills, this could solve your problems.
TVDude310

...edit: If the solder connection looks really good, you might not want to mess with it unless you have good soldering skills. A bad solder job will make things worse.
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Last edited by tvdude310; Mar 20, 2008 at 03:46 PM. Reason: addition
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Old Mar 20, 2008, 03:50 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Germantown, MD
Joined Mar 2006
3,376 Posts
Another great suggestion. Well, we know that the antenna provided in the kit is definitely not ideal. It is not a dipole, as it has no ground connection. As for the length, since the element is not visible through the rubber case, I have no idea if it's correct or not. I do have another antenna though, that I purchased from Hyperlink Tech: http://www.hyperlinktech.com/web/900...antenna_sm.php I will try that tonight and see if it's any better. Although I do have a vague recollection of trying it already. Hmm, can't remember for sure though. Need more sleep. lol
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