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Model Forum / Radio Controlled / Land Models / August 2006Servo Problems
I have a thunder tiger EB4 S2 which until yesterday had the standard Ace TR202A 27MHz Rx in it. I changed the Rx to a Futaba R122JE 40MHz and one of the servos to a HiTec 645MG. So current setup is R122JE Rx 40MHz Ace S2008MG Servo HiTec 645MG Servo The problem I have is that the S2008MG servo does not work correctly. When I switch everything on it sits ok, as soon as I try to get it to move it judders backwards and forwards. It does not matter if the servo is in by itself or they are both plugged in, the result is the same. I have taken the gear out of the car so its not interference. Servo works fine when plugged back into the TR202A so its not faulty. So in summary. 645MG works fine in both channels, S2008MG judders in both channels when in R122JE. 645MG works fine in both channels, S2008MG works fine in both channels when in TR202A. Can anybody offer any advice of what I can check? thanks Gav >I have a thunder tiger EB4 S2 which until yesterday had the standard Ace >TR202A 27MHz Rx in it. I changed the Rx to a Futaba R122JE 40MHz and one of [quoted text clipped - 19 lines] > > Can anybody offer any advice of what I can check? <stupid question here> You did change the transmitter to a 40mhz one as well yea? And the wires are all plugged in the right way? Does the Rx have a built in failsafe? Are the batteries fully charged? Better servos need more power is all...  SignatureDan - on his PC > <stupid question here> You did change the transmitter to a 40mhz one as > well yea? Yep! Reason I got 40MHz Rx was so I could use it with my Futaba Megatech. Want to use same Tx for all cars. >And the wires are all plugged in the right way? Yes. And seen as both servos work in the 27MHz Rx they are both the same way round and must be the right way round. >Does the Rx have a built in failsafe? For what? >Are the batteries fully charged? Better servos need more power is all... Yes. Tested Tx & Rx power with multimeter too. Running 6v pack on Rx so should easily cover it, servo with the problem has been running on 4.8v for ages (previous pack). Using same power source when I run tests on 27MHz setup too, so no issues here. I'm going to take out a 40MHz Rx from another car and test it with that, although I don't think the Rx is the problem. Had the servo apart too to check for loose connections although didn't expect to find anything since it works fine on 27MHz Rx, no problems found. Strugling to find a logical explanation for the behaviour, same characteristics as interference but there is none as far as I can see. Typical when I need it for the weekend, see myself rapidly rebuilding my Fireblade Evo and using that instead. Grrr. Well now I am confused. Plugged servo into Rx on Fireblade exact same model Rx (R122JE). Wired differently though because of ESC, Rx gets power through channel 2 socket rather than power socket due to using BEC on ESC. Servo works fine. Unplug channel 2 and get power from EB4 power source into power socket in Rx from Fireblade and I get the same problem. So tests done so far. Using 27 MHz Rx (original) EB4 power source (6v humppack), 645MG and S2008MG work perfectly. Using 40 MHz Rx (new) EB4 power source (6v humppack), 645MG works ok, S2008MG judders. EB4 power source (6v humppack), 645MG works ok, S1903 works ok. (S1903 is a servo 645MG is replacing). Using 40 MHz Rx (From fireblade) Fireblade power source (from ESC), 645MG works ok, S2008MG works ok. EB4 power source (6v humppack), 645MG works ok, S2008MG judders. Conclusion... All Rx's are ok 2x 40MHz & 1x 27MHz. Power Sources are ok. All servos are ok. Next test, find another external power source to run Rx from power socket. Eliminate humppack. Gav Try using the standard EB-4 "AA" battery tray (4 alkaline batts) and see how it reacts. From what you have described it sounds like the servo doesn't like that hump pack in combination with the new RX. Make sure you don't have any cordlees phones nearby and have your TX antennae extended and atleast 4 or so feet from the RX and also that you aren't under any overhanging powerlines. Also if you are using rechargable batts in the TX try standard alkalines. > Well now I am confused. > [quoted text clipped - 27 lines] > > Gav > Try using the standard EB-4 "AA" battery tray (4 alkaline batts) and see > how [quoted text clipped - 6 lines] > aren't under any overhanging powerlines. Also if you are using rechargable > batts in the TX try standard alkalines. Tried it after searching high and low for more battries. :o) Same problem. Don't have any alkalines to try in the Tx but seen as its fine with the other cars (using same model of Rx) I assume its fine, all 8 battries have been individually peak charged and tested with multimeter afterwards. Not sure about cordless phones, I don't have one but neighbours might. Having said that it works fine with any other servo so not sure that would be the issue. thanks for the input. Gav >> Well now I am confused. >> [quoted text clipped - 31 lines] >> >> Gav I would still try the standard alkalines in the TX just to see. (as well as further suggestions / "y" harness stated in thread) Most rechargable AA batts are 1.2volts whereas standard are 1.5volt which could make a difference in the set-up. > > Try using the standard EB-4 "AA" battery tray (4 alkaline batts) and see > > how [quoted text clipped - 55 lines] > >> > >> Gav > Well now I am confused. > [quoted text clipped - 25 lines] > Next test, find another external power source to run Rx from power socket. > Eliminate humppack. That's just... odd :-) Some kind of compatability issue maybe? To be fair, those Ace servos aren't actually bad anyway. SignatureDan - on his PC >> Well now I am confused. >> [quoted text clipped - 28 lines] > That's just... odd :-) Some kind of compatability issue maybe? To be > fair, those Ace servos aren't actually bad anyway. Must be, however its strange how it will work with the same Rx when it is powered through channel 2 instead of the power socket. Yeah have no issues with the Ace servos, they've been fine up to now, and still are if used in certain combinations or with the Ace Rx. Only reason I have changed is because I wanted a higher torque servo for the brake and wanted to use a decent Tx instead of the crappy green plastic one. :o) > Well now I am confused. > [quoted text clipped - 27 lines] > > Gav If you can check the voltage drop at the battery pack and the S2008MG using the R122JE when you operate the 645MG and then when you operate the S2008MG and then both. If it drops quickly below 5 volts that could be your problem. There is some mention in the 645MG manual about a Y harness for high powered servos to supply the servo with power all the time. Also being that the S1903 is a low torque servo which means its also a low power consumption servo this could be why you dont get the glitching from the S2008MG. Also your Hitec servo has a current drain of 450mA, I dont no if that is loaded or unloaded amps but given that the Ace servo is also a high torque servo you could be getting to much current draw. If your multimeter has current on it you can also check the current drain to see if its to high for your power supply/battery pack. Maybe the Futaba R122JE is just not up to the standard for your setup and can not handle all the high powered servos running off it. Cheers >> Well now I am confused. >> [quoted text clipped - 43 lines] > S1903 is a low torque servo which means its also a low power consumption > servo this could be why you dont get the glitching from the S2008MG. I don't have manual for the HS-645MG, have to see if I can download one. Didn't get one with the servo, however the 645MG works absolutely fine its the S2008MG that has the problem. > Also your Hitec servo has a current drain of 450mA, I dont no if that is > loaded or unloaded amps but given that the Ace servo is also a high torque > servo you could be getting to much current draw. If your multimeter has > current on it you can also check the current drain to see if its to high > for > your power supply/battery pack. I suspect that the S2008MG is drawing enough to lower the voltage and set off the BEC. So the reason it is jumping backwards and forwards is because the servo starts to move, the BEC kicks in and tries to centre the servo. Think I'm going to go out and buy another 645MG today, S2008MG might just upgrade the S3003 in my Fireblade. > Maybe the Futaba R122JE is just not up to the standard for your setup and > can not handle all the high powered servos running off it. Possibly but the 645MG works fine and thats a higher torque servo. > Cheers >>> Well now I am confused. >>> [quoted text clipped - 67 lines] > > Possibly but the 645MG works fine and thats a higher torque servo. Consider a 625MG for throttle and brake work - slightly faster and still easy enough to lock the wheels. Or the 635 with carbonite gears, fast and strong. Although, as Richard stated, it may just be that you need to run with a Y-Lead - so battery and steering servo into Y, and Y into the steering channel on the RX. SignatureDan - on his PC >>>> Well now I am confused. >>>> [quoted text clipped - 75 lines] > with a Y-Lead - so battery and steering servo into Y, and Y into the > steering channel on the RX. Yes, sounds good to me. This is what I am going to try first. >>>>> Well now I am confused. >>>>> [quoted text clipped - 81 lines] > > Yes, sounds good to me. This is what I am going to try first. I'm sure this has jogged a memory of a problem we had once that was the same, and solved by a Y lead. I run on a Y lead on mine because it seems to give the steering more power - which in a great big brute of a Savage is important :) SignatureDan - on his PC Well I went out today and bought another HS-645MG and a Y Harness. Car is now finished, running with: Futaba R122JE 40 MHz Rx Hitec HS-645MG Servo x 2 6v 1100mah Humppack. Runs great, might be wishfull thinking but I'm sure the steering is better than before. Thanks to everybody who offered their advice. Gav |
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