LiPos cause motor to stutter except at full speed

[no stick]

I sent the following email to Steve and Sarah Hill of Robotics Power Solution aka battlepacks. Sarah asked me to post on the OSE forum to see if you all can help to come up with a solution to eliminate motor stuttering below full throttle.

"Hi Steve and Sarah,

I ordered 4ea 7.4V 3600mAh 12C/16C batteries for my SV-27 as per your site. Using these batteries I have not been able to get the motor to run consistently except at high speed. At all other speeds the motor seems to stutter like hit and miss. All my other batteries seem to work well including the E-moli Liion 4S2P 6000mAh as well. I have tried your batteries in both a 4s1P 3600mAh and in a 4S2P 7200mAh and there is no difference in eliminating the mid range motor stutter. I sometimes will run slow speed for awhile and then jump forward which is difficult to bring in to the dock. Any help to resolve this will be most appreciated."

Have any of you had similar problems with LiPos and if so what was your solution?

Ed

[JimClark]

You need to post way more info on your setup for anyone to help.

Jim

[avengersteve]

how old is your sv? what radio are you using? do you have the BEC hooked up?

[no stick]

I purchased my SV in Jan, 2007. I am using a Spektrum DX-7 radio and AR-6000 RX. My prop is the Octura M-445 BPS and I use OFE adjustable trim tabs. I use a second port turn fin, and a separate Traxxas water pick up mounted on the transom. I am not using a separate BEC. Interesting concerning the BEC as the system only uses one servo. The battery wires seem to be thicker that the 12 guage wires on the ESC which may mean less resistance.

Ed

[Fluid]

Why is it 'interesting' about the BEC and 'only' one servo? All my FE race boats run without BEC and none have more than one servo. The ESC needs power too and it is possible that the new packs exceed the maximum voltage for the ESC except with the voltage depression at full load. That is not likely, but I can't see another explanation given the information we have now. An intermittent loose conection might do it, but I am stumped. Try a separate receiver pack....



.

[no stick]

Why is it 'interesting' about the BEC and 'only' one servo? All my FE race boats run without BEC and none have more than one servo. The ESC needs power too and it is possible that the new packs exceed the maximum voltage for the ESC except with the voltage depression at full load. That is not likely, but I can't see another explanation given the information we have now. An intermittent loose conection might do it, but I am stumped. Try a separate receiver pack.... .

Tks, I'll try a separate RX pack. Did you mean you run "without" BEC or you run with a BEC? If you run with a separate BEC which one do you use?

Ed

[Rex R]

iirc, space permitting, that Jay runs his boats using a rx batt pack. given the current trend in boat hulls...space is only an issue with micro-hydro's

[JimClark]

What speed controll are you using? Is it programmed properly?
JIm

[no stick]

Ths SV-27 comes with a 45amp ESC. There are no specs available from Acquacraft or Tower Hobbies, but I believe it is the Silver Series from Great Planes with two Deans Ultra connectors to run two 6cell sub C in series for 14-18 volts. The Great Planes specs show a programmable brake but nothing else I believe.

If I use a separate 6 volt Rx battery, should I cut the red wire coming from the ESC to the Rx so the ESC will not power the Rx?

Ed

[JimClark]

just pull the red out of the plastic connector it slips out very easially.
Jim

[no stick]

Tks for the help.
I switched ESC from another SV-27 and there was no stuttering on the first set of batteries and some start up stuttering on the 2nd set which went away after 2 minutes. I will try the dedicated Rx battery next, but it appears there may be a difference in timing. Specs for the ESC say 12 degree timing angle. Specs also say 4S LiPo, 2ea 2S packs in series. If it was a Castle Creations i could set the paramenters and download from my computer.:p

I wonder if the voltage under load is very high due to new batteries and perhaps after use it will settle down. Thoughts?

Ed

[no stick]

iirc, space permitting, that Jay runs his boats using a rx batt pack. given the current trend in boat hulls...space is only an issue with micro-hydro's

OK, so no need for a seperate BEC in electric boats and you eliminate the BEC in the ESC by using a Rx battery pack? What are the advantages to doing this? I'm not that familiar with electric boats but I fly a lot of shock flyers. Standard in shock flyers is seperate switching voltage regulator (BEC) for more than 4 servos or more than 3S LiPo or a separate Rx pack if there is room since the only way to cut down the voltage using the non switching voltage regulating ESC BEC is to release heat, hence the different ESC/BEC amp ratings.

Ed

[Rex R]

the esc can send/cause radio intererence through to the radio via the bec circut. by eliminating the bec you reduce the chance of a glitch. jay runs boats that do over 50mph, as well as some that are in the neighborhood of 100mph! if it were my boat going that fast...I'd really not want to have it runaway(and maybe kill some one) due to a radio problem. in your case well, lot of the bec circuts can only handle 12 cells w/o causing prob.s