Problem with r/c in corvette model

[Michael BordParticipant @michaelbord10152]

Hi, haven't posted on here for a while but have been slowly moving a couple of projects on (plus operating current boats) but do enjoy reading the various forum topics.

Ok, advice now needed. I've got my Revell Corvette to a point where I can try it out. various flotation trials in test tank (aka the bath), got radio, motor speed control and rudder working fine. I'd previously run the motor connected directly to the battery for some time to try out various propellers , settled on one where the motor drew under 1 amp on 6 volts.

Having fitted and tried the electronics, I took ship down to the pond on a very calm day this week. Looked like I'd got the ballasting ok as it sat very well in the water. she was very controllable, ahead and astern, enough power to go above scale speed, but throttled back went at a scalish looking speed. Also steered very well. All was well for 20 mins or so.

Then disaster, everything cut out and the ship was stationary. Neither the rudder or prop would turn. Turning transmitter on and off did nothing. Eventually the model drifted to the other side of the lake.

1. there was no power to the radio. (green or red no signal light not on)

2. I turned off the switch to the esc then turned it on again. This time there was power, could run motor forwards and backwards, and operate rudder.

I've tried this again in the bath (so under load). Moving rudder to full position seems to cause the motor to hesitate as if there is a small blip where the current is cut off. If the motor is running slowly this makes it stop then it won't restart and power is cut off to motor and servo. Turning esc switch on and off then resets it.

The battery is a 6v 3.4 a/hr lead acid one. The voltage after 20 mins was just under 6 volts. The motor is an MFA 385. The esc is an mtronics viper marine 15 and the radio is Tamco with a 6 channel receiver. Servo is just standard. All very straightforward kit, all components new for this boat (existising transmitter with new receiver, bind was fine). That sort of set up has been fine in other boats and very reliable.

Has anyone had any problems similar to this? Not sure which part to change first – higher voltage battery? Could it be servo suddenly drawing a high current, or faulty esc perhaps ?

Advice gratefully received!

[Michael BordParticipant @michaelbord10152]

[Kev.WParticipant @kev-w]

I had a similar problem, it turned out to be a faulty ESC, I phoned the mtronics help line & the first thing he asked me to do, was to give each of the thin black wires to the switch a tug, he said sometimes the fine wire breaks at the soldered switch connector.

This turned out to be the cause of my intermittent power outs, the cure was just to solder the wire back on.

Edited By Kip Woods on 15/06/2018 22:49:28

Edited By Kip Woods on 15/06/2018 22:49:54

[Mark Jarvis 2Participant @markjarvis2]

Hi Michael, a possible cause is a 'brown out' motor and servo drawing power below what the receiver can take, a move to a 7.2 battery may cure the problem, or a lipo, just to bring the voltage spike above the cut off.

Mark

[Charles OatesParticipant @charlesoates31738]

Hi, I'm 99 % sure it's just a flat battery, the most common problem of all rc failures. A lead acid battery is considered to be flat at 5.9 volts and has been said you will get a brown out..

I run an almost identical set up in a Corvette, with a similar battery so there's nothing wrong with the set up. Charge the battery properly, and see how long it all works for. Charged it should read 6.2 to 6.3 volts, on load or off. If it doesn't, change the battery, I use a 4.5 amp hr in mine without problems.

Chas

[TelstarParticipant @telstar]

Hi Michael. Mtronics accept a problem with some Esc. http://www.mtroniks.net/prod/Boat-Speed-Controls/Viper-Marine-15.htm#description . Don't know if this includes your one, link to their web page FAQ gives their comment.

Cheers Tom

[Malcolm FraryParticipant @malcolmfrary95515]

If waggling the black switch wires does not cause the problem to happen, that should be that problem eliminated.

Since the problem only happened after a 20 minute run, it looks like either the battery was not as charged as originally thought, or is not capable of delivering the required current over time. The servo "might" be putting too much demand on the battery when the charge gets marginal. This would have the effect of dropping the input voltage to the BEC which, if it went below the BEC's minimum, would also drop the output voltage.

Since ESC's and servos rely on accurate timing, and this relies on stable supply voltage, any variation is bad. Results are, variously, jitter and/or the radio cutting out. If the radio cuts out, depending on design, it "might" need to go through a power off and back on sequence to come back to life. I've had this when running on 4 cells (nominal 4.8v), but a nominal 6v SLA in poor condition might easily produce the effect.

Using a 5 cell NiMH pack should give the same performance, but without the trouble, downside is that a bit of ballast might be needed.

[Michael BordParticipant @michaelbord10152]

Thanks to everyone above who kindly provided advice on possible problems, given me a good structure to follow.

1. I tried pulling the black wires from the on/off switch to the esc and they are firmly fixed.

2. I attached an nimh 7.2v 4.2 ah 6 cell battery pack, fully charged and put the boat in the bath without the superstructure so I could see what was going on.

The motor speed control worked ok (boat was a bit more lively on full throttle!) and the rudder turned.

The receiver has a green light when receiving power and there is a signal, and a red light with power but no signal (and nothing runs in failsafe mode).

The motor was fine being throttled up and down from max ahead to max astern etc.

However, if the rudder was turned quickly to one side or the other with a quick stick movement, the receiver light would flicker from green to red to green. Jiggling the stick a bit, or letting it flick back to neutral from full movement, could make the receiver go to red mode and stay there. Turning transmitter off and on made no difference. It was necessary to switch the on/off switch wired to the esc off then on again. This turned on the receiver again (green light ) and motor/ rudder servo worked again. Until the next full servo movement.

I'm going to try another servo and see if that makes any difference, the current one seems to move erratically at times (bit jiggly).

The rudder movement problem happens without the motor running so I don't think there is any interference (motor has capacitors soldered on anyway).

I'm now thinking that this is what happened when the boat was on the pond, and I just hadn't tried a maximum and quick rudder movement to start with?

Thanks again, I shall report back.

Edited By Michael Bord on 16/06/2018 22:19:00

[Dave MilbournParticipant @davemilbourn48782]

It does seem that the servo is the root cause of the problem which, as has been mentioned, sounds like brown-out. Is it slowing down or even stalling before it reaches full throw? That will certainly take a lot more current and could cause a brown-out. Check the rudder linkage for free movement. throughout its full travel.

Is the servo a "digital" type"? I've handled several different types but they all seemed to shiver and twitch [a bit jiggly] even when the stick was at neutral. Whatever the reason was, this didn't seem at all desirable so I won't use them now.

Dave M

[Charles OatesParticipant @charlesoates31738]

I too avoid digital servos, they just aren't happy with my gear. As Dave says, the linkage is suspect. Try dissconecting the rudder arm and see what happens. If it's OK, something is binding, if not try another servo.

Chas

[Michael BordParticipant @michaelbord10152]

More testing.

1. I disconnected the linkage from the servo to the rudder. The rudder turns freely. I connected the nimh battery pack, turned on "esc to receiver power " on /off switch and transmitter. Green light on receiver. Motor runs forwards/backwards ok, no problem. Throttle to neutral so only servo being tested.

Moving rudder stick made servo shaft turn, but same problem as before, receiver light flicking to red then back to green. Servo could also be a bit jittery but intermittently. After a few full movements of the servo the receiver cut out again and needed on/off switch being moved to off then on again to reset.

So looks like the problem is with the servo.

2. I dug out another servo, but the only other standard size one I could find was the same make and type. I plugged that in in place of the one fitted to the boat. Exactly the same problem happened, and it was also jittery. This sounds like Dave Milbourn's comment about  digital servos above, but the Alturn spec says it's pulse width control so I'm guessing that isn't digital?

The make/model is Alturn USA AAS-700STD. I must have bought 2 together. I've looked on-line, found some details of this (still current type) but there doesn't seem to be anything unusual about it.

3. I then plugged in a micro servo and that worked perfectly. No glitches at all with receiver.

4. I then put another boat next to the corvette on the bench and connected the rudder servo in that to the corvette receiver with an extension lead. That's a launch that has been running reliably for 6 years. Again the rudder servo worked perfectly. That is a Graupner c577 servo. I've looked that up as well and the torque is the same as the Alturn ones(3.6 kg/cm) so I'm guessing the current draw etc should be about the same? So similar spec standard servo?

Next step is to avoid the Alturn servos for now and get an different standard sized one and fit that in corvette.

More news later!

Thanks again for advice.

Edited By Michael Bord on 17/06/2018 18:03:36

Edited By Michael Bord on 17/06/2018 18:05:21

Edited By Michael Bord on 17/06/2018 18:07:17

[Dave MilbournParticipant @davemilbourn48782]

Michael

Despite the confusing "digital" name, all servos are pulse-width controlled because that's the way the receiver sends their signals to them. The difference is in the way that the voltage pulse is dealt with once it gets to the servo. Quite why some "digital" servos behave in the way they do is a bit beyond my pay grade and also my give-a-damn threshold. I stick to using known brands from reliable UK suppliers – mainly Hitec servos from Steve Webb Models aka Servo Shop. They may be a bit more expensive but if things don't work they can always be returned and replaced with no problems. In the context of the material cost and time taken to design and build a model boat the saving of a few quid on servos makes little sense to me.
A standard Hitec HS311 will do the job for less than a tenner. **LINK**
Other suppliers may be cheaper.

Dave M

[Michael BordParticipant @michaelbord10152]

Thanks, Dave. The explanation about digital servos is very useful, first time I've learned about them.

The first servos I used were from Graupner which have lasted well. The ones I'm now having trouble with I picked up at a show somewhere (probably London model engineering exhibition). Because of the time taken to build the corvette that was several years ago!

Hitec sounds just the job, I'll get an HS311.

[CookieParticipant @cookie15923]

I have had nothing but trouble with digital servos over the years ,i now whenever possible use King Max analogue servos from Comp Shop and been trouble free since.

Dave

[Michael BordParticipant @michaelbord10152]

Bought a Hitec HS311 servo mail order just before I went away on holiday and it was awaiting my return. [There used to be an r/c model shop down the road but nearest one is now over 20 miles away]. Connected it up and works very well, the previous problem with the radio cutting out doesn't now happen.

Now fitted into model, rudder turns perfectly, motor control fine with no blips. No problem with radio cutting out. Should be ok for another test sail next week. (Should be perfect weather!).

[Malcolm FraryParticipant @malcolmfrary95515]

In retrospect, it looks like another case where a servo tester would have uncovered the problem early. When run on its own battery, it eliminates everything else as a source of trouble. This is a good thing as something like this can have multiple causes, and there is nothing in the rule book that says there is only one problem at a time.

[Tim CooperParticipant @timcooper90034]

I bought a cheap servo tester from a well known on line retailer. Delivered from China , cost about £3. Works fine and is very useful.

Tim

[Michael BordParticipant @michaelbord10152]

Just an update, having fitted the HS311 servo, the r/c set up has now been reliable. Had a test sail and all was well. Used a 7.2 nimh pack which has been used ok in other boats. Hope to have another longer run this week if it isn't too hot!!

Historical note: the first Flower class, HMS Gladiolus, broke down on her full power trials due to a hot bearing and had to be towed by a trawler. My model's power failure on it's first lake trial was therefore historically correct!

Re servo testers, sounds a good idea to be able to try components separately. I found one for 99p on e-bay, free postage from China! Same picture as ones for £5 or so. I'll let you know if it works…

[Michael BordParticipant @michaelbord10152]

Just as a postscript to this, I've had a couple of further trial runs with the corvette, and everything (especially the 311 servo) has functioned perfectly. Used a 7.2 battery pack and ship has sailed for nearly an hour with no problems, so should be ok for longer sails later.

So r/c equipment now working as it should, thanks again for advice.

The corvette does sail well with a 385 motor, enough power to get out of trouble, but throttled back cruises along at a realistic speed. Problem is avoiding knocking off delicate detail…

[Malcolm FraryParticipant @malcolmfrary95515]

The handrails were the biggest problem. After a few years they were more repair than original.

[Tim CooperParticipant @timcooper90034]

My Revell Flower uses a 385 motor as well.

I changed the railings to one's made out of soldered brass wire. Most of the vents etc near the superstructure did not survive many outings on the pond.

Tim

[Michael BordParticipant @michaelbord10152]

Reinforced brass railings sounds a good idea. I've still got some details to add, no armament at moment. I've sailed it in "initial builders trials" mode. Still, looks good on the water and does steer well.

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