A short while ago I completed a second conversion of the Severn lifeboat from the Chinese electronics to a twin motored 2.4GHz set-up. I used the new Mtroniks ESC “plug and play” for each motor to give tank steering, with counter rotating propellers. The transmitter was a Radiolink T4EU. The initial choice of motors were two JP 400, to give a bit more speed. Power was from 6 x 1.5V alkaline batteries.

The first “problem” encountered was having left and right hand propellers. The electrical set up for the ESC requires polarity to be followed. One BEC was used for the receiver, the other having its red lead decoupled. On switch on the two ESC powered up, they then recognise the stick positions on the transmitter as the neutral (centre) position and the first movement of the transmitter stick is memorised as ahead. Ah, with counter rotating propellers I discovered that one stick needs to go ahead, the other astern, so that the ESC then rotate the shafts in the desired direction when both pushed forward. This is NOT a problem as such, it just has to be remembered at each switch on, as the “plug and play” learn each time they are powered up. So centre sticks, switch on, move sticks in direction required, “problem” solved. It also means you don't have to reverse stick movement.

The second, real problem was discovered when on the water during first “sea trials”. For some reason the response of the sticks reversed after first full use, indeed it became almost uncontrollable, and it was obvious that the “failsafe” was operating in part during this episode.

NOTE: the failsafe on the Radiolink transmitter is on channel 3 [THR] and is factory set to full back on whichever stick is THR, remember it alters with Mode selection. Most 2.4GHz sets are designed for flying where the THR operates in one direction only, tick over is full back and full throttle is full ahead, so the failsafe is cutting the throttle (on a boat that's full astern!)

I was using both sticks up/down for throttles, and was in Mode 1, which meant that the righthand stick had the failsafe. This stick also had the boats rudder as left/right. My solution was to swap the channel stick connections inside the transmitter (re-soldering them) so that channel 3 became the left hand stick left/right and channel 4 now became the right hand up/down starboard throttle. On the bench it worked ok.

Sea trials again, a similar uncontrolled episode as before, but without any apparent failsafe full throttle cutting in. So I had dealt with that, but what was causing the confused controls. Why were the sticks changing settings and neutral positions being ignored? Reversing the stick settings back on shore and trying again did not help at all. Help!

Back on the bench. I decided to try and replicate what was happening in the water. The first thing was to put load on the motors to simulate the water effect, immediately the throttle controls were erratic and when centred, stabilised but sometimes reversed. Of course, on the bench when things get out of control one's instinct is to put the sticks to neutral. It was only by looking at the receiver and not the moving parts that I saw what was possibly occurring. With one motor running full all was ok, but powering on the second motor (regardless of direction) caused the receiver LED to blink, followed by electronic confusion. The power drain caused when the second motor started up was causing a dip in the BEC voltage to the receiver, hence a temporary OFF and no signal, so the failsafe kicked in, and the “plug and plays” established new stick positions for neutral and ahead as if the receiver had just been switched on again (which it had). And the sticks were every where but centred.

Sounded good to me. Checking the power on the JP 400, about 4A when both full on, so quite a pull when switched hard on. I swapped the motors for two MFA 360 3-pole. Slower motors but a lot less power consumption (0.5A @ 12V). Testing on the bench, all was smooth as a baby's. There was no blinking on the receiver LED.

On the water, perfect control, both motors working fine, tank steering no problems, no glitching or stalling or erratic behaviour.

I think I've found the cause, and provided a solution. I'm not saying it's a major problem but be aware that the plug and plays can reset if the power interrupts to them, and likewise, a lowered voltage to the receiver can cause the failsafe to cut in. My digital meter could not measure the voltage dip as it occurred, it was of short duration but was still significant.

Has anyone else experience of this or any comment to make, I'd really like confirmation of my findings. I have another tale to tell about failsafes and switch on for a later thread, concerning the Spektrum DX5e.

Kimosubby

Thanks both, I appreciate that the power unit itself is small – but thats the maximum I could get in because of weight. If it was my boat, I'd have gone brushless and used Li-Po batteries. Six re-chargeables means less voltage (7.2) as against six throw aways (9V).

I tried, as an experiment, a separate receiver battery – the set-up worked just fine with the JP motors. So the problem is a voltage dip under load. Again, had to save weight so avoided carrying another battery.

Malcolm, you may not have used the Plug and play yet, but no matter what way around you wire up, the ESC will always sense the polarity, and assume that the first stick movement is ahead (cos that's what it's been programmed to receive.) The instructions with them require the polarity be maintained from the ESC to the motor too. My explanation does read odd and seems odd, but believe me, the way I got it all to work is as written above.

Having used these "plug and play" I'll revert back to the manual setting ESC, at least you can then depend on them being the same as last time used (most of the time).

At least it gets the grey matter working.

Cheers, Kim

I understand all that you are saying Malcolm.

What I was getting across was that when the receiver lost signal out on the water (due to the power drop) and then found it again, the ESC then had new neutral points and probably stick movements not necessarily forwards, hence I then had a vessel "not under control" as I had no idea where the new neutrals were and what direction the ESC had assumed was forward. And then the cycle repeated again several times before I could get the vessel back. Amongst that was the failsafe acting with each drop on the starboard motor as well. It was the combination of events I was describing.

It's no longer my boat, and with the smaller motors suits the newcomer well. He will, no doubt, upgrade to Li-Po shortly, the motors being capable of taking 15V. I'll also, if he does that, suggest he get a small 4.8V pack for the receiver (as he'll have some weight to play with.) I could then swap over the 360's for the JP 400's.

Have you any experience with the Spektrum DX5e? I'm struggling to set one up for sail winch control.

Thanks again, Kim

I've been building and sailing yachts for several years, both free sailers with Braine gear and radio controlled too. I agree the old 27 and 40 MHz sets were ideal with just the two channels, but with bigger fields of entrants there became a need for owning several additional crystal pairs. There are still only 13 frequency slots for 27MHz although the band is now split to 32 possible with only 10kHz gaps but old gear is not that well tuned.

Of course, the advent of 2.4 does away with the need for crystals, and far more yachts can sail together. It's now a question of which sets are best use for sailing, and strangely enough it's the cheaper sets, although end point adjustment does appeal. The Radiolink and the Planet 5 can both be simply used as 2 channel units. I have a spare Spektrum so gave it a try as it does have marine receivers available, and it is attempting to train it to what I want it to do that is annoying. Currently I cannot change the failsafe position.

We use large powerful sail winches, as you know, with continuous loops under deck, driving sheets on deck held taut with elastic. We do tweak on deck as you put it, but mostly with 2.4 sets we set end points for the sticks to control winch travel. That facility is not present with the cheaper sets though, so we rely on a repeatable end point of winch travel.

I am just finishing a "footy" Vintage boats "Bob-A-Bout" and have incorporated one of the enclosed-cup sail winches as supplied by Component Shop. I'm curious as to how that will perform.

Aye, Kim

Hi Malcolm,

is that salmon backing braid the yellow coloured one? I found it and its excellent, no stretch at all. I use it as the main loop and then a slightly lighter strength white braid for the sheets. 100m for £11, as apposed to the exorbitant £5 for 5m from some suppliers. In fact a lot of my sailing/yachting gear is sourced from fishing tackle shops.

Happy sailing, Kim

OK Dave, I think they know who you flogged it to now……….