I have one model which is, by far, the most difficult to keep sailing on a straight course. No model will sail continuously in a straight line if the rudder is untouched, but this one requires continual rudder movements. If I set it sailing straight it will sail a yard or two, and then start to turn in a circle. The direction is random. I've eliminated wind and water currents as causes of the sensitivity. It has two rudders, props, and ESC's with independent control. Tinkering with rudder alignment and prop speeds has not improved it. I have tried a couple of helicopter gyros as a means of keeping a straight course but they are ineffective on this model. I tried adding a 1" deep brass strip below the hull as a keel plate, also with no noticeable change. Anyone have any suggestions on how to improve this?
Hi Trillium, my thought is the esc's are they feeding of 1 battery or 2??? if 2 maybe they are discharging at a different rate, supplying a slightly different voltage to each motor. Have you tried 1 esc to both motors??? or 1 battery to both esc's??? just try these to eliminate the possibilities
It is your choice as to which one you buy BUT clones are available from ebay. I offer one of these as a solution because it is possibly the most capable of all the autopilot systems.
It is the core of autonomous vehicles in many hobby spheres. You can set it to hold a heading. It has GPS and magnetic compass capability.
Youtube has many many videos on this beast.
Having had time to think ( always a dangerous situation)
Try adding a weight to front of the boat and see effect pls. I am thinking the problem has to be a combination of thrust lines, CofG, and centre of buoyancy. A radical change of the CofG should change the behaviour of the boat ( for better or worse ) seeing the effect of such a change could indicate way to go .
"that's not a bug its just an undocumented creature."
Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)
Thanks for the suggestions. The batteries are arranged in series to provide a single 12V supply. I have also already tried replacing both drive motors and one shaft seal (they are waterproof shafts). You would expect that having independent control of the shaft speeds would enable any tendency to turn to be countered by adjusting relative speeds. The direction of turn is random and defied those attempts.
I will try changing to one ESC and see if that helps. I will also try a weight near the bow and test its effect.
The gyro was about as high-tech as I wanted to go in looking for a solution. The pixhawk looks downright scary!
Seriously the weight up front needs to be enough to move CofG a significant amount ( please note it may make things worse) its a test to see what effect it does have and to try to figure out what's going on. If your CofG is to far aft then the forces you would expect to keep a boat ( or any other vehicle) following a path have too little leverage to compensate for the wayward behaviour of a real world wind/wave/passing bumble bee etc.
The pixhawk is capable of fully autonomous control of a vehicle. It can follow waypoints and depending upon how its configured control many other functions as well.
If you ever saw the BBC tv James May and his glider he used an 8 bit precursor of the pixhawk to control the glider on its 20 mile flight and landing.
I will shift the C of G as suggested simply to see what effect it has, but it will be difficult to isolate the effect of the change in hull immersion, from the effect of rudder immersion. It can only be an experiment and not a solution; it's a scale model and it's loaded down to the correct waterline.
I experimented with shifting the C of G, moving it from 15" from the bow to 13.25" and 16.5". There was no noticeable change in the model's straight line behaviour. I have still to try connecting both props to one ESC. I also plan to increase the size of the rudders (which are already oversize) and reduce the servo/rudder arm ratio to see if that makes any difference.
I have a couple of twin screw boats. As you say, maintaining perfect straight line is pretty much impossible, but it sounds like you are having more serious issues. In my set ups, both motors have their own respective esc, but then connected by a "Y" lead, so only one common source from the receiver. It might be easier if you read my Fireboat build here on this forum.
So, one motor has its own battery source, its own esc, but operating from one receiver channel (I also have twin motor planes, that have a different set up, but we wont go there!)
It sound to me with your elimination process its one of your components failing, try swopping everything form port to starboard, does it favour one direction?
I bought a simple rev counter from ebay, if you can get one of these, then you can static test the revs and see if there are any fluctuations, or a rapid decrease of one of the motors
Hi Trillium What is the model boat you are having problems with? I agree with Paul some pics would be helpful of the insides, including all wiring and connections. Also a view underneath your model from stem to stern and also port to starboard. Is the hull self built? The advice so far has helped you investigate many of the electrical problems so perhaps we need to look a bit wider to help you resolve the issue(s). Dave
I have not been able to do more testing yet, but I can provide more information as requested. I have not seen any consistency in which direction it deviates from the straight line. That is the most puzzling part of this. If it always went one way, it would point me in the right direction, so to speak. I do know that before I replaced both motors, one shaft would always run a little slower than the other, but I used to compensate for that with the throttle to get it sailing straight. I now have two Electronize motors installed, which appear to run at the same speed, but I haven't put a meter on them. Mtroniks Viper Marine ESC's are used for control. This is a 1/64 scale model of the Royal Iris, the Wallasey cruise/ferry vessel. Amongst other operational tricks, they would depart from a landing stage by going astern on the outboard screw and ahead on the inboard, to swing the bow out before moving ahead. Straight line sailing is necessary, but manoeuvring is more fun, which is why I have (and want to keep) independent control of the screws. The hull is self-built, balsa plank on frame and then fibreglassed. It is powered by four 6V NiMH battery packs arranged in series-parallel to provide a single 12V supply. This also supplies the lighting in the superstructure. The radio is powered separately by a 6V non-rechargeable alkaline battery pack. NiMH batteries are used to keep the weight down so that the hull immersion is correct; four packs are used to distribute the weight and trim the hull correctly. The model also carries a speaker/sound system, which plays period music, and has its own battery.
The hull seems sound, no dinks etc, in photo 4 the starboard shaft looks slightly out of line and in photo 3 the port rudder is slightly more than the starboard.
There does not seem to be any item in the hull to cause a balance problem, you mention the old motors running at different speeds, could you have a shaft that is seizing slightly, then releasing? that might cause erratic steering, or possibly a duff U/J
Hi Trillium I used to cross the Mersey on the ferries and they all had a tendency to crab their way across the river. Depending on the state of the tide they did use to leave the landing stage as you describe. Looking at your hull I agree with jarvo's observations. The rudders are inboard of both propellers so will not be balanced as would be the case if they were in line. The hull shape is basically a box with minimal free flow over the rudders. Once the hull starts to wander off centre it will require quite some rudder effect to correct the drift. Where your rudders are placed near the centre line, their effect is shielded by the hull and will not be as effective as rudders further from the centre. The randomness of the drift rather supports this as it is some random effect (wind, current or motor mismatch etc) that starts the deviation. I can't see the angle of the propshaft so it is difficult to comment on what effect that might also cause. I have sailed several twin propped models and all were best kept straight by use of independent props, with the rudder(s) used to counteract wind drift. I believe your chosen method is the best approach, but you will have to keep adjusting the revs on the props to maintain a straight line. I normally have one motor on a ratchet control stick and can then just worry about the other motor and rudder, in my case both on the right hand vert and horiz sticks. Hope this helps you understand the possible cause of the effect. There is another member on this site who has a whole fleet of Mersey ferries and he may be able to give further guidance. Dave
Thanks for all the thoughts and ideas. The shafts are parallel, but the angle of the photo may suggest otherwise. The rudders are not exactly parallel, but I find it hard to believe that the amount of mismatch can be the cause of the problem. I have been careful to do any tests when the water is calm and there is no wind, and run them in both directions ( as would be done on a measured mile), to try and eliminate extraneous influences. (Doesn't mean that's been entirely succesful, but enough to convince me they are minor effects.) I had previously contacted Max (4clubs) and knew that his model did not have this problem, so he couldn't help me at the time. I now learn that the Hoylake club has 3 models of this vessel and none have this problem. These models all have the rudders inline with the props, (so not true to the prototype, but each to his own.) This points to the offset rudders being a major contributor. I still plan to increase the size of the rudders, to see if that improves the directional stability.
Hi Trillium I agree the external influences may be mild, but they are sufficient to start your hull pivoting about its centre. If you can increase the rudders to a size and depth that will counteract this then your model will respond. I suspect you will need to develop a sailing technique to keep correcting the rudders to achieve a straight course. Please keep us posted on your progress. Dave
if we go back to the beginning, the deviations on a straight line are quoted a saying random, so I cant see how the rudders are going to create a random fault.
Can I suggest try it without one rudder, then the other, then none obviously sailing along the lake edge with an inboard wind!) You will have to block up the rudder tubes with grease or something. If the problem is still there, its not rudders.
Is it speed related, I've seen this before on a friends glass fibre hull crashtender, it kept rolling to one side or another at speed, turned out to be the hull had an imperfection, we tried motors, props, esc's all sorts, and it was a concave section on the hull.
It's certainly not a silly thought, but it would be major rework. So if that were to be the only cure, I'd have to live with the present behaviour. The screws and the rudders have been moved forward of their correct scale position to place the rudder posts inside the walls of the passenger compartment. I considered it the least offensive compromise to give access to the rudder posts. Moving the rudder posts outboard to the screw centrelines would mean major rework to the walls and deck of the superstructure, as well as the hull. Even with the rudder posts in their adjusted position, they are close to the walls and there was not enough room to swing a rudder arm. Rudder control is arranged using toothed belts and pulleys on the rudder posts.
Hi Trillium, what you describe with the rudders might be the problem, water dynamics are far stronger than air. pushing in slightly different directions with the thrust of the props acting on different angles of the rudder blades, PM's idea of removing one then the other rudder is sound, also cheap!!!
Possibly increase the blade area so there is more bite, particularly depth, have you considered a fixed bow rudder to hold the bows straight like a dagger plate for fast boats, the belt drive to the rudders, is this through one motor or two?? possible they are not acting together so creating a differential and potentially stalling one or both rudders in the prop wash.
Are your props conta-rotating? if so have you tried reverse rotation, ie, port prop on starboard shaft, motor wireing reversed as well??
Hi Trillium As you have moved the screws and rudders forward of their design position the balance of the boat has been altered and as a result is now very prone to becoming un-balanced. I do understand the reasons why you made this adjustment and your solution to increase the size of the rudders is probably your best option to avoid major structural changes to your hull internals. We often have to increase the size of rudders on our model yachts and this is best achieved by having a much larger bolt on rudder attachment for use when sailing. You can then take the attachment off when out of the water. Initially I would use rubber bands to hold the attachment in place to see the effect. Dave
I appreciate all the good ideas and suggestions. I'm going to work through the list in an order which I think will be easiest and/or most effective. Starting off with increasing the rudder size by mechanically attaching something grossly oversize. If that works, I'll reduce the size step by step to find out what's the minimum size that makes sense. The rudders at present are oversize compared to the plan of the original. One of my early fixes attempted was to attach a 1" deep brass plate about 20" long under the bottom centreline of the hull as an external keel. I considered that would make a big improvement, but it made no difference. Steering control has a servo rotating a toothed pulley. The toothed drive belt goes around it and the two rudder pulleys. The toothed belt ensures the rudders move and stay synchronized. Roy
Hi Roy My Solent lifeboat has a large keel all along the hull. I had to increase the rudder size as the keel was counteracting the rudders. Possibly why your 20" brass plate didn't work. Good luck with your trials of the bigger rudder, I see no reason why this shouldn't work. Dave
In view of the several comments relating to relative prop speeds, I decided I needed to do some retesting to check how reliable my recollections were. The conclusion was that operation is worse than I remembered. I connected both ESC's up to the same servo tester so that they were both receiving the same signal. I placed the model in my backyard testing basin; only about one inch of water under the keel, but the same for both props. Turns out that the port prop runs slower than the starboard. At low speed, around 1000rpm on the starboard, the port was only turning at about 300rpm. THings were better at higher speed, 2000rpm on the port and 2500rpm on the starboard. Instantaneous readings showed fairly stable speed on the starboard shaft, but 2:1 variations in the speed of the port shaft. This suggest to me there's some stick-slip friction. Switching ESC's created no significant change. So this needs to be investigated before toying with rudder size. Both motors are new, and the port inboard shaft seal was also replaced at the same time as the motors. The motor/shaft alignment is good, and the couplings are double universals, so none of these are likely to be a cause. So my next step is to pull the port shaft and check for crud, and maybe run a reamer through the outboard shaft support. Offset rudders means I can pull the shaft without having to remove either the rudder or the motor, of course. Roy
If you are using left and right hand props your motors will be running in either counter or counter clockwise directions. Some motors are designed to run in one direction and can show unpredictable running in the reverse direction. A bench test with an ammeter in each motor lead should show the same reading over a range of speeds in both directions.To eliminate any external factors you could run the test with the motors fully connected or free running. Dave
First of all, disregard all the speed information in my last post. After a frustrating few hours trying to understand inconsistent and erratic readings, I discovered I was holding the tacho incorrectly. There was no guidance in the instruction manual, but I learnt that it is necessary to hold the body of the tacho at right angles to the shaft, ie athwartships not fore and aft. At least the readings are reasonable, and repeatable, so I think they're correct. Having said that, removal of the port shaft revealed no evidence that would account for any slow running. Turning by hand indicated it was quite free. So fresh test data is as follows: Stbd ESC feeding Port motor, and vice versa - Ahead rotation; servo tester set on mark 1: Port 750rpm, Stbd 1060rpm - Astern rotation; servo tester set on mark 2: Port 530rpm, Stbd 650 rpm Stbd ESC feeding Stbd motor, and port ESC port motor - Ahead rotation: servo tester set on mark 1: Port 840rpm, Stbd 1210rpm - Astern rotation: servo tester set on mark 2: Port barely moves, Stbd 1550 rpm The port motor runs consistenly slower than the starboard, whichever ESC is used, and whichever direction it rotates. Suggests that there's a problem with the port motor. Next test will be with the radio to learn the control stick settings necessary to match the speeds. Might be worth testing with another new motor. Any other thoughts? Roy
Matching motors are expensive, I have had a quick look at the earlier posts but cant see what type of motors you have, if they are cheap ones, buy another and see if you can match 2 together, were the motors in your hull or on the bench? try a drop of oil on the motor bearings could be running dry!! also have you put a spot of oil into the shaft bearings? I mad the mistake of putting grease into my shafts and it nearly stalled the motors, still not got it all back out.
Hi Roy You clearly have two motors that are not equal. The fact that the port motor requires a higher voltage to start confirms this. Also the fwd and reverse rotation suggest the motors are happier running in one direction. As Mark says matching motors can become expensive as they are mass produced to a particular spec which may not meet your particular requirements. You could try free running the motors for a long period (15 mins at slow revs) in both directions to see if this helps bed in the bushes. If you run one in the forward direction of the stb prop and the other in the forward direction of the port prop they may become more matched. Problem is they may then not be as matched in reverse but it should help your forward straight running. If you cannot match the motors you have two options; use two left or right handed props;or use a gear on one motor to reverse the rotation so both motors run in the same direction. Dave
The motors currently fitted are Electronize model 365/14. Does anyone else have experience with this model? Electronize motors are generally not cheap, but this model is one of the cheapest in their range. What would be a recommendation for a "good" motor? The test data above is with load on the motors - I should have mentioned that. Motors in the hull and the hull in the water, loaded down to the waterline. The prop shafts are Raboesch waterproof shafts, with a "G" seal, so they are water-lubricated. The connectors to/from ESC are as supplied on Mtroniks Viper models. To motor are all bullet type. THey are sound - clean and a bugger to separate. On the input side they are Tamiya connectors - look clean but how to test? Battery supply wires to ESC connectors are from screw terminal strip - I'll check cleanliness and retighten.
Wouldn't it be nice if the motors were made with a shaft extension at both ends; just a thought. Roy
Hi Roy, your readings of prop speed, between 750 and 1500 rpm, what size are your props? could be that the props are loading the motors to much. A change to 545 type motors would give a lot more torque, also more revs up the power band, you don't need the hull planing just throttle back when up to speed. The propshafts are great, so bigger motors might just do the job
Hi Roy I do believe your problem could be solved with prop shafts extending from both ends. I am not familiar with the motors but expect they are mabuchi or similar rebadged. The Electronize site has a section on motors http://electronize.net/motors.htm . This gives the expected current for different size props at various voltages. The stall current at 12v is given as 2.6amps for the 365-14. Can you measure the current with your props? If one motor is drawing higher current this may indicate an internal fault. I am not a fan of 360 size motors as they can be very greedy current wise and have a tendency to overheat resulting in deteriorating performance in a very short time. I had two in a Coast Guard cutter but now have two brushless which are much more powerful and reliable as well as running for much longer. Not that I am suggesting such for your model ferry. My personal preference for a scale model is a"555" type motor. It is a high tork low current motor that works very well in low speed models and allows scale size props to be fitted. I use three in my 1:96 scale RMS Olympic and have several smaller scale models that also use a single motor. Regarding your Tamiya connectors they can after some use become unreliable especially if high currents are involved. You can static test any connection by using a multimeter on the lowest Ohm range. There should be no resistance recorded if the joint/connection is good. I doubt if this is a problem as you are feeding all from a single battery (or pair). Dave
A scale model that mimics the behaviour of the prototype has to be a good thing, and that description certainly fits my model. But it's not so relaxing sailing this one. The props are 3-bladed 40mm dia. Current readings taken today are as follows: Stbd ESC feeding Port motor, and vice versa - Ahead rotation; servo tester set on mark 1: Port 0.62A, Stbd .54A - Astern rotation; servo tester set on mark 2: Port 0.7A, Stbd .4A Stbd ESC feeding Stbd motor, and port ESC port motor - Ahead rotation: servo tester set on mark 1: Port 0.5A, Stbd .42A - Astern rotation: servo tester set on mark 2: Port .42A, Stbd .54A Battery voltage was 12.6V. Since the port motor runs slower and generally draws more current than the starboard, all suggests that I should at least replace the port motor. But I am inclined based on the comments and this experience to replace both with the larger size. That may have to wait awhile since suppliers with good stocks of motors are on your side of the pond, and we have a threatened strike by Canada Post. Roy
Didn't you say that your boats steering prob was random. One motor running slow wouldn't cause that I would have thought. Rather that it would be the same direction all the time.By the way which Royal Iris are we talking about. The odd looking "FISH & CHIPS BOAT " as we knew her. Or the latest incarnation that ran aground? I meant the F&C when I talked about the steering
We're talking about the 'fish and chip' Royal Iris, built 1950, diesel-electric, currently moored on the Thames downstream of the Thames barrier. In the course of investigating the random steering problem, it has become clear that there's a motor problem. It appears to be fairly consistent, but there might be a random element. So I'm trying to resolve that, before I move on to some trials with larger rudders.
Hi Roy As I suspected one of your motors is not as efficient as the other. Probably a poor internal connection on the armature but difficult to be certain. If it was my model and there was room, I would fit two 555 type motors as they are very powerful, low current and low revs. The specs are: Very low drain motor for small/medium workboats on 12V. Excellent low speed & torque. Voltage: 12~30V, Revs: 5050 (12v), Weight: 218g'. Type (RS555PH-23300) Min Max Voltage Revs (r/min) Current (A) Power (W) Torque (mN-m) 218g 12 30 12 5050 0.36 380.3 Dimensions: 57 (mm long) x 37.1 (mm dia) Weight: 218g Shaft Length: 13.4mm Shaft Dia: 3.175mm There are several suppliers in the UK. Try looking at, http://www.componentshop.co.uk/ in their motor section, for a comprehensive list with specs. Lower revving motors tend to start more consistently than high power and high rev motors which have been tweaked to give max efficiency at high revs often at the expense of easy starting. I hope you manage to find a suitable replacement pair, notwithstanding the best efforts of the Canadian postal service! Dave
was the original statement, its highly unlikely to be just one of the motors as the deviation from straight course would always be constant. It could I agree be a bad connection, coming in and out, and I agree, those Tamiya connections are pretty much the worst on the market, tiny thin pins, and loose, cannot carry volts Roy, just flip the motors over, see what happens before you go buying new equipment, have you tre3id the rudders as suggested, and have you got a video yet? seeing the problem would certainly help as your take on what is going on might be misguiding us, just a thought 👍
Very soon after my last post I was offered two motors matching the specs given by Dave to try out, so I did. With the stbd ESC feeding the port motor: - Ahead rotation, servo on mark 1, Port .46A, 1450rpm; Stbd .4A, 1800 Rpm. -Astern rotation, servo on mark 1, Port .24A, 315rpm; Stbd .14A, not turning - Astern rotation, servo on mark 2, Port .54A, 1700rpm; Stbd, .28A, 1800 rpm With the stbd ESC feeding the stbd motor: - Ahead rotation, servo on mark 1, Port .38A, 1390 rpm; Stbd .34A, 1610 rpm - Astern rotation, servo on mark 1, Port .1A, not turning; Stbd .2A, 440 rpm - Astern rotation, servo on mark 2, Port .42A, 950 rpm; Stbd .32A, 2450 rpm Battery voltage 13.0V. So generally a better match between these motors in the ahead direction, than the 365/14's. Difficult to say, based on this data, if the motors are better running in one direction vs the other. With some trim adjustment on the control sticks I'll be able to obtain closely matching ahead speeds. I have also learnt that motors to the same spec are available from the USA via Ebay for US$8 each. I have used Banggood, but delivery of anything from China to Canada takes a minimum of 6 weeks.
Hi Roy Seems like you have found a workable solution without too much alteration. Interesting to see your price at US$8 converts to £9 in the UK for a similar motor. Please post some pics when you manage to get on the water, hopefully sailing in a straight line. Dave
Hi Roy,with the new motors, try running them in in the direction you want them to run, the brushes will bed down and they may become more of a match, try 3 volts for 30 mins then 6 volts for 30 mins, a drop of oil on the bearings every 15 mins would help as well
Hi Mark, I'll give that a try. I have a question for the experts. Are the bronze bearings in the Mabuchi motors plain bronze, or a sintered bronze with a lubricant such as graphite or PTFE embedded in them? The reason I ask is that information I found on the Mabuchi website suggests suitable applications for these motors are automotive, inkjet and laser printers, and massagers. These are devices which are unlikely to have any kind of follow-up intermittent lubrication.
I followed Mark's suggestion and gave the motors some running-in. After that, I found that with a small tweak on the stbd trim tab I was able to get a good speed match on the shafts with the radio control sticks at the same setting. I dropped the voltage to 6V, which is entirely adequate for the model. (I need 12V for the lighting, so I'll have to fit a voltage reducer for propulsion at some point.) During the testing I had a mishap with the batteries and have replaced the four 1600mAh batteries with two 2500mAh. These are heavier, so the model sits a little lower in the water, which will have an effect. Today was the first run in the pond after all the experimenting. Not the best conditions because there was an intermittent breeze. It appears to be better, will sail further in a straight line before it wanders off and makes a circle; still random. Next step will be to fit the larger rudders and wait for a windless day to test it. No video yet, but will try and get some on that occasion. I think progress has been made.
I'm happy to report that increasing the rudder area has made a significant improvement in this model. The as-built rudders on the model are ~8 sq.cm, and I have temporarily increased this to ~27 sq.cm., more than 3 times. The biggest dimensional change is in the fore-and-aft length, so they are as long as they can be without projecting beyond the stern of the hull. Today was not windless, but even with slight gusts of wind it sailed along serenely with barely a touch on the rudder to keep it straight. Also surprising is that it will no longer "turn on a tanner". Also , turns are much smoother and better controlled; can only be due to the rudder change. As on the last trial, it is sitting slightly lower in the water, but I think I'll leave it that way. The next step will be to reduce the length of the rudder in decrements of 5 sq.cm. and see what effect that has. Roy
That's true, but I need much more capacity for powering the motors than for the lights. Another option is to put two batteries in parallel for the motors, with a third 6V battery in series for the lights. The batteries are already being charged individually. Interesting option. Roy
Hi Haverlock, In my original post I mentioned that I had tried a couple of different gyros and neither had made any noticeable improvement. The rudder movements were very small in off-water trials, presumably because helicopters are much more sensitive. I have increased the size of the rudders and that has made a big improvement. I am in the middle of tests where I am reducing their size step-by-step. I have not yet got down to a size where I get the original poor sailing. Roy
That could well have been a solution. However, a trial I ran this morning has established the minimum axial length for the rudder. With a 40mm length and greater, straight line sailing was very good, with 35mm it now tends to wander away from a straight line. So one of my winter projects will be to make two new rudders 40mm long. Thanks to everyone who provided input into this quest. Roy