Broad Ambition - The Model

[grendel]

well I have eased the baseplate, removed 1 layer of the ply at the back end, and its still 1.5A, I think there is some drag of the grease in the prop shaft, but that is better than running it dry. it sounds 100% better than it was previously, I now know what to expect on model #2 so I can start progressing that. maybe if I get the chance tomorrow I will take a run to the local boating pool and test the new power levels, see if it is what is required.

[ZimbiIV]

There still seems to be some distortion in that coupling.

Try backing off all the screws/bolts 1/2 a turn and give it a quick run to see if it self centre's itself.

paul

[grendel]

well that was enlightening, I took the model to Herne bay, to the pond used by one of the local boat clubs, and took some advice.

The motor - even running flat out wasnt really pushing the model any faster (well maybe a little) but no spare power, when I bought her out of the water the motor was well hot, the binding somewhere in the drive train, and the resistance of the water on the prop was making the motor work hard.

The motor guru at the club showed me one of his models with the same motor, andthough a much smaller model it was a lot faster. he recommended a bigger motor for the size of boat - a 555 motor - low revving - high torque. 

I tried different props - no real difference. bigger motor will be looked at next.

[grendel]

hmm further investigations and easing one point, and its still not running as free as I wish - more powerful motor required. The only thing I can think is that the grease in the prop shaft is dragging the speed down, I will try cleaning it out and retest the motor current.

OK, so I forgot to post this, but I have been out, blasted the prop shaft through with a light oil, and retested the motor, 0.6A, - so it was the grease causing the problem. I now have a slight problem with the back bearing, where its made up from two pieces, its chattering, if I hold it it quiets down, so I may make some brass bridging pieces and bolt them around that bearing to hold it rigid, if the sound is anything to go by the motor is running a lot faster, so more testing may happen next weekend, before I opt for bigger motors. I did try a bigger motor, but that started at 1.6A and rose to over 3A when on the model.

[grendel]

getting all technical, I was wondering the difference in rpm between a current draw in the region of 2A plus and 0.6A (remembering the resistance of the water will push the current up a bit) so could I find a chart anywhere - no. the data sheet gives 3 pieces of data - the no load revs and current, the peak load revs and current, and the stall current (0 revs). so from this I drew a graph, now all 3 points are on a straight line - good, that makes it easier.

so the new current draw is 0.6A, this equates to over 10,000rpm

the current draw with the greased prop shaft was generally between 1.8 and 2.2A (best ever was 1.5A) this equates to between 7000 rpm and about 8000prm.

if we say that the current draw in the water is +50%

now we are looking at .9A 10000prm

we were looking at 2.7 - 3.3A - 5000 - 6000 rpm - and one very hot motor.

about 1A is peak efficiency for that motor, so it looks as though it will be just about right now, and we will have nearly doubled the speed through the water, tonight we will be testing the motor at the  new out of the water current draw to see if the motor gets hot- or not. oh and making the brackets to reinforce the bearing for the prop shaft and hopefully reduce the vibration there.

[grendel]

with the gearbox on at a 2.5:1 reduction at Beccles we were getting pretty much the same speed as I did at testing on Sunday, this would have equated to about 4500 rpm at the prop, which is why - if the prop under load was only managing 5000 rpm the speed didnt look any different. we will see how she goes next weekend.

[Happy]

On ‎17‎/‎09‎/‎2017 at 14:41, grendel said:

well that was enlightening, I took the model to Herne bay, to the pond used by one of the local boat clubs, and took some advice.

The motor - even running flat out wasnt really pushing the model any faster (well maybe a little) but no spare power, when I bought her out of the water the motor was well hot, the binding somewhere in the drive train, and the resistance of the water on the prop was making the motor work hard.

The motor guru at the club showed me one of his models with the same motor, andthough a much smaller model it was a lot faster. he recommended a bigger motor for the size of boat - a 555 motor - low revving - high torque. 

I tried different props - no real difference. bigger motor will be looked at next.

I bet the guys at Herne Bay loved the model?

Regards Alan

[grendel]

well they correctly identified it as a broads cruiser, then said they had never seen a model of one before.

this evenings bracket was made, motor testing done - after 20 minutes the motor was still hovering around 0.7A and was barely warm - result, next to see how it performs on the water.

[Wildfuzz]

Have you considered a brushless motor, I used these a lot in model aircraft, much more powerful and efficient.

 

S.

[grendel]

I am having enough problems with this motor at 11,000 rpm, it was fine at about 4500, but at 11,000 a bearing block had to be added at the free end of the prop shaft, greasing the prop shaft helped, but caused too much drag - slowing the motor down yet again.

[grendel]

so pending further sea trials, last night I have been clearing up the workshop - finding places for tools etc. as I had some danish oil left over the bench hooks received a third coat, as did sections of the bench that will be heavily used (next to the vice). Once the power plant on model #1 is performing as required I can fit the power plant to model #2 and progress that model.

[grendel]

right - just back from testing, and one pleasing result was that she was faster, the downside is the motor is still getting very hot however, so the next step is to go to a bigger motor - its not higher revving, just more torque, so it should expend less effort to move the prop in the water, so the motor should not get so hot - more work to be done and more testing next weekend. next to make a motor bracket. the downside is a higher current consumption.

[BuffaloBill]

I'm not sure how much room you have for clearance under the

shaft where it then goes to the drive shaft, but could a 4 blade

model aircraft prop be fitted to push cool air back over the motor?

Hobbyking do a fare range from 35mm up in both CW and CCW.

It won't stop the drain on the battery but may help to keep the motor cooler.

[ZimbiIV]

Water jacket? copper pipe.

 

[Guest]

5 minutes ago, ZimbiIV said:

Water jacket? copper pipe.

 

Bang on the money there , soft copper tubing wrapped around the motor fed from a pick up behind the prop but in front of the rudder discharged over the side   iv used this plenty of times on fast electric boats and it does work , also done it on glow plug engines round the head when no water jacket was available .

[grendel]

all great ideas, but now unnecessary, after slaving over the motor swap for a couple of hours, just after 5pm I loaded up again, and had a quick half hour at the boating pond, success, the bow wave is quite large at full speed, this is just faster than a walking pace, to be honest I dont think I will get much more out of her, without getting a lot more power into the water.

as for cooling, there is no space under the motor to fit a water jacket, but that too is not necessary any more, the bigger motor was barely breaking a sweat, this motor has a built in fan for cooling. i need to tweak the pictures, I used the wrong camera setting so they are a bit washed out - aw heck I will put them in. I also need to save some pictures my daughter took on her phone on the first session.

[grendel]

my daughters pictures

[grendel]

hmm the washed out ones didnt improve much, here they are anyway as they show the bow wave.

I did notice on this run that forward there were only about 6 steps in the speed, and it maxed out well before getting to full stick, so I reversed the wiring, and reversed the direction of operation, and now the more steps are in the forward direction, while reverse has the fewer steps.

here is some video too, the model makes fleeting appearances.

 

[Guest]

1 hour ago, grendel said:

hmm the washed out ones didnt improve much, here they are anyway as they show the bow wave.

I did notice on this run that forward there were only about 6 steps in the speed, and it maxed out well before getting to full stick, so I reversed the wiring, and reversed the direction of operation, and now the more steps are in the forward direction, while reverse has the fewer steps.

here is some video too, the model makes fleeting appearances.

 

Speed looks good to me very much like the real thing , glad things power wise have worked out now models are just like there full size cousins as far as power trains are concerned ie difficult to get perfect first time though model components are far cheaper to change to fine tune things .

[BroadAmbition]

Looks much better, sound considerably quieter too.  So perseverance and innovation in heaps has paid off once again.  Well done that man or even BZ

Griff

[JennyMorgan]

Even the wash looks to scale!

[Polly]

Good work!

[grendel]

more tweaking and testing, got the motor as quiet as I could, and tested the current draw, 0.7A - not far off the current draw of the smaller motor, I reckon we can bank on double that pushing against the water, so 1.4A (I will take my meter along and try and measure this next time I go.) at this rate she should have max 5 hours of sailing, on the main battery, the secondary battery will also be tested, this is a 6.5Ah 6v battery, which will give another 4 hours or so of reduced performance. I will know better once I measure the consumption in the water.

[grendel]

so its been a busy day today, trips to parents and generally running around until 3pm, then out to the workshop, model #2 accompanied me out there, looking at the (not fixed yet) prop shaft, this allows me a bit more space under the model - enough maybe to get the bigger prop in, but this seems to have been achieved at the expense of the space inside, the prop shaft is quite tight to the bottom of the hull, now with the original motor this wouldnt have been an issue, but with the bigger motor it is a problem. also, as I am pushing the prop further back nearer the rudder, the shaft inside is shorter.

Time to get creative, my silicon tube could take up the difference, but I really would be losing power into the coupling. OK my box of bits comes out, there is the remains of a nitro powered car in there - 4 wheel drive, complete with cv joints and half shafts, well I could use 2 sliding couplings, but I want to get one of these cv joints in there, the brass splined couplings used in the standard boat joints was a perfect fit into the ends of the half shaft couplings. how to get the drive from the output of the cv joint to the prop shaft, well the standard coupling goes through a pin into a hub the wheel bolts to, well happily the same end I fitted to the motors splined fitting, fits to the prop shaft end, and slides onto the axle end of the cv joint over the locating pin for the wheels hub.

I could just use these two fittings and a half shaft, but wheres the fun in that. this also means the motor can be mounted off line with the prop shaft. in one of those pictures below, the motor is running full chat without a problem, despite the prop shaft and motor being way out of alignment, next job, working out how I will fit it into the boat.

[grendel]

ok so trial fit into the model, and manufacture of the mounts to hold all the parts, motor tested with shaft and accessories in place, free running current 0.45A, driving the prop - 1.0A. we have the 35mm prop on, and this time the prop shaft support has had the extra leg soldered directly to the hub, so we should have no vibration there either,