I'm gonna need a bigger lake.
Oh, and a new speed controller
A lot has happened in the last two weeks. I followed George's guidance: made the front running shoes about 30% wider, got rid of the rear wedge, moved the prop to the right and moved the CG forward. Apart from the shoes, the rest turned out to be a pretty complex, slow process, partly because I only have 'slow' glue. The wedge was very difficult to remove. Once it was off, I set about re-setting the prop. As things stood, I would have needed a severe S bend in the tube (already in bad shape) so it was off to the local hardware shop for a new length of brass tube. Looks like gold (and cost about the same!). I rebuilt the entire drive line, which involved hacking out a fair bit of structure and re-making the motor mount. I set up the drive with the prop at the recommended height the motor as low as possible and the shaft dead straight. This gave me the 'bit of down' on the prop that looked about right so I set everything in place, leaving a couple of inches of flex shaft free to give me some adjustment should I need it. I've kept the flex shaft and strut for the moment, because that is what I have. I've left the rudder behind the prop because that seems to work rather well (even though the transom does look a bit like a construction site - hardly 'scale!). I removed some structure under the cockpit and made a new home for the battery way up in the nose (I have to push it in with a (soft) stick that also locks it in place). I also removed the dummy engine as this was rather heavy and right on the stern. Net result is that the CG is a little further forward than suggested but now easy to adjust by moving the battery. Finally I added little fins to the front shoes and fitted the stabiliser fin as per the plan - I found it in a drawer. (But you may notice it's on the wrong side!!)
Friday afternoon was spent preparing for an evening run and the boat was behaving very badly, as if it were reluctant to go back in the water. Every nut, bolt and washer fought back. Glued bits fell off, wouldn't quite fit.... Last straw was when the Tx battery gave up as I was trimming the rudder but we got there in the end. In the water. Cameraman ready? 'Battery's dead, Dad'.
So, in words. One click and some low speed taxiing to encourage the local wildlife to move on (except for three signets, who decided this was all jolly interesting and they would stay to watch, thank you very much). Another click and she's moving well -
in a straight line! Up to 1/4 throttle and she rises gently onto the plane. Now that's what I was hoping to see; not a sudden lurch but a controlled transition - a silly idea, I know, and the cause of many problems. Getting bolder, I push the stick forward and she's away, fully planing, just kissing the surface as she goes and straight as an arrow. And travelling at one helluva rate of knots! A few seconds later and it's time to pull back - she's almost out of sight. Turn around and off we go again. Steering is good. Of course, I wouldn't try to turn corners at this speed but 'course corrections' are easy and precise. If anything, she looks a little light on the stern and there is a hint of hopping up and down. That can be fixed.
A few speed runs and I'm getting the hang of it (almost). At this point, I realised I'm at half throttle. What? It's already too fast! I couldn't resist the urge to give her the gun so up went the stick. Oh my Lord! She took off like a rocket on steroids! I have no idea how fast she was moving but she was covering about fifty yards in a very few seconds. Shut down quick before she ended up in the Solent. Clearly, full throttle runs are not going to be marathons.
I did a few more runs at 'sensible' speeds (interspersed with the odd sprint) and then suddenly the motor stopped. I had already found out from the maker of the ESC what should happen, so I shut the throttle and waited for the ESC to reset so I could bring her in under taxi. And waited, and waited. Nothing, zilch, nada, though I could still wiggle the rudder. Oops. Something's wrong. There she sat, about twenty feet from the shore - and the wind had dropped to nothing. Not a breath. Not even an irate swan to come over and chase the intruder off its patch.
I left nipper on guard duty and popped home (half a mile) to find a rope or something. No luck there, so it was plan B. On with the shorts. By the time I got back, Bluebird had drifted reasonably close to the opposite bank but was still out of reach. After a little more waiting, there was only one thing for it. Into the lake. The water was below waist deep, not a problem - but cool. However, although it's an artificial lake, there is a thick layer of mud on the bottom. After a few steps, that layer was getting seriously thick and I decided that calling the Fire Brigade to pull me out would take some explanation so I retreated.
Plan C. We started throwing stones over the boat so that the ripples pushed her to the side. That worked - but.... How difficult is it to hit a small model boat with a hefty stone at twenty feet? Not that difficult, it turns out. I read that Bluebird had suffered a bird strike on the rear boom before her final run. Am I taking realism too far?
Eventually the boat was recovered. I looked inside and there were signs that the ESC had got pretty hot. Then I noticed that two of the motor wires had come unsoldered and the two capacitors on the feed end had come off. Serious heat!
Saturday morning I was resigned to buying a new ESC but took a careful look at the old one first. There were no signs of damage to any of the chips. Maybe... The capacitors had me going for a while as I wasn't sure which way round to fit them. I applied a bit of logic (positive to positive lead etc.) and looked closely at the pads they had come away from. Under an eyeglass, I could match up the legs to the right pads from the shape left behind. What's to lose? Soldering iron out, eyeglass in. You need a lot of heat to get those big wires back on and there's a real risk of burning you nose when you are that close. Connect up, waiting for the bang. Bleep bleep... We're back in business!
I see what they've done with the speed controller. It's a marvel of miniaturisation but at the expense of robustness. I worked for many years on 'electronic packaging' and I have to say, if someone passed me that design for approval, I would give them a slap! Hopefully, it will hold up long enough to get some video (if I lay off the throttle!).
And so, plan for the day. Pack is charged, Tx on charge, camera on charge. Brain still running on empty. If the weather hold out, it'll be off to the lake this evening, armed with a 'rescue boat' (nipper has a 'toy' speedboat that he's not that impressed with but it will do to nudge Bluebird in if we get another disaster) and a 50m ball of string to make a drag line if all else fails. Oh, need to charge the 'rescue' boat's pack!
With luck I'll be able to post some pictures and video tomorrow
(I need to find out how to reduce the file size of my pictures first as they are far too big to upload)
Author
Topic: Donald Campbell's Bluebird K7 (Read 88050 times)