Finally purchased a 7.2v Lipo.(2100Ma 25C). Much better control but motor runs hot so I will need to reduce the prop size to reduce the current. Only had one run and with new battery duration was about 15 mins, Still very hairy from 3/4 throttle setting but much better than before. Easily outran a 650 powered MTB sailed by a fellow club member
Dave

Hi 😛 eter me again tried the shed found the K40 it is 3.18 stainless,cut it to the length and borrowed a dia-set,greased and inserted into boat working fine very quiet now,so of to the lake tomorrow for test.may be able to get a video so I will try and post it .PS:Great this site gets the old brain matter working,Thanks again might see you at the lake then ? wanted to go-to runcorn but the weather don't look so good.So its Newbrighton.TTFN Gerry

HI Peter:nice to hear from you,will try that I have a K40 in shed somewhere,I will measure it and see if its the same size,they used to be 3 or 4mm stainless,thanks for that I will post you if I succeed,its many year's since I used a die-set,will have to borrow one and do it pronto,need boat out wed for more trials.thanks again Gerry.

[ hi gerry I have a good idea . do you have a steel or brass rod off the old k40 you did have. if so cut to length and add screw threads at each end . you will need a tap and die set it should work give it a good coat of oil dont use greese in the middle only on the ends . let me know. peter

Hi:All ,I had my rttL out last week for a trial run she went ok.But now I find a problem with the prop shaft and prop.
The prop has sheared of and I need to find a replacment,
the prop is a 50mm three blade,and the shaft is stainless steel 250mm long ,but I can't find a supplier as it is a 1/8" or (3.18mm)dia and it has two screw ends approx 15mm.
any help please.Gerry

HI Rob, you may be interested in seeing my latest testing video


Extensive testing, direct drive, various Graupner brushed motors, then gearbox (ratio 2:1), then testing with various props, has produced almost 15mph, with a stone cold motor, water cooled. At the start of testing with direct drive the amp draw was too high. Since fitting a gearbox, I have been able to maximise the prop size due to a much reduced amp draw. prop is now a 4 blade brass cleaver style, 2mm clearance from hull,

The boat is going way too fast for nice turns, hence the reduction in speed when turning. HS93 has helped Immensley, could not have done it without his skills, the propshaft was too high in the boat, making the cog too high, this had to be realigned, and the rudder had to be extensively modified to assist fast turns and to stop the bow digging in.

Dave,

If possible I'd like a photo of your prop plus any of the purchase details - Manufacturer name, diameter, model number etc.

My copy of the Aerokits Fast Patrol Launch - is almost too fast for its size. its hull has the same narrow proportions as the Fireboat and the ability to dip too deep in a fast tight turn. Not good !
My copy of a Norstar Kingfisher is really nice and stable in a tight turn but does not have the same speed as the Patrol Launch. I'd like to make it go quicker on the existing (6) sub C Nimh cells, which means either just a different prop or new prop and motor.
Hence the interest in your prop. My 32mm two blade gives me the best performance to date. I have larger two blades but they limit my revs. 32mm is the smallest 2 blade I have. I may try a 3 blade scale type next.

Rob

Excellent just what I required. I have contacted the US supplier to arrange uk delivery. Their web site assumes we all live in the usa!
I intend to purchase another LI Po 11.1v but this time will ensure it has a balance connector. Don't know why they sell them without as the risk of over discharging a cell is quite high. if the experts are to be believed even a momentary over discharge by the tiniest amount can cause Irreparable damage.
Will try to get some video to post on the site - hope it doesn't flip whilst filming is in progress!. 😊

Good point re soldering Robert, Dave, I doubt the commercially available buzzer type alarm systems would manage each cell discharge, maybe running the boat, and checking the cells via a balance charger for example every 4 mins or so, then when you have a guide of run time under neaviest load conditions, you can just time your runs accordingly.
This looks like it will measure individual cells.

http://www.xtremecx2.com/servlet/the-164/Xtreme-LED-fdsh-Lipo-Alarm-Kit/Detail

Xtreme are "upgrade" parts for RC Heli's, I regularly use a USA company www.miracle-mart.com
If you email fao Kim, she is excellent at customer service, they are the main distributors for Xtreme products, if you require any info , something like this might do the job?

HI Rob
I do understand the principles involved with LI Po's and was keen to avoid any cell dropping below 3.3v. My understanding is that discharging below a certain voltage causes copper to be cumulatively deposited in the cell, this can over time result in a short as the battery heats in normal use resulting in total destruction. I have a commercial charger (Graupner Utramat 16) that looks after my batteries and will balance them provided a balance lead is present, all the available battery balance type connectors are supported. I also have a simple plug in voltage monitor that gives a rotating display for each cell voltage and the pack voltage.
In the model my esc will shut down when the voltage reaches 9.9v but this assumes all cells are balanced. ideally a check on each cell voltage would overcome this, hence my desire to use the battery balance lead to get this information. This can easily be achieved by a simple comparator circuit for each cell, the output being fed to a loud buzzer to give a warning. I should have mentioned that electronics is another of my hobbies.
Not sure what details re the prop. Can you give me some guidance on what details you require?
Thanks for the feedback
Dave

Dave,

Don't do it!!!

I have been using Li-Po's for a few years in airplanes.
Firstly you never discharge them in order to re-charge them. They have no memory effect and discharging them with a low current will over discharge them. in a typical airplane application, the ESC will trip when the voltage (under load) drops below the programmed level. This is visible by the prop stopping. By closing the throttle and then re-opening the throttle you can carefully ease it home at a low throttle. The idea is that when the load is off, the battery voltage will jump back up into the OK zone.

Li-po's are very temperature sensitive, to solder a connection you need special low temp solder so as not to over heat the cell/s.

I doubt that manually you would be able to balance to the accuracy of a commercial unit. For what they cost and the risk involved it makes more sence just to buy one with a compatible cell.
Not all balancer and the connections / connectors are the same.

For your ref' I attach the instructions for the Thunder Power unit.
When charging I connect the balancer to the cell and it works independently draining each cell if in -imbalance. You can watch the LEDs flashing away as each cell is drained. I then connect in the Triton charger and charge the complete pack leaving the balancer to keep everything in check.

Hope this helps.

PS - We still want more details of your prop.

Rob

HI PMDevlin.
My Esc is programmable so that it cuts off at 9.9v (3.3v per cell) but this assumes balanced cells. Do the LI Po alarm buzzers work on the total voltage or are they measuring each cell and giving a warning when any cell drops below 3v?
I am thinking I may need to build my own device to monitor individual cells via the balance connector if the commercial alarms don't.
Thanks for the advice on 7.4v and lower C values. That being the case I will either use one of my fully adjustable radio sets to reduce the pulse or design a small converter to do the same job between the receiver and esc.
Dave

HI Dave, with regard to lipo batteries, I use them with electric rc heli's, and as Robert has pointed out, its Important not to overdischarge. You may want to invest in a cheap lipo voltage alarm/buzzer/led, they usually are found on heli/fixed wing suppliers, if you google there are plenty, as you dont want to discharge past 3 volts per cell. if they start to puff up, get rid! 3 cell are 11.1v, 2 cell are 7.4, but I doubt a 2 cell will give you the "c" rating high enough to push your heavy ply hull without going flat pretty quick. I would stick with the 3 cell 11.1 for now . With a heli, its easy to tell when the battery is going off, the rotor speed goes down, with a boat I would think that its harder to check on the battery. The J perkins "twister skylift" has a nice led that sigifies low voltage, and it can be bought seperate, but my money would be on a buzzer so you dont miss it 😊

HI Peter
I will try and get a video of the model on the water so that you can see how fast it goes. As regards the car motor I will have to find the particular one I used. My son used to race model cars and had some fairly hairy set ups and I just chose one at random. it was heavy ran hot and needed loads of volts and amps. This all added up to some considerable weight and needed careful placement to allow the model to plane. I think the motor I was using needed some work on the armature as it kept stopping and wouldn't go until I recovered the boat and moved the armature. I am sure with the right motor / esc and battery pack you can achieve good results but am not sure I can add much of value at present. However I have a 48" Precedent Perkassa and intend to use brushed motors in that so will advise progress when I get round to working on the model. Could be quite soon as I have become quite interested in fast models after the Crash Tender,

Dave Have you any video's of your boat running that you can put on hear or utube. it looks very exciting. and what car motor did you try I am trying to get a list of usable and not usable motors and set ups together so when some one wants to go down this route they know what to stear clear of as it all seems to be a bit experentey at present

Peter

hI Rob
Yes the rpm is awesome. Probably why I can,t use full power. Assuming half tranny stick equates to 6volts at the motor this gives 20000 less some revs for friction, prop load etc I suspect it is running 12/15K.
I totally agree re your comments about LI Po. As you say each cell should be balanced every time you charge, This requires a simple connection to each cell terminating in a small plastic connector which plugs into the charger. Each cell voltage can then be measured and selectively adjusted so that there is minimal variation between cells. it is very Important that no cell drops below 3volts and does not exceed 4.2 volts. Go outside these limits and as you say they can explode. My charger is a Graupner Ultramat 16 and this discharges the cells before giving the correct charge for the battery capacity. With a balancer connected each cell is dischrged to the correct level. I purchase an e-book from Gibbs Guides.com with a very informative book on LiPo's. As I was experimenting with my set up I went for the cheapest option. I intend to purchase another battery 7.3v with a balanced connector and if I can source a supply will add a balance connector to the battery I have. I also store and charge my LI Po's in a Core-RC.com safe pouch.

Dave,

What an outstanding motor!

http://www.rcmodelland.com/index.php?p=6&id=277&new=&cat2=0&cat1=46&cat0=7&s=beadab0abde3c06f2d5c679f9bef42c6&lang=en

Being a 3850, it should be doing 3850 rev/volt.
A 3 cell Li-po is just over 12V = 46,000 rpm!
With this sort of rpm I can understand that it would fly but I would think the load of trying to turn it this fast it would get really hot. its true the spinning mass of an outrunner body adds torque similar to running through a gearbox but even so its trying to turn that prop really fast.
What size is the prop?

The price of the Li-Po is good but what you have to be aware of is cell Imbalance. if one cell is low, the high cell will get even higher as it reaches its charge peak. if it gets too high, thats when they catch fire.
I now use Thunder Power Li-Po's because they have a balance connector (matches their own auto balance).

Good work Dave

Rob

HI Dave, the video you mentioned, I for one would be very interested in seeing it running, can you upload please?

Hi
I purchased two motors from RC Model Land Co in China via e-bay. A 3480 $8 inrunner and a 3850 $3 outrunner. Both came with 30 amp speed controllers, but wouldn't reverse. So I bought a Tekmodel RC car brushless motor 60A ESC & program card $15. The 3480 was too fast and little tork but the 3850 works fine. Pictures attached of the internal set up. I bought a 11.1v LiPo for Steve Webb models in Frodsham for A£24 and already had a Graupner Utramat16 charger A£120 from Model Power in Warwickshire. The prop shaft is 4mm stainless steel (316 marine grade) tapped at both ends. I made the phospher bronze bearings on My ML7 lathe and both ends have 10mm touching the shaft. I use a simple oil tube soldered to the shaft to introduce oil. I have viewed the video and estimate that my model is doing the same speed on less than half throttle. I daren't go any faster as the model leaves the water and the prop over revs. Runs cool and I ran for over 20 mins and the battery was showing no signs of flagging or overheating. Weight is 2kg with battery and some lead weight I added to the motor compartment. The ESC programmer only allows adjustment of the reverse speed, which works fine. Also this is a car esc so you have to flip reverse twice before it kicks in. Saves the gears on a car. The smaller esc are not reversible and this 60A was the cheapest I could find.

Dave,

I jumped in too soon, I see that its a 34" Fireboat.
I'm intrigued to see a 45min run time with a 2200mA battery (avg draw = approx 3A), yet your using a 60A ESC.
Any reason why the ESC is so large?

Rob

Dave,

Looks like quite a handfull.
We need more info -

What size Fireboats do you have 34" or 46"?
What was the previous motor spec and votage, gearbox?

What are the details of the new outrunner?
How hot does the motor get?
What ESC and do you have reverse?

Rob

I have the same problem with my seaplane tender, it leaps out of the water and almost stands verticaly.

to slow it down I reprogrammed the ESC. instead when you are meant to give it full power then press the setup button I gave it just over half.

I can now pull the trigger all the way back and the boat planes safely now. 😀

another thing I tried whilst using my spectrum conroler was to just adjust the end point for the throttle.

Can you tell us what motors you have tried, and have you any pictures of the instalation.
Thanks
Peter

HI Dave, looks good!, what run time are you getting, and have you any way of measuriing the speed? Any video, that would be great!
HS93 and I have done extensive testing, and we had the same problem, the narrow hull gets to a point where its becomes very unstable and difficult to control. I have experience of brushless set ups in RC helis, but have stayed with brushed for now in the boats to save money!, and, it seems at just under 15mph we are at the max speed the hull will take, its on the edge of its handling!




video taken last week, you see its a big power back off to do tiurns or it rolls too much!

I have fitted an outrunner brushless motor to my model. I have tried using a 3 blade brass prop but the speed is still too fast. I have added extra lead to the front compartment but the boat is still almost flying. Has anyone had a similar experience and found a solution? I am using a basic Futaba 2 channel 40Mhz am set but could change to a different set with adjustable travel/end point settings but would prefer to stick with a simple set and modify the hull in some way. Another option would be a lower battery voltage (11.1v 2200ma at present).