Efficient electric boat

Discussion in 'Boat Design' started by Jeremy Harris, Jun 22, 2009.

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BertKuSenior Member

Thank you Jeremy,

I found the agent here in RSA. Will try to pop in on Thursday. One need well an university degree to absorb all the information throw at you. I am still searching for a simple table or curve with proposals for KW in >>> belt out.
Will I be so lucky.!!!

Let see what the experts have to tell me on Thursday.
once again, thanks
Bert

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Jeremy HarrisSenior Member

Unfortunately, Bert, it's difficult to have a simple table relating power to belt size, as the belt capability for transmitting power is a function of speed and tensile strength. If you run a belt slowly over a given pair of pulleys then it will only be capable of handling a fraction of the power that it would if you ran same belt quickly (because power is proportional to the product of rpm and torque). This is further complicated by the fact that these belts have a linear speed limit as well, so there is always a maximum rpm (dependent on pulley diameter) that you can run them at. Add in the need to maintain a minimum number of belt teeth in contact with the pulleys, in order to achieve the belt working tensile strength quoted, plus the need to account for pulsating torque loads, which need derating, and there's no simple way to use a table to do what you want.

The belts are effectively torque limited, in as much as you have to work out the maximum torque that your system will transmit, then use the radius of the pulley to calculate the load in the belt, then use the belt max allowable working tensile load to find the right size belt.

Gates Corporation have a calculator application available for download if you register with them, I believe, that will determine belt and pulley size for their specific products. I've not used it, as I use off-the-shelf generic HTD belts, that have a lower rating than the Gates GT2 series (and which are a fair bit cheaper!).

Jeremy

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BertKuSenior Member

Hi Jeremy, Yes I agree, for that reason I said, you need a university degree. I also downloaded the 2,8 Mbyte pdf file from Conidrive. That one is even more complicated. When I am back and have some more time I will go back to my study years and burn the midnight oil .
Thanks so much for all the information.

It will be quite a difficult drive to Cape Town. The fog is dense and not too many drivers are able to handle fog. They slow down, stop at the most ridicules places, or drive too fast.
Next week Tuesday I am back again.
Bert

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MCDennyJunior Member

Bert,

The Gates "driveflex" program takes out all the engineering work, very easy to use and offers a wide range of solutions sorted by price. Once you have Gates part numbers your local bearing and power transmission retailer will be able to interchange to whatever brand they sell.

The parts are easily availble on the web as well.

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BertKuSenior Member

Hi Jeremy,

It must have been my lucky day, because the first place I visited, was a small manufacturer, not even the agency of Gates, who makes the pulleys in one off’s. Although their place is full of “pipes” of Gates belts. Am I correct in guessing that 4 rows mean, the width of the belt is 4 cuts wide. i.e. a “pipe of 3 meters” has pre-prepared cuts to make it easier to make a belt as wide as one like to have.

They only charge Pound 10 for a small iron pulley and Pound 22 for a 10 cm pulley. It does not matter how many teeth it has, whether 5 mm or 10 mm or 14 mm pitch, the price is the same. Only for aluminum, they ask 10% more. Also, if I want stainless steel, I have to pay Pound 30 for re-sharpening of their tools, as stainless steel is not the friendliest material to work with.

The belts are quite pricy. 45 pounds for a small T5 - 525 mm long (Mectrol)belt and 40 mm wide

Should you have a problem in getting the correct pulley for your project, maybe we can give a hand and post it to you.

Just one question, what is better to have a pulley with even or odd teeth’s ?. I calculated the pulley with 31 teeth. Somehow my instinct tells me that it is better with odd number. What do you use?

I did some mid-nite oil burning and came up with the following.

I am planning to use:
1) a 5 Kw motor i.e. 6,6 Hp.
2) Rpm small pulley 2750
3) Belt style 4 rows (i.e. 40 mm wide)
4) small pulley diameter 98,72 mm (31 teeth)
5) large pulley diameter 200,63 mm (63 teeth)
6) N = number of teeth in engagement
7) n = number of cavities per small pulley
8) D = Diameter of large pulley
9) d = Diameter of small pulley
10) C.D. = Center distance mm

N = n ( 180 – 60 (D-d)
----- ----------
360 C.D.

N = 31 (180 – 60 (200,63 – 98,72)
------- ------------------------
360 200

N = 12,867

500 is according to the table with the number of teeths engaged and pulley D
2750 = rpm

H.P. = 500 x 98,72 x 2750
------------------------
12,867 x 10-6

H.P. = 10,549 i.e. safety factor of 1,598

Jeremy, I am not a mechanical expert, how does this compare with your calculations?

Thanks Mc Denny, but I do not have access to too many Gates agencies and have to work on a more primitive manner. Thanks for your hint.

Last edited: Apr 20, 2010
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BertKuSenior Member

Hi Jeremy,

My apology, I overlooked the fact that you are stated:

" I'm using a 72 tooth driven pulley and a 28 tooth drive pulley, so I have lots of teeth in engagement and the whole lot is going at a moderate rpm."

Odd number of teeth is probably only used with tooth wheels and not with a belt. I will re-calculate and use even numbers. Probably easier to manufacture a pulley with even teeth in anyway.

Thanks for all the help.

Bert.

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Jeremy HarrisSenior Member

Hi Bert,

Those prices seem pretty good, but the T5 profile isn't quite as efficient as the HTD 5M profile, so you'd need to take that into account. For your application this may not matter - I'm a bit like Rick, in that I'm chasing down every last lost watt of power!

As far as I know it doesn't make any appreciable difference having odd to even or even to even teeth ratios with these belts. Unlike chain, they tend to wear evenly no matter what, I believe.

I finished making the first part of a new drive system this evening and have to say that I'm impressed with the low losses when compared to the Mitrpak gearbox. I'll post some pictures later in the week, when I have things a bit more finished, but the drive shaft and double universal joint I've put together seems to have virtually no power losses at all. I can spin the 72 tooth driven pulley by hand and the prop shaft keeps turning for a few seconds. What I've made is a 1" OD stainless steel tube, with a 10mm diameter shaft running inside it, supported on ball races at either end. The lower end has an angled composite housing containing a double universal joint (to give constant velocity) and another ball bearing supported shaft that will be connected to the prop.

Jeremy

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Squidly-DiddlySenior Member

your specs and model match an Aluminum Grumman Sport Boat

in everything but "Victorian".

I heard those are perfectly paint-able.

They are also maintenance free and tough as nails.

Even better, they will be worth something to a wide range of buyers if you need to sell.

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BertKuSenior Member

Hi Jeremy,

I am dying to see your work. Judging from the previous box, it will be cool.
Bert

What power do you drive the prop? 3,3 Kw/48Volt motor at 12 Volt? i.e. about 220 Watt?

Diddly, Maybe you have replied to the wrong thread???

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portacruiseSenior Member

Jeremy, think your idea of a double universal is really cool. Wonder if it is a first in marine application? Perhaps something you adapted from your aircraft years?

Porta

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BertKuSenior Member

Indeed Porta, it is a very unique way of doing it. I wonder what sort of power could be transferred in this way.
Bert

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Jeremy HarrisSenior Member

I'm not sure that it's that much of a novel idea, as I got it from the shaft drive system used on these old Canadian "Dippy" motor boats: http://www.dippy.ca/ although I've seen aircraft that use the same approach for transmitting control motion (next time you fly, take a seat over a wing and peer down into the gap that appears as the spoilers pop up. With luck you'll see the multiply-universal jointed shafts that drive the control jack screws).

The "Dippy" only uses a single joint, running at a modest angle, but with a double joint you can theoretically turn the shaft through 90 degrees if you wish. I've opted for a more modest angle, as it allows me to get a better position for the motor inside the boat.

The amount of power that can be transmitted depends on the angle and type of joint. The plain bearing joints I'm using (from here: http://www.techdrives.co.uk/html/universal_joints.html ) are limited to about 1000 rpm and have a torque rating that depends on angle. There is some useful information on them here: http://www.techdrives.co.uk/Multimedia/Universal Joints/Selection & Installation.pdf

For example, at 45 deg per joint (90 deg total angle for a double joint) the torque rating needs to be derated to 25% of the nominal rating. This means that the small (10mm bore, 22mm OD) joints that I'm using will only transmit about 250 watts continuously at 1000 rpm and 90 deg total angle. At the 45 deg total angle that I'm running the joints at they will handle about 600 watts continuously, far more than I need.

They run smoothly even at 90 degrees, with very little increase in friction with increasing angle.

Jeremy

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Jeremy HarrisSenior Member

Here's an update on the universal joint idea. First off, I tried a joint that operated at 135 degrees, as I thought that the losses in the joint might be a bit high if I ran it at a sharper angle. Here's a picture of it:

I made the housing by laying up some glass fibre on to a mandrel, then cutting the moulded part to the required angle. This turned out to be a bit cumbersome though.

When I just clamped the bearing housings to the moulded part and ran it up I was very surprised to find that it ran extremely smoothly, with no detectable power loss. This made me wonder about running at a sharper angle, which would make the whole drive leg a bit more like an outboard.

For the next prototype I changed the mould technique. Using the mitre saw I made two 20 degree cuts in the mandrel, then bonded the pieces together with epoxy. Before making the cuts I made a line with Sharpie down the length of the mandrel, so that I could easily align the parts to the right angle when bonding them up.

I then just wrapped glass fibre around the waxed, angled mandrel. Once it was cured, I cut the glass fibre in half, using a Dremel. This proved to be a quick and easy way to make a housing that I can finish off by simply wrapping some glass fibre tape around. Here's a photo of the 100 degree joint:

This turns every bit as easily as the 135 degree one and gives me a near right angle drive with no noisy gearbox. I can't hear any noise at all coming from the joint, even running in the open, so I'm hopeful that when the tube and housing is filled with light oil I should have a quiet and reliable unit, that doesn't need any maintenance. As the unit is cheap and fairly easy to make I'm not going to make it repairable - I'll just have to make another one if it breaks or wears out.

Overall, the UJ solution seems a good one, as it's cheap, fairly easy to build and runs evenly and quietly. The downside is that these UJs have to be derated when run at sharp angles, so the maximum power handling is limited.

Jeremy

14. BostonPrevious Member

I been reading along for quite a while on this thread just kinda absorbing things but wanted to stop in and say how slick that thing is Jeremy

question though
what were the losses for the various angles you tried
I kinda thought you believed from post 362 that there were no appreciable losses

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