Suter drive system

[Eddy Matthews]

Here's the basics of the drive system for the Suter sternwheeler - Still a lot of work to do to finish it, but it's coming along and it actually looks like it will work! :-)

The motor drives a shaft via a toothed belt, the shaft turns the crank arms which will be linked via wooden arms to the slider mechanism at the back - This in effect turns rotary motion into linear motion - The slider is then linked via two more wooden arms to the paddlewheel itself.  I hope that makes sense?

The motor in the photograph is a dummy just used to show how things will go together. I've just ordered a 50:1 ratio motor and gearbox from MFA/Como which gives 158 RPM on 6 volts, so it should be fairly close to what I need, and I can always vary the motors top speed by increasing or decreasing the voltage slightly.

[gbritnell]

Eddy,
I'm assuming that the crank at the end of the countershaft has the same stroke length as the crank on the paddlewheel. My next question is: What is the length of the arms that go from the countershaft crank to the slider mechanism? Are they going to be the same length as the main pitman arms that go from the slider mechanism to the paddlwheel crank? The reason I'm asking is because you will get into a mathematical problem with the angle of the crank when it's between 0 degrees (top dead center) and 90 degrees. I will draw this up in autocad and try to post it for you.
George

[Khephre]

Eddy, where did you obtain your toothed belt and pulleys? And what specs did you buy to, i.e. is the ratio 1:1, number of teeth, size of belt, etc.

I've been tossing up drivetrain options for the split-sternwheeler Jean build I've been thinking about, and am torn between the toothed belt option running pitman arms and a chain-and-sprockets alternative connecting directly to the wheels.

Gary Nelson did a corker version of Jean using chains direct to the wheels but from the few photos I have I believe that the prototype was driven by pitman arms on each wheel, so I'm more enthusiastic about that option and a couple of sets of toothed belts, pulleys and a couple of MFA Como geared motors, etc wld fit the bill nicely.

One other question - aren't you overspeed at 158 rpm on 6V for a sternwheeler? I have it in my mind (somewhere in the dark corners, just behind the cobwebs) that a sternwheeler should be geared to 30-40 rpm.

Many tks for your clarifications
Tony

[Eddy Matthews]

Eddy,
I'm assuming that the crank at the end of the countershaft has the same stroke length as the crank on the paddlewheel. My next question is: What is the length of the arms that go from the countershaft crank to the slider mechanism? Are they going to be the same length as the main pitman arms that go from the slider mechanism to the paddlwheel crank? The reason I'm asking is because you will get into a mathematical problem with the angle of the crank when it's between 0 degrees (top dead center) and 90 degrees. I will draw this up in autocad and try to post it for you.
George

Yes the cranks are identical George, I made two left hand and two right hand, all exactly the same length.

To be honest I didn't consider different length arms to be a problem - But since the motor/countershaft unit and the slider mechanism are seperate items I can easily adjust the length to make that distance the same as the distance to the sternwheel.

I'd be interested in more information on this if you could do something in AutoCad as you suggested George.

[Eddy Matthews]

Eddy, where did you obtain your toothed belt and pulleys? And what specs did you buy to, i.e. is the ratio 1:1, number of teeth, size of belt, etc.

The toothed belts and pulleys I got off a friend at my local club, but they originally came from http://www.hpcgears.com in the UK. The pulleys are 1:1 ratio.

I'm not sure if I can get all this stuff to work properly, as the slightest difference in lengths or angles will cause the whole thing to lock up solid. But I'll give it a try - If the worst happens, I can always resort to using a belt or chain drive, but like you I'd love to have a system of working pitman arms that looked like the original.

One other question - aren't you overspeed at 158 rpm on 6V for a sternwheeler? I have it in my mind (somewhere in the dark corners, just behind the cobwebs) that a sternwheeler should be geared to 30-40 rpm.

I'm basing my speed on the Dumas Creole Queen I used to have - It used about 110 RPM. So allowing for the drag of the drive system and the drag of the water on the paddlewheel, I hope that I'll be somewhere close to what I need. I like to have a reserve of power to get out of trouble quickly and to have the power needed to go against a headwind when required.

I can always vary the top speed by reducing or increasing the voltage - An easy thing to do as I use Nicads, or I can change the pulley sizes. If I'm way off the mark you'll hear about it here when I get the model onto the water for testing.

I hope that helps?

[towboatjoe]

Tony, Let me speak from experience. If you don't have a minimum of 100 rpms on your wheel(s), you'll kiss your boat goodbye to the cross winds and current. Remember that most paddle boats float like a styrofoam cup on the water and the wind loves to play with that. Even the real boats have to fight cross winds.

[gbritnell]

Eddy,
Do you or someone you know have the capabilities of opening an AutoCad file? If not I'll print it out and take a picture of it and then post the picture. I have used this method before and it works fairly well.
George

[Eddy Matthews]

Eddy,
Do you or someone you know have the capabilities of opening an AutoCad file? If not I'll print it out and take a picture of it and then post the picture. I have used this method before and it works fairly well.
George

I can view AutoCad files George, but perhaps a normal image posted on here would be better, then everyone can benefit from the information?

I'm still confused by your statement about the length of the arms - NOT that I doubt you - just my poor little brain cannot grasp why it should be a problem!  :-)

Work on the drive system has stopped until I hear from you again - That's not a problem, I have plenty of other bits to do! So don't worry if it takes a few days to sort out...

[Khephre]

Tks Joe and Eddy, without your advice I'd be dead in the water. Tks also re the contact for the belts and pulleys.

Tony

[gbritnell]

Eddy,
 What happens is this. With one end of the arm sliding along in a flat plane and the other end going around the crank pin you have a situation which is referred to as the angularity of the rod. Lets say you have a crankpin that is 1inch away from the center of the paddlewheel therefore giving a 2inch stroke. Now you have a pitman arm which is 10 inches long. When the pitman arm starts from top dead center and travels halfway down it's guideway (1inch), the crankshaft has not turned 1/4 of a turn. Depending on the length of the pitman arm it could vary by as much as 3 degrees. Therefore if you use a pitman arm up front that has a different length than the pitman arm going out to the paddlewheel you will have a mathematical difference in angular stroke at 90 degrees. I will post a picture as soon as I get a chance.
 George

Paddleducks <drivesystems@paddleducks.co.uk> wrote:
 

   The following message was posted on Paddleducks, by Eddy Matthews  
    gbritnell wrote:  Eddy,
Do you or someone you know have the capabilities of opening an AutoCad file? If not I'll print it out and take a picture of it and then post the picture. I have used this method before and it works fairly well.
George

I can view AutoCad files George, but perhaps a normal image posted on here would be better, then everyone can benefit from the information?

I'm still confused by your statement about the length of the arms - NOT that I doubt you - just my poor little brain cannot grasp why it should be a problem!

Work on the drive system has stopped until I hear from you again - That's not a problem, I have plenty of other bits to do! So don't worry if it takes a few days to sort out...


 
Regards
Eddy


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[Eddy Matthews]

Thanks George, I'm sure your right, but I still don't understand why.... Hopefully when you get round to a drawing of the situation it will become clearer?

My few brain cells take a while to grasp things like this! :-)

[Khephre]

Crikey, you said a mouthful there George.

Can I clarify - by using an output rod or pitman arm that is exactly the same length as the con rod from the motor crank, you're mirroring the angularity of the con rod with the pitman arm, and by doing that you're eliminating any tendency to bind at difference angles of the crank?

And - in effect, Eddy's slider mechanism is equivalent to the cross-head guides in a slide valve steam engine?

Yours in bewilderment
Tony

[gbritnell]

Tony,
 That's it exactly. When I looked at the picture Eddy posted it looked like he was going to have a short link up front which would have caused the problem. Thanks for the simplification.
 George

Paddleducks <drivesystems@paddleducks.co.uk> wrote:
 

   The following message was posted on Paddleducks, by Khephre  
Crikey, you said a mouthful there George.

Can I clarify - by using an output rod or pitman arm that is exactly the same length as the con rod from the motor crank, you're mirroring the angularity of the con rod on the pitman as well, and by doing that you're eliminating any tendency to bind at difference angles of the crank?

And - in effect, Eddy's slider mechanism is equivalent to the cross-head guides in a slide valve steam engine?

Yours in bewilderment
Tony



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[Khephre]

Crikey George, you said another mouthful there!

Did you actually use the word "simplification"? My limited math is stretched beyond its outer limits mate so you give me too much credit. I'm simply trying to understand what you've already spotted.  

Having said that, this has been an invaluable series of postings so thanks a heap, team! It's helped me start to grasp the mechanics behind Joe's pitman arm drive system that he has on his website.

http://www.dragg.net/jbrown/construc2.htm

Joe, do you have any photos of your pitman arm drive mechanism other than the ones on your website?

And another question or two for you - I'm OK with soft soldering but not up to scratch on silver soldering or brazing. What are the loads like on the mechanism? Will soft soldering be strong enough or wld you recommend a more substantial approach? Any other learnings or recommendations that you'd make for someone wanting to follow your approach?

Praise Be for knowledgable people!

[derekwarner_decoy]

Hi PD's - Tony you question the strength of soft solder which is naturally considerably less than silver solder, but  if you apply some simple principals all will be OK for say most model work & typically model wheel linkages or the like

If you had two sections of 1/4" brass angle iron normal thickness from a hobby shop [typical 0.013" flange thickness] - good cleanleness [steel wool the joint surfaces & good clean liquid flux etc] the resultant 1/4 of a square inch of wetted soldered joint will be extremely strong and I suggest the brass angle iron would distort under load before the soldered joint failed

Another trick for highly loaded soft soldered joints [brass paddle wheel frames or ribs] of thicker 0.050" brass material is to use a few 10BA brass screws & nuts and combine them into the soldered joint

Having said this I do understand soft soldered joints are not acceptable for a model steam engine construction & this is where silver solder comes into its own as a correctly dimensioned & silver soldered joint has similar yield strengths to the parent materials [grey cast iron or steel] being joined

Segmented belts - you will find a limited range of 6 mm wide segmented belts & pinions [or differential housings] at model shops that cater for fast electric or nitro R/C cars - Derek