aew

Radio control for an oar-powered model.

37 posts in this topic

As some of you may know, some time ago I built Amati's model of a Greek bireme. Although it's a 'Static' model, I opted to make the oars actually operate. I used a couple of radio control servos to raise and lower them ant to sweep them back and forwards.


I built a simple electronics circuit to drive the servos. Operation is limited to a simple straight ahead rowing action. However, that set me thinking about ways to have full control over the oars. I had no thoughts of actually building an RC oar powered model, but I did consider various ways in which it could be done.


 


Some time later Jim (bensid54 on the ModelShipBuider site) contacted me to say he was thinking of building an RC version of the bireme. That started me off again thinking of how to control the oars. I'd recently fitted a microprocessor in my model of Vanguard to flicker the lights so I decided to try using one to drive the oars.


 


Jim recently posted a Video of his system on YouTube which I thought was a great idea.


He's used some advanced feature of his radio system to control two modified servos so he has variable speed control of each set of oars.


I had to make do with my son's basic 2 channel radio which is specifically designed for use with a model car, (trigger for throttle, steering wheel on the side) but the microprocessor does allow me to get round those limitations.


 


Anyway, I've copied Jims's idea and posted a video on YouTube:


 



 


As you can see, I've raided the Technics Lego drawer again. It's great for working mechanisms, but all the Technics parts have holes in them so I don't think there's much chance of it actually floating! :)


Edited by aew
4whelr, AntonyUK, mtaylor and 9 others like this

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Hello Arthur,

 

Thanks. It's a wonderful sight to see those oars working.

 

Anja

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Looks like that was fun to figure out Art.  Are you going to put that set-up in your model?

 

 

Scoot

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Thanks for your interest  and comments folks.

 

It was an interesting challenge and what worked perfectly in theory didn't work quite so well in practice!

First problem was that when you want to steer going backwards, the logic of what to do with the stroke also works backwards.

Secondly, when you centre the controls, it just sits there doing nothing, right?

Wrong! The slightest disturbance and the oars popped up and down like a demented crab as it tried to figure out which way it should be going. :)

I had to build a little dead-band into the direction and steering so it would sit quietly at rest.

 

Scoot: I don't think it would look quite right fitted in Vanguard and there's no way I could squeeze it into one of the ship's boats!

Perhaps a Viking long-ship when I've finished Vanguard - but don't hold your breath, that's some time off yet!

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That's great Arthur! I love the lego approach my youngest son has a bucket of the stuff in the downstairs storage I better liberate it for my next project after the Bireme. You mentioned about getting the neutral spot on the controls being difficult to attain and I found with the band of any radio at neutral is very narrow and to my knowledge there is no way to adjust the neutral band on a two channel RC system. My radio is a Futaba 12 channel with a 14 channel receiver both of which I acquired through trades on an RC website so that kept the cost down and took some time to get. Because the Radio is for RC helicopter it has many adjustments and mixing options plus I can adjust the neutral band width on all channels so it really opens up what I can do when it comes to my tinkering. You can pick up a Futaba 6EX radio system for around $100 with a receiver I don't know what it costs in Pounds but you will find six channels can really increase your horizons and six channel receivers are about $20. Thanks for all the credit but the only idea you used of mine is the rack the rest you figured out on your own and to be honest I watch what you are doing because every so often you give me clues as to my next move.

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Jim: The neutral point is set in the microprocessor so there's no need for anything clever in the radio in this particular case.

'Neutral' is actually a 1.5mS pulse width, I just programmed in a small dead band centred on that time.

 

I tested it using my son's radio which is only two channel. I just hooked up a breadboard circuit to test the third channel.

As you say, multichannel radios with added bells and whistles are now available.

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Arthur: I've never used a microprocessor which makes me behind the learning curve electronics wise and with what I'm seeing from the work you have done they open up a world of options. My life experience has been as a Mechanic therefor I think in terms of how machinery moves so I lean in that direction, your posts and this hobby has been a blessing in my understanding new things in electronics. Are these processors costly, how do you make them waterproof ? Can the speed be adjusted at specific points along the servo travel? Sorry about all the questions but I can see where knowing these things is going to be very helpful to me and others.

 

As far as my Bireme goes I'm scraping the one I built and am going to build one bigger in size. I thought about starting a Kayak or a Viking ship but this Bireme thing has a hold on me and I need to make this one work with what I've got in mind to operate the oars. I'm going to take your example and build the mechanics before I build the ship but first I have to go shopping for parts.

 

I love the setup you posted it is much smoother than other RC rowing mechanisms I've seen and my guess is the electronics you use can be tweaked to your liking and I want to know more about it. Time for me to put away the ring spanners and break out the multi meter.

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The one I've used is the Atmega 168 (DIL). It's available from about £3.

It cost more than that for three servo extension leads to cut up for the inputs from the radio.

As far as waterproofing it is concerned, it depends how sophisticated you want get. Silicone sealant is probably the quickest - and messiest method!

 

I'm not sure what you mean about the speed at different points on the servo travel. Basically, divide the normal range of movement into 255 steps and you can tell it to move to any of those positions. It's then a case of how often you tell it to move to a different position.

If you count up 1 second at a time and tell it to move one step forward, it'll take 4 1/4 minutes to travel from end to end. If you count up one step every 100mS between 60 and 120, it will move 10 times faster over that part of the range.

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OK I'm getting it! So each one of those 225 positions can be timed individually to make the travel speed slower at the ends and faster in the centre of travel?

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A little rounding goes on. 250 steps of 40μs is a nice combination to use. That adds up to 1ms which is the difference between the minimum and maximum travel positions of a servo.

You can either move the servo the same distance each time but send the new positions more quickly, or you can send it new positions at fixed time intervals but move it further between some of the steps. Normal practice is to send the servo a pulse approximately every 20mS so what you do is calculate where you want the servo to be every 20mS.

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I'm interested! I love watching the progression of things as one gets the bugs out. When I built the mechanics for my Bireme I had many bugs and alterations along the way to fix. When it comes to my builds that is the fun part and from what I know of you Arthur you enjoy those challenges too.

Canute likes this

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As some of you may know, some time ago I built Amati's model of a Greek bireme. Although it's a 'Static' model, I opted to make the oars actually operate. I used a couple of radio control servos to raise and lower them ant to sweep them back and forwards.

I built a simple electronics circuit to drive the servos. Operation is limited to a simple straight ahead rowing action. However, that set me thinking about ways to have full control over the oars. I had no thoughts of actually building an RC oar powered model, but I did consider various ways in which it could be done.

 

Some time later Jim (bensid54 on the ModelShipBuider site) contacted me to say he was thinking of building an RC version of the bireme. That started me off again thinking of how to control the oars. I'd recently fitted a microprocessor in my model of Vanguard to flicker the lights so I decided to try using one to drive the oars.

 

Jim recently posted a Video of his system on YouTube which I thought was a great idea.

He's used some advanced feature of his radio system to control two modified servos so he has variable speed control of each set of oars.

I had to make do with my son's basic 2 channel radio which is specifically designed for use with a model car, (trigger for throttle, steering wheel on the side) but the microprocessor does allow me to get round those limitations.

 

Anyway, I've copied Jims's idea and posted a video on YouTube:

 

 

As you can see, I've raided the Technics Lego drawer again. It's great for working mechanisms, but all the Technics parts have holes in them so I don't think there's much chance of it actually floating! :)

 

 

Hi Arthur,

 

came across your post with the video today first time....

well made technique for actuating the oars, congrats, it really works !!   ;)   :)

 

Nils

bensid54 likes this

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Works better by a long shot! I checked it out and the control is great it functions better than mine. You could squeeze all that into a small space with right linkage or gear train. This will be a great system in the right boat with the right mechanics.

aew and donrobinson like this

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I think so Arthur, I haven't had the Bireme in the water since Fathers Day when I had my son help me with the video. Need a new camera based on the quality of my old one. I haven't done much hobby work in my shed except for gluing the odd part on my Bluenose but I have made something on the lathe at work I'll post pictures.

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Thanks Arthur it was a quick build so I'm happy with the results. Four inches wide 6 1/2 inches long and about 7 inches tall. The bore is about 1 1/8 inch 4 1/2 inches deep and I'm sure would make a very nasty bang.

mtaylor likes this

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