Changing Servo Speeds

[Khephre]

I want to change the speed of a servo without going to the expense of buying a new transmitter and wonder if there are any electronic wizards amongst us who can help.

Typically a stock Futaba 3003 servo takes around 0.2 sec to rotate sixty degrees. What I'd like to do is to slow that speed down to as low as a full second. I know there are new TXs available which allow you to change the servo speed at the TX but that would cost me way more than the project is worth.

I've tried smaller horns - these didn't deliver the slower speed and they reduced the throw of the linkage by more than I wanted.

I had fondly imagined that I might be able to find a replacement set of gears for the gearhead in the servo but have been told that such replacement gears are not available.

I've thought of retrofitting external reduction gearing to the servo and remounting the horn on the output end of that reduction gearing. But that would introduce other complications to the modification.

I've also thought about stripping the power and neutral wires away from the servo lead and connecting those to a 1.5V battery - effectively detuning the motor from 6V to a 1.5V supply. Is that workable?

Any other bright ideas?

Many thanks for any help.
Tony
Auckland, NZ

[Eddy Matthews]

Hi Tony,

There are units around designed to do exactly what you want by slowing a servo's speed.... Take a look at the following link:

http://www.sussex-model-centre.co.uk/Servo_Slow_,_On_Board_Glo_Switch_and__Servo_Tester-1408.htm

This unit allows you to alter the servo from normal speed to a complete crawl at over 20 seconds..... The amount of slowdown is fully variable.

Regards

[Khephre]

Fantastic Eddy, that's exactly what I want to do. Tks for the response and the link.

Kind regards
Tony
Auckland, NZ

[Eddy Matthews]

Perhaps not the cheapest solution Tony, but definately a LOT cheaper than buying a programmable transmitter!

I'm sure it could be done using suitable resistors in the servo, but if like me, your not that good at electronics, it's a good alternative...

Regards

[Khephre]

Well the servo slow worked a treat - slowed things beautifully and has 8 or 9 preset speed settings as well to get the fine tuning right.

Had a few words with one of our local model air stores about this - they wanted to sell me the programmeable transmitter solution for a zillion bucks. You can imagine the smile on my face when I showed them the servo slow unit and suggested it'd be perfect for undercarriages - and almost a zillion bucks cheaper!

Tks again Eddy

Tony
Akl, NZ

[Eddy Matthews]

Hi Tony,

Fantastic, I'm glad the unit did what you wanted.... You never did tell me what it was being used for, and I'm a nosey old so and so.... :-)

[Khephre]

Eddy, it's a bit off topic for Paddleducks but here goes ...

... you might recall that a few months ago I posted a few notes to the RC Model Boats group at Yahoo about a Ship Assist Tug model that I was building for my six year old son. My efforts were cribbed from a specification sheet put out by Robert Allan, a naval architect in Canada and is a stand-off version of his RAmparts 2500 Azimuthal Stern Drive tractor tug (check out the two Quigg hulls at ttp://www.diversifiedmarineinc.com/ for a few photos of the real deal - ugly as sin, but surrounded by swathes of rubber belting, tyres and other fendering - perfect for a six yr old, and the multichine hull was a quick and easy build).

The model's powered by a couple of 540 size motors running on 12V and two Graupner 1775 Schottel drives - those drives rotate up to 100 dgrees either side of dead centre and so with a reasonable amount of throttle on the motors and a flick of the rudder joystick the model can effectively do a marine version of the petrolhead's classic handbrake turns - i.e. it comes honking along and can suddenly flick its stern around to head in the opposite direction, in less than the length of the model.

Pretty spectacular to watch as the tug heels over and flicks around - and happens because the schottel drive steering movement is geared up through a rack and pinion gearset that's integral to the drive. So a 45 degree movement on the steering servo becomes a 90 degree movement of the kort nozzles on the bottom of the schottel drives.

In other words a little rudder joysticking generates a large movement effect on the model. Slowing the servo down has resulted in a slightly less spectacular handbrake turn effect but much finer steering control. Only needed to slow the servo response down to around 2 seconds but that's made a heap of difference.

I've been so impressed with the graupner drives that I broke the piggybank recently and bought a couple of larger versions - two graupner speed 900 BB torque 12V motors and two 2335 schottel drives - so that I can build myself a larger version. I thought that for the next version I'd look at Robert Allan's Z-Tech tug Indee (www.ral.bc.ca/news/2004_04_30.pdf).

The speed 900/ GR 2335 drive train combo is massive compared with what I've done so far - each of the the contoured kort nozzles has an internal diameter of almost 4 inches narrowing to around 3 inches at the rear! So I anticipate the bollard pull of the larger model will be very substantial indeed - the Graupner Tito Neri has the same drive set-up but my Indee will be around six inches shorter and a tad lighter.

My son's tug was a short summer project  so now it's back to completing my paddler Reliant and a few postings on progress will no doubt be in order. Then on to Britannia, then Indee, then I thought I'd have a lash at the Thomas A. Edison sternwheeler, or will it be a Windermere-style open launch side paddler with clinker hull? - you know the story!

cheers for now
Tony

[Eddy Matthews]

Thanks for that Tony - I can hardly blame you for going off topic when I asked the question that led to it can I ?? :-)

But I would be interested in hearing more about your proposed project with the large Graupner Schottle drives via email if you would? It sounds fascinating!

[mjt60a]

Excellent, I was looking for a way to slow a servo too.
The reason I wanted to do that was.... I wanted to connect two servos to the throttle, one operating a mechanical speed control (a rheostat type that I already have) that will take around 3 seconds to react, the other servo at normal speed  would spin a shaft with centrifugal weights that will swing out and strike bells (from an old type telephone or possibly a 'ding-dong' type doorbell!) giving the effect of the helmsman operating the telegraph and the engineer operating the engine controls in response...
...something like this;

..or maybe using a rack & pinion?
...frivolous? probably - and I won't add that feature until I get well used to how the ship handles - but I think it would be 'interesting' mooring at the side of the lake and having it sound something like waverley does calling at southend pier  

*I forgot to add, the 'fast' servo will be altered to increase its travel to 180 degrees (how to do that - http://mypage.yhti.net/~dmcdnld/s148retract.htm )

[Khephre]

Fascinating approach Mick. Reminds me of a bicycle bell.

[mjt60a]

now you mention it, yes, that's pretty much how a bicycle bell works...

[derekwarner_decoy]

hi PD's - some 45 odd years ago my parents took me on the Sydney harbour ferry South Steyne [screw steam triple expansion]  - she was Scottish built & steamed out (boarded up) to OZ under her own power

On the lower internal deck level was a huge observation opening [well huge for a ten YO kid maybe twenty foot long x ten foot wide] & the kid spent an hour or so watching the engine thunder away with all her shiny brass pipes & yes you could hear the engine telegraph bells ring as the vessel approached Circular Key

An important point to remember here is that bells were originally used for bridge to E/R commands for engine speed & direction. Later, bridge engine commands came down via cables & levers to the clock face & the chief or [engine] engineer would mirror the telegraph pointer to control the engine

The point here was that the bells were still used on the premise that in a noisy engine room, the captain needed to know that the engineers were not asleep!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! - Derek

[David Allinson]

Hi there Derek.  
Regarding the use of bells with the telegraph. Just to clarify the real use of the bells associated with a ships telegraph.  
As you say the engine room on a ship is a pretty noisy place, there is also a lot going on when manoeuvring the engines. The bell is to draw the attention of the engineer (keep him awake!) who is operating the engine that a new order has been sent from the bridge. The engineer will then move his lever to accept the order; this rings a bell on the bridge to alert the pilot that the order has been accepted and understood. In the event that the pilot needs some very rapid response from the engineer (usually FULL ASTERN!) then the pilot will swing his lever on the telegraph a number of times. The engineer will then do whatever it takes to get the engine to run astern. This is not as easy at it seems. The way of the ship through the water acting on the propeller continues to cause the engine to rotate (unless it is going very slowly) and it is quite difficult to get it to stop and reverse. There are a number of ways but none are good for the engine!! So if you hear frantic repeated ringing of the telegraph bell you know that there is a problem!!!!    
As an ex marine engineer from the 60s I can tell you it is quite a daunting experience when as a young man you are given the levers of an engine with 1,000 HP per cylinder!! It is quite an adrenaline rush when the telegraph suddenly rings with repeated rings and you have to get the engine running astern as quickly as possible. You have no idea what the problem is, so you have visions of the ship heading straight for the wharf and wait for the crunch, if you don’t get it stopped and running astern.  
Don’t get me started on “… when I wer’ at sea…..”!!  
All the best  
Happy sailing  
David  
     
<![if !supportEmptyParas]> <![endif]>  
-----Original Message-----
 From: Paddleducks [mailto:construction@paddleducks.co.uk]
 Sent: 08 April 2005 07:48
 To: construction@paddleducks.co.uk
 Subject: Changing Servo Speeds  
<![if !supportEmptyParas]> <![endif]>  
The following message was posted on Paddleducks, by derekwarner_decoy  
hi PD's - some 45 odd years ago my parents took me on the Sydney harbour ferry South Steyne [screw steam triple expansion] - she was Scottish built & steamed out (boarded up) to OZ under her own power
 
 On the lower internal deck level was a huge observation opening [well huge for a ten YO kid maybe twenty foot long x ten foot wide] & the kid spent an hour or so watching the engine thunder away with all her shiny brass pipes & yes you could hear the engine telegraph bells ring as the vessel approached Circular Key
 
 An important point to remember here is that bells were originally used for bridge to E/R commands for engine speed & direction. Later, bridge engine commands came down via cables & levers to the clock face & the chief or [engine] engineer would mirror the telegraph pointer to control the engine
 
 The point here was that the bells were still used on the premise that in a noisy engine room, the captain needed to know that the engineers were not asleep!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! - Derek
 
 
 
 Email reply, imported by Paddleducks Mail System.

[derekwarner_decoy]

sorry PD's -  a little off line -  and thank's David - but I cannot resist - many years ago I had the pleasure as a shore side hydraulic/marine engineer witnessing once per month the 13 cylinder- yes thirteen cylinder [IHI Japanese built under licence to Sulzer] BHP - Iron Sirius - confirm engine repairs post discharge & prior to sailing from Kembla

The as built Chelsea Bridge = Sig Silver = Iron Sirius, was the first 100,000 tonne vessel built [Kobe 1986 from memory] & produced some 9,000 Kw from those 13 cylinders - newer Sulzer or IHI engines produce similar Kw output from nine cylinders

Being on the engine room top plates on the Sirius on firing was amazing - 13 jets of flame until the bleeders were closed

The engine room console on the Iron Sirius was not insulated from the six stories of the engine room proper & the telegraph was there, however the ambient noise level was only approx 90Dba - Derek