Re: Elevate sevo. [TANKS]

[Grant Mahalek <gmahalek-at-shaw.ca>]

Fellow Tankers,

Frank, thanks for the very detailed comments on your experiences with 
various elevate mechanisms....hopefully this will save me alot of trial and 
error.

Fellas, which elevate system do you guys think would be the least expensive, 
simplest and most compact elevate mechanism for the compact Hetzer hull?
My Hetzer is crammed full. There is very little room for the marker and 
elevate mechanism, thus I need an extremely compact elevate mechanism that 
is not prone to the dreaded BBS :-( .

Cheers,

Grant "reminded I'am green-horn again" Mahalek



----- Original Message ----- 
From: "Frank Pittelli" <frank-at-rctankcombat.com>
To: <tanks-at-rctankcombat.com>
Sent: Friday, December 16, 2005 11:20 PM
Subject: Re: Elevate sevo. [TANKS]


> Grant Mahalek wrote:
>> I was thinking about yours and Garnet's ideas.....what about balancing 
>> the gun and barrel.....and then use a sail winch servo with stainless 
>> steel fishing leader line in a closed loop(or anchored someway) to 
>> control the gun from bouncing up and down??
>
> I don't have a lot of experience with these things :-)
> but here's my two cents worth on the subject of elevation systems.
>
> You should always "balance" the gun to take the load off of the lifting 
> mechanism.  A couple ounces of lead is all that is needed to balance the 
> Tiger-1 (mark III) barrel.
>
> A perfectly balanced gun will want to bounce when the tank is moving or 
> shooting, so you always need to "dampen" the gun from oscillating.  I use 
> two air springs (surplus car parts).  Since they oppose each other (and 
> the gun is already balanced), it doesn't matter how strong they are, as 
> long as they a stiff enough to dampen the oscillations.
>
> With a balanced and dampened gun, you still need a mechanism to move it up 
> and down. Since the gun is balanced, the mechanism doesn't necessarily 
> have to be strong, but it has to be "durable".  The lifting mechanism 
> needs to be able to withstand the dynamic shock of the gun moving up and 
> down, as well as when you hit something accidentally. (Yes, these are 
> tanks and we hit things occasionally.)
>
> It's not the "motor" or "power" that's the problem, it's the "linkage". 
> There are basically three types of linkages:  arm, lead screw, and winch. 
> All of these linkages provide positive control in both directions.
>
> If you use a straight linkage, it will transfer the shock directly to the 
> servo/motor, so you'll need a strong hub and arm.  My current servo uses a 
> geared motor with a 1/2" steel hub, which replaced a 1/4 scale servo that 
> had a 1/8" plastic hub.  If you want proportional control, a servo with a 
> straight linkage is the obvious choice.
>
> If you use a screw-type linkage, then the lead screw takes the shock 
> directly, so make sure it is up to the task (1/4" threaded shaft comes to 
> mind).  Although it's possible to make proportional screw-type linkages, 
> they are generally used with on-off controls.  These linkages can also be 
> made very compact.
>
> A winch-style linkage absorbs much of the shock in the wire (synthetic or 
> metal) and the rest by the capstan.  Although they are usually controlled 
> by on-off switches, there are winches sold for sailboats that provide 
> fully proportional control.  I use one in one of my sailboats and it works 
> great, although it cost a lot as well, because it has the highest 
> strength-to-weight ratio, which is important for sailboats.
>
> Having built and bought numerous versions of all these approaches over tha 
> past 15 years of modeling, my latest choice for the Tiger was the servo 
> board from Oakley (for proportional control) and a geared motor (for 
> robustness).  My choice for the Navarrone gun was a geared motor (for 
> robustness) and an on-off switch control (for simplicity).  Both 
> approaches provide accurate fire control and are robustness enough for 
> years of abuse.  Geared motors take up more space than servos, but they 
> are more robust.
>
> Frank "Tried Everything More Than Once" Pittelli
>