i want miniature pneumatic or linear actuator

Prabhu, it is easy to make an actuator yourself.. use a sliding servo, or convert a servo in to sliding.. big gears..  more arm travel.. 

how to do that roopeshkrishna how to do sliding servo

Prabhu, sliding servos are bit costlier.. but you can make it simple at home.. waht you need is one conter gear from DVD lens mechanism of lens drive.. (CCM), and its sliding rail with teeth.. so, can attach the gear to the servo arm gear, then the rail to the conter gear, with some foam board, or plastic reinforcement.. works nice.. bythis, the arm, travels in a reiprocating mode instead of rotation.. and also can make a dumping gear mechanism, by adding a big rond flange of your servo, by cutting it like a cam..  another mode of actuation is screw jack, that can make easily, with M3 screws and nuts in 3 inches length.. works perfectly.. another easiest method is to tip the carrier of dump truck is the cord and winder.. attach a cord, (radio dial cord, shuttle bat cord, etc..) at the bottom area of your carrier tray.. root it to chassis through some taperecorder pulleys, and attach a simple plastic gear box, and fix the tip of the cord to the shaft of the gear box.. apply a aslight slack in cord.. then apply battery.. can see the tray is actuating.. reverse the battery.. can see the tray coming down.. and you can also add a mock up cylinder just under the tray, with a ball point pen body, ( reworked for scale appearence), and cycle spoke.. this will be about 20 or 30 Rs cost.. works..? perfectly for years.. have some nice ideas.. and enjoy the coffee... with omlett.. 

give me a little time.. will add a build log that how to make a sliding servos.. and will make a good dump truck for you, from your inspiration.. will ship you, if you bear the courier charge.. will be in 1:10, or such scale, as the material with me.. 

tell me your price and i will take it from you

i need not any money for the craft.. as i can realize it by things around me, and paint by a little as balance.. but have to bear the courier charge.. and Prabhu, need a little time as i am promised to complete some models..

ya i have time and i can pay the courier charges and thanks for your help 

done..

roopesh sir any idea about when my model will complete