As there has been much interest about the mods done to this gun I have prepared a quick little tutorial.
First picture shows the Heng Long recoil unit. In the picture I have already removed the plastic that would normal rest on the Heng Long rotating cam elevation unit. As I am now using the new elevation unit I know longer require this. I have drawn in the outline of the plastic that was removed.
THis picture also shows the bbl inserted into the rear of the gun. Doing this means you don't have to make any mods inside the gun or reattach the spring.
Second picture shows the recoil unit with a contact switch in place and the necessary wiring to get it to work. Also I am using a graphic to represent the gun motor, which is not visible in the picture.
So let me explain what is happening in this little circuit.
1 Power is supplied to the gun motor from the smoker jack. The resistor (20 ohm)drops the voltage to the recoil unit to slow down the return speed.
2. The power is routed through the contact switch on the gun. In its current position the contact switch is closed, and the power is fed from the HL board to the motor. If this was hooked to a battery the gun motor would be running and the gun would be moving back to it's fully extended position.
3. As the gun extends the contact switch is tripped open by the returning striker(A). As soon as the switch is open the power is interrupted and the motor shuts off with the bbl in the fully extended position.
4. To fire the gun you move the left joystick. A quick blip up. This supplied power to the motor, moves the gears to release and allow the spring to pull the bbl back. As soon as this happens the contact switch on the gun closes, and power for the smoker jack is allowed to power the motor again, and the cyle repeats.
If you wanted a gun flash, you would hook up a superbright LED with the short lead to the yellow wire, and the long lead to the Brown wire.(Add a 68 ohm resister to protect the LED. When you blip the throttle up this will power the LED to simulate a flash(Of course if you hold the left joystick up the LED will stay lit and not look very convincing. However all you need is a momentary connection to start the recoil motor and this works fine for a flash.)
That is all that is required to mod the Heng long recoil mechanism to achieve the results I demonstrated on the Sherman.
I won't bother talking about the internal gun mods, as they are not required if you use this alternative. However a tutotial was done on RCuniverse by someone else ,and in that, it describes all the internal mods that are required if you don't want to , or can't use this gun 180 degree from what it was intended.
Red/Black/Black 20 ohms should work. However you need to be aware of the current capacity of the resistor. IF you use a 1 watt 20 ohm resistor you should be good. Or I have recently learned if you took three 68 ohm resistors and wired them in parallel you would have a net resistance of 22 ohms that could handle three times the current. I harvested this resistor off of a HL ESC.
You know where to find me if you have any questions.
Update. Just wired this up in my stug. Wouldn't you know it the Heng Long smoker jack has red as negative and black as positive. So use a volt meter to check the pins before you wire it up. In my illustration red is positive.