UPDATE 2 : Added "K'nex Motor Heavy Duty & RC Modification" step (08.11.2015)
I mentioned my tank in my previous ible and here it is... I've completed it like 9 months ago, made some modifications today. I named it Altay, took approximately 8 months to complete. Actually I'm very proud of this tank and like it a lot...
It is a remote controlled knex tank that can move (like a tank), turn its turret horizontally, shoot, reload and shoot again multiple times. I've used mainly knex parts and some rc components... I made a prototype to gain some experience before the main thing...
Here is the list:
• ~3000 knex parts
• 6 modified 6v knex motors
• 1 servo for trigger
• 4 ESC (electronic speed control)
• 6 channel radio transmitter & receiver ( 5 of them is used)
• 2S (7.4 Volt) LiPo battery
• Amper and voltmeter
1. Left track ( Two motors )
2. Right track ( Two motors )
3. Turret rotation horizontal ( left - right) ( One motor )
4. Ram pin puller ( One motor )
5. Trigger ( Servo )
I planned the 6th channel for vertical turret motion but due to the complexity, I decided not to do it for the time being.
It has a unique magazine, it uses "clip with hole" as ammo.
In order to increase power and overcome the extra weight of the body and turret, I used dual motors for each track. All motors are 6v dual speed motors and all of them are set at low rpm - high torque mode. I made extra cable connection between the motors and their corresponding esc's so that they can be remotely controlled.
I also modified the motors to hold on the rods more tightly. This is necessary as the motors are equipped with a system that holds the rods loosely in order to protect the motors. This system is over protective and easily lets the rod slip in the slightest need of extra force. Since my tank is heavy and needs high power to move motors were continuously slipping the rods before the modification.
I designed a special gear mechanism that puts the ram pin puller motor in to an idle (neutral) gear so that when the ram pin is pulled all the way back, even if I don't stop the motor from the remote it won't continue to try to pull the ram pin and break things apart...
Trigger mechanism is pulled by a servo.
Let's take a closer look now...
Step 1: View From All Sides
What a magnificent thing you are... :)
Step 2: Details
I've ordered 6 channel receiver & transmitter and other rc equipment from hobbyking . Knex from http://www.knexusergroup.org.uk
Step 3: Body
It's easy to separate the body and the turret. Let's look at the body first.
Step 4: Turret
There are two very important details here:
When the ram pin is pulled back purple clip which is attach to the middle gear is pushed back by the orange connectors at the back of ram pin. This moves the middle gear in to idle position and lets the pulling gear spin freely even the motor continues to rotate.
The motor turns the rod, the rod winds the rope, the rope pulls the ramming pin. When the ram pin is pulled back enough trigger moves up and blocks the ram pin. Middle gear is moved and motor gear and the pulling gear is detached ( idle position ). But there is still a problem, if we pull the trigger the gun wouldn't fire, because the rope is winded. So we have to unwind it before firing. The rubber band that is winded while rope is winded does this. When gears are set to idle this rubber band unwinds the rope so the turret can fire.
Step 5: K'nex Motor Heavy Duty & RC Modification
I've already made a separate instructable for this, so I'll make a summary here:
K'nex motors have a mechanism that makes attaching rods possible. This is a plastic part that is somewhat flexible and expands a little bit when you push the rod through the hole. I guess this mechanism also serves as a safety precaution that protects the motor by slipping the rod when it's too hard to turn the rod.
While this is nice it also causes the motor to under perform. Under heavy loads, even if the motor has enough power it doesn't turn the rod because of this mechanism. We can hear a clicking sound when this happens.
This was a great obstacle for my RC Tank - Altay. There was another requirement for my RC Tank project, preparing the motors to be remote controlled. So I dismantled all the motors and made these two modifications.
First the easy part, making the motor RC ready. Cut some plastic as seen on pictures two make way for the power cable. When we have the power cable soldered it will be ready to be plugged to an ESC for remote control. AFAIK all k'nex motors are brushed motors not the fancy brushless ones. SO when you are picking an ESC it must be brushed motor ESC with the correct voltage parameters.
This is the HobbyKing X-Car 45A Brushed Car ESC which is brushed, 2 cell lipo (~7.4 V OK for 6v motor) with reverse capability. This is almost only ESC I found on internet that can be used for this application. There are two options about where to solder the cable:
1- Directly to the motor.
2- To the battery department.
Soldering to the battery department has an advantage of not bypassing the forward reverse switch of motor. So after you've done the RC modification you still have a switch to reverse the motor rotation. So I soldered to the battery department. One more side note, if you have multiple motors to modify solder all red/black cables the same way so once you set all the motors to forward position from the switch they all turn the same direction.
To get to the battery department soldering points you must remove another plastic panel that is used to divide the battery compartment in to two.
I used XT60 connectors at the other end by the way.
Heavy duty mod:
You must take out the gear that holds to the rod. Separate all the parts of that gear set. Take a good look, take notes or take photos before you dismantle the parts, you will have to assemble it all the way back.
At the end of dismantling there will be a plastic part that holds the rod. This circular part is not full circle, one side is cut to give it flexibility. There is also a spring around it to keep it tight. The condition of this spring determines how easy the motor will slip and make the clicking sound.
We will hunt down this flexibility with this modification. But since the flexibility will be gone so will the possibility attach or detach rods. So we will put the circular part on the rod we are going to use (black rigid rods in my case) and make the modification with the rod already attach and we will never try to take this rod out again.
The core idea is to make this circular part so tight that it holds the rod and doesn't let it slip. Wrap the circular part with adhesive tape ~10 rounds. Cut the extra pieces so that it can still attach to the other parts. Put on the spring back. Assemble all the parts back. Take care of the rc cable and the blue switch mechanism while closing the motor. Blue switch is the mechanical speed selector that changes the position of middle gear.
Note: In the video and some pictures you may see some white band pieces around the circular part, this is from the previous modification which has worn out in time.
There is also another point where you can *leak* power : the Interlocking clip. If you have motor in good condition - that doesn't slip - and a heavy load then your Interlocking clip may slip the rod and if this starts to happen it wears out the Interlocking clip and if it's worn out it will happen more. You can see the difference between two Interlocking clips one is in good condition, other is dead. Solutions is once again to wrap it with adhesive tape.
After the modification:
Step 6: Last Words
I've recorded a FPS view video before:
I've introduced my tank before on teknoseyir.com :
Will add some more videos soon...