Remote Control Personal Tracked Vehicle (RC PTV)
Author: Leonardo Georgescu
Date: Last Edited 08/26/2017
Keywords: PTV, Remote Control, Autonomous, Automation, Binding, Spektrum,
The PTV, personal tracked vehicle, was originally designed as a one person off-road vehicle. The track design, combined with a 212cc single piston engine, unleashes enough power for the vehicle to conquer most terrains. When modified, the PTV has many applications in the real world; it can be used as a search & rescue vehicle, military IED detector, personal transportation, autonomous medical ambulance, etc.
The videos below shows the DASL PTV doing things that most one person vehicle cannot.
The first step into making the PTV autonomous is making it remote controlled. This tutorial will explain how to turn an already built PTV into an RC PTV. The DASL PTV was built using the plans found here.
What powers this PTV?
The PTV has a 212cc single piston engine (right) that can deliver a torque of 8.1lb-lbs and 4 horsepower at 2500 rpms. The engine is connected to a torque converter that turns a sprocket that is attached to the drive shaft that drives the open differential. It is estimated that the top speed of the PTV is around 5 mph. It is important to note that the speed of the PTV can be adjusted based on the size of the sprocket and at the cost of decreasing torque.
The right picture shows the engine currently mounted on the DASL PTV. The silver aluminum rectangle is the throttle. When pulled via a cable, the throttle valve opens a little allowing for more air to enter the manifold.
How does the PTV stop?
There are brake disks attached to the drive shaft that is connected to the differential. When the driver squeezes the brake handles, the cable pulls the aluminum rectangle up, creates tension, and then compresses the brake disks, slowing the vehicle.
The blue arrow in the picture points to the braking mechanism. The cable runs from the brake handle and goes down to the brakes. The aluminum parts serves to apply equal tension when the vehicle brakes.
How does the PTV make a right or a left?
As mentioned, the engine ends up turning the open differential, which is connected to the front drive wheels. The open differential allows the wheels to move at different speeds. For example, when the PTV driver turns to the right, the right brake stops the shaft from moving, allowing the differential to transfer the power to the other side, thus turning the vehicle.
Below is a short video showing you how the PTV runs. As one can see, the vehicle can turn and accelerate at a decent speed. As with anything in the lab, modifications to the PTV can be made to allow for an increase in speed, mobility, or towing capabilities.
You finished building the PTV and it can perform as expected. The next step is to make this vehicle capable of being remote controlled.
This remote control design chosen will not make any major changes to the structure of the PTV.
Step 1: Change Brake Position
As seen in the right image, the original PTV plans have the brakes established facing the driver.
If you have not started building the PTV, I strongly suggest you have the brake drums facing the ground. If your PTV is already finished, then I will show you how to flip the brake caliper so they can face the ground.
The first step
Step 2: Purchasing Materials
The next step is to purchase the necessary equipment to make the PTV remote controlled. The cheapest method is to use servo motors to control the two brake calipers and throttle. The throttle does not require very much torque to be moved so most servo motors will be alright to use. On the contrary, the brakes require a lot of force, and will need a servo with a high torque. Below is the list of all the equipment necessary.
|FEETECH FT5335M servo||Mini Maestro 12-Channel USB Servo Controller (Assembled)||Rechargeable Batteries|
|Hitec HSR-5995TG||A-Star 32U4 Prime SV microSD||Jumper Wire|
|Spektrum DX6i||Extension Cables - Qty:4|
The two extra material required for this project are the nuts/bolts and the acrylic. The reason I have not included them on the list is because any size acrylic and most “”“ inch bolt can be used. I do suggest that the acrylic be thicker.
Step 3: Attaching Servo Motors
You purchased all the equipment; the next step is to attach the servo motors to the PTV. There are multiple ways of doing this.
Brake Servos: To control the brake calipers, we will need to use the two FEETECH servos. This is how the brake servo motors should look after attachment.
Before actually placing the servo on the PTV, the support needs to be designed in Solidworks and then cut with the laser cutter. The space between the two bars is … The pictures below depicts the measurements for the Solidworks drawing. See Santiago's laser cutting tutorial for extra information on how to cut acrylic pieces on the Full Spectrum Laser Cutter.
After the piece has been cut, it should look something similar to this. The thickness of the acrylic may not be the same, and that will not affect much. I would suggest using the thickest piece since it will not break easily.
Slide on of the acrylic parts in sideways and then straighten out. Then, place the motor in, followed by the other acrylic part. Try to bring the piece in as parallel as possible to the brake caliper. As you can see, the motor stays in place.
Is it crucial to note that on the left side (the side with the CVT transmission) the acrylic should be placed in between the chain and the servo motor will be in the middle. If not placed correctly, the chain may hit the acrylic part and damage it.
The next step is to completely ensure that the piece stays in place by using the bolts. Do not forget to place a washer on both sides. Then tighten by hand until the acrylic part does not move.
Step 4: Attaching Brake and Throttle Cables
Step 5: Binding
Before we attach the boards and cables to the PTV, it is important to connect the board and start programming the servos.
The first step is to bind the receiver to the remote control so it is able to receive signals. If you have a binding plug, then follow this step. If you do not have a bind plug, then you can make one and connect the receiver to the remote.
1) Use a female to female cable to connect the BND port to the negative port (brown cable).
2) Use a female to male cable. Connect any middle pin to a 5v power supply. In this case, I used the a-star board (yellow cable).
3) Connect the negative Aux 1 pin to the ground (orange cable).
If done correctly, there should be a blinking red light inside the receiver. The next part is to take the remote controller and actually bind.
1) Turn on the remote controller.
2) Click on the right nob until adjust list comes up.
3) Scroll down to Model Select and click the nob again.
4) Select whatever model is free on you remote and press the nob again. It will say “Download…“
5) Turn off the remote controller.
6) Then pull the trainer switch towards you and turn on the receiver. It should read “Bind.”
7) Wait for the red blinking light inside the receiver to stay red and then the process is complete.
Step 7: Download Software
We will program the servo motors via the Arduino platform.
1) Download Arduino
2) After the download is complete follow these steps to download the a-star board on the Arduino interface.
Step 8: Download Software