I have been showing an army tank model (pic attached) to kids at shows for a few years. The tank is a hybrid of Meccano and Vex. Kids, even very young (around 3 and up) ones, like to drive the tank using the Vex 6 channel transmitter. They seem to have educated thumbs these days at a very early age.
I am now building a six wheeled armored car along the same lines. What is the best way to remote control Ackerman (the most common) type steering? I was thinking of using a Vex servo motor like I used for the tank turret and gun, but three positions are really not enough for wheeled vehicle steering. Is there a different Vex (or compatible) transmitter with a steering wheel as well as a few levers? Then I could use a regular Vex motor.
Any suggestions would be appreciated.
What do you mean by only three positions? I’ve never used a PIC Microcontroller or 75 Mhz radio before, but is it possible to use the y-axis channel of one joystick to control the forward and backward motion, and the x-axis of the same (or other) joystick to directly control the steering servo?
The joysticks on the 75mhz controller are analog, so I’m pretty sure you can get proportional values from it when programming (the farther you push the greater the value). You can use a Y axis control for steering and a X axis control for forward/backward speed, the amount you move the joystick is the amount the wheel steers.
For the steering I think a servo is better than a motor, because you can control the exact position it needs to go to and stay there, which would be dictated by how the joystick is moved.
The most common control system is the newer Cortex, Joystick, and VEXnet system, but if you have the PIC 75mhz system and it works fine I don’t see any reason to spend money to replace it.
If you want to get fancy, you can construct something to connect a steering wheel to the Y-axis joystick. As a bit of a side note, while it isn’t relevant to what you want to do, I’ve used this Lego design and it’s really cool and maybe you can get some ideas from it: Power Functions 'Thumbstick' Joystick - LEGO Technic, Mindstorms, Model Team and Scale Modeling - Eurobricks Forums
Interested in this as well. I build an F1 car for an event we did which has pushrod steering using a VEX servo but not Ackerman geometry.
No suspension either which makes things easier.
I’m going to be doing a VEX IQ 4x4 vehicle using the new IQ differentials and a transfer box when I get a chance this year. The idea being that 2 or 3 motors in the front of the vehicle will drive all 4 wheels with a differential on each axle.
The problem I am having with this is designing small ball joints using IQ parts so that the steering arms have movement when the wishbones rise and fall. I am trying to do it with 100% IQ parts but I am thinking I may need to 3D print the ball joints for where the steering arm meets the suspension hubs.
By 3 positions for the servo motor, I mean left center and right. I should also have mentioned that I am using the Signal Splitter, not the Micro Controller so programming is not currently and option. Yes, I can use the left and right action of a joystick to control the servo but just to the 3 positions that I mentioned with no in between positioning. I may have to go to the Micro Controller for more options.
You should have proportional steering with the signal splitter. The easy way to get the mechanical part of the Ackerman is to use the Swerve Kit on the steering drives. You can either gear connect or chain connect them to your servo/motor in the middle.
You can change the programming settings in the transmitter to give you a little better control. There is also a way to slave one channel to another. The transmitter programming was one of the really cool things about the V0.5 family.
Thanks Foster, I just realized that just touching the stick moves the servo a small amount. Duh! Previously I had just used servos for the full 120 degree range to elevate or lower the gun on the tank. Also thanks to sazrocks for pointing out there are lots of positions available within the 120 degree range of the servo motor.
I’m not sure if this is what you’re referring to,
but here goes.
Ackerman is the shortening of the steering link.
As you can see here, this is no Ackerman.
Excuse my crappy MS Paint technical drawings.
This is Ackerman.
The ideal setup for your 6x6 would be as follows. Ackerman is most effective when the steering link location is on an imaginary line that connects the front hub to the center of the rear axle in a car. However, since you are making a 6x6, you would use the center of the middle axle. This is because the rear wheels would also be steering, in the other direction. For the rear side, the Ackerman would be mirrored.
I just use the term Ackerman Steering to distinguish my plan from the simpler versions like a steam roller or a 3 wheeler. I may not be shortening the linkage. I will only steer the front pair of wheels.
Be careful here. The term Ackerman Steering refers specifically to designs such that the arc described by each wheel has a common center (see pages 12 and 13 here). If you don’t shorten the linkage or align the arc centers by some other means, it cannot truly be called “Ackerman.”
If the steering wheels are parallel at all times, this type of design appears to be colloquially referred to as “parallel steering,” but I am having difficulty finding a standard name for it.
//Andrew
Thanks RD, I am currently using “parallel steering” but I may convert it to Ackerman after I solve some of the more pressing problems.
I’ve sometimes seen these types of drives referred to as “car-type drives”, e.g., this link, pg. 6.