Controlling a robot base with six high powered motorized wheels is not going to be cheap! If you are serious about building such a powerful machine with six controllers you are going to be up for big bucks.
The hard part is not the mechanics but the software control systems if you want an autonomous machine. It is easy to build a remote controlled machine to do all sorts of things under the guidance of a human brain. Current autonomous robot brains are more like insect brains if that.
The robot I built used 24 volt windscreen wiper motors and it was very powerful and capable of carrying a human or pushing a large heavy couch around the room. It had no problem pulling itself through grass. It worried me that such power without a brain was dangerous. It could squash a cat or child against a wall. If it hit a brick wall the wheels would burn rubber as they rotated. Imagine what six powerful wheelchair motors could do!! I had no problem using the robot base to carry heavy loads and it only had two powered wheels. How much torque also depends on the gearing and wheel size. You can have it fast and weak (high geared, big wheels), slow and strong (low geared, small wheels) for any given motor size.
@robotbuilder Yes, fair enough. I am thinking autonomous will be quite a ways off, if ever on this platform. This design definitely has power. In order to test the suspension yesterday, I had to use big boulders. Smaller rocks the size of water melons, and 4x4 steel beam cut-offs were too small. It just shoved them around like shuffle board pucks. I will take your warning under advisement.
I am starting to come to the conclusion that the speed control circuit is not going to be cheap. Currently looking into price of a home made controller based on the SSR-DDs in H bridge. However, just all the generic SSRs alone, straight from China, are not cheap.
I am starting to give more weight to your suggestion of hobby servo motors controlling the wheelchair joysticks, since I have all that kit & caboodle already.
It's titled Robot Mechanisms and Mechanical Devices Illustrated. Check out chapter 4, it has a six-wheel skid steer design similar to what you have done.
Tom
To err is human.
To really foul up, use a computer.
@robotbuilder Yes, fair enough. I am thinking autonomous will be quite a ways off, if ever on this platform.
Remote controlled machines like rovers being controlled by a human can be very useful as it gives you a telepresence at some other location. It means you can do dangerous things and go into hostile environments. It also means you can be anywhere in the world if you have internet access to your machine. You might adapt the electronics being used in simple radio controlled cars or drones to your rover.
Not counting the cost of your smart phone this cost $100 in Australia you could not build it cheaper yourself from parts.
I am watching Bill's new video about vision systems. Very excited!
So I decided to do the "hack" and link the wheelchair's 3 joysticks to a series of servos. This has some disadvantages, but a good few advantages, too. Number one, being low cost since the wheelchair controllers are salvage. Here is a video of the proof of concept:
Next step is to model and build proper linkage and add the third joystick. BTW, I found it quite simple to drive multiple servos in sync with each other on a single RC channel. This solved some linkage and force issues, and allows the use of the little 90g hobby servos. I can upgrade them later. I can also remove the springs from the joysticks, which will reduce force required considerably.
Although probably an ugly hack I thought maybe two servo motors could be used by an Arduino or RPi to mechanically control the toggle handle on the controllers. One would pull it left or right and the other forward or backward. They would be positioned at right angles to each other. These could even be the servos used in remote controlled cars so you would have radio control.
Yep, just implemented your idea. I used CAD to design a housing, and then 3D printed it. I ran it up the flagpole, and it flew. (on the bench, at least) So now to fine tune linkage, add the third joystick, and test it on the 6wd rover. See two posts up for my implementation, pics and video.
This idea of servos moving joysticks is moving forward, and we have proof of concept. Here is a play list of videos documenting the process. The Python code is for my class Final project.
Rover style robot is now operating by RC control. The servo-joystick drive system needs work. It is kludge to say the least. But lacking proper speed controllers, it can do the job in a pinch.
I've also added an aluminum platform frame for electronics and two larger main drive batteries. The batteries are on rough CG, the back half used for drive circuitry. The front half of the frame is, as of yet. unspoken for, to allow for payload, attachments, manipulators, sensors etc. (or biological passengers... )
Watching the rover trying to climb over a pile of wood I was thinking spikey wheels would work better than the rubber tyres. Maybe make some spikey snow chains for it. Maybe lower the air pressure as you would do for a vehicle driving on sand. A simpler solution is don't drive over logs of wood 🙂
@robotbuilder Yeppers! I was thinking of putting a heap of screw heads, or studs, into those tubeless-tires. The day was icy and cold, and log pile was a wee bit steep.
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