Wondering how to make a drive with a suspension system where wheel(s) will go over the bump, but then return to ground level to continue driving.
My prototype that I am in the process of making is a 8 wheel, deciding 6 or 3 motor drive. My plans for the two outer wheels to be stationary while the two wheels in the middle have some sort of suspension system that allows it to move up and down freely yet motorized for it to be able to move. When the drive goes over the bump I hope to have the two wheels return to the floor mats to have a fully functioning 8 wheel drive.
Right now I have seen robots with 8 wheel drives but the two wheels in the middle are just hanging whenever it is on the floor mats and is only used for going over bumps.
The issue with a suspension is that it heavily affects the rest of the robot. Let me explain.
In order to build an effective suspension for the bump, your spring rate must be pretty stiff, or else your robot will sink/get stuck to the ground and stop moving with or without a load. Too stiff however, and you might as well get rid of the system.
The balls are a type of load. When it comes to scoring, you will have a lower ride height than you originally designed and intended for.
When it comes to movement, depending on the spring rate, the balls in your robot might be like putting a cup of water in an old Cadillac. You want to minimize body roll.
There are better ways of going over the bump. How about a higher rideheight, shorter wheelbase, or simply just reducing the gap between the wheels?
If you still insist on doing this, there are two ways:
Let the motor, axle, and wheel move freely on the L shaped metal with the line of empty space in it and suspend it from the top.
Build some sort of individual suspension, and then a flexible differential in the middle of the robot, just like a car.
I do realize that there are many problems and challenges that come along with creating a suspension system in VEX. Well an idea I had that could address the problem of the spring rate was that I would use either rubber bands or pneumatics to control it. For example a sort of hydraulics on the robot. Well as of now it is still an idea that I am just try to put together.
when we first started vex we thought that a suspension would b a good idea, and we did some thinking and after a while we came up with a design using sprockets and gussets, it worked ok but was fairly complex and was likely to go wrong
Heres some pictures of a prototype for a pneumatic “suspension” I was working on. It was just a fun project but it never got off the ground because we needed the parts for competition robots. Maybe this will inspire you however.
I had an idea along these lines of having a low drivetrain that raises up on pneumatics to go over the bump and drops down to fit under the bridge, but I realized it was too complicated to bother. You can just use a high clearance between the wheels, or even simpler, use 6 wheels instead of 4. Or, use tank treads as a chain linking the front and back wheels and drive on that while going over the bump.
I think the biggest issue is weight. If you plan on hanging that’s a lot of extra weight that really isn’t needed to perform the task. When we first started brainstorming while we were in Anaheim this idea came up, but it was pretty quickly dismissed when we looked at how the game was scored and how important hanging with a ball would be. I just don’t see it as a worth while trade off myself, while it would be an interesting project that might even be worthy of a design award if properly documented. I personally think that giving the robot a little over 2" of ground clearance and designing your lift to stay below 12" when lowered is the best strategy.
Alright sorta kinda have an idea of what to make now!
Imagine a sort of scissor lift suspension held down by rubber bands. It will be powerd by one 393 motor that is chained. This is really hard to describe so try and post a pic later.
I was thinking of a bogey style suspension as well. The nice thing is that it works out very well with the way the bump is for the competition. The bogies will follow the contours perfectly. Thats a good picture. The actual bogey in that picture is the 2 wheels that articulate together(just for clarification). You also could use 1 motor per bogey for the traditional 4 motor drive and use gears to connect the motors to each of the 2 wheels on the bogies.
I think the Original Poster and others interested in actually putting a suspension into their competition robots would do themselves a big favor by answering these questions before doing anything else.
What problem, that affects whether or not my alliance wins a match, am I trying to solve; and what is the magnitude of that problem’s effects on match outcome?