Propulsion for a Robot on near frictionless surface.

[Just_Cetn]

Some of you are familiar with the US FIRST Robotics organization, a program that introduces robotics to high school students. This years game/task involves playing on a surface that is VERY SLIPPERY, intended to effectively simulate "floating" in 1/6th Earth's gravity as if the robot was on the moon. The only objects allowed to contact the surface of the field - a special white polymer "is made of “Glasliner FRPtm” gel-coated, fiberglass-reinforced, polymer material. This forms a tough, rigid surface that has been specifically selected to have a low coefficient of friction with the acetal-treaded ROVER WHEELS used by the ROBOTS. (FIRST 2009 Manual)" - are wheels coated in the same slippery polymer. Standard forms of propulsion (all forms are required to use electricity, no liquids or gases) such as the motors will simply spin the wheels, providing very low agility. To top it off, the robot has to attach to a small (50lb?) trailer that rests on the same wheels. All in all, you can use any number of wheels you want and angle them any way you want (the axis of rotation the wheel resides around MUST be parallel with the ground), and the robot + trailer will weigh close to 200lb's. The coefficients of friction between the wheels and the polymer floor are .06 when "rolling" and .12 when "slipping / skidding' sideways.

Videos and examples show robots sliding all over the place, smashing into walls, other robots, and game pieces. I require a superioir form of propulsion to simple electric motors and spinning wheels, or something that can provide a direct torque or impulsive energy to sufficiently re-orient this robot (static friction is nigh impossible to achieve). At the moment I have though of Gyroscopes (a speculative concept, and a real pain in the butt), creating downforce with a vaccum, and using sideways wheels as "brakes." Further questioning also brings up the question of whether or not more wheels would be better or not. Less fricition per wheel but more wheels...

Hand me your thoughts physics guru's!

 

[mgb_phys]

If the point of the low friction is to simulate the moon's lower gravity I don't think that you will be allowed to use a vacuum.
Are you given the wheels or can you choose their size?

You can't use a gyroscope to generate linear motion. You might be able to use a stick-slip type drive with a moving weight - like spinning on an office chair.

 

[Just_Cetn]

If the point of the low friction is to simulate the moon's lower gravity I don't think that you will be allowed to use a vacuum.
Are you given the wheels or can you choose their size?

You can't use a gyroscope to generate linear motion. You might be able to use a stick-slip type drive with a moving weight - like spinning on an office chair.

You are Given the wheels and may purchase more. They are all the same size. They are similar in size to wheel chair wheels, except instead of the gray rubber there is that same slippery white polymer.

 

[psyaubs]

first time poster... I had one idea that might help.

You might be able to use gravity to increase surface resistance. When an object is "falling" its velocity is increasing, so by timing the landing with movement you might have more control.
When I say landing I am thinking more along the lines of a vibratory mechanism. In fact removing the wheels altogether might be easier but probably not allowed.
Sounds to me a good project for laser gyroscopes and inertia sensors...jk

Just my two cents...Who knows maybe I'll come up with another penny.

Oh, just had another possible solution, ill try to explain... Okay assuming you can turn the wheels 45-90 degrees (increasing friction) to the desired direction of movement you can thereby stabilize your position. Then a weighted device on a linear track (presumably rotatable) is SLOWLY brought to firing position. Weighted device explosively propels forward (beware of bounce effect). Return weight and repeat... Maybe a linear motor some kind of pulley or spring system. Weight would have to be sufficient to propel your trailer payload. Increasing wheels would increase friction. Think V of wheels in back with forward wheels aligned with weight mechanism. but like every prototype keep it simple as possible and test it thoroughly.

Or you could try a design based upon what ice skaters call the "Swizzle". Start with your wheels in a "V" then the wheels expand out to "| |" then contract to "A" and back to "V".

 

[michael18284]

Sorry for possibly reviving a dead horse with this comment, kinda want to know if my idea would be useful to you or even possible in this competition. Or if you think it'd even work.

what about electric powered air thrusters? :)

you've got the friction coefficients for rolling and skidding, so it should just be an adjustment in the power sent to the air pumps depending on direction. make ALL of thrusters EXACTLY identical, i can't stress that enough. that way, its much easier to tune. use a regular microcontroller to control the voltage in PWM signal. its just a square wave (digital signal). electric motors interprut a faster frequency as a percentage of the highest voltage. I.E. 12v on a 12v motor. once you buy the micro controller, just do a google search for "generating a PWM signal ______" where ___ is the micro controller. or maybe do that search first, to see which ones controllers have a tutorial for it :)

i can help with the circuitry also, just want to find out if you need it before i go into it.

then all you have to do in programming is do testing to figure out how fast of a PWM you need to produce the right % of "full voltage" for the air pump to create enough thrust to do the movement you want. and set those values as up, down, left, right on a bluetooth wireless keyboard. (or if you have an iphone like everyone else, you can link it using a bluetooth adapter on the micro controller. allowing you to control it with your screen. you can look that up also, its not bad) or an adult gas/electric power rc car. you can buy all the parts you need for steering from a hobby store. or cheaper online. they have electric airplanes, maybe you could use a propeller from it mounted on a roataing stand. (several of them)

as you can see, i can keep going. let me know if you need help.

 

[Integral]

This game is now history. The robots have long been built, and now, on the edge of a new build season and a new game the old robots become part of a stack of older 'bots.
Mentor for team 957 SWARM

I am locking this thread as it is now done.