Commets on these drive trains

[Creator Mat]

i came up with these ideas to present to my team tomorrow any commets on them would be appreciated.
the first idea is a air boat type drive train where a giant fan would drive the robot. Then servo powered flaps would direct the air flow for steering. All this would be on caster wheels.

the second idea is kind of like a snowmobile. in the back there is a mini tank drive that would drive the robot. in the front is 2 swerve wheels that would be used to steer the robot. or the tank drive could do the steering and the swerve wheels would just be casters.

[dtengineering]

There are lots of possibilities for fans to be used in this game. You should be able, as part of your presentation to your team, however, to be able to estimate how much thrust your fan could develop. The power available to your robot is similar to that available to many radio control airplanes, so you might want to look around in some RC forums for software or empirical data to help you estimate how much thrust you might get. I would suggest that you not ignore the 9 pounds of tractive force that you can get from driving the wheels.

In the second design you probably don't want to leave the front wheels undriven. Depending on where your centre of gravity is you may be giving up 1/3 or more of your robot's pushing/turning abilities.

Jason

[BenB]

Remember you have a trailer attached behind you. All the air your blowing backwards will hit the poles (and balls), reducing your thrust.

[spc295]

Originally Posted by 2166BlueBotics

Remember you have a trailer attached behind you. All the air your blowing backwards will hit the poles (and balls), reducing your thrust.

that is what i have been saying as well.

[Elgin Clock]

Originally Posted by spc295

that is what i have been saying as well.

It won't only reduce your thrust, it will push against something that is attached to you in the scenario you are thinking of & basically become worthless energy as far as moving is concerned.

HOWEVER, if you have your fan pointed towards the opposite side of the bot that the trailer is attached, & you push a goal around instead of pulling it, it may work.
In theory anyways, with a lot more powerful fan & speed of fan blades that you will be able to use with the provided KOP parts I'm guessing. (Unless you want to build a serious transmission to maximize the output of that fan blade to warp speed, which is certainly possible... I guess, but just remember safety as well when making a huge fan with spinning blades!!)

Btw, your first idea you say "all this would be done on caster wheels".
You can only use the wheels they provide you in the kit & not off the shelf caster wheels, so keep that detail in mind.

[Josh Goodman]

Originally Posted by Elgin Clock

Btw, your first idea you say "all this would be done on caster wheels".
You can only use the wheels they provide you in the kit & not off the shelf caster wheels, so keep that detail in mind.

Yeah, I noticed that too. But after looking at the pictures I think he means a caster style wheel using the kit wheels. They would just be free rotating and not powered.

[The Pre]

Propulsion that does not involve driving wheels

this is a HUGE thread talking about fans and how they might be used.. might wana skin through the 4pages of it

enjoy and good luck

~jp

[Cooley744]

I may be mistaken, but I think you can hook the trailer onto your robot on any side. So if you put your trailer in the front, the fan would still be an option.

[gburlison]

I have been brainstorming a two wheel bot. Not just two wheel drive, but 2 wheels total. I realize there will be issues with inspection. But just think about this. The trailer connection only rotates in the horizontal plane so the trailer would provide stability. You would want it to be very close to perfect balance since you do not want to transfer robot weight to the wheels on the trailer. To pass inspection, you could have a third wheel that is about 1/16 in off the ground during competition. Comments?

[nitsua60]

Originally Posted by gburlison

...You would want it to be very close to perfect balance since you do not want to transfer robot weight to the wheels on the trailer....

I might argue that you want it out of balance -- in the opposite direction than you mention -- to take some of the trailer's weight onto the robot wheels. A big theme has been about how to increase the normal force and gain traction....

[gburlison]

Originally Posted by nitsua60

I might argue that you want it out of balance -- in the opposite direction than you mention -- to take some of the trailer's weight onto the robot wheels. A big theme has been about how to increase the normal force and gain traction....

So just to make sure I understand your point.
Assume the trailer has a tongue weight of 5 pounds.
Build a two wheel drive bot with a third wheel opposite the trailer and balance the bot such that the third wheel has 5 pounds of weight.
Attach the trailer, then the front wheel has no weight and therefore no traction.
All of the robot weight and the tongue weight of the trailer is now on the two drive wheels.

I am trying to figure out the CONS to this approach.
It seems that pushing the trailer would be more difficult, but since it is going to be difficult anyway I don't think many driver will be pushing unless they have to.

[nitsua60]

Originally Posted by gburlison

So just to make sure I understand your point.
Assume the trailer has a tongue weight of 5 pounds.
Build a two wheel drive bot with a third wheel opposite the trailer....

Not just two-wheel drive, but two-wheeled, if you like.
I don't see it so much about tongue weight as about the torque that the clevis (or whatever's pinning the hitch) will sustain.

Imagine a robot. Put a pair of wheels on it and hitch a trailer to it. Move some robot weight as far forward of the wheels as necessary to get the trailer hitch to lock up (there's a barrel pinned into C-channel, and you're trying to rotate it the "wrong" way). Now if you move more weight forward it's not just the tongue weight of the trailer pressing down on your hitch, but rather the weight of the trailer -- like you're actually trying to lift the trailer. I haven't built a trailer, but from kicking across some regolith I might estimate it at 20 lb. At max, you could actually have the whole robot+trailer weight balanced on your two wheels, as long as that pin and C-channel hold.

On the PRO side:
Ironically, by trying to flex the hitch in the "wrong" direction and making it harder to flex in the "right" direction, you might make some maneuvering easier.
You've increased F_n (and everything downstream of it) by ~12%

CON:
Minimal resistance to spinning the whole assembly -- you've both taken load off of the trailer's wheels and eliminated the degree of freedom intended in the hitch.

I don't really think it's worth doing, but I think it's well worth reminding ourselves that mg and F_n are not always synonymous.

[Enigma's puzzle]

The idea of turning the fan around and pushing the trailer will not work, as soon as you try to push forward the trailer will jackknife, you will then be pushing against the trailer wheels, and i don't believe you would have the power to do that in your fan. Even if you did thought, you would be an easy target because whenever you try to move the robot you will be pushing against yourself, essentially the same problem you were avoiding.

[purduephotog]

Originally Posted by gburlison

I have been brainstorming a two wheel bot. Not just two wheel drive, but 2 wheels total. I realize there will be issues with inspection. But just think about this. The trailer connection only rotates in the horizontal plane so the trailer would provide stability. You would want it to be very close to perfect balance since you do not want to transfer robot weight to the wheels on the trailer. To pass inspection, you could have a third wheel that is about 1/16 in off the ground during competition. Comments?

I've been working this idea since a student mentioned it. The concept seems sound but until we have a working test chassis (or find some mech e's that know how to model it) I'm uncertain.