Contemplating Gyroscopic Forces for fighting robot weaponry

[some bloke]

TL;DR Summary

I am trying to work out how to maintain momentum in a vertical drum spinner without the gyroscopic tilting when steering.

The premise is that whenever you watch Battlebots or Robot Wars, there's usually a robot on there which has a vertical drum spinner which weighs half the robots weight and spins at thousands of RPM, and whenever the robot turns, it cocks one wheel in the air due to the gyroscopic forces at play.

Now, we can safely assume that if it's raising the centre of gravity of the robot upwards, then the spinner is losing power, plus the robot is losing controllability, and it's leaving its underside open to attack, which is bad.

I am wondering if there is a mechanism by which the drum spinner can be adapted to reduce this energy expenditure, and keep the robot planted on the floor where it belongs, without simply slowing down or reducing the wieght of the spinner.

My first thought was to have the spinner be a set of wheels which spin on the opposite axis, but I now realise that would just comprise of having many gyroscopes constantly trying to turn, and would generate greater energy loss. I also contemplated a liquid core, before realising that this would not expend its energy on the target, making the weapon less effective.

IS there any mechanism which I could use to minimise the gyroscopic tilting?

 

[Baluncore]

IS there any mechanism which I could use to minimise the gyroscopic tilting?

Two counter-rotating circular-saw blades, mounted on a vertical axis, driven against each other, not against the chassis.

 

[Lnewqban]

Could the single drum be horizontal instead?

 

[A.T.]

The premise is that whenever you watch Battlebots or Robot Wars, there's usually a robot on there which has a vertical drum spinne

The solution is to have two of them counter rotating on parallel axes, for example at the font and back.

 

[sophiecentaur]

TL;DR Summary: I am trying to work out how to maintain momentum in a vertical drum spinner without the gyroscopic tilting when steering.

whenever the robot turns, it cocks one wheel in the air due to the gyroscopic forces at play.

When the robot turns, its gyro axis shouldn't change so why would there be any precession? Translational movement in a horizontal direction needn't provide any torque. Perhaps giving the gyro a flexible mount so that it's decoupled from any tilt of the wheels?

 

[Baluncore]

When the robot turns, its gyro axis shouldn't change so why would there be any precession?

Because the axis of rotation is horizontal, across the machine.

 

[A.T.]

When the robot turns, its gyro axis shouldn't change so why would there be any precession? T

I was confused too. It looks like by "vertical drum spinner" they mean it spins in a vertical plane, thus around a horizontal axis.

 

[sophiecentaur]

Because the axis of rotation is horizontal, across the machine.

Ah. The axis of the drum is not vertical. I get it now. I now realise that a horizontal axis would be better as a weapon. (The last time I watched Robot Wars, Jeremy Clarkeson was hardly more than a lad.)

 

[A.T.]

I now realise that a horizontal axis would be better as a weapon.

I think one aim is to lift up and flip over the other robot. So to have two counter rotating drums (to avoid gyro effects), that are both lifting colliding objects, you would place them on opposite ends of your robot. You could additionally do the same pair arrangement across, and have drums on all 4 sides.

 

[some bloke]

Thanks for the replies!
So, I had considered a pair of counter-rotating drums but my corns are:
1: The weight limitations means having 2 drums on opposite sides of the bot would result in two less dangerous weapons, which is bad. I need to get all the weight in one drum, ideally
2: Having two drums on one axis (so they both hit at once) could be powerful, or it could just counteract one another and put the armour into compressive stress, rather than the rapid tension on bolts & joiners achieved by siezing the opponent and launching them into the air.

I am now considerign if I could have a drum spinner where there is a second drum counter-rotating internally, connected by something like orbital gears to the outer drum. The hard link of gears would mean that when they connect, all the energy would go into the opponent, whilst at the same time, the internal counter-rotation would keep the robot in check, gyroscopically.

Regarding the force exterted by the gyroscopic effects on this sort of thing, the inner drum would need to be smaller than the outer, so logically it would have to spin faster? Does the radius of the gyro actually affect anything, or is it just the mass that is rotating? IE if I had two drums of mass 1 rotating in opposite direction on the same axis, but with one with radius 1 and the other radius 2, would they need to spin at different speeds to effectively counteract one another?

As this is doubtless connected to conservation of momentum, if they were driving off one another (as suggested above) then would they automatically balance themselves out to have the same momentum, thus resulting in a balanced spinner?

Edit - another contemplation, the idea of havbing 2 or 4 drums positioned around the bot, this could be brought to extremes by using a flexible ring aorund the robot, effectively creating a 360 degree vertical spinner, and if they were all connected, then their momentum would be shared so the impact would remain quite effective. Main concern would be the number of moving parts that could go wrong! I would probably use cabling of some sort, I guess, rather than universal joints.

 

[sophiecentaur]

Main concern would be the number of moving parts that could go wrong! I would probably use cabling of some sort, I guess, rather than universal joints.

this is a good point. You are dealing with another robot that is out to getcha and the weakest link theory could well apply. This robot wars thing has been going on for decades now and I doubt that an individual design is very likely to beat 'evolution'. Perhaps a lot of viewing of past designs could yield an answer.
These wars are a bit 'rock - paper - scissors' and a winner in one fight can easily be a loser in another.

 

[A.T.]

1: The weight limitations means having 2 drums on opposite sides of the bot would result in two less dangerous weapons

Not if they are rotationally coupled, wich they must be anyway if you want to drive them with a single motor. If you connect them such that they can only spin at the same rate, then they are not "less dangerous" than a single one with twice the mass, because their rotational inertia combines. You just need a very robust connection, which can withstand very dynamic energy sharing, when one of the drums hits something.

I am now considerign if I could have a drum spinner where there is a second drum counter-rotating internally, connected by something like orbital gears to the outer drum.

This is the same thing as above, just that you have hidden one drum, so it cannot act as a weapon.

 

[sophiecentaur]

Not if they are rotationally coupled,

The problem is that any coupling needs to be strong enough to transfer a high angular impulse from one wheel to the other. That could involve very chunky gears which would only add weight to the robot.
If the purpose is to 'flip' the opponent, then the total impulse could be delivered over a longer period of time which would allow a more resilient linkage.

 

[A.T.]

The problem is that any coupling needs to be strong enough to transfer a high angular impulse from one wheel to the other.

Yes, as I already noted. But the same problem occurs with any counter rotating masses, that are coupled mechanically. Including a "second drum counter-rotating internally, connected by something like orbital gears to the outer drum", as proposed by @some bloke.

 

[sophiecentaur]

Yes, as I already noted. But the same problem occurs with any counter rotating masses, that are coupled mechanically. Including a "second drum counter-rotating internally, connected by something like orbital gears to the outer drum", as proposed by @some bloke.

Yes. The linkage has to be rigid or the two rotations will not cancel. I think the strength required would be gained at the expense of net available angular impulse.

 

[some bloke]

Thanks all for the replies again!

So I am now considering using a pair of vertical spinner wheels in a dustpan designed bot, where the wheels are beside one another and linked together with gears. I reckon I'll use the shock absorbing rubber mounts akin to in the sprocket mount of a motorcycle wheel to reduce the jarring impact of the weapons, whilst allowing the second wheels to use their momentum to aid in the damage, and to bring the attacking weapon up t ospeed again almost instantly if the target has already been flung away.

looking forward to starting my designs!

Edit - realised I was very vague on what I meant! I am going for 2 counter-rotatign wheels, front and back, so both will fling the target upwards if struck. The axle for each will be just ahead of/behind the other, so that the wheels overlap - the front will be central, the rear will be two half-weight wheels flanking it.

Now, to maximise the impact, I am thinking that the most important thing is to have the most mass as close to the outside of the wheel as possible. As the restrictions are on weight and top speed (in mph, not rpm), the logic is to have the most mass moving at the maximum speed, ergo at the outer periphery of the wheel. Now, my next question is: If the wheels are counter-rotating at the same speed, with the same mass, will they still resist turning the robot? Will they cancel out the tilting and simply try to prevent the robot from turning at all?

 

[A.T.]

Now, my next question is: If the wheels are counter-rotating at the same speed, with the same mass, will they still resist turning the robot? Will they cancel out the tilting and simply try to prevent the robot from turning at all?

If the two wheels have equal but opposite angular momenta, there will be no gyroscopic effect at all when turning. Neither lifting, nor resistance beyond what you have if they aren't spinning.

 

[jbriggs444]

If the two wheels have equal but opposite angular momenta, there will be no gyroscopic effect at all when turning. Neither lifting, nor resistance beyond what you have if they aren't spinning.

There will be torques on the bearings as the two wheels try to precess in opposite directions. The torques from this attempted precession will be equal and opposite, so they will cancel. All will be well... as long as the frame does not twist under the stress and the bearings do not seize.

 

[A.T.]

There will be torques on the bearings as the two wheels try to precess in opposite directions. The torques from this attempted precession will be equal and opposite, so they will cancel. All will be well... as long as the frame does not twist under the stress and the bearings do not seize.

Yes, I meant no net gyroscopic effect, that affects the turning of the whole robot, which was the question.

The frame and bearings need to be stable. If the wheels are to be interlaced, there should be enough gap left between them, in case they wobble a bit.

 

[FinBurger]

One aspect of these spinner weapons is that they apply a similar terrible force to your own robot. Unless you can make the point of weapon contact be at the center of gyration, you will get a strong kick-back. Just like when you hit a baseball incorrectly with the bat - it stings your hands.

There might be something to said for mounting the weapon's weight at the end of a piece of chain. Then when it hits the victim there will be less kickback. You know, like a flail. https://en.wikipedia.org/wiki/Flail_(weapon)