Drum or beater

Ok I know there are plus and minuses to both but from what I can gather it seems drums are heavier and spin faster, which = more damage and more destruction, making it better. However I've heard from multiple people that a beater is better if done right. How does one make a beater right? What advantage does a beater really have over a drum? Our team has always used hammers in the past so I am lost in this topic. Please help!

It boils down to a few factors: cost, weight, machining complexity, and moment of inertia. A smaller (less massive) drum will typically have the same moment of inertia as a larger (more massive) beater, simply based on its shape - more of a drum's mass is typically at a further distance from the axle than you would find in the same size of beater. The greatest advantage I see in a beater is they're really easy to machine. All you need to make a beater is a decent mill and one rectangular piece of stock material, where a drum needs several different pieces of stock and potentially some lathe work. The downside is to get a large enough piece of stock for your beater, you're going to be spending a lot more money and wasting a fairly large quantity of material. In addition, it's very difficult to repair beaters because they tend to have fewer parts. A good example of this is when a drum has a tooth break, you can usually just insert a replacement tooth; when a beater has a tooth break, you'll either have to weld it back on and possibly ruin the balance on the weapon, or replace the beater entirely.

EDIT: Beaters also seem to be a slightly better shape to get good contact with a target. Since they're just a plain profile with nothing blocking contact with the striking surface, I'm willing to bet they might be a tad more efficient at transferring energy than drums.

I was talkng to frisco earlier and he mentioned a small drum that's low to the groud which would therefore bite lower and throw bots better like a beater. Also I was thinking what if you had a channel in the beater and screwed the teeth in so it would be replacible.

What's your opinion on these two options?

be very very careful with screwed in teeth. They tend to shear off in almost every instance I've seen them, with the exception of something like Nightmare or Surgeon General... BIG bolts on BIG bots with BIG teeth. In the smaller divisions, there's just no way to get enough strength out of your fasteners and materials.

I'm a big proponent for drums, but I only speak from experience. I've never built a beater before. And my experience rests on one particular 120 lb example:

https://www.youtube.com/watch?v=6uO2d1dAGG0&feature=related

When you say material do you mean for the drum an teeth or the material for the fasteners? Hah or both? Are carbide teeth too hard? Because I don't seem to see a lot of those in the 15lb class. Also am I right in saying a small drum with decent mass spinning fast would be better than a large drum spinning a little slower?

Fast Drums tend to skip and only give good hits when there is lots of forward motion.

Fast Offset-Single Toothed Drums do not need as much forward motion to get a good hit.

Slower Heavy Beaters give the best hits. around 7,000rpm.


Slower Beaters thou, are not going to win Weapon to weapon against the faster drums....

the debate between small/fast and heavy/slow has been much discussed here. rjw has done a bit of r&d on it. I personally believe in slower/heavier rather than fast and light, but that's probably just my opinion.
Remember that momentum = mv and kinetic energy = mv^2 - I know that this is for linear motion, but the principle still holds for angular momentum, in that velocity is to the second power. Choose which you want to maximize. I am of the opinion that "momentum is always conserved" and therefore is better, and kinetic energy is not. However, there is evidence to support either camp. Copperhead's drum only spun at 3700 rpm, but was 50lbs and had a 6.25 OD on the pipe, so still got a tooth-tip speed of 95 mph. The 3 lb bot Sting's drum spins upwards of 40k rpm, and delivers some wicked hits as well, so I don't know what the ideal formula is. You just have to guess and try things out yourself.

I am going with the smaller faster side on this issue due to what i had seen RJW's bot do against undercutters.

With a slower drum you are still vulnerable against undercutters but with a faster smaller drum you can have the speed to protect against anything coming underneath of you.

Would fluffy be an example of an offset single toothed drum, because I'm not sure what that is?
I'm thinkin of maybe making an adjustable weapon arm and idler so I can test out different spinners. Haha well provided I can find enough sponsors to get parts that is.

Andy,

I would go with a drum for the first time doing this kind of build. There are many things that need to be learned when going with a beater plus you will need backups in case of breakage.

BTW what happened to the female advisor that I had spoken with over the winter????? I did not see her at the competition?

You might want to look at the buillders database to get an idea of some of the builds that have happened in the past and take a look at some of the changes that were made since some of the first drums that were out there.

Whether you want to go small or large or beater or drum or a vertical, you will need to look at the designs that were used on those bots and and where those same designs are showing up on here with some added armor or thickness here and there and some of the positioning changes that have been done to the weapons.....

Once you pick what you want to build then start designing and looking at what ays you can make your design different and better....

We have often taken a design like Solaris for our first bot Rellik and a design like Surgical Strike for DoomsDay and a design like El Touro for RockO and a design like K2 for To The Roof and incorporated them into our Robots but with a totally different twist or look. Some ideas work and some are a bust (SPUN).

That is the reason we put those robots on our shirts because they were the inspiration for our builds so we give the originals some credit.

Whatever you do, start designing now so you have plenty of redesigns and feedback to get started fresh for next years robot.

We met today and decided which bots we were going to retire and which bots we were going to make new for next year.

It looks like our test bots are going to be RockO, DoomsDay and resurecting Rellik.

Our new and redesigns are going to be To The Roof, Bar Exam, Our Spinner Radio Flyer (Too Gyro'd out to drive at this point) and a new Unannounced Design.

We are finally doing away with some material we used in the past (3 inch tubing) (2 inch Square tubing) and using some different materials.

We are also switching up some motors and armor for next year.

This is all already decided upon for next years bots so dont waste time and wait for next year, get some drawings done and look at what motors to use then you will have an idea where you need to start come August (Fundraising).

BTW..... Dont be amazed if you see another local tournament being held in November so get something going now.

My Plans are to get three tournaments a year.... One here in December..... Motorama in February...... and the IQ Tournament in April....

I am hoping that everyone jumps on board and has fun with the extra time to batttle and the numbers start improving from Comp to Comp..

I figure that between Pitt, Ohio, Meadville, Eastern PA there should be around 70 High school's being represented in the Fall... Quite a field!!!!!!!

I'll keep everyone posted on the progress!

Frisco

Andy wrote:

Would fluffy be an example of an offset single toothed drum, because I'm not sure what that is?
I'm thinkin of maybe making an adjustable weapon arm and idler so I can test out different spinners. Haha well provided I can find enough sponsors to get parts that is.

Andy

1) First read the entire Riobotz tutorial....so that you understand how things kind of work (around page 160 for drum theory)

2) Fluffy's drum is a standard (but somewhat BIG) aluminum drum with 2 teeth of equal size/weight and they are mounted diagonally opposite from each other, so as to keep the drum balanced. Other examples are the Plum drums, maximum impact (Bloomsberg) and others

3) Riobotz has been experimenting with a SINGLE tooth drum, you can find out why when you read the tutorial.

4) Offset tooth drums are hybrids, not quite a true single tooth, but balanced by design as opposed to needing counterbalance. They perform similar to single tooth drums.

5) If you haven't found the 'Ready to Runmble Combat Robots' section in the team area on this forum, maybe you should have a look. Plenty of pics of offset tooth drums.

6) BIG 2 tooth drums are easier to design and build, without semi exotic equipment and if weight and speed are correct, give the biggest hits. They can also be run slower and on bushings, so there will be less chance of damage to the internals and motor/esc choices are simpler and cheaper.

7) There may be NO perfect weapon that will win against ALL opponents. Again read the tutorial. Not saying that I agree with all of it, but you need to get there and understand the principles before you ca n move in your own personal preferred direction.

Look for and watch a LOT of video...in many cases, the driver makes ALL the difference. A great driver could drive a cardboard box and win against a powerful weapon. (well maybe...lol)

9) Also keep in mind that the structure of your bot needs to be able to withstand the power( energy ) that your weapon creates AND that of your opponent. Some chosse a BIG weapon and then find out that they destroy their own bot with it, especially when fighting other big weaponed bots

Good luck with it....jmo

rjw

Frisco- our female advisor (Miss Mills) was there, she was just usually not in the pit. Also I definately see where you are coming from wit the drum, but we have the material for a beater. I'm hoping to get sponsors, design, order parts, assemble, test, refine, repeat starting this week or next and continue to work through summer if I can get autodesk on my computer. I have done a lot of researchig and it seems the biggest problems are gyro and weak frames, especially in the weapon areas( ie: bearings, pullys especially the plastic kind, and the spots where the bearngs are attached to the bots frame as well as how the weapon is attached.)

Rjw- thanks for the advice, I'll be sure to check out that tutorial, it sounds really interesting. I read something about Marcos book on a different thread. Is that a book about building battle bots? If so where could I find such a wealth of knowledge? (I googled Marcos book and it was unsuccessful)

thanks again guys this is really helpful, our school doesn't do anything with battle bots and our advisors help as much as they can but they don't know too much about this stuff so any advice or info I can get is greatly appreciated!

Andy....you're killing me

There's a link to it as a sticky at the top of THIS section on design...lol

Oh haha I saw the riobotz thing, I'm on my phone and it couldn't handle such a large PDF so I'll have to look at it later on a better computer. I just wasn't sure if Marcos book is the same thig as that tutorial or not because I haven't been able to open the PDF yet but I followed the link and saw the website and all

stay away from plastic pulleys of course.

Did you go to the CalU teacher training two or three years ago?

yes i did go to the teacher training two or three years ago

they had the arena set up at half height?
i think i might have met you there

I was at the other teacher trainings. I missed the one where we got to test drive a bot. I think that was Adam who went to that one because I couldn't make it. He graduated last year though.

Which spins up faster?

less drag on a drum usually. It all depends on the design and motor etc

The difference is so small it can be ignored. Really, it will boil down to how good the motor driving the weapon is.

Jeff L wrote:

The difference is so small it can be ignored. Really, it will boil down to how good the motor driving the weapon is.

I tend to disagree....

If weight, diameter and length of the 2 are the same, along with gear ratio, motor, etc. and if both are properly balanced, the drum can draw a lot less amperage and/or spin a lot faster.

But that's just my experience

I believe the target rpm is the biggest factor. Spin it to the moon,a drum would be your better bet. 5-20k rpm there prob isnt much of a difference

Cody wrote:

I believe the target rpm is the biggest factor. Spin it to the moon,a drum would be your better bet. 5-20k rpm there prob isnt much of a difference

I can agree with that.

It may be possible to reduce the drag on a beater to counteract the effects at high speed, but as far as I know no one has ever really tried it (and it would likely be a fair deal more expensive to manufacture).

sorry if im repeating anyone, and if im throwing the topic to far off the way its heading.

There is a lot of information so far and just reading it myself (and somewhat understanding what is being said as iv asked the same question) , its still very hard to take all in at once. so il try to keep it really simple, once again sorry for just ripping what Alex, RJW, and everyone else said


beaters: easy to make, and they give just about the same big hits as drums, but drums can just give these hits more often because they have a faster spin up, this is because they are smaller in size and have a smaller amount of inertia (most the time, at times teams may have a drum that spins up slow. but this is because 1( their motors are lacking or 2( gear ratios 3( big drum

drums: fast spin up, good hits, win weapon to weapon most the time due to their fast spin up. HOWEVER, if you ask the teams that made very successful drum bots such as Plum and Dan's team (sorry if i left anyone out), it its extremely hard to make a drum that is "good". there are tons of variables that can throw off your entire drum, even its teeth being offset by the smallest amount will throw you off balance and at 10k+ rpm, its disastrous.

we are doing a beater this year, mainly because they are much easier, and if made right, your bot can easily destroy other bots. but as stated earlier, there's a Large chunk of wasted material, and when it breaks, it BREAAKKSSS (as you saw in the picture earlier)

on a side note, it really all comes down to driving, a good wedge bot may not smack opponents off the ceiling, but when it comes to the judges decision, points are all that matters, and if you drive circles around your opponent the entire match its an obvious choice who wins