What the heck Weapon should i choose?!

Well to get this thread back on topic...



close to final beater design. Same thing worked for Redemption. Its thicker, so should hold up to the forces better. Added the sharped grabby teeth that i didnt get to do for Redemption.. Same shaft design that i am very proud of. This time its thicker, even though our previous ones NEVER EVER showed a sign of deformation or anything. They were perfect.


If i do plan go the beater route (as designing this ShamWOW! drum is getting on my last nerve..) I will stick to a slower rpm of around 7,000rpm-8,000rpm.

This means i can use 4xA123s and have plently of batt life. I will prolly use a Scorpion 4025 1100kv, as that was a fantastic motor. It will be a very very simple electronics layout. I will put most of the efforts towards good driving to defeat faster weapons. Or just make it durable as hell to survive the weap2weap loses.


But if i can design a lighter, easier to make drum then i may consider the holy-balls-speed-on-weapon approach and pack as many a123s as i can....

Why not go with a cylindrical design where the shafts go through..... It would give you better in and outside support by wrapping the cylinder around the outer edge of the beater....plus you could put some conial air deflectors through the cylinder wrap to throw the air through the middle hence creating less drag by equalizing pressure a little inside the beater..... Just my 2 cents... One of our kids is designing a beater similiar to this but used the 2" round Ti instead of keeping it squared up ( inset and overset if you know what I mean).... Also, are you sloping the backside of the contact ends? A little less drag there too..

Are you gearing it at 12-30 ????

Frisco wrote:

Why not go with a cylindrical design where the shafts go through..... It would give you better in and outside support by wrapping the cylinder around the outer edge of the beater....plus you could put some conial air deflectors through the cylinder wrap to throw the air through the middle hence creating less drag by equalizing pressure a little inside the beater..... Just my 2 cents... One of our kids is designing a beater similiar to this but used the 2" round Ti instead of keeping it squared up ( inset and overset if you know what I mean).... Also, are you sloping the backside of the contact ends? A little less drag there too..

Are you gearing it at 12-30 ????

I don't follow. Are you talking a new shaft design? or a drum that wraps around the beater to shield it, thus making it more aerodynamic? I don't need much improvement of airflow if im doing 7000rpm. Won't factor too much. Air tests on redemptions at 8,000 gave null results. It moved some air, but not much. Now at a test of 15,000 that sucker was creating some violent turbulance. And drawing ALOT more amps while remaining at constant speed of 15,000rpm. Amp draw at full speed at 8,000 was like 10-20amps. The start up is what killed the batts more than anything. Peaked at like 170amps when the throttle was slammed on. But it lasted for less than a sec. Amp draw at 15,000rpm constant was around 50-60 at times, with a constant of about 40-50. When we moved it (drove it/moved beater through the air, we observed little change at 8000rpm, but at 15,000 the change was bad, it was everywhere from 20amps to 80amps at constant. Not to mention a beater going that fast sounds like a train...Peak when slammed on was around 200+ for a sec.

Basically at these speeds, i don't need the extra aerodynamic changes for the beater. It is going slightly slower, its lighter, and will be on bearings most likely.

Gearing is gonna be around.. 2:1. That pulley is a placeholder of sorts.

qty 4 of A123s is a pack of 13.2 volts. each cell is 3.3v.

13.2 x 1100kv = 14520. ran through a 2:1 gear reduction 14,520/2= 7260. factor in effiency of the motor, and overvolt when charging and you get 7,000-7,500rpm.

So i was just thinking maybe shockwave could be used for bot hockey, the frame design was pretty similar to XLR8Ted(sorry if im wrong haha) which i think would work great for it.

If theres anything I could do to help your team or your competition please let me know, Im not sure if youve seen dan curhans name floating around but he's at CMU i could probably get him to help a little and he has a drum ant.


DANNNN DANN come out!

My fault.... I thought you were shooting for the 15K from 7K..... IF I can get the kid at school to save a render of his design I'lll post it tomorrow.... Did you slow it down to get more bite???? or to cool the amp draw???

Both pretty much. I am not just thinking weapon speed and hitting. I gotta factor in my driving time aswell.

Redemption ran at a 1.6-1.7:1 ratio. It was close to 2:1 but gave us more speed. Hence the 8,000-9,000rpm we had at Century III and Ohio with the 1100kv Scorpion. That gave us good batt life and plenty of KE. Both are evidenced by both rumbles from Ohio. Those are the most demanding because they last longer, and you have more bots to hit (pretty self explanatory) more hits = more peak amp draw.

I took it down to 2:1 to just get more batt life and a bit quicker spin up. Hoping to use a 60%/40% of weapon power and driveablity (respectively) to win with Icarus. Redemption relied on a 85%/15%...which cost us a few matches once our weapon went, we were done....

I may speed it up, but it depends on weight, which would allow more batt cells = more voltage = mre speed, and space for electronics.
The max i will go before i consider aerodynamic enhancments is 10,000rpm. Once i get past that the trouble starts.

But like i said the game might change if i can design a easy to manufacture drum.

Only gots 12 pounds to work with as there are not many 15 leagues that allow non-schools... and that are close to me...

Some real world results from single or staggered tooth designs.

1) In a beater/drum to beater/drum battle, please note the following

a) tip speed is an advantage
b) lower/smaller diameter might have an advantage
c) if using single blade, then you need more than twice the tip speed of a 2 blade design

2) single/staggered blade designs require at least twice the strength in blade retention hardware

a) from personal experience
b) Marco (Riobots) has ha the same problem with his Touro bots.

3) Advantages of single or staggered design

a) Better bite...more energy from smaller, lighter faster spinning drum
b) Less drive speed required to get tooth engagement

4) Disadvantages

a) Easier to throw out of balance
b) If not better than 2x tip speed of 2 tooth design, then the head to head battle is in question

Conclusion...testing

Ready to Rumble combat robots has been experimenting with single/staggered tooth drums/beaters

what we found so far is this

1) we spin them in the 20 to 40k range, so head to head has been very successful against larger weapons, in that we get better than twice the tip speed

2) Our weapons are light, so the extra speed more than makes up for the energy lost due to smaller diameters. Plus he smaller diameter seems to help getting first bite

3) we have had problems holding blades in the head.....forces against them are much greater

4) In battles against soft materials, it's been wonderful

5) against Ti clad bots, this is the worst case scenario

remember , that if 2 drums/beaters are head to head, then both weapons spin in the same direction (up), so the forces are much less than against a non-spinning Ti bot.

Worse case would be against an inverted bot weapon spinning in opposite direction...while this could be bad for the inverted bot, the single/staggered tooth design had better have things WELL fastened.

Hope this helps

On the edu side, MLEC is hoping to have 1 or 2 single/staggered drums running on Nov 14th in Miami.

Some examples

In the video below, tip speed wins over a much larger beater...Sting is using a staggered beater



Against Ti wedge, bite was good, but teeth needed better retention (Sting is using a staggere tooth drum

https://battlebots.forumotion.com/ready-to-rumble-combat-robots-f25/sting-makes-it-s-debut-at-rmp-t229.htm

final note: It has been said that a true SINGLE blade design is more effective than staggered teeth, but while this may be true, we have been using slight overlap of the staggered teeth and have been getting double hits. Think about this.....If you make contact with a single tooth, you can get the big hit, while against other drum/beaters, you have he potential for 4 times the tip speed, if you make contact at the overlap of the blades.

Wow Loads of info! Thanks rjw!


How much does your teeth weight and entire weapon assembly?


I wanted to use your bot as a basis for a "golden ratio" of weapon weight to bot weight. Usually for the 15 pounders its around 1/3 of the weight in the weapon, i.e out of 15 pounds, 5 pounds into the weapon. And at times less. the 1/3 rule applys to floorsweepers and eggbeaters quite well. But for super-ultra-giga fast offset drums it it gonna be much much less. And your offset design is the most successful i have seen yet.

The eggbeater weighed about 1/3, but I need a bigger battery pack, so it's on hold.

Same deal on the drum, even a bit more.

My latest attempt wil be under 1/4 the weight of the bot, but it will have Ti nutbars holding in 4 blades

If you look at the calcs, the biggest factors for energy are diameter and speed. Weight isn't all that significant, plus lightweight weapons get up to speed much faster. It depends on your take on MOI and Joules.

As I stated earlier, holding it together (especialy on a drum with inserts) is critical to success.

Here's a pic of the beater and of the latest drum with TI Nutbars





Oh...by the way....the shape of the cutting tips on both seems to help get a good bite as well...better than your usual square edge.....still not 100% sure tho.........

On the drum, the flats and holes run the full length...if one set gets trashed, then the blades can be moved over as a set. blade end to end overlap is just over 1/16". the beater obviously has NO overlap.

Also we use timing belts running on the flat side. Especially on my 3 lbs bot, all I want to do is back up get to speed and move forward...I use 2 half width belts as opposed to one wide belt. This is more flexible and easier on startups, especially if you have a very small high kv motor like in the little bot.

The MLEC bots are set up the same way, except the weapons are powered by mamba Monsters, so there is NO problem getting them going....We always run esc's that can run the motor in both directions...in that inverted operation is a must (for us).

Running 2 half wide and kind of loose belts, loses a bit of top speed, but shock to the motors is greatly reduced.

Will Bales adopte the reverse timing belts on his Fluffy, so we'll see how that pans out.

I'm advisor to MLEC, but we share a lot of our findings, both good and bad with the members of this forum.

Yea i got a curved tooth for my beater. It does help biting quite a bit. From what i saw in other bots.

Thanks for the info! While weight may not key in for the energy as much, it does factor in for amp draw which dictates your battery life.... electronics are my biggest problem.

I am having trouble being able to get a insane speed without drawing too many amps.

Hence why i would like to stick to a tride and true 8,000rpm beater. Easier for me to do the electronics (and cheaper i hope)

Tonight (provided my new PC doesnt come in. ) i will make a copy of Icarus, and resign it to incorporate a smaller, offset drum, and the do some calculations to predict if i can get good batt life. Everything i have done before has involved a 4.5-5" drum/beater, and me trying to get that up to 15,000 wasn't a walk in the park...let alone 20k+

What diameter is your latest beater? and weight?

On my little bot, amperage draw was double with the beater as opposed to the drum.

The beater is about 5.1 Diameter, and weighs about 3.5-4 pounds.



Draw should be fine. It is the same diameter as Redemptions, going at a slower speed, and is lighter. Redemption at 8,000rpm lasted long enough, so this should have no trouble.

So your tip speed is at 8k is around 178 ft/sec

MLEC's TTATT drum has a tip speed between 275 and 350 ft/sec

Do you have any blade tip overlap on the staggered edges? A little might help in weapon to weapon battles....

I cant say that i really saw a difference between flat and curved teeth on our drum

The curved tooth will get a little more bite than chatter or slippage at low RPM....
One thing that I am not seeing mentioned here is the speed at which a bot goes in for the hit.....
Cody if you remember right Shockwave got beat by .....or almost beat by just cant quite remember Steel Center...
Their driver had a great strategy on you guys and just stayed as close as he could to you so you guys could not get a run at him and get a good bite... He did corner you guys quite a bit.... With him being so close you could not get up to speed and get a run at him to get a good hit.
The speed at which you run at an opponent has about 1/4 of the puzzle when it comes to getting a good hit.
The other 1/4 comes from design.....1/4 weapon speed... and 1/4 where you hit (luck)

A Funny find...
I just watched Doomsday on Youtube and man did it take us a year to come up to speed on that blade..
It's even funnier watching seth try and drive that thing..... He had no idea.......
HILARIOUS!
I hope we can do better with that bot this year!

Frisco

rjw wrote:

So your tip speed is at 8k is around 178 ft/sec

MLEC's TTATT drum has a tip speed between 275 and 350 ft/sec

Do you have any blade tip overlap on the staggered edges? A little might help in weapon to weapon battles....

Well, i don't care about weap2weap. If i go the beater route, i will get beat weap2weap. The advantage of me going beater is the MUCH less worry about battery life. Which means i can focus on hard powerful driving. Which involves avoiding the weapon.

It becomes a more balanced bot, and gives me less new things to worry about. I can stay with the tride and true electronics setup i used for redemption, and not have to learn much new (beside shock proofing them)


Currently working on a Icarus redesign for a smaller fast drum. As for the beater, there is nothing to improve upon or anything. It will do its job fantasic. It will hit hard and with the added curve tooth it will grip a bit better than Redemptions.

Don't take what I said the wrong way...just putting up some numbers.

In the end, anyone can win.....just throwing out food for thought.

An 8k 3 or 4 pound beater is a serious weapon....good driving helps a lot

Good luck with it.

rjw wrote:

Don't take what I said the wrong way...just putting up some numbers.

In the end, anyone can win.....just throwing out food for thought.

An 8k 3 or 4 pound beater is a serious weapon....good driving helps a lot

Good luck with it.

Don't worry i wasn't taking it the wrong way.

Just being straight forward. Its a chance to hope my driving will beat better weapons, but its a heck of alot easier and cheaper than getting a weapon that sounds like a jet engine.

Redemption proved that the weapon has PLENTLY of power to throw a bot/destroy.

5 inches diametter with 4lbs of weight, and 8,000rpm is enough to kill anything. Its the driving and "damage proofness" of the bot that matters aswell.

I have no idea what speed, power , etc bots like Hummdinger, Aftershock, Exterminator or others are or were making, but you have to go with what you are comfortable with.

Good luck...I'm sure it will be awesome!!

rjw wrote:

I have no idea what speed, power , etc bots like Hummdinger, Aftershock, Exterminator or others are or were making, but you have to go with what you are comfortable with.

Good luck...I'm sure it will be awesome!!

EXECUTER! Noone gets his name right.

He is doing about 14,000rpm on his drum, idk about aftershock, and Humdinger has a 5.25 Diameter 4-5lbs beater doing about 4,000-6,000rpm depending on which battery he uses.

Years of Solidworks really pays off. I scrapped this assembly up in about 20min.

smaller drum took out a good 16-20% of the weight off the bot. And gave me extra space to increase in the electronics compartment for MOAAARRR BATTERIES!!


But yea. This drum version may be viable!



Also, this version if it gets made will be called Boreas. The greek god of wind (north wind at least). Because its gonna be making LOTS of wind.






EDIT! I did some math, and i can get that drum up to about 25,000rpm! And have enough run time hopefully.

This is what Ive been talking about...

You throw out ideas (and many will say that they are not new) but in any case, a student with some knowhow can make it real.

Did you check the balancing in SW?

Remember that the blades will require at least twice the retention strength of a 2 tooth design

I hope you build it...it may become a new trend of higher speed drums..lol

great job!!!

Edit: bearings are a gray area....It's a tough act to come up with bearings that will hold up and yet spin 25k...

How much energy at 25k? wind noise will be amazing.....haha!!

Excpect between 16k and 22k even with a hell of a motor/esc setup

rjw wrote:

This is what Ive been talking about...

You throw out ideas (and many will say that they are not new) but in any case, a student with some knowhow can make it real.

Did you check the balancing in SW?

Remember that the blades will require at least twice the retention strength of a 2 tooth design

I hope you build it...it may become a new trend of higher speed drums..lol

great job!!!

Edit: bearings are a gray area....It's a tough act to come up with bearings that will hold up and yet spin 25k...

How much energy at 25k? wind noise will be amazing.....haha!!

How do you check the balancing in SW? If you knew that and could tell me how to do that, it would be VERY helpful. That isn't the final drum design, just something i threw together to get the weights correct. The general tooth layout will be the same, i may move the pulley into the middle, and take the drum out to the edges to cover those corners better, and give myself some even space for the weapon motor.

Dont worry, those suckers will not leave the drum. I have some special ideas for holding them in..

Have not checked the energy yet, i never really calculate joules. You just know when its gonna hurt something.

The first thing is to do a static balance check

1) Design a balancing shaft, same length as the drum.

2) bring the shaft into an assembly and move it until it so X,Y an X center of mass values are ALL ZERO (In mass properties). When the shaft is in the correct location, FIX it

Then bring in the drum, end pieces, blades, hardware, etc and keep checking that your values don't change. Some Z offset (along the length of the shaft) may be tolerable, but X and Y should be either zero or very close to it.

Dynamic balancing is another story, but usually results in requiring a better static balance anyhow

Feel free to contact me if you have questions/problems....I'm here to help

ShamWOW! I'm good. Pretty well balanced according to SW.

No hardware yet, but i always design my weapons symmetrical. So it should be fine.