120 lb. Drum Bot

We're building a 120 drum bot this year for BattleBots in Miami in February. We don't have any cad or solidworks drawings yet because we haven't yet been able to acquire the software, but the gist of it is:
- Staggered s7 teeth on the drum
- Some 7" OD 1/2" wall steel pipe that's 13-16" long for the drum. I don't know if the alloy's any good, but something like this:
http://www.onlinemetalstore.com/items/DrawnOverMandrel_DOM_Steel_Round_Tube.cfm?item_id=200&size_no=52&pieceLength=cut&len_ft=1&len_in=3&len_fraction=0&pieceCutType=26|4&itemComments=&qty=1
- Live Shaft, cylindrical roller bearings in the shaft supports
- clamp collars to hold the drum to the shaft
- 1" thick 7075 aluminum chassis/frame.
- slanted sides, armor thickness undecided, but probably spring steel or chromoly. Unless we run out of money, then we'll do stainless.
- 2 drive motors, 4 wheels, the front two being driven by a timing pulley.
- Not sure about drive motors or brushless weapon motor because I've never made a 120 and we don't have anyone with experience. Any suggestions (non-Pine View people)?

Sounds decent but heavy, and timing belts will shred in the 120# class, chains are much more common

why a live shaft? I prefer dead shafts because they add some structural support to the frame

Yeah I think we'll have to pocket the 1" thick aluminum. If weight turns out to be an issue once we've done serious weight calculations, then we'll just make the drum shorter, maybe 12" long at the least.

Chains and sprockets for the drive then, thanks for the advice.

I like dead shafts for the same reason, but I was just thinking that with a dead shaft we'd have to put the bearings in the drum, and if we did that, we'd need bearings that can take a lot of thrust load in case the drum was hit with a horizontal spinner. With cylindrical bearings in the aluminum supports I don't think they'll be subjected to as much thrust load, and they can handle a lot more radial load and higher speeds...Correct me if I'm wrong, I've never really done this before. And with the shaft spinning as well, wouldn't you have more spinning mass, meaning more energy in the impact?

Is it a bad idea to use a timing belt for the drum, or even belts in general?

Your team built copperhead, did you guys have problems with bearings in the drum?

I am a bit strange and prefer to use the nice bronze bushings over the rollerbearings myself. I feel that they are just a lot sturdier although lacking in efficiency, but they work just as well when properly lubricated. Plus they are cheap and easy to replace. BUT I might be the only person on this forum who feels this way, so i may just be wrong

Belts are always the way to go for the weapon because they allow slip on impact sparing your weapon motors from drawing a massive current spike. Inverted timing belts should be fine but V belts are more conventional

Nobody from the team that built copperhead is left except for one person who was a freshman at the time, so I wouldn't know. What type of bearings did copperhead use? Also, I don't know if copperhead ever faced a well built horizontal spinner that got a good hit on the drum, but if it didn't then the bearings were never tested to their limit.

What's the point of using an inverted timing belt? Is it better than a v-belt?

inverted timing belt is just a flat belt(Slippy when needed), I think the v belts are the way to go because i find them easier to work with, and they are more durable in most cases

I built copperhead!

V-belts are the way to go, since chain/sprocket systems are really heavy.

Cylindrical roller bearings aren't so good. They don't allow for much misalignment, and especially if you're opting for a live shaft, you're gonna need all the misalignment capability you can get since the shaft won't be a structural member and the frame is much more likely to get bent. I would highly recommend a dead shaft. It's just much more structurally sound. Copperhead had no problems with bearings in its drum.

Otherwise, yeah, sounds heavy.

V-belts for the drive too?

We decided on the dead shaft for those reasons and also I think we'll try to put the batteries (and maybe other electronics depending on drum diameter) inside the drum, mounted to the shaft to save space and weight in the rest of the bot.

Dan, I've been meaning to ask you a couple questions:
Do you have a list of Pine View Engineering Club's former sponsors, if there were any? I already have a list of companies I plan on contacting about sponsoring us, but if I knew who sponsored us before it would be helpful.

How could I quickly obtain 1 or 2 copies of Solidworks or Autocad for free? I'm going to a SAMA (sarasota area manufacturer's assoc. or something) meeting on Wednesday and I'll ask them, but we need design software fast. No one even knows how to use it yet, and the competition is a month earlier this year so we're not doing well on time.

Thanks in advance for the help. It's hard starting engineering club up again from nothing...

Here is the link for solidworks sponsorship application(Takes about 2-4 weeks to get the actual disks):
http://www.solidworks.com/sw/education/student-design-competitions.htm

Chains for drive not v belts



using the inside of a drum is a great space saver, but remember that you need easy access to the batteries during inspections.

Consider putting your weapon motor in there instead?

I'll fill out the application, but really I need them sooner. If we can find nothing better, then we'll just start learning with a trial version or something and wait the 2-4 weeks.

I don't know how we'd mount the motor inside and still get a decent amount of torque without having a large pulley. We could use an outrunner, but I don't want to take extra time figuring out how to mount the motor inside. No one on the team has any experience and we're short on time, so I'm going for simplicity (in most areas). I'm willing to remove a few screws, take out the shaft, and move the drum for inspection.

Do you think drilling a hole in the shaft on one side, inside the drum, to feed the battery wires through to the outside will compromise the strength of the shaft, or is it no big deal?

the motor in the drum trick is really for the smaller insect classes...you have 120 pounds to play with

Before rushing off to cut parts, tweak the design and make it very stout and easily serviceable.

Forget the insect class tricks. A 120 pounder needs to be serious, not like the little guys.

I've said this before on a few occasions, think minimum volume. a 10" diameter drum only 5" long will be almost as effective as a 10" diameter drum that is 20" long, but it will way far less.

energy comes from diameter and speed. Wieight and length are way down on the list of creating ke

shrink your bot and make it stronger

jmo

rjw wrote:

the motor in the drum trick is really for the smaller insect classes...you have 120 pounds to play with

Before rushing off to cut parts, tweak the design and make it very stout and easily serviceable.

Forget the insect class tricks. A 120 pounder needs to be serious, not like the little guys.

I've said this before on a few occasions, think minimum volume. a 10" diameter drum only 5" long will be almost as effective as a 10" diameter drum that is 20" long, but it will way far less.

energy comes from diameter and speed. Wieight and length are way down on the list of creating ke

shrink your bot and make it stronger

jmo

I am not talking about pressfitting an outrunner can into the end of the drum I am talking about something similar to what will does with fluffy, or i do with LOLcano. This is a method that i feel is more secure than the just having the motor outside the weapon because there is NO way for the weapon belt to be cut by an opponent. Granted it only works with Large OD weapons. And i can match any pulley ratio that you would have otherwise. Plus it saves ALOT of space.

I agree that the design must have ease of access in mind, Which is why i use beaters rather than drums... I have no idea how will changes weapon belts with out taking his entire bot apart. He must use magic

Ryan McKinney wrote:

I don't know how we'd mount the motor inside and still get a decent amount of torque without having a large pulley.

These are just a few pics of how i did it...





I had speed in mind rather than torque, but those pulley diameters could have easily been switched

Ha, rushing off to cut parts...we don't even have access to a machine shop. It'll be a miracle if we get a 120 built by February. Speaking of machining, to what extent do we ourselves have to make the parts? Obviously there are liability issues if a company lets us use their tools so they would more likely want to have their own machinists do the work.

As for the drum dimensions I actually read one of your posts just a couple days ago saying the same thing...it's good advice. I think we'll make the drum diameter larger and length shorter and put the batteries and maybe speed controllers inside. What do you think of 1" 7075 aluminum for the chassis? Not enough?

I'd like to go with a brushless inrunner, but I have no idea where to get a fairly priced brushless motor of that size. Most brushless motors for the smaller classes are readily available because they're used for hobby R/C planes, and large ones are available for electric cars, but there's not much in between. Any ideas?

Jeeves: I knew what you were talking about with the motor inside the drum; I just don't want to mess with that, and I don't think you can match ANY pulley ratio...maybe you can, but I'd rather not for the sake of simplicity.

that still doesnt seem like the best idea to me.

Putting the drum into the motor is pretty cool and is nice to save space but you have to keep in mind being able to work on it. Thats alot of hassle to change a weapon motor when we can take out 4-6 screws depending on the bot and have the weapon motor swapped out

old school says to slap a mag motor inside the frame of the bot and pulley drive to the drum (on the side) ...that's basically the conventionsl way of doing things...look at the riobotz tutorial and at the Touro bots....they've been doing this since the dawn of time.

other brushed options are available...or Cody can point you to some of the brushless outrunners from hell....via Hobby City or whatever the HongKong/China company is called these days.

You should try to put up a drawing. hand sketch or whatever of this bot....very hard to make suggestions without a cad or a hand sketch.

I wouldn't rush to go to chain drives, personally I hate them. They are totally inneficient and heavy.

with today's technology, you could get more than adequate drive power out of some of the wider timing belt/pulley combos out there. The lastest generation from gates and some sold thru sdp is better than 90% efficient, quiet, light and super cool. just protect them.

MLEC's 120 drumbot was going to use these, until it got nixed in favor of a melty....which will probably use timing belts as well, just not inverted like in our little bots.

Just some food for thought...we need a drawing, cad or hand sketch

Cody Harris wrote:

that still doesnt seem like the best idea to me.

Putting the drum into the motor is pretty cool and is nice to save space but you have to keep in mind being able to work on it. Thats alot of hassle to change a weapon motor when we can take out 4-6 screws depending on the bot and have the weapon motor swapped out

Thats EXACTLY why I use the beater bar rather than a drum. But Ill shut up about this now.

Ryan,

According to dan, copperheads 1&2 were built almost completly in a garage with hand tools and cordless drill.... I think they did end up finding a company that allowed the kids to machine called hydrogel for the third one.

Im assuming that you may have or have not seen this:
Pineviews robotics blog

It has alot of info and how you guys operated in the past, and a list of your previous sponsors. check it out if you haven't already seen it

RJW: I'll put up a few drawings. What do you think of these motors:
http://magmotor.com/hev/hev.html
http://magmotor.com/brushless/brushless.html
Jeeves: Thanks for the link. I've seen it before but I never noticed the sponsors at the bottom. And I think they got access to Hydrogel because Dan's dad works there. Now that Dan's not on the team, I don't know how that would work out.

jeeves_m_d wrote:

Cody Harris wrote:

that still doesnt seem like the best idea to me.

Putting the drum into the motor is pretty cool and is nice to save space but you have to keep in mind being able to work on it. Thats alot of hassle to change a weapon motor when we can take out 4-6 screws depending on the bot and have the weapon motor swapped out

Thats EXACTLY why I use the beater bar rather than a drum. But Ill shut up about this now.

Ryan,

According to dan, copperheads 1&2 were built almost completly in a garage with hand tools and cordless drill.... I think they did end up finding a company that allowed the kids to machine called hydrogel for the third one.

Im assuming that you may have or have not seen this:
Pineviews robotics blog

It has alot of info and how you guys operated in the past, and a list of your previous sponsors. check it out if you haven't already seen it

The motor in beater option looks to be more easily servicable than the motor in drum option....that's if you want a beater?

Will's Fluffy was an unusually good version of the motor in drum trick...He could R & R that baby in just a few minutes.....

i believe he had complete spares of the drum motor and everything on the side just incase. I'd really worry about a motor being eaten

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142

just sayin

Cody Harris wrote:

i believe he had complete spares of the drum motor and everything on the side just incase. I'd really worry about a motor being eaten

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142

just sayin

that's the one...lol talk about a monster motor...maybe 2 of them? haven't really checked out the specs, cause it's nothing that I would ever use...but it sure looks nasty!!!!

Either two of those, this magmotor:
http://www.robotmarketplace.com/products/MAG-S28-400.html
or this:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=14427

It wouldn't really work to run two of those brushless outrunners and the speed wouldn't be higher than the magmotor so I think I'll go with the magmotor...

rjw wrote:

Cody Harris wrote:

i believe he had complete spares of the drum motor and everything on the side just incase. I'd really worry about a motor being eaten

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142

just sayin

that's the one...lol talk about a monster motor...maybe 2 of them? haven't really checked out the specs, cause it's nothing that I would ever use...but it sure looks nasty!!!!

I'm pretty sure this is what was in Witch Doctor.

rdubard wrote:

rjw wrote:

Cody Harris wrote:

i believe he had complete spares of the drum motor and everything on the side just incase. I'd really worry about a motor being eaten

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142

just sayin

that's the one...lol talk about a monster motor...maybe 2 of them? haven't really checked out the specs, cause it's nothing that I would ever use...but it sure looks nasty!!!!

I'm pretty sure this is what was in Witch Doctor.

yeahh it is!
The hardest part about using these motors is finding a suitable ESC