Designing my 4wd belt drive 3lb beetle weight

Hi I'm building a beetle weight with 4 wheel drive powered by 2 motors with belts and pulleys and slave shafts.
It's going to be a wedge so I need pushing power also I'm trying to design a fly wheel for the top or maybe a lifting arm, I don't have any questions about that part.

ESC
I have been jumping from brushed to brushless with the design over and over.
I found options either way for brushed or brushless.
brushless esc http://www.hobbypartz.com/ezrun-25a-l-brushless-esc-for-rc-car.html I can turn off the brake
brushed esc most likely the sabertooth 12, unless there is something better
Or for the cheap way out on the brushed esc, 4 of these hobby king esc's I can turn the brakes off
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6468

Motor
I need a motor with a (3mm) shaft either brushed or brushless with alot of pushing power and speed.
for brushess a motor like this http://www.hobbypartz.com/96m05-car-2040-3600.html
I'm not really sure which brushed motor I would use , it's hard to find one with a 3mm shaft.
Maybe you know of a better motor with a 3mm shaft?

I'm looking for an expert opinion on this someone with more experience on this subject
Thanks

Also I'm trying to choose the pully size for my drive here's the link to the pulleys http://www.robotmarketplace.com/products/timing_pulleys_fingertech.html
I'm thinking a 15 tooth on the motor and a 42 tooth on the slave shafts

List Of Part's I Already Have
6x BaneBots Wheel, 1-7/8" x 0.4", 1/2" Hex Mount, 30A, Black/Green
4x Hub, Hex, Series 40, Set Screw, 3mm Bore, 1 Wide
2x Hub, Hex, Series 40, Set Screw, 3mm Bore, 2 Wide
4x 16mm Slave Shaft Kit 1.5 inch long 3mm shaft
half inch aluminum angle (to go around the polycarbonate)
sheet of polycarbonate (for the chassis)
big roll of aluminum flashing (for armor, also might add a sheet under the polycarbonate)
Spektrum DX7 remote

As for your electronics, i cannot say for sure because i have no experience in the 3lb division's electronics.
However there are plenty of people here that have won titles with 3lb and tons of other threads to check to see what the competition is thinking about.

as for the pulleys, while robot marketplace is a great start, there are websites that offer a huge variety of timing pulleys and belts to fit any situation, my team and and a lot others use SPD/SI, which specializes in plastic and metal timing pulleys. the site is a little confusing so if u have any questions feel free to ask. (P.S make sure its in stock, if not call to see when it will be, sometimes the delay is crazy)

also mcmastercar has a decent selection of timing pulleys and almost guarantees stock

www.sdp-si.com/
www.mcmaster.com/

for more places to shop around, check the "Resources Thread of Glory" posted on here by Jeff, its extremely helpful
https://battlebots.forumotion.com/t467-the-resources-thread-of-glory?highlight=glory

Thanks both of those websites went into my bookmarks.
They have a huge selection compared to robot marketplace.

Maybe I read it wrong but why do you need 4 ESC for 2 motors?
I cant say there bad Ive heard people have more troubles with Dimension Engineering ESc then anyothers
Maybe look into the banebots 3-9 or i beleive people have used fingertech tiny esc's in beetles

i agree with Cody, banebot esc's are arguably the best all around. their simple, sturdy, and pretty resistant to frying even if your robot catches on fire =p

also they have they have their own BEC for if you go with your brush-less motor design

The reason that I would use 4 esc's with the hobbyking 30 amp's , because they are single channel and it would require 2 for each side 1 for reverse 1 for forward movement totaling 4.

The sabertooth 12 seems to be a good choice because I can run it on one stick on my dx7.
It has a 5v bec, lipo cutoff.
What does this mean though Acceleration Ramping - Selectible by DIP switches. Replaces the flip function.
I know what the flip function is but I'm not sure what acceleration ramping is?

Have you heard of anyone using 2 of these brushless esc's for their drive?
http://www.hobbypartz.com/ezrun-25a-l-brushless-esc-for-rc-car.html
You can turn off the brake so you can go from forward to reverse instantly.
I just wonder if it could handle the stall amperage of this motor http://www.hobbypartz.com/96m05-car-2040-3600.html Or would it even have much pushing power at low rpms?

The only reason I was going to use the sabertooth 12 was to have it all on 1 control stick on my dx7 (easier to control that way imo).

The banebots 12 would require me me to buy 2 and that would be around $120, I feel like I could go brushless in my 3lber for that price.

What esc do you think I should go with?

And what's your opinion on the brushless setup I'm thinking of using?
ESC http://www.hobbypartz.com/ezrun-25a-l-brushless-esc-for-rc-car.html
motor http://www.hobbypartz.com/96m05-car-2040-3600.html
I just wonder If their would be a way to program some mixing on my dx7 so I could control it on one stick instead of 2?

I'm really considering going brushless with my build.

the brushless esc idea doesnt seem like the best idea to me, but i dont know all that much

You can set the banebots or other esc to one stick

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I just wonder If their would be a way to program some mixing on my dx7 so I could control it on one stick instead of 2?

I would almost guarantee that this is possible. We do that with the dx6i.

I have no clue as to how the brushless idea would work, but if you really want to do it then go ahead and try. Those esc's should also have a reverse to them because they're for an r/c car so you shouldn't need 4 of them, just 2 like you said so that should work.

I'm also not too sure about the compatibility of that motor and the esc but that's just because I don't know much. My understanding of brushless motors is that they have max torque at 0 rpm's and the faster they go the less torque they have.

i thought brushless didnt have any torque at 0 rpm (which was the problem with derry's brushless flipper?)

I came to the decision from the parts I already have that I will build an antweight and I will save the brushless beetle build for a later build.
A while back I bought 5 50-1 6v copal metal gear motors and a b gearmotor used really cheap.

So I will use
2 motors copal 50-1
2 wheels banebots 1 7/8
and a brushless spinning weapon (powered by a hobbyking outrunner)
and most likely a sabertooth 5

I'm thinking about a vertical spinning disc built into a wedge scoop, What size brushless and how many amps would you use for a antweight weapon , and are outrunners or inrunners better for that application?

I'm going to go buy a oxygen and acetylene cutting torch and welder today so that may help in my build a little bit.

4goodbuys2 wrote:

The reason that I would use 4 esc's because they are single channel and it would require 2 for each side 1 for reverse 1 for forward movement totaling 4.

The sabertooth 12 seems to be a good choice because I can run it on one stick on my dx7.

Have you heard of anyone using 2 of these brushless esc's for their drive? . . . Or would it even have much pushing power at low rpms?

I have never heard of anyone using two separate ESCs, one for forward and one for reverse. Have you actually done this, and does it work?

The Spektrum joystick-style transmitters (not the pistolgrip) have an 'elevon' or "V-tail" mixing option, that automatically makes single-stick control using the elevator and aileron channels, regardless of the ESCs you choose. It's not too difficult to do, I suggest you read your manual. However, even if you choose not to do your mixing in the transmitter, an elevon mixer will do it for you inside the bot. I would NOT choose my ESC based on the mixing option, and probably not on the BEC options either (If all else is equal, then they are nice options to consider, but power, reliability and size are the key specs)

To my knowledge, the starting torque on a brushless is poor--if you try to start it up and there is too much load it kinda makes a buzzing/grinding noise, heats up, and doesn't move. This is called cogging. HOWEVER, I have never successfully worked a brushless drive (weapons, absolutely, but drive, no) --you really should PM rjw if you are considering this because he has made it work quite well, and he is generous with his support.

One last thing--and my apologies if this does not apply to you:
If you are using belts and pulleys for the first time, the most common error is to assume that you can just choose two pulleys and mount the shafts at whatever distance you want and then pick a belt to fit.

IT DOES NOT WORK THAT WAY.

I am speaking from experience with a lot of students. I am not sure why everyone at first assumes this is how it goes, but sadly it does not.

Belts are only available in specific lengths. You must design the distance between pulley centers/shafts (this dimension is called the center distance) to match the pulley and belt sizes available. the utility at http://www.sdp-si.com/Cd/default.htm is excellent for performing this calculation.

If you (like so many of my students) absolutely refuse to do it the right way, then you should make provisions to either move one of the pulleys/shafts to adjust to the correct belt tension, or add in an idler pulley, which must also be adjustable. If neither of those options is appealing, you can do what Will Bales does and custom make/turn your pulleys after everything else is done--with some trial and error you can end up with a good fit, but it's kind of annoying to assemble/test/disassemble/lathe/repeat until it works.

What really sucks is that I am pretty sure I'm wasting my breath--almost every student does this wrong the first time and then learns (sort of) from his/her mistakes. amiright?

It seems that everyone said to use the banebots 3-9 , 2 of those are equal in weight to the sabertooth and they seem like it would be harder to short them out being shink wrapped and all.
So I would need 2 of those , I could just run them off the same battery.
And try to use my remote to mix it to one stick.

Also that belt size calculating tool is a good idea, but that will be a different build.

What esc and motors do you run in your brushless weapons?

4goodbuys2 wrote:

I came to the decision from the parts I already have that I will build an antweight and I will save the brushless beetle build for a later build.
A while back I bought 5 50-1 6v copal metal gear motors and a b gearmotor used really cheap.

So I will use
2 motors copal 50-1
2 wheels banebots 1 7/8
and a brushless spinning weapon (powered by a hobbyking outrunner)
and most likely a sabertooth 5

I'm thinking about a vertical spinning disc built into a wedge scoop, What size brushless and how many amps would you use for a antweight weapon , and are outrunners or inrunners better for that application?

I'm going to go buy a oxygen and acetylene cutting torch and welder today so that may help in my build a little bit.

in that case i have to say that fingertech tiny esc are the only way to go.

The fingertech v2's seem like the way to go 2 weight just as much as 1 banebots, but they only do 2.5 amps which should be fine in a ant weight.
My only concerns , does it have lipo cutoff if so at what voltage?
Can you run 2 bec's on the same receiver?


Are these motors any good in the 35-1 gear ratio? http://www.fingertechrobotics.com/proddetail.php?prod=ft-spark16-xxx

Ha ha. No, you don't design around belt length, but you cannot ignore it either. Ideally, you design around your desired pulley ratio, and then space your axles to fit one of the available belts.

One major complicating factor is the use of 'flipped belts." I am unaware of an easy way to figure center distance if the belts are used in a nonconventional way. For those applications it is probably best to make things adjustable or do it Will's way.

We have used Razor brushless motors from NEU in our beetles, with BB 24mm gboxes, 16:1 ratio and they work great.

We've found that as long as you have enough power to spin the wheels when up against a wall, then sensorless motors will work pretty well.

On a side note....I have few to sell if anyone wants them...Razor 300, $30 each. With this combo of ratio and motor, they are powerful enough to spin 4 1 5/8" diameter Colsons.

If your sensorless motors stall and cannot spin, you'll burn something out.

As far as timing belts and pulleys, as stated previously, determine ratio and then choose pulleys and belt for proper center distance. In some instances, we've used ecentric axles to fine tune cd.

rjw wrote:

In some instances, we've used ecentric axles to fine tune cd.

rjw, you crack me up. There is NO WAY I'm gonna let you just drop a coy little statement like that out there and not ask for elaboration.

So, OK, I'll bite--How do you use eccentric axles to fine tune center distance?

Ohh. I was thinking of 'live' shafts, and this made no sense.

With the pulley free to spin on the shaft, then it is pretty simple to understand. (and makes me feel a bit stupid for not understanding it in the first place!) Thanks.

Yes , with dead axles.

We've done a fair amount of testing in the past. We've found that center distance isn't always ideal, using online calculators.

For example, without any provisions to adjust CD, other factors can come into play, such as

1) belt length tolerances...different molds/manufacturers belts can vary , in some cases noticeably
2) pitch...lighter duty belts can jump teeth under heavy loads, if CD is a bit on the loose side
3) very short CD's vs very long CD's....belt width/thickness used with very short CD's can cause slight or not so slight binding problems. Longer belt runs are much more tolerant of CD error.

An amp meter is your friend. One good method is to the following and to log results for future reference and troubleshooting...

1) Measure amperage draw of motor, with nothing connected .
2) Measure with motor connected to a properly assembled/lubed gearbox (not installed in bot)
3) Measure with Gbox/motor installed in bot (no belts/no wheel(s))
4) Measure with wheel or belt installed (if more than 1 belt, measure all combos)

5) Modify procedure as per your setup, and make note of amp draw readings in all cases and also on both sides of bot.

6) You can use these noted readings to determine problems as they arise.

On a side note, we've used dead shafts with eccentrics turned on the ends. the eccentric portion slides into recesses in the frame rails..this takes the radial load off of the fasteners...

As stated by Alex, eccentric axles can also help to fine tune bot height and/or help in getting all 4 wheels to touch the ground...on a flat surface

Re: upside down timing belts.....best used for weapon drives, and needs provisions to adjust CD/tension.

An exception to this is my meltys, whiich so far have all been running upside down timing belts for the drives, although on bigger bots, conventional mounting along with true timing pulleys would probably be better (12 pounders and up)

Just some observations.....and we've been playing with all this for long enough (I think)

why does every topic on the forums always spark side conversations xD, it makes it impossible to just skim =p

Is there a correct way to use "eccentric" shafts? Because I can think of several ways to use them and I'm not sure how they would work out.

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Define correct way?

Tried-and-trued method?

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We always just made sure to lock them in place tightly or we would loose belt tension.

Do you use a locknut, a bolt that's similar to that on a bike axle, or just a screw and some loctite?

shim it with tooth picks till you get the right tension