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 3lb design and questions.

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Koolaid64
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jolijar




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Registration date : 2010-11-21
Age : 38
Location : Chicago

3lb design and questions. Empty
PostSubject: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 3:49 pm

Hello. I have been lurking for awhile and decided it was time to sign up.
I am currently designing my first battlebot. I have lots of experience with R/C gear and a little in manufacturing. I decided that I wanted to build a 3lb robot. I have several questions before I get too far along in the design process.

What materials do people usually use for armor on their robots?
How thick?
roughly how much of the weight of the robot should be armor?

I am designing a 4 wheel wedge with a small lifting fork (think panic attack)

My budget is $500 for the robot / spare parts
I already have a suitable radio.

3lb design and questions. Dooma

This is what I have designed so far. SW says it weighs in at 2.14 lbs
the sides are made of 1/4" 6061 Aluminum and the top and bottom are 1/8" high impact acrylic
the motor shafts wont stick out I just haven't trimmed them yet.

I am using 4x
Banebots 10:1, 25mm Spur Gearmotor, FF-180 Motor
and Banebots 1 7/8 wheels
I

It is missing the following components
Bearings for motor support
ESC
Battery
Receiver
Wedge
Lifter

I know I am going to be overweight so I suspect that I have overbuilt the frame.
this design is more than likely destined for the recycle bin but I figured I would show it to you guys and ask for your expert advice.




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rdubard
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3lb design and questions. Empty
PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 4:52 pm

You gotta make weight.

How about using only two drive motors, and belts to get to 4wd? This will give you something to work with.

Do not overlook the weight of the battery--it can easily equal a drive motor or two.

High impact acrylic? Is this the same as polycarbonate, or not? My experience is acrylic is awful, but polycarb has been used with some success.

A 3lber really won't required bearings for the motors.

Just my two cents.
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jolijar




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Age : 38
Location : Chicago

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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 6:29 pm

I meant polycarbonate. I want to use 4 motors for the pushing power. I havent purchased anything yet. Do you know of any lighter motors that are similar in performance to the Banebots motor I have selected?

They weigh 2.6 oz each.

Gearmotor Specifications
Physical
Type : Spur
Reduction : 10:1
Gear Material : All Metal
Weight (Gearbox only) : 1.5 oz (41g)
Weight (with motor) : 2.6 oz (73g)
Length (Gearbox only) : 0.8 in (20mm)
Length (with motor) : 2.1 in (53mm)
Diameter : 1 in (25mm)
Shaft Diameter : 0.16 in (4mm)
Shaft Length : 1.9 in (48mm)
Mounting Holes (2) : #4-40

Calculated Performance*
Motor : FF-180
Operating v : 3v - 4.5v
Nominal v : 4.5v
No Load RPM : 1280
No Load A : 0.2A
Stall Current : 6.7A
Stall Torque : 31 oz-in 218 mN-m
Kt : 4.6 oz-in/A 32 mN-m/A
Kv : 284 rpm/v
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Cody
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 7:51 pm

i cant say ive ever heard of anyone using the banebots with spur gears, usually the discountinued planetary gearboxes are.
I think there more for antweights but I've seen beetles using 4 spark motors from fingertech
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Koolaid64
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 8:20 pm

most beetle builders that don't already have the planetary 24mms from banebots are now using these with quite a bit of success, plus they are fairly cheap http://cgi.ebay.com/2-x-12V-1000RPM-Mini-Torque-Gear-Box-Motor-Hobby-DC-NEW-/400174400196?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d2c40c2c4
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jolijar




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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 10:17 pm

Are you sure? The banebots has 31 oz/in of torque and the linked motor only has 2.1 oz/in of torque.

I modified my design a bit and removed the need for bearings. I also brought the weight down to 1.9lbs
without the rest of the gear. I think I might be able to make weight now.
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Cody
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeSun Nov 21, 2010 10:50 pm

alot of people do use the ebay motors in beetles now since there was very limited availibility of others for awhile. Most we used in weaponed bots
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Koolaid64
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 11:48 am

both these robots use four of the ebay motors, they both burn out long before the motors stall. and i don't trust banebots stats much any more, i've had 3 of their spur motors break outside of battle just from regular driving
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jolijar




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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 4:15 pm

Ok I think you sold me. Those motors are much lighter so I will be able to put my weight elsewhere. Thanks. Smile
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SamM
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 5:46 pm

I also agree the "1000 rpm ebay motors" are the way to go.

They qualitatively seem to have less torque than what I was replacing:
http://banebots.com/pc/MP-24XXX-370/MP-24016-370

BUT, what they are is robust, I have taken multiple wheel hits, and still not had a failure.
I use 4 in my beetle wedge, Ramvac:
https://www.youtube.com/watch?v=nRz2INC4tmQ

and 2(overkill) in my Ant
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jolijar




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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 5:54 pm

Wow SamM your wedge took a ton of abuse before the match was over. If there had been a pit in that arena I would have bet on your bot.

Anyone have a datasheet for these motors or a solidworks model? How far apart are the mounting holes and how wide/tall is the brass colored bearing? in the front?
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SamM
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 6:40 pm

Yeah, that was one of my favorite fights there, and my only loss. I had on the old wedge that had been through 1 or 2 too many matches, and had several cracks through the lexan and steel already.

Pete Smith has a solid model, among many others on his site. follow the links Solid Models>Motors It will be at the bottom.
http://www.teamrollingthunder.com/

A few notes:

At 76g these motors are heavier than the the BB spur motors(73g), but lighter than the planetary(94g)

Before you use them in combat you will need to disassemble them and loctite both the two screws that hold the motor to the gearbox and the two screws that hold the gearbox together. If I recall correctly when i first got mine they were actually loose from the factory.

Pete also sells them already battle hardened on his site, but It's not clear whether the price is for one or two of the motors(there are two in the picture, with mounting plates, but it states the plates don't come with them, and no where does it say 2x)
http://www.kitbots.com/product.sc?productId=20
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SenaiERI
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 7:41 pm

rdubard wrote:
My experience is acrylic is awful

Why? What happened? I was planning on using either acrylic or poly carb. Which is better for what?
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Cody
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 7:46 pm

polycarb
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jolijar




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Location : Chicago

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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:09 pm

3lb design and questions. Doom2x

Due to weight I am no longer considering adding a wedge

This is at 2.3lbs
It is missing the following components
Servo/arm for the lifter
receiver
Batteries
Screws

I need to go with a 12v Battery though I am unsure of what capacity to purchase. Should I run lipoly for the weight reduction or use nimh or nicad?

what do you think about this speed controller?
http://www.robotmarketplace.com/products/0-SABER2X5-RC.html

Any ideas for suitable servos or gearmotors for lifting? I only expect to get a few degrees of lift and thats fine with me.


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SamM
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:22 pm

SenaiERI wrote:
rdubard wrote:
My experience is acrylic is awful

Which is better for what?

Acrylic is good for fish tanks.
Polycarb is good for bots.

Acrylic's advantage is that it is cheap and if i remember correctly can be bonded by fairly safe and conventional glues. It's disadvantage is that it cracks and shatters way too easily. I think Jeeves is using "high impact" acrylic and thinks it will be ok, but I'm not sure about it. I once figured out a scrap plate that i thought was polycarb was actually acrylic when it broke in half while i was cutting it on the band saw...

Polycarb is much more tolerant of impacts, but it is far from ideal.
Some comments:

As far as I know, the only glue for it is classified as a hazardous substance, so shipping is extremely pricey. Some hobbyists have had mixed results with superglue or goop, but i'm pretty sure that most glues weaken it chemically. and will fog or crack it. I once tried acetone to bond it...that was a joke.

If you tighten a bolt down on it too tight it will develop hairline fractures radiating out from the hole.

Rigid mounting is generally a bad idea. The more it can flex the better.

All things considered, it is still a good material for the weight, especially in applications where you want something to absorb an impact and return to its original shape

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rdubard
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:25 pm

I see someone posted a good answer while I was writing this one. Here it is anyway (so you don't think I was ignoring you)

Acrylic is brittle and comparatively weak. Plexiglass is a common brand name.

Polycarbonate is basically bulletproof glass (depending on the thickness)--much tougher. One brand name is Lexan.

They look about the same, but Lexan costs more.

Battlecages are made of Lexan, NOT Plexiglass.
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jeeves_m_d
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:41 pm

well I wish i knew how crappy acrylic was before i ordered it.

to be honest although it has much lower capabilites/specs than poly carb

this high impact stuff from mcmaster really hasn't been to bad, its machined beautifully and hasn't cracked, also the stuff is much more scratch resistant, I have it in a spot where it hopefully should not take any direct blows.

Although I would never suggest using it in heavy weight or a 120, its seems fine for lower weight classes such as internals for a 15, and it should definitly be more than enough for a beetle weight.
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Koolaid64
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:47 pm

you could probable use 1/16" garolite for you top and bottom plates, that should give you more weight in your design. I've even used 1/32" thick plated with quite a bit of success but i wouldn't recommend it in a long term robot, I usually only run mine for one comp then build something different
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SamM
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:49 pm

The weight reduction of LiPo's is really nice. I use a 3s 1050 mAh:
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7449
and it has way more than enough capacity for these motors with the ESCs I have. I am actually going to buy some 4s packs and see how these motors work at 15v.

This may be overkill, and i defer to anyone with experience running them on smaller ESCs, but I use two of the sabertooth 5, I had the sabertooth 10 but they were out of stock on it when i sent my 10 in for repair. (Note: Dimension Engineering is very good on their warranty, but sometimes lacking in quality control. Mine never worked correctly right out of the box, my brother's has taken some serious abuse with no issues).

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jolijar




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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:52 pm

just be careful with those hobby city batteries. some are +- 25% capacity and you need to make sure you never go below a 20% charge. I am surprised they allow lipo battery's as the can be a fire hazard.
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Cody
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 8:54 pm

Some competitions do not allow lipo batteries. Usually they are only banned in larger weight class. NRL does not allow lipo batteries
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Koolaid64
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeMon Nov 22, 2010 10:16 pm

@SamM

i had a sabertooth 10 that also didn't work right out of the box, sloppy solder on one of the receiver leads was causing it to short out. when i spotted it it was a easy fix just had to clean it up.
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jolijar




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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeWed Nov 24, 2010 1:06 am

Instead of 1/8" polycarbonate I think I am going to use 1/16" 6061 Aluminum. The weight is almost the same.

which is a better ground clearance?
1/4" or 1/8"
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Cody
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitimeWed Nov 24, 2010 1:37 am

little bots more is better i think.

Alot of arenas use wood floors that you will get hung uo on
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PostSubject: Re: 3lb design and questions.   3lb design and questions. I_icon_minitime

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