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 Alex's Melty Project

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rjw
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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 9:48 am

I guess that you are going to start with wheels on motor shaft.

small fets are way more efficient then the Darlingtons...they are heavy and heat monsters.

the sparkfun led's (rebels) are very bright and around $5 each....

you could get away with a lot cheaper, but they scale very well...I use the same ones in my 1,3 and 12

find, download and install avr studio (i think 4) . it requires xp sp3 or something. another freebee is winavr with programmer's notepad.

It's all freebee stuff...

Rich Olson's code requires only a basic radio setup, no mixes... (3 channel)

Mind you, inverted op = fwd/rev is backwards, which mixing can fix.

I am off in a direction that will require some extra channels, switches and possibly mixes.

Don't you already have a dx6i and receiver?

remember that a single wheel melty will self balance. a conventional 2 wheel will require very good balancing.

Show us your cad, so we can critique


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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 11:14 am

I have a ton of fets that worked and somethat I was going to test, but any fet npn with a logic level gate will do.

If I can dig some out, I'll give em to you....they require a diode and possibly a resistor on the gate...it' been so long, that I don;t remember.

but for your test platform, if are using small motors ...low current and can aford trhe darlingtons, they'll work fine (try to heat sink them

the tank drive is still a pie in the sky, but I am working on it

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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 11:18 am

on a side note my ant fought nearly the whol event on 1 wheel drive....I didn;t even bother to investigate, but it was probably an esc that went south, in that one wheel pulley was totallt oor and I never bothered to make a new one.

also 2wd spins up a lot faster

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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 11:22 am

also, weed therough the melty facts and take em with a grain of salt.

Colsons actually turned out to be too soft on wood.....(preformas) they all wore down pretty quickly, especially on the 12....

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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 1:06 pm

Alex Udanis wrote:
So how hard is it to go from brushed to brushless?

until I find another board, it requires 1 tricky solder onto a .009" diameter wire in a small hole and 1 other onto an existing pin...

and a change to my code...until either Rich or someone else comes up with a version...then there will be options.

Outside of that, 1 pair of compatible escs and brushless motors..preferably escs with a bec built in

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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 1:10 pm

Alex Udanis wrote:
Placed my polou order.

Alright about to place my Mouser Order. Just wanted to check:

Here is what I got so far:
-Diodes-1N4007 Mouser # 512-1N4007
-Resistors: Metal Film Resistors - 100ohms 1/4w (I can use 1/4w right?) Mouser # 660-MF1/4D52R1000F
-Transistor: TIP142 these are 10 amp NPN Mouser #511-TIP142

I think that's all the components i need minus the led stuff. Right?

if you are buying Darlingtons, then you don;t need the diodes...they're built in, but you'll need the 100 ohm resistors .

if you went thru the list and that's it then you're ok


are you going to use a bec or a voltage regulattor?

also, you'll need a resistor for each led .

Rich has a link to accel calcs and led resistor calcs on his site (open melt)

Just remember that the baby o board takes no power except for the leds, so you can;t go over 1 amp or you'll cook the onboard H bridge

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Last edited by rjw on Fri Oct 15, 2010 1:11 pm; edited 1 time in total
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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 1:22 pm

that is Pertu 's diagram and he is NOT using Darlingtons, just simple fets.

If you buy fets , then yes, you need he diodes and I think other gate resistors

If you guy Darlingtons, they have a built in diode and you use Rich's diagram...what are you ordering????

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PostSubject: Re: Alex's Melty Project    Fri Oct 15, 2010 1:34 pm

buying the fet, diade and the correct resistor could be cheaper , but it's a bit more work.

If you can afford the crappy Darlingtons (which I burned out 3 of them, with 540 motors) at least the wiring is simpler...especialy if you use the small motors.

Use the Darlingtons and follow the OTHER diagram (Rich's) just to getup and running and to feel confident that you can handle things.

Alex...at first it's a bit scary, but after a while, if you get it running, it isn't rocket science, especially for a guy like you.

Just take your time soldering the little stuff. the babyo pins don;t like much more than 300-400 C and not for a long time.

I you areusing a small iron, try maybe a 25 to 50 watt max on the board and acclerometer

another warning...anything that isn't strapped in well, will eventually torpedo out of the bot..and probably soone than later.

why not just grap a chunk of wood and zip tie everything in..cheap easy way to get up and running...a lot of Rich's test platorms were just zip ied to mayb an alu plate

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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 7:59 pm

You have a bec, Yes?

Battery... best to use 1 that is total overkill..this way you get some run time...3 minute goes by in a heartbeat

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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 8:25 pm

I don't think that the baby o is good to 15 v???

In any case, what is the rating of your led?

I'd still do the bec thing and dump it down to 5v...Do you have a resistor for your led? remember the babyo can only handle maybe 1 amp max thru it's h bridge.

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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 8:35 pm

did you go to the site linked by Rich and calculate the resistance and wattage needed for your led...most leds have a forward drop rating,etc....yur sounds like it won't need much of a resistor, but the normal packs of resistors that you by are usually only rated at 1/4 or 1/3 watt...better to be aft than sorry...or baby o goes poof... affraid

also, you will need some pwm cables to go to the receiver

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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 8:53 pm

I'm tired but while a bit sloppy, it's probably do.

for the Darlingtons, I think that anything will do (100 ohms)

test bed? how about a round cookie sheet and zip ties.....a Rich Olson special.

How fast are you going to spin it at first?

Just remember that the darlingtons are very over rated, but with 280 motors you should be fine.

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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 9:04 pm

you know how to calculate the rpm of the bot?

darlin gtons....just don;t slap a pair of big 540's in there thinking that everything will be fine

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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 9:17 pm

you take the distance between the wheels (center to center or outside to outsde for a conservative estimate) and use that as a diameter. Multiply that by 22/7 and you have the circumference of a circle that is the track that your wheels will follow

example distance between wheels = 10" 10 x 22 / 7 = 31.4"

calculate circumference of a wheel Example: 1" diameter wheel = 3.14"

divide 31.4 / 3.14 and you get 10 as the ratio between track circumference and wheel circumference

Kv of motor x battery voltage example 2000 x 7.4 = 14,800 rpm

14800 / 10 = 1480 rpm top speed ...not taking load into account or wind resistance or friction.

if you make it as far as wanting brushless motors, make a mental note to ask me about kv, becuase for best tracking, you need some overhead.....i.e. if you want to spin 4k, your kv, battery, etc should be capable of 20 -30% more

Why? cause you can't speed a wheel up that is already going as fast as it can




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Last edited by rjw on Sun Oct 17, 2010 9:20 pm; edited 1 time in total
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PostSubject: Re: Alex's Melty Project    Sun Oct 17, 2010 9:21 pm

simple isn't it?

reread my post, I modded while you posted....

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