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 1 lb drum bot!

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Dan Curhan
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PostSubject: Re: 1 lb drum bot!   Fri Jun 19, 2009 9:00 am

omg. i promise i'm not that stupid! I just couldn't see!!

my pwm was just plugged into + and - instead of signal, + and -. I missed. oops... all better. :]
but still, the one wheel spins SO MUCH BETTER than the other. I think I'm gonna go replace the motor.

I do have a question concerning LiPo batteries though... my battery is a 2S 8C 800mAh Common Sense RC battery. It was the only battery that would fit in my design. It charges in about 9 minutes at 1.6A (2C). Is this normal? The charger says it only has a charge capacity of like 0043 (I'm using an eflite lipo balancing charger) but I'm not sure what that means. 0043mAh? that's not even close!?

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PostSubject: Re: 1 lb drum bot!   Fri Jun 19, 2009 9:11 am

AAHHHH it's FREAKING OUT!

the bec that i plugged in wrong, I think i screwed it up. At anything less that full tilt (stick in the corner so 100% goes to that one motor) it twitches, going like forward, stop, forward, reverse, forward, and even keeps moving for like a second after i let go of the drive stick. shiiiit... I guess it's a good thing I bought four? Two were supposed to be for my dad's bot... Oh well. He's no where near ready for them yet though lol. His bot is FAT!

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Dan Curhan
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PostSubject: Re: 1 lb drum bot!   Fri Jun 19, 2009 9:37 am



here's a video of what my wheels are doing.... eesh. it's weirdd.

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SenaiERI
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PostSubject: Re: 1 lb drum bot!   Sat Jun 20, 2009 12:31 am

Is your speed controller set to coast down to neutral or cut off immediately? I had that problem in san fran but I just lived with it.

SenaiERI
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Will Bales
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PostSubject: Re: 1 lb drum bot!   Sat Jun 20, 2009 11:19 am

well that sucks! I was hoping to see some videos of this thing throwing stuff around!! I won't make it to the competition because I'm in Hershey, PA. (HERSHEY AMUSEMENT PARK) Tell me all about it! TAKE LOTS OF PICTURES!!!!!!!
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PostSubject: Re: 1 lb drum bot!   Sat Jun 20, 2009 6:22 pm

Dan

If you went to Barf, let us know what happened...

Thanks
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Cody
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PostSubject: Re: 1 lb drum bot!   Sat Jun 20, 2009 9:04 pm

will i dont really see you as a hershey park kid hahaha
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Will Bales
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PostSubject: Re: 1 lb drum bot!   Sat Jun 20, 2009 9:37 pm

lol me neither! my little brother wanted to go
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Will Bales
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PostSubject: Re: 1 lb drum bot!   Sat Jun 20, 2009 9:38 pm

lol me neither! my little brother wanted to go

So, how'd the competition go?! pictures??
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PostSubject: Re: 1 lb drum bot!   Wed Jun 24, 2009 11:07 pm

the drum spins! I mean it REALLY SPINS! damnnn.
so i'm getting really excited.

Everything is done except the top armor and securing things with hot glue.
I'll post videos tomorrow - i'm too tired tonight lol

i AM running into a weird problem with my thunderbird though.

when it starts, it beeps and kinda jiggles forward/backward if I start up slow. Otherwise it's fine... but then if it's spinning and i start driving, it stops, and i have to unplug the battery and then reconnect it in order for it to work again. any ideas?

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Will Bales
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 1:10 am

The motor is "cogging". It's that weird sound and stage that it gets in when it just doesn't want to run! sensorless brushless motors all have this problem to some degree. As far as the running problem goes: I think you don't have enough current to run both the weapon and the drive at the same time.. oops!

But I'm only guessing Wink
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 7:44 am

I agree with Will...

Best thing to do is bench test with a higher capacity battery pack and then take it from there

What battery are you running at the moment?
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rdubard
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 9:32 am

The problems at startup sure sound like cogging--Fluffy had an extended case of this ailment while the team was tweaking the software to eliminate belt stripping. Eventually Will and Tyler hit upon the right combination of settings to eliminate cogging in that particular setup. I'm guessing that's exactly what you are going to have to do--play with the settings in Castlelink. I thought I heard there was a forum member who worked for Castle. . .
OTOH, shutdown when driving has always been an issue with battery current delivery in my experience. I remember one time we had attempted to wire two deWalt motors in parallel in Woodynator (brushed, not brushless, but still) and it would shut down whenever we tried to run the weapon and drive simultaneously. We wired the motors in series and the problem went away.**
(of course, one motor alone would deliver more power, so that's what we ended up doing)
Bench testing your setup with higher capacity or higher current rated batteries should reveal the problem--finding a suitably sized battery might be a more difficult task.


**Which led to an interesting discussion about a setup in which the motors are automatically switched from series to parallel depending on the speed--this is something I really want to investigate further some time in the future--if this were done right it would mean rapid spin up to very high speeds. In retrospect such a setup may have been a possible solution for the multimotor spinner that was smoking motors prior to Nationals (was that Matt's robot?) ahh hindsight
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 10:21 am

Here's the deal on cogging and battery capacity...imo

As stated earlier, start with a high cpacity battery pack..same voltage, but lots of amphours, then run the drive and try the weapon.

As far as cogging goes, try loosening the belt tension and check if cogging happens in both directions or just one.

If just one and in the WRONG direction, try movng the 3 motor leads over one position....this is a hint from castle when I had a similar problem.

I'll bet that loosening belt tension fixes the cogging...It's a fine line between slippage and cogging, especially on smaller bruhless setups. been there, done that.

Stiff v belts contirbute to the problem

We are running timing belts upside down (flat surface of belt against drum and pulley.

They are much more flexible and less prone to cogging....Best are the soft ones..usually not black in color.

hope this helps
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 11:00 am

nooo!! don't tell me that!! lol
this battery was the ONLY ONE that fit perfectly in my design. It's the only battery short enough to fit inside my frame and the frame is all one-piece aluminum machined by HAND guys NOT CNC... noooo!!! haha

it's a common sense RC 8C 2S 800mAH battery...
http://www.robotmarketplace.com/products/0-2S800-8.html
6.4A continuous and 9.6A burst discharge. The motor supposedly has a max draw of 7A. Was it unreasonable to assume it would only draw around 7A on initial spinup? I tried using my multimeter (with a 10A capacity) but I don't think I was doing it right. You're supposed to put an ammeter in series in your current, right? so i put it across the contacts of my switch, and it read 1.8A but the bot didn't turn on...

My dad has a 2S eflite battery that's got 430 mAh and 20C (8.6A max continuous). Would that be better to try? Or is it not different enough?

Since I know next to nothing about brushless motors and stuff, I just connected the three leads, and got it to spin in the right direction, then soldered them. I didn't know anything about cogging lol. My drum only has one direction of spin (it's a thunderbird 18). I agree that my belt tension may be too much... I'll slot the holes for my motor mount. I'm running timing belts too, but I've actually got mine teeth down in the pulleys cause I thought the backs of them might be TOO slippery... They're extremely flexible but are black and don't stretch cause they've got kevlar cords in them...

Then I was spinning the drum, and I was just letting it sit at 3/4 throttle ish and after like 20 seconds, it just stops. The radio light went out and it started beeping cause it was searching for the radio signal.

So sometimes, the radio disconnects and I have nothing, then other times, it'll disconnect, then reconnect pretty quickly and I have drive but no weapon... :/ hmms

Here's a video I took of my problems. (that sounds really funny lol)



And I never made it to full throttle...

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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 11:43 am

The radio is disconnecting because battery voltage is dropping out.

Try a test with a separate battery for the receiver....a small 6 volt camera battery works

startup amperage on the motor could be a lot higher than you think

You might be in trouble with the burst rate of that battery pack

I've modified lipo packs, you could get a 20 or 30c pack and separate the cells into different locations in the bot to make things fit

Until you know the max amp draw, you're shooting blind.

A smal suggestion as well....dump the connectors and use micro deans
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Will Bales
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 12:27 pm

AHA!!!!!! I THINK I'VE GOT IT!!

The Castle Controllers have Voltage cut-off for LiPo Batteries! Also, Some have Amperage Limits!! You're tripping at least one of those!!!!! GO IN AND PROGRAM THE CONTROLLER! that should fix it!

I think... Surprised
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 12:38 pm

Will Bales wrote:
AHA!!!!!! I THINK I'VE GOT IT!!

The Castle Controllers have Voltage cut-off for LiPo Batteries! Also, Some have Amperage Limits!! You're tripping at least one of those!!!!! GO IN AND PROGRAM THE CONTROLLER! that should fix it!

I think... Surprised

actually, receivers don't like more than .1 or so voltage fluctuation, so that is more likely the problem.

We had this problem when running higher voltages, where the bec on the esc was de-rated to like 25ma....baaaah
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Dan Curhan
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 9:53 pm

but isn't the receiver supposed to work from like 4.5 to 6 volts? I can't imagine a battery charged to 7.4+ volts would drop below four to spin up the drum, but I could be wrong...

In order to program the thunderbird, I need to buy something, right? Castle link?

I'm not too worried about the cogging, so I'll leave that be for now... there are bigger problems to solve!

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-Captain of Copperheads 2 to pi, mastermind of the Dethinator, Creator of Conundrum, and Sultan of Shred. Heh. Sultan of Shred. It's kinda catchy... I like it!
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 10:30 pm

with a fully charged battery there seems to be much less of a problem... but the drum isn't quite perfectly balanced, so the whole bot vibrates... let me tell you a story.

I put the throttle up to about half. I put the controller down on my stool and knelt to look at my bot vibrating in a little circle on the floor. I stand up and knock the controller off my stool, which pushes the throttle (of course) all the way up. Immediately the motor screams and the whine of everything spinning gets much much more high pitched and urgent sounding. As I'm reaching frantically for the controller to turn it off, I hear a frrrrrpptt as something gets chewed. When I finally get everything stationary, the receiver chip vibrated its way into the path of my drum teeth, and I ripped off part of the side panel and one of the antennae. It still works sans antenna and the light is brighter now, but it really scared me lol. To be not in control of something spinning that fast (est. 8K rpm?) is frightening. Especially in my bedroom...

I'm gonna wait til tomorrow when I hot glue everything in place to do more testing so I don't do any more damage lol.

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-Captain of Copperheads 2 to pi, mastermind of the Dethinator, Creator of Conundrum, and Sultan of Shred. Heh. Sultan of Shred. It's kinda catchy... I like it!
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 11:42 pm

Dan...you're killing me!!!

You need a lasso and I hope you have safety glasses and full body armor in your bedroom

It's voltage FLUCTUATION that can cause the receiver to fall out.

But with the light shining brighter and no antenna, maybe you fixed it ???

I'm glad you didn't get hurt...so I have to laugh....it's a funny story

The 1 pound out of control bott in the bedroom trick...hahaha

What's next?

btw: charging the battey helps, no?

I believe that voltage cutoff is disabled by default, but if the tbird can be used with castle link, you could tweak the throttle curve and get a bit more startup juice. minor in light of the current situation
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PostSubject: Re: 1 lb drum bot!   Thu Jun 25, 2009 11:46 pm

yeah there's more than enough power in the motor to go right up to half throttle+ with almost no hesitation, so I'm not too worried about it...

haha yeah it definitely freaked me out lol.
I'm putting testing on hold til i secure things and put safety glasses on in my garage Razz

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Will Bales
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PostSubject: Re: 1 lb drum bot!   Fri Jun 26, 2009 1:23 am

lol!
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PostSubject: Re: 1 lb drum bot!   Fri Jun 26, 2009 1:44 am

I would have loved to see a video of the event

THE WITTLE BOT BOUNCING AROUND ON THE FLOOR, SHREDDING IT'S OWN GUTS WHILE YOU'RE CHASING AFTER THE TRANSMITTER

Definitely a Kodak moment
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PostSubject: Re: 1 lb drum bot!   Fri Jun 26, 2009 9:20 am

Careful, K?
It may be small, but 4S liPo at 6amps current draw can deliver around 50 watts, and the spinning drum accumulates energy up to full speed. You could definitely lose a finger (or toe, if you're barefoot), and the safety glasses are pretty much a necessity.

Of course, this sage advice is coming from the guy who thought it would be OK to have a 10 bot rumble in a parking garage, and ended up with a postage stamp sized gash in one student's face.

My point is, we all can be stupid sometimes--at least in your case no one was hurt!

It seems you have eliminated the cogging issues, but if you want to program the Tbird:
Here's the CastleLink USB programming kit
It's a worthwhile thing to have and to understand, especially since Brushless is definitely here to stay.

Lastly, about the belt tension--I have preached to my team til I'm blue in the face that one MUST do the calculations if one wants to use belts, but it seems no one wants to hear it. SDP/SI (Stock Drive Products) has a great online utility that allows you to enter the pulley and belt sizes, and it tells you exactly what center distance you need.
Center Distance Calc
Of course, if you later decide to change your pulleys/ratio, then things need to be adjustable.
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