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Dan Curhan
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PostSubject: hot motors?   Sat Mar 28, 2009 3:13 am

Does anyone have any idea why 2 550 size motors, spinning a 5 lb shell with a 1.3 to 1 pulley ratio and good bearings, 12V, speedmax-40 ESCs are burning up every time we test the bot? And I'm gentle with the throttle!

For those of you going to miami tomorrow, you'll see it... and it still twitches when we turn it on...
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PostSubject: Re: hot motors?   Wed Apr 01, 2009 9:18 am

Dan Curhan wrote:
Does anyone have any idea why 2 550 size motors, spinning a 5 lb shell with a 1.3 to 1 pulley ratio and good bearings, 12V, speedmax-40 ESCs are burning up every time we test the bot? And I'm gentle with the throttle!

For those of you going to miami tomorrow, you'll see it... and it still twitches when we turn it on...

Is this on your Dethinator bot?

If so, and if they are the motors that are driving the shell through belts and pullies as per pictures that I saw, then...

typical 550 motors freewheel at around 19k rpm's and peak efficiency is in the 17k range.

If you do the math, 17k/1.3, the shell should be spinning at around 13k+ rpm's, otherwise the motors are being overloaded.

Typically these motors are driving 5 to 1 or greater gearboxes.

You might try attaching an amp meter to see what curent is flowing, with and without the shell installed.

I believe they should draw around 1.2 amps unloaded and maybe 10 amps loaded.

If the unloaded amps are too high, then you may have a problem with the drive setup. perhaps the hose clamps are tight and distorting the motors?

If the problem only happens with the shell installed, then it gets a bit more complicated and you may need to remove the belts and check the startup and running torque required to spin the shell.

While you may not care tp spin the shell that fast, it should still be able to achieve those speeds without binding, otherwise you ar constantly overloading the system and the motors/esc's will heat and burn up.

Hope this helps

Richard
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PostSubject: Re: hot motors?   Wed Apr 01, 2009 2:21 pm

Its really hard to judge an average motor specs
I dont think youd be overvolting them because your ESCs would burn out before the motor
Im thinking that just may not be a big enough motor, even though your using two.
Whats the weight of the shell now and how many volts are you running to the weapon motors?
Your motors are obviously going to get hot but im guessing its a little out of hand in your case?
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PostSubject: Re: hot motors?   Wed Apr 01, 2009 4:26 pm

I belive that he might be using these motors

http://www.robotmarketplace.com/products/0-DTXP5737.html

Not sure about these, but typically 550 motors are not really happy much over 10 amps continuous.

Oddly, the site lists a very low efficiency rating....wonder if it's a misprint. typically 70% o better is common with $5 cheapo versions that I've been using successfully.

His esc is rated at around 40 amps??? so i can't see it burning out before the motors. Mind you I believe it is rated at 12v...not sure how much more it wold take?

My point is that even at lower r's, if there is any binding or whatever, and the motors are drawing too much current and constantly, then heat and motor burnout can result.

All good points as far as questioning ratios, etc. but bottom line is to accurately measure the amps under load.

How else is he to determine where the problem(s) lie?

jmo
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PostSubject: Re: hot motors?   Wed Apr 01, 2009 7:13 pm

Alex Udanis wrote:
the big thing i see is your gearing. if you can make it higher like 2 or 3 to 1


-Alex
PR

thats what i was getting to lol
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PostSubject: Re: hot motors?   Wed Apr 01, 2009 10:29 pm

alright... time to answer questions... Razz

shell weighs 4.6 lbs and runs on good bearings.

Motor output to pulley to wheel driving the shell is 1 to 1.3 (bigger pulley on the driving wheel) and from there, it's about a 5:1 ratio from drive wheel to shell.

We tried the duratrax 550's but they got WAY too hot (I still have a nasty, scabbed burn on my finger from where I accidentally touched it after one of our tests) so I switched to 550 size banebots motors that run much cooler and better (albeit slower...).

The motor heat problem no longer applies, since the banebots motors run SO much nicer. However, our ESC's definitely didn't like our third match in Miami. I think it's partly my fault, I forgot about the throttle being all the way up in my desperate attempts to drive out of the corners I kept finding myself in, and I think I may have been stalling the motor (but V-belt + friction wheel should equal major slippage?) but that doesn't explain why not a single one of our extras worked. They had signal and power but output 0V. Could the BR6000 receiver have done something weird?
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PostSubject: Re: hot motors?   Thu Apr 02, 2009 12:10 pm

Hey Dan

At the risk of repeating myself, and in that you will be taikng this bot to CA soon, if I was advising, I would still STRONGLY recommend that you check the amperage draw of the 550's.

Hopefully you have access to a DC ammeter?

This is just part of the building/testing phase of robot construction.

That said, it should be simple enough to test your BR with servos, other esc's or what ever you have laying around.

Also, is there any burning smell from ANY of the motors that you have used? This would be a sure indication of overload.

Again, until you know the amperage, you aren't dealing with a full deck of cards.

With your current final ratio, it would be very easy to stall those motors.

Even using them to drive wheels through a 16 or 25:1 gearbox, (which has 4 to 5 times the mechanical advantage of your setup) itis easy to smoke the 550's.

Let me know how you make out, I would hate to see you travel that far without knowing the whole story.

Richard
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PostSubject: Re: hot motors?   Fri Apr 03, 2009 12:34 am

we've definitely smoked a duratrax (and it even broke off a brush...) but haven't smoked a banebots yet. they run much cooler.



We just redid the whole wiring setup to work with relays and a picoswitch. I'm hoping that our NiMH battery with 60A max draw can handle a shock ON to spin up the shell from a relay signal... I looked for soft-start relays, and even considered wiring a capacitor in series before the relay, and have it ground when fully charged, but I couldn't think of a way to use a capacitor that was small enough to not be a burden weight-wise.

I did discover, though, that the duratrax 550 motors had built-in RF interference suppression capacitors, while the banebots ones don't. This could be some of the problem... Another possible answer could be that the flag terminals we had on the tabs on the back of one of our weapon motors touched the outer casing on the drive motor. I covered the drive motor with several layers of electrical tape, but it's kind of chewed up, and there's a chance it may have shorted.

Anyways, I was looking at the magmotor website (because I know and trust the brand) and looking at their small 4-pole neodymium series, and I found some motors that look pretty good (this series). I'm too tired now to check the dimesions and make sure it would be compatible, but I will. If we can use one of these motors, should we?
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PostSubject: Re: hot motors?   Fri Apr 03, 2009 10:35 pm

Check specs against an AXI 4120, which is a proven motor for your application

Richard
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 12:35 am

Dont even bother with a Axi let alone the 4120 this isnt even close to what you would use.
The Axi is an outrunner that is alot bigger then what your using now, the 2826 would be more compareable in size to the 540/550 but like i said its an outrunner
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 1:02 am

Cody Harris wrote:
Dont even bother with a Axi let alone the 4120 this isnt even close to what you would use.
The Axi is an outrunner that is alot bigger then what your using now, the 2826 would be more compareable in size to the 540/550 but like i said its an outrunner

I could be wrong, but I think that he is thinking of replacing all his 550s with 1 motor????

btw: here's a spinner using an axi 4120....not too shabby Death star vs Chucker

Also, if he can deal with the spinning motor shell, it is a combat proven motor in this weight class, especially with a few minor mods. You might remember Humdinger 2 from last years national?
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 2:05 am

I now humdinger2 uses the 4120 but not to many others (exluding MRL bots aforementioned)really use that big of a motor in the 15lb wieght class, the more common being the 2826/12.
I actually just posted on the RFL forums about axi motors, being an outrunner not many teams support the spinning can. Big hits on these motors cause the set screws on the end of the can to work loose and throws off the balance of the armature, even after putting loctite on the threads. I have even seen the armature get bent in our bots (we used axi in both shockwaves).Another example being our fight with UKnight. Havent had any experience with them friction drive but in my oppinion he's alot better off with two 540/550 inrunners (which seems to be very common in friction driven FBS). Plus these motors tend to be alot more expensive then what he's seems to be looking at, not to mention he said he hasnt had any problems yet with the motors he's using now
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 2:24 am

I agree that there are many choices....some expenisive and some chinese and who knows?? and a lot in between.

I haven't really looked at his robot with repect to forces, power requirements, etc. i am still curious as to the amperage draw with his current setup???

As far as impact related problems, I believe that the rattler bots from MLEC have flown as high and hit as hard as any. All of our banebots gearboxes would have self-destructed if not for some minor tweaks.

The axi's can be made combat ready without much effort and with a little common sense. A lot of inrunners can easily lose an endcap if precautions aren't taken.
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 2:50 am

Uknight- more or less a build flaw shown but they also had trouble with the set screws at the same time[img][/img]
I mean hits given not hits recieved
The banebots are great products but same thing they need tweaked as the motors constantly work loose from the gearbox among other things
I would much rather loose an endcap then destroy the entire motor
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 3:06 am

Is that picture from nationals last year?

Was the motor only mounted by the front plate? No rear support?

My bet is that an inrunner without rear support could also fail in a bot that hits or gets hit as hard.

I've had it happen to a (not so cheap) inrunner and without getting hit hard at all.

It's human nature to judge from our own experiences and to go with what we feel comfortable with.

I'll guess that the new shockwave bot is using an inrunner and supported at both ends of the can??
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 10:49 am

Yeah thats what i was saying, no one puts rear supports on outrunners because of the spinning can.
Alot of teams using innruners such as Bloomsburg use rear braces on there motors but they hold the can not the end cap, and to my knowledge theyve never had a motor problem doing that way, or the obviously would change it hahaha
We only had a brace on Aftershock last year and didnt have a problem, but they redisgned it alittle bit so it holds the end cap too
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 7:00 pm

Cody Harris wrote:
Yeah thats what i was saying, no one puts rear supports on outrunners because of the spinning can.
Alot of teams using innruners such as Bloomsburg use rear braces on there motors but they hold the can not the end cap, and to my knowledge theyve never had a motor problem doing that way, or the obviously would change it hahaha
We only had a brace on Aftershock last year and didnt have a problem, but they redisgned it alittle bit so it holds the end cap too

We have a Scorpion outrunner that we were going to use last year if we couldn't make weight. It's a hk3026...specs are simlar to axi 2826, I believe.

Anyone have any success with those?
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 10:49 pm

I know you guys are talking about brushless stuff... my reluctance to switch to a brushless setup comes from two things: 1, I have zero experience with brushless motors. I know they're much more expensive, but I know nothing about how their performance compares with brushed motors. I'm looking for specifics, like torque curves, and power. and 2, the whole brushless setup is WAY more expensive than brushed, and I've already sunk too much time and money into this bot... we know it's not likely to win, so I'm hesitant to spend much more money (that frankly we don't have) on it. It's time to focus our attention on Copperhead, which has a chance...

We switched to relays (not sure if I already mentioned that) and in testing we completely seized up the banebots motors; totally burned them out. Switched back to two duratrax's and they survived a (gentle) 3-minute torture test. The battery got hot and the motors got hot (and our LED turned off while the relay was switched on, then turned back on when it turned off...) but it survived. I'm putting it aside as DONE and just bringing a lot of extra motors to san francisco.

but rjw, if you could clarify the main advantages to using brushless motors, and what they're like, and how the speed controllers work... because i really am totally out of my element.
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 11:09 pm

hey Dan

Sorry to hear about the latest problems....but i think that you may have a problem with your setup, causing all your motors to burn up. Until that is solved, brushed or not, things will burn up.

I've been trying to get you to answer the amperage draw question, in order to determine what's going on, but you haven't responded.

I wish that you were closer, cause I could have a first hand look and also measure the current myself.

Hopefully it is something not too complicated.

when you do get it sorted, you will probably be able to spin it up with any of the motors that you have tried.

Going to a brushless would just be , possibly some icing on the cake.

I only have 1 or 2 lousy pictures of your setup, do you have a link to some with more detail. I am curious and might be able to help...although time is getting short.

I also MAY have some banebots 550's if you need them.

let me know if I can help

Richard
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 11:18 pm

Ok, I looked at one picture that i have of your setup.

Looks like you are bolting the outer shell onto a housing with bearings in the middle.

Also, you have some small plastic or whatever rollers down near the bottom.

lastly, you have 3 colsons with motors, belts pullies, etc driving the shell.

Is this correct? Or did i miss something?

If so, how many bearings or small wheels are around the base plate? 3, 4?

Secondly, are all the rollers, wheels etc. touching the drum running on bearings or bushings? and does everything spin freely?

Third....how are you attaching the shell to the center shaft and have you allowed for heat and expansion?

Lastly, what rpm's does it spin at and will it spin for a while before the motors burn up?

Richard

edit: you mentioned something was rubbing on a motor or connector in a previous post. has all that been resolved?

Also, is the shell getting hot and in any sepcific area (s)?

we may be able to troubleshoot this right here on this forum lol
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PostSubject: Re: hot motors?   Sat Apr 04, 2009 11:51 pm

Dan Curhan wrote:
I know you guys are talking about brushless stuff... my reluctance to switch to a brushless setup comes from two things: 1, I have zero experience with brushless motors. I know they're much more expensive, but I know nothing about how their performance compares with brushed motors. I'm looking for specifics, like torque curves, and power. and 2, the whole brushless setup is WAY more expensive than brushed, and I've already sunk too much time and money into this bot... we know it's not likely to win, so I'm hesitant to spend much more money (that frankly we don't have) on it. It's time to focus our attention on Copperhead, which has a chance...

We switched to relays (not sure if I already mentioned that) and in testing we completely seized up the banebots motors; totally burned them out. Switched back to two duratrax's and they survived a (gentle) 3-minute torture test. The battery got hot and the motors got hot (and our LED turned off while the relay was switched on, then turned back on when it turned off...) but it survived. I'm putting it aside as DONE and just bringing a lot of extra motors to san francisco.

but rjw, if you could clarify the main advantages to using brushless motors, and what they're like, and how the speed controllers work... because i really am totally out of my element.

A quick google search came up with this brushed vs brushless, but there is much more info on the net

outside of being more effiicint in many applications, a decent brushless esc can be tuned to the application.

Changes to torque curve, soft start, current limiting, top speed, regenerative coasting, braking, etc are common parameters that could help spin a shell up to speed, although most of that could be overkill in your application.

we should start a thread on this, maybe
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PostSubject: Checking the amperage draw   Sun Apr 05, 2009 7:12 am

Here is a web site that might help.

http://www.rcgroups.com/forums/showthread.php?t=393591
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PostSubject: Re: hot motors?   Sun Apr 05, 2009 12:26 pm

rjw wrote:
Ok, I looked at one picture that i have of your setup.

Looks like you are bolting the outer shell onto a housing with bearings in the middle.

Also, you have some small plastic or whatever rollers down near the bottom.

lastly, you have 3 colsons with motors, belts pullies, etc driving the shell.

Is this correct? Or did i miss something?

If so, how many bearings or small wheels are around the base plate? 3, 4?

Secondly, are all the rollers, wheels etc. touching the drum running on bearings or bushings? and does everything spin freely?

Third....how are you attaching the shell to the center shaft and have you allowed for heat and expansion?

Lastly, what rpm's does it spin at and will it spin for a while before the motors burn up?

Richard

edit: you mentioned something was rubbing on a motor or connector in a previous post. has all that been resolved?

Also, is the shell getting hot and in any sepcific area (s)?

we may be able to troubleshoot this right here on this forum lol
Ok. Since I have been working on it a lot, here is general answers to all your questions.

1 - 2 Motors with pulleys spin 2 wheels. 1 Idle Wheel for stability

2 - We make sure all wheels touch. Have a system for adjusting pressure on the wheels when we put the shell on. Plastic guide rollers at the bottom are just to prevent a collapse of the shell on impact but do not provide constant pressure(although the vibrations of the bot and general movement causes them to bump into the shell sometimes).

3 - Shaft collar attached to the shell is tightened around the shaft. Shaft has a support structure inside the bot to keep it centered. Shell has never gotten hot during our tests, only the motors, pulleys and battery.

4 - Latest test with a tachometer showed the shell spins at around 1600 RPM's with the Duratrax motors. On relay, spin up time was around 3-5 seconds. We ran it for like 2 minutes without them burning up. We can probably last 3 minutes with them, but replacing them after each match is probably a good idea. Bigger worry on the relay system is the battery. As was said before, the LED shuts off when weapon motors are active and our drive system slows down significantly. That implies a huge current draw from our motors. And that means our batteries will probably burn out after a match or two. The battery also gets really got. And the constant on and off of the motors during a match will probably be even worse on the batteries.
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PostSubject: Re: hot motors?   Sun Apr 05, 2009 12:40 pm

no word on measuring the actual amperage draw?

If what you say is correct, no heat on the shell anyhere, my first thought is this

Clamping presure on rubber wheels may be too tight.

Possible solution is spring load the wheels or the shell (with belleville wahsers?)

Another thought is the width of the wheels.

being fairly wide, you may be getting a kind of differential effect., similar o trying to turn a car with a solid rear axle. The wheel on the outside needs to travel further than the one on the inside, if you follow me.

So, is it possible that with the width of your wheels, that the system is being overloaded?

If you have other wheels, maybe try an experiment where you cut the wheels either rounder or slightly pointed.

I did notice a lot of discoloration of the wheels in the pic hat I have.

just some thoughts, if you say that everything else checks out
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PostSubject: Re: hot motors?   Sun Apr 05, 2009 12:45 pm

rjw wrote:
no word on measuring the actual amperage draw?

If what you say is correct, no heat on the shell anyhere, my first thought is this

Clamping presure on rubber wheels may be too tight.

Possible solution is spring load the wheels or the shell (with belleville wahsers?)

Another thought is the width of the wheels.

being fairly wide, you may be getting a kind of differential effect., similar o trying to turn a car with a solid rear axle. The wheel on the outside needs to travel further than the one on the inside, if you follow me.

So, is it possible that with the width of your wheels, that the system is being overloaded?

If you have other wheels, maybe try an experiment where you cut the wheels either rounder or slightly pointed.

I did notice a lot of discoloration of the wheels in the pic hat I have.

just some thoughts, if you say that everything else checks out

We only adjust just beyond the wheels not touching continuously. As I said above, we have a way to adjust pressure on the wheels when tightening the shell. Maybe spring loaded wheels would be better, but I don't know enough to say. We did have that previously though.

As for differential effect, Mr. Curhan accounted for that recently and he tapered the wheels so that minimal surface area was touching the shell. So that has been resolved.
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