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IBC Controller
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dustpanboy911



Joined: 15 Jul 2004
Posts: 17
Location: USA


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IBC Controller

I have used the IBC on my 12 pound (5.5 kg) robot and it is using 4 Black and Decker drill motors at 9.6v to run it. After about 4 minutes I can barely touch the heat sink. Has anyone else had this problem with the IBC or am I overloading it?
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Post Thu Jul 15, 2004 7:44 am 
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andrew



Joined: 16 Jun 2004
Posts: 3110
Location: Castle Hill, Sydney. N.S.W


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Well i wont lie the IBC does get quite warm. Not sure if 4 9.6 volt drills really should get it that hot but if theres a half descent drill then they probably have diferent specifications to the 20 dollar drills we get out here

Theres a victorian brick house called KO that uses 4 12 volt drills run at 24 volts for its drive train and he does get them warm to pretty well hot.

Ill have to wait to brett gets in here and answers as he knows more than i do.
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Post Thu Jul 15, 2004 8:13 am 
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dustpanboy911



Joined: 15 Jul 2004
Posts: 17
Location: USA


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Ok, thanks. They are one of the more expensive brands. Is there a good chance of me burning it up? I just have one competition then I am changing to four speed 400 motors to decrease the current draw and hopefully save the controller from meltdown. I was just worried that my IBC was defective or something and no matter what motors I use it will still get hot.
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Post Thu Jul 15, 2004 9:05 am 
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andrew



Joined: 16 Jun 2004
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Location: Castle Hill, Sydney. N.S.W


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I woudlnt think so really that it would be defective. If possible maybe look at cutting a small slot in the box or case (if it is mounted in one) or bolting a fan over it to cool it off a bit. This may help a lot and really just being careful not to stall your motors and if it looks like a gearbox is broken or one side is dead than dont thrash the controlls as a old now retired featherweight minataur (basically a featherweight version of blue max/maximus) used 4 drills and phat colson wheels but broke 3 gearbox's and that stalled the motors which popped teh fets like crazy.
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Post Thu Jul 15, 2004 10:41 am 
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dustpanboy911



Joined: 15 Jul 2004
Posts: 17
Location: USA


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Its not in a case. Its mounted to my baseplate by the four screw holes in the corners. The motors have fans on them that blow air around inside, but the air from the motors is actually cool despite their high temperatures. The stalling isnt a deal since it has enough torque to push 22 times its weight and it doesnt fight spinners so ther gearboxes are pretty much safe. There are holes in the top of the bot to help cycle air in and out. It actually gets hotter with the top off than with it on. I think its from the fans on the motors.

I see most of the Australian bots use smaller motors such as the 100w scooter setups. My drive setup is more like 800 watts.
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Post Thu Jul 15, 2004 11:25 am 
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Nick
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Joined: 16 Jun 2004
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Thanks SO much for reminding me about that Sad . Since changing to 2 drill motors @ 14.4 volts with 3" by 7/8" wheels, my IBC barely gets warm. That's using RS550 motors in a featherweight with no active cooling and running full 3 minute matches.

If you have an ammeter available, I would check the total current draw from your battery pack while the bot is stalled and the wheels have broken traction. My bot draws less than 20A and the controller is rated up to 50A, at least for short periods. You might also try testing the current draw under no load - if you have a drive train problem, you might be drawing a high current all the time, which will warm up any small controller.
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Post Thu Jul 15, 2004 11:29 am 
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dustpanboy911



Joined: 15 Jul 2004
Posts: 17
Location: USA


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Those wheels sounds like the same as my colson wheels. Do you think that if I changed down to 2 motors on the next version or to smaller (400 sized) motors it would help?

How would I know if I have a motor/gearbox problem besides testing the current draw without load? I cant hear any noises when I pick it up and run it without load. Also, the bot drives in an exact straight line.
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Post Thu Jul 15, 2004 11:37 am 
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Nick
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Woops, I just caught your last post while I typed my previous one. 800 watts from 9.6v drill motors? That seems a bit high. I tried two Thingap motors (260W each) and blew the FETs on an IBC to pieces when one motor broke and stalled. At that point the IBC was taking about 120A so your rig could be too much for the IBC.

I am using Colsons from CNCbotparts (probably just like yours) so the current draw thru your motors when the wheels spin should not be incredibly high. I can't think of any way to tell if you have drive train problems apart from the current draw - if the draw from a bare motor is much lower than when spinning the grarbox, then you could have problems. As an example, my 12v drill motors draw about 1.7A by them selves and less than 3A withthe grears and wheel attached.

Can you post some more detail on the motors and drive train? that might give us some ideas...
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Post Thu Jul 15, 2004 11:49 am 
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Spockie-Tech
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Joined: 31 May 2004
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Location: Melbourne, Australia


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Hi Everyone, nice to see one of the US guys visiting our humble abode.. Laughing

Voltage doesnt bother the IBC at all, it will happily run 5v motors or 35v motors. its *current* that gets things warm.

The Fets have an internal resistance (a very small one - .005ohms). if you suck lots of current through that resistance, a small voltage drop develops across it and the power that the heatsink needs to dissapate is that voltage drop multiplied by the current. so effectively Power dissipation goes up as the square of the current, or P =Isquared *R.

If you are using RC car type motors, they are designed to run at low-voltages (7.2-9.6v) but at very high currents, which will make the IBC work much harder than getting an equivalent amount of power out of a higher voltage (12 or 24v) system.

To get a 200watt drive from a 24v drill motor, you only need to feed it 8.3 amps, which means the IBC only has to dissipate .345 of a watt per Fet (2 per motor).

To get the same power (200 watts) from a 7.2v (less than 1/3 of 24 volts) motor you need to feed it 27.7 amps (3.3 times as much current), and as the power dissipation goes up as the *square* of the current, the IBC now needs to radiate 3.85 watts per Fet or more than *11* times as much heat for the exactly the same output power. No wonder it gets hot..

What all this means is trying to get the same power out of high current low voltage motors stresses the controller a hell of a lot more than getting the same power out of a higher voltage lower current motor does. If you are running 4 of these low voltage motors, you are working it *hard*.

We have 4WD 4 x Drill Motor powered 12Kg (twice your weight) robots running on 24v with the IBC in a sealed, unventilated box without a problem. They get warm, but they handle it ok, provided they dont have to maintain a stall.. so higher voltage and lower current draw motors is definitely the better direction to go.

Failing that, give it a Fan. The IBC's heatsink is designed to absorb surges of power with high thermal mass, but doesnt have much surafce area to radiate sustained power input away into space (we didnt want to have big finned heatsinks hanging off it), so if you are constantly drawing high currents through it, some cool airflow across it will really help)

edit: corrected some stuff ups in my calculations, squared, not doubled Rolling Eyes


Last edited by Spockie-Tech on Thu Jul 15, 2004 2:32 pm; edited 2 times in total

Post Thu Jul 15, 2004 11:52 am 
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dustpanboy911



Joined: 15 Jul 2004
Posts: 17
Location: USA


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Nick, my drivetrain is just the four 9.6v motors at their rated voltage. The battery is a 3300 NiMH battepack. It lasts about 5 minutes so that would mean I am pulling about 45 amps average. This is only half the rated current of the IBC but it still gets toasty. My wheels are 3" by 7/8" colsons so they have a good grip to push but not enough to stop the wheels from spinning during acceleration. The top speed is about 6.25 MPH and 8 MPH with my spare 12v battery. My spare 12v battery was made from a DeWalt battery pack and cant really take the load from the drivetrain. After a match it gets hot and starts getting flimsy. The weapon is a wedge in front and so far it has been able to very easily outpush/wedge any bot that it has faced.

Edit: More info at http://www.freewebs.com/dustpan-robotics/trebuchet.htm
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Post Thu Jul 15, 2004 12:57 pm 
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Nick
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Joined: 16 Jun 2004
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It sounds like you are going reasonably close to the long-term current capability of the IBC - you are drawing twice the current of most of our featherweights and that is likely to give any small controller heat problems.

Take it from Brett (spockie-tech) who designed the IBC, a small fan will do wonders. If the heatsinks are only getting uncomfotably hot and not actually giving you burns, you would still be operating in the safe zone.
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Post Thu Jul 15, 2004 2:05 pm 
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Spockie-Tech
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Corrections to the earlier post. you are actually working the controller *11* times harder than it would need to at a higher voltage. go back and have a look at my corrected figures.

Post Thu Jul 15, 2004 2:30 pm 
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Nexus
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Joined: 17 Jun 2004
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I would just replace the motors, not wth speed 400 but with 12 volt 540 size motors. That way you can keep your gearboxes. Changing to 400 motors will require special mounting. Recently picked up some 550 size motors that stall at 98 amps at 12 volts. On other project have used 540 motors that stall at 17 amps at 12. Have recently found a 550 size that stalls at about 30 amps so that would be more suited to using 4 motors togethet on the IBC. If the system is complete then all you need to do is basicallly choose a motor with specs to match. Depending on the motor you could also change your top speed so its sort of like tuning up your system, getting the most out of your equipment without redlining the system.
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Post Thu Jul 15, 2004 2:58 pm 
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Totaly_Recycled
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Joined: 15 Jun 2004
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Hi we have one of the earlier versions of the ibcs in our pusher feather weight bot T2M (12 kgs ) we have two electric tow winch motors that will pull well over 140 amps stall on each motor so far i havent blown any fetts in the ibc even though i routinely (show off by sitting on the robot I weigh 60 kgs and then i push a ride on mower across the shed aprox 150 kgs rolling weight with it )
As soon as i recieved my ibc it got a small cpu computer fan put on it wired directly to the power input leads and it is mounted directly on top of the heat sink .this drasticly reduces the heat build up in the heat sink when i did some measure ments a while ago i was pulling up to 100 amp surges and the heat sink didnt go over 40 degrees celcius. I wouldnt even try it with out the fan .

Post Thu Jul 15, 2004 8:24 pm 
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dustpanboy911



Joined: 15 Jul 2004
Posts: 17
Location: USA


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The 400 sized motors will give me a slightly higher speed and still enough torque to easily spin my wheels and push my opponent around. They are called handiwork drills and are meant to run at 4.8v but everybody in the US runs them at 7.2v-9.6v.

I have two little fans but they dont put out much air. I will try to install them today and see if they make a difference. I've taken a ride on my bot for short periods of time and it doesnt seem to make too much more heat than when I regularly run it. Regularly it gets hotter than being uncomfortable. I went to a robot meeting outside last week and we had a few fights. With the combined heat of the sun and the heat from a match nobody there could touch it longer than one tap on the heatsink so I think it could probably cause burns. I had to let it cool down a while between matches.
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Post Fri Jul 16, 2004 12:19 am 
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