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Not robots but related, speed controller help
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nick_75au



Joined: 22 Oct 2007
Posts: 11
Location: Brisbane


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Not robots but related, speed controller help

I've just joined the forum looking for a few answers regarding speed controllers. I've come to the conclusion that any controller i make myself is not reliable or powerful enough for my radio controlled boat and R/C hobby speed controllers are limited in their voltage or current capacity so I've been looking at the robot type controllers.
My motors I'm using are large 16 pole 3 turn motors that have a maximum amp draw of 80 amps at 24 volts( rated 12v 15 amps but modified for better cooling), this is almost absolute worst case scenario save weeds or fishing line etc stalling the motor. I'm looking at the RS80D or the Sidewinder possibly the IBC, I understand that in general robot controllers tend to be time limited in use because of the heat sinking used. I have, being in a boat the option to water cool the heat sinks to extend that time, would this much higher cooling capacity increase the current ratings or is it the components themselves limiting current.
The other difference is in this application it wont be put through the rigours of robot combat so physical robustness is less of an issue.
I would like to ask your opinion on whether any of these choices are suitable and what other options may be available. Your opinions and advice would be greatly appreciated.
Here is a link to my project
http://www.rcgroups.com/forums/showthread.php?t=651582
Regards
Nick

Post Mon Oct 22, 2007 7:56 pm 
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Glen
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your not using brushless why? Razz

but your cheapest option would probably be one of the high current victors. there tiny and not that expensive. and i dont think youd be wanting to spend $ on a two channel controller if you have a rudder on it.

http://www.robotmarketplace.com/marketplace_ifi_esc.html

edit - quick look over the build thread and those motors at the start look seriously dodgy. almost like 100w scooter motors..

for the money youd be much better off getting the JETI rip off speed controller and a brushless outrunner from united hobbies. much better.
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Post Mon Oct 22, 2007 8:03 pm 
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Nick
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Was the 80A at 24V per motor or a total?

Which controller is best depends on the features you need: If you don't need reverse, then you are wasting money on FETs you don't need and an ESC like the IFI Victor or Thor Spin controller has a high current rating in a very small package.

If you don't need separately controlled motor speeds, then a regular Victor 885 controller should do the trick as Glen mentioned.

Of the RS80D and the Sidewinder, I would go for the more compact Sidewinder. It has a more durable construction and the heatsinks are just as easy to either fan or water cool.
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Post Mon Oct 22, 2007 8:19 pm 
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nick_75au



Joined: 22 Oct 2007
Posts: 11
Location: Brisbane


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Hi Nick and Glen,
Wow you guys are quick.
Its 2 motors 80 amps each, not the purple and black ones they are model airplane starter moters and they are dodgy. The motors I want to use are the all metal zinc ones towards the end of the thread. They are ball-bearing and appear to be high quality motors. They spin at 10000 rpm under load on 24 volts. Going on calculations the boat should go around 25-30 Kph
I've machined openings in the can and in the end-bells for cooling and I'm planing to brush cool as well dependant on how hot they get..
I need 2 independent reversing motors hence looking at the dual controllers. This gives me the same control as the full sized boat, its similar to tank steering. Rudder as well but tank is good for low speed maneuvering and the rudders are better for high speed turns. Also I may be able to use the Aux output to operate the bow thruster (7.2 V speed 400 type. Only needs on-off-reverse, no pwm)
Why not brushless? because Im looking at big dollars for reversing speed controls at the power ratings I need plus I don't know anything about brushless, I cant find anyone else who has used brushless in a boat with so much power that isn't a pure racing machine. Cots would be at least 150 each for the motors and around 180-280 each for the speedies all in US dollars. Maybe later i will give them a go.
Regards
Nick

Post Mon Oct 22, 2007 9:12 pm 
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Glen
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incorrect my friend wrt to brushless. each of my motors is $45US and they spin my robots 6kg drum to 4000rpm in 1 second even. your boat would be no problem Razz the controller is $100 but no reversing. make no mistakes, its a monster setup!

https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=4691

https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=4572

you can quite happily make a relay reverse for the brushless setups (only have to switch two phases around) just have to mind you dont do that while its still running foward,

come to think of it i wonder what would happen if you reversed two of the phases while it was running?? perhaps just more current draw? perhaps silicon explosion Razz
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Post Mon Oct 22, 2007 9:26 pm 
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cerberus3112



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hmm tempting so very tempting but the part about Speed controller exploding makes me wince
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Post Mon Oct 22, 2007 9:54 pm 
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Nick
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OK, based on your feedback, I'd say the RS80D is an easy one board solution if it fits in the space, while the Sidewinder is a bit less sophisticated and much easier to fit in small spaces. The RS80D has a very complex PCB and in robotics circles, it has a reputation for stopping mysteriously and being very hard to repair.

If you don't mind a little extra wiring, a pair of Victor 885 controllers and a mixer will cost the same as a Sidewinder and gives you and extra 40A, which I find makes them unbreakable.

How do you do the brush cooling? Its something robot motors could use too...
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Post Mon Oct 22, 2007 10:04 pm 
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nick_75au



Joined: 22 Oct 2007
Posts: 11
Location: Brisbane


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Hi Glen
I need 10000 rpm to get the prop pitch to give me the speed. Like a limitation on wheel diameter. That setup would do it but then I need more voltage more batteries more expense and I'm close to the weight budget. I've been drooling over some of the specs on the brushless stuff, it really is the way of the future but If I could be confident it will do what I want then I wouldnt hesitate in getting it.
I'm kind of locked in at the moment with what I have, I know that the setup will give me the performance I want I just need the speed control to get it in the water.
I did speak to Spockie-Tech/Brett maybe six months ago about the IBC and this project but didn't pursue it any further as I thought maybe the controller wasn't quite enough. By the sounds of it reading through the IBC thread it actually may be enough with watercooling. The 80 amp controllers get me closer to max current ratings that the motor will draw, the average running current will be closer to 50 amps or less plus even then it may only be for short bursts and the rest of the time just pottering around at maybe 20 amps
I had been leaning towards the sidewinder anyway but only recently found the RS80, same specs essentially but $80 dollars cheaper. It just doesn't look quite as well made as the sidewinder.
Thanks for your replies,
Regards
Nick

Post Mon Oct 22, 2007 10:19 pm 
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leo-rcc



Joined: 04 Aug 2006
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I would definatly look at the Sidewinder. You might want to get in contact with Chris Baron, he is the man behind the sidewinder and Scorpion series. He was working on a version of the sidewinder that uses both mosfet sides for 1 motor, making it a single motor 160A continues speed controller. I dont know if he persued this any further (Chris mentioned it to me more than a year ago) but you migh be able to get one of those.

Post Mon Oct 22, 2007 11:49 pm 
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Valen
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if you drilled the block on the IBC and flowed water through it i see no reason it wouldn't handle ~75A or so. You are limited at that point by the legs melting off. Provided you keep the current around there you should be fairly ok. In this sense the IBC is a nice one to do this to. RS80 is also achievable, the sidewinder could be more difficult and the victor is basically imposible.
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Post Tue Oct 23, 2007 12:49 am 
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nick_75au



Joined: 22 Oct 2007
Posts: 11
Location: Brisbane


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Brush cooling how to

http://www.rcgroups.com/forums/attachment.php?attachmentid=1222788
is a pic of a motor fitted with brush cooling. there are a couple of others pics in there as well.
In boats to brush cool basically its a piece of brass tube soldered to each tab but isolated from each other and the case, then plumbed up with silicone tubing to run water through the tube, Usually a scoop is placed behind the prop which with forward motion forces water through the tubes and cooling the brushes. In a robot type application no reason why it wouldn't work but is a little more complicated. A pump and radiator of sorts is required such as found in PC water cooling systems. Somebody could come up with an innovative air-cooled version as well,. An other option is to use very large copper wire to the brushes say 6 or 10 or 25mm , this would draw the heat away from the brushes as well. In boats its usually not required until 18 cells plus are used and an average run is probably more than 10 minutes, robot combat is only for 3 minutes isn't it, I'm not sure obviously. If it is then the extra complication probably isn't worth it.
Hope this helps
Regards
nick

Post Tue Oct 23, 2007 9:30 pm 
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leo-rcc



Joined: 04 Aug 2006
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Our maximum time limit is not due to heat or power restriction in the speed controller, but simply the amount of batteries we carry. It makes no sense to carry for 20 minutes of batteries if the fights are done in 5.

We run sidewinders with Boshes on 36V for 5 minutes in our heavies where the load exceeds 50 to 80A and though they get warm, they are not a problem.

Post Wed Oct 24, 2007 5:54 am 
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nick_75au



Joined: 22 Oct 2007
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Location: Brisbane


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Im now tossing up between two Victor 885s or the Sidewinder. I think the RS80d is a little too complex for me.
Do the Victors definitely need the extra PWM cable to run off a std 36mhz receiver?
I don't think water cooling the sidewinder is a problem, just make an extra alloy plate with holes for water to pass through and bolt onto the case using the existing case/heat sink screws on top. The Victor I would probably make up watercooled heat sinks as well. It just doesn't feel right to me just air cooling the fets only. there is bugger all surface area on them. Trolling the various robot forums there were a vague reference to someone who had added extra heat sinks to a Victor but I couldn't find any more info.
leo-roc For me more runtime is better and weight is needed to ballast the boat so it might as well be batteries. As with all things though its a compromise more speed less runtime.
I would like to think that I could get an hours running out of the boat at low throttle with an occasional full power Blatt to scare the ducks Very Happy Knowing myself I probably run it the first few times at full speed until the batteries are flat.
So where is the best place to get them, I guess robot marketplace ?
Any one have a couple of victor 885s or a sidewinder they would like to part with?
Regards
Nick
P.S thanks for your input guys, It really is appreciated.

Post Wed Oct 24, 2007 7:18 pm 
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Nick
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Joined: 16 Jun 2004
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The Victors run with some brands of radio and not others - I needed the boosters with a Futaba receiver and not my current Nomadio. From what you were saying earlier, you wanted tank mixing and unless your transmitter does its own mixing, you will need a mixer between the receiver and the Victors. It is likely that the mixer WILL be able to run the Victors directly; the IMX-1 from Robot Marketplace definitely does.

You would probably have major problems attaching heatsinks to the FETS in the Victors; they are very close together and you will not be able to get any metal between the FETs, except at the top of the tab. I have been using the 885 controllers without fans for several years now and the high current rating means they barely get warm, even when the motors they drive seize up.
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Post Wed Oct 24, 2007 10:49 pm 
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Nick
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I don't know if you have already seen these motors or if they are in the right price range, but they would be ideal for your boat: http://www.astroflight.com/e/env/index.html?sid=0001ZmUEiVHk6rQXWo9p4N9&link=/index.html

The 640 or 940 sized cobalt motors would be about the equivalent of the starter motors you are using and they are designed to run up to 24V. They will be much higher efficiency than the starter motors, so your run time would go right up.
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Post Wed Oct 24, 2007 11:22 pm 
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