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Author Topic: 120A ESC for 150A motors?  (Read 700 times)

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Offline gerardTopic starter

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120A ESC for 150A motors?
« on: October 18, 2013, 06:10:19 PM »
Hello, I had a question about the Sabertooth 2x60 dual motor speed controller.

http://www.robotmarketplace.com/products/0-SABERTOOTH2X60.html

It can drive 60 amps continuous, and 120 amps peak on each motor.
Would It be possible to use with these motors that have a 150 amp stall current?    http://www.robotcombat.com/products/0-PDX256.html
It shouldn't stall too often, but when it does, would it burn out the motor controller or would it just cap at 120 amps?
I'm worried whether the controller will get damaged by the motors trying to pull 150A when it can only supply 120A.

Also, are there any other dual motor controllers that could power these 150A motors without breaking $300?
I looked at the RoboteQ controllers, but they cost $600 for a dual 150A controller :(

Thanks for all the help!

Offline jwatte

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Re: 120A ESC for 150A motors?
« Reply #1 on: October 18, 2013, 09:09:56 PM »
I don't know about the Sabretooth, but I have experience with a similar RoboClaw controller. The RoboClaw documentation claims that, if you hit the ratio between 1x and 2x current (so 60A - 120A) the claw will auto-drop the current down to rated levels within a second or two. However, if you draw more than the rated max current (120A) it will disable itself. Thus, I would not recommend it with a 150A rated motor, unless you significantly de-rated the voltage. Rather, the behavior documented would be appropriate for a motor rated for 60A, because if you drive it out of stall, into the reverse direction, the motor may temporarily actually draw 120A in the other direction. I would expect the Sabretooth to be similar. You should get the manual and check for yourself!

The product listing for the motor does not specify what the winding resistance is or what voltage the stall current will be drawn at. If you run it at half the voltage, then the stall current will be more under control, although you will of get approximately half the torque, half the max RPM, and quarter the power.

The only way I know of controlling 150A (you need a 300A rating, really) under $300 is to hook a number of IRS2101 drivers and high-power MOSFETs in parallel, for each side, and drive the entire thing from a microcontroller yourself. You'd need two pairs per side, and two sides for an H-bridge. You'd also need some reasonable solution for wiring and hooking up the MOSFETs in question -- a 1 oz copper PCB trace will likely melt if you try to draw 150A-300A through it.

Something like this, times four, plus something to drive it:
http://www.digikey.com/product-detail/en/IXFN360N10T/IXFN360N10T-ND/2116933

The 2101 is pretty good, as long as you don't need a continuous duty cycle -- you need to run it with PWM with a duty cycle that's sufficient for the drive capacitor to recharge. (You can turn it off for 0.1 ms every 10 ms and it will probably do fine.)
« Last Edit: October 18, 2013, 09:20:18 PM by jwatte »


Offline gerardTopic starter

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Re: 120A ESC for 150A motors?
« Reply #3 on: October 19, 2013, 10:16:20 AM »
Would putting a 100 or 120A fuze work?
(are there even fuzes with that high a rating?)
I would really prefer getting the $200 2x60A Sabertooth instead of a $500 RoboteQ 150A controller...

Offline Roman505

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Re: 120A ESC for 150A motors?
« Reply #4 on: October 19, 2013, 07:22:20 PM »
Putting a 120A fuse in will be frustrating when the robot stops, and superfluous given the Roboclaw/Sabretooth will disable itself over current anyway, saving the fuse the problem.

You could buy two 2x60 RoboTooth and parallel each of them to get 120A continuous 240A peak but by then your cost is pushing the RoboteQ anyway. Is the RoboteQ you have in mind the VDC2450? I notice it is rated 80A continuous and 150A for up to 30s depending on ambient conditions. That ought to be enough to handle your stall conditions except that 150A is the channel sum under ideal conditions, not per channel: http://www.roboteq.com/index.php/docman/motor-controllers-documents-and-files/documentation/datasheets/vdc24xx-datasheet/66-vdc24xx-datasheet/file] [url]http://www.roboteq.com/index.php/docman/motor-controllers-documents-and-files/documentation/datasheets/vdc24xx-datasheet/66-vdc24xx-datasheet/file[/url]. i am unsure of the corresponding specification (channel sum) for the SabreClaw (or was that the RoboSabre?)

I think you need to use the right equipment for the job or else to change your design parameters, such as lowering the maximum stall torque via different motors or lower voltage.

Offline gerardTopic starter

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Re: 120A ESC for 150A motors?
« Reply #5 on: October 19, 2013, 09:54:12 PM »
Thanks.
Also, if a 18V motor that has 130A stall is run at 12V does that also bring down the stall current by 1/3?

Offline gerardTopic starter

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Re: 120A ESC for 150A motors?
« Reply #6 on: October 19, 2013, 10:34:58 PM »
For information on the Sabertooth, your best bet would be to contact Dimension Engineering    at [email protected]

They have great customer service and will surely be able to answer your question


They haven't answered me yet, but I looked further into their controllers and I noticed this:
"Overcurrent and thermal protection means you'll never have to worry about killing the driver with accidental stalls or by hooking up too big a motor."
The motors I am planning to get are 130A stall, and they have so much torque I don't expect them to stall often...

These are the motors:
http://banebots.com/pc/MOTOR-BRUSH/M4-R0062-12
And they will be geared down 144:1
Almost 350Nm!!!

I think it should be possible to use these motors with the Sabertooth 2x60A and have no risk of burning out the controller.

PS: I have seen many people use huge wheelchair motors with a 2x50A and not have any stalling issues...and those wheelchair motors must draw over 100A stall for sure.

Offline Roman505

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Re: 120A ESC for 150A motors?
« Reply #7 on: October 19, 2013, 10:50:49 PM »
..., if a 18V motor that has 130A stall is run at 12V does that also bring down the stall current by 1/3?
Yes. For an 18V motor, keep within 120A peak by keeping voltage under 14.5. I see since I started writing that you are proposing a 6-12V 133A stall motor. This seems to me to be getting quite manageable.

By the way, are your motors/drivers under the control of a micro? If so, would your problem be resolved by ramping drive to the motor controllers rather than delivering full power instantaneously? Where the motor actually stalls while being driven then let the controller deal with it. Direction reverse would then be a step-fall in voltage followed by a ramp up in the other direction (PWM), alleviating the current-doubling from instantaneous reverse.

Offline gerardTopic starter

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Re: 120A ESC for 150A motors?
« Reply #8 on: October 20, 2013, 09:03:05 AM »
..., if a 18V motor that has 130A stall is run at 12V does that also bring down the stall current by 1/3?
Yes. For an 18V motor, keep within 120A peak by keeping voltage under 14.5. I see since I started writing that you are proposing a 6-12V 133A stall motor. This seems to me to be getting quite manageable.

By the way, are your motors/drivers under the control of a micro? If so, would your problem be resolved by ramping drive to the motor controllers rather than delivering full power instantaneously? Where the motor actually stalls while being driven then let the controller deal with it. Direction reverse would then be a step-fall in voltage followed by a ramp up in the other direction (PWM), alleviating the current-doubling from instantaneous reverse.

Yes, I am using a RC radio to control it. So I guess if it stalls I shouldn't hit full throttle and the motors won't draw the full 133A.
Sounds great :)
Thanks for all the help!

Offline Roman505

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Re: 120A ESC for 150A motors?
« Reply #9 on: October 20, 2013, 02:46:27 PM »
I meant to be asking whether you were using a microcontroller like an Arduino or Picaxe, where code can control the ramp time and reverse-switching duration either autonomously or by reinterpreting your RC commands. If you have direct control via RC I can only add to be soft on the throttle when switching forward-reverse and to get off the throttle immediately you see a stall. Full acceleration from idle should be fine but don't try pushing over any brick walls :).

 


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