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        Question ESC Response at low throttle.

#1 RGinCanada Dec 09, 2004 08:21 AM

ESC Response at low throttle.
 
Well my "perfect motors" arrived yesterday, and they are... perfect. They turn at (rough guess) 60 rpm at 1.2V (One NiMh cell). The torque on that one cell is such that you can barely stop the shaft with your bare fingers. Even at 7.2V they are whisper quiet. Really, I can't say enough good things about these motors. If I didn't have Christmas shopping to do, I'd buy the entire lot this guy has.

Unfortunately (of course there's an 'unfortunately') my low cost ESC (~$20 w/shipping on eBay) won't spin the motor as slowly as it is capable of turning.

My understanding is that an ESC is basically a high speed switch, that controls the amount of time the switch is "on" and "off" per cycle in order to control the speed of the motor.

My motor and speed control abruptly transition from 'coughing' starts and stops to (400?) RPM at approximately 1/8 throttle.

Is this because my ESC is junk, or because the motor can't run on the heavily clipped waveform generated by the ESC at low throttle? Would a $$$ ESC give me the full range of throttle on the motor?

Regards,

Ray

#2 martin richards Dec 09, 2004 01:39 PM

you might find the last paragraph of bath trials in http://www.astecmodels.co.uk/elco.htm interesting.

#3 RGinCanada Dec 10, 2004 08:27 AM

Thanks Martin,

After reading that article, It sounds like the ESC is the culprit.

I checked around for "scale boat speed controls" and in addition to astecmodels' I found the one available from www.modelcontrol.com and one from astroflight. Are there any others out there, and has anyone done a review comparing them?

I'd like the full range of control from dead slow (prop just turning) all the way up to wide open throttle. What ESC would you recommend?

#4 martin richards Dec 10, 2004 02:51 PM

My main interest is fast electrics and an on/off switch would almost do for that. Hopefully some ot the scale types will be able to help with recommendations for specific types. How many amps do you think the motors will draw?

#5 RGinCanada Dec 10, 2004 03:02 PM

These are slow efficient motors

Starting (inrush) current < 8A, Maximum continuous operating current 2.5A. Almost any ESC on the market will handle this, but which ones offer the best low speed control?

Anyone who's got an opinion, please chime in!

#6 Brutusjm Dec 10, 2004 03:04 PM

Esc
 
I have used both Mtroniks and Electronize ESCs and have been very pleased with the results. Just my newbie 2cents.
Jason

#7 cop56 Dec 10, 2004 04:20 PM

I'm hearing alot of good things about Hitec's EZX-R. I'm planing on putting one in "Father Goose". You might want to talk to Pat. He's who told me about them. Could
you please post the ebay thread for the motors again?
Fred

#8 RGinCanada Dec 10, 2004 07:03 PM

Thanks for the tip. I'll be sure to check it out. Pat, if you see this, would you add your comment?

Here's the motor links:

Motor:
http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEWA:IT

Specs:
http://www.mpm.maxonmotor.com/files/...f/04_124_e.pdf

#9 Kiwimodeller Dec 12, 2004 03:24 AM

I have used several Electronize controllers and have been very happy with them, especially the help I received and the low parts cost to repair one when I managed to fry one (entirely my own fault). I have not tried the new models yet but have heard one good report. The explanation on their website of why variable frequency of pulse gives gentle start up and max power seems logical and you can also choose to stay locked on low or high frequency to get the response you want. I will certainly try one for the next project. That's my 5cents worth! Cheers, Ian.

#10 patmat2350 Dec 13, 2004 09:22 AM

See my note on low cost ESC's over in the SCALE forum.
You may/may not really need your motor to just "tick over"... real question is, does it go slow enough to make the boat just crawl?
And keep in mind that a geared solution may give you really slow prop speeds if that's what you're after. Using the Condor 20 ESC (at a lousy 50 Hz PWM frequency!) on a Speed 600 geared down 3:1, I can watch my tug's prop turning over, blade by blade...
Pat M

#11 RGinCanada Dec 13, 2004 10:36 AM

Hi Pat,
Thanks for the input. I read through the info on your website with great interest (particularly enjoyed the DUKW build).

It looks like the Hitek EZX-R may be the way to go, although I am considering investing in some higher end equipment as I intend to continue in this hobby for some time to come.

What I'd really like to do is try them all and buy the one I like best :) Ah well, lets wait and see what Santa brings...

Regards,
Ray

#12 whanderson Jan 07, 2005 08:30 AM

Quote:

Originally Posted by RGinCanada
Hi Pat,
Thanks for the input. I read through the info on your website with great interest (particularly enjoyed the DUKW build).

It looks like the Hitek EZX-R may be the way to go, although I am considering investing in some higher end equipment as I intend to continue in this hobby for some time to come.

What I'd really like to do is try them all and buy the one I like best :) Ah well, lets wait and see what Santa brings...

Regards,
Ray

Poor low speed motor control can be the result of 2 things. Some ESCs set a dead band where any throttle position below a preset value is considered no throttle. This causes a jump from nothing to a moderate speed as the throttle stick moves in a linear fashion. This is a simple method of compensating for variations in throttle trim. The other possibility is the ESC's switching frequency. At low motor speeds, low ESC switching frequencies are ineffective. RC ESC's operate in the several khz to several 100khz range. 100khz ESCs are very popular in the helicopter community. I have tested several of these and they have excellent low speed control. I can forward you a Microchip datasheet that gives more detail. Some of the ESCs you mention have low and high frequency capabilities. Anyway, for your application higher ESC switching frequency, 8khz or higher, will give better low speed control.

Bill

#13 patmat2350 Jan 07, 2005 10:27 AM

I dunno... I have an ESC that runs at 50 (yes, fifty) Hz in my tug... I can slow the motor down to where I can see the prop blades ticking over one at a time... 3:1 gear reduction helps that a bit. One nice effect of the slow rate PWM is that the motor growls instead of whining at part throttle.
Pat M

#14 Kmot Jan 07, 2005 11:53 AM

In my experience with rock crawling r/c trucks the higher the ESC frequency, the slower I can get the tires to turn. So slow in fact, that I can watch the lettering on the tire and read it easily. This with a 7K Hz esc.

#15 whanderson Jan 07, 2005 01:36 PM

Quote:

Originally Posted by patmat2350
I dunno... I have an ESC that runs at 50 (yes, fifty) Hz in my tug... I can slow the motor down to where I can see the prop blades ticking over one at a time... 3:1 gear reduction helps that a bit. One nice effect of the slow rate PWM is that the motor growls instead of whining at part throttle.
Pat M

First off, the 3:1 reduction helps quite a bit more than "a bit." Second a 50Hz ESC uses different technology than modern ESCs.

Bill


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