04-17-2018, 10:39 AM | #1 |
Not Yet Wild
Join Date: Dec 2017
Posts: 71
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Motor Speed Control Issue
After getting my Alltrax controller up and running I came across and interesting issue with the motor speed sensor. When I intilally set up the Alltrax I used the same max motor speed setting as was set on my Sevcon personality....3700 rpm. So far this has worked fine but working with Alltrax engineering to refine the motor field map we found that the car was achieving a max speed of 27 mph at 3100 rpm but when we calculated the speed based on the gear ratio and 22 inch tire diameter the max speed should have been ~19 mph.
Tech support informed me that the max motor rpm is 4800 and sure enough at that motor speed the calculated top speed is ~27 mph. I then remembered we found a 10K resistor across two of the speed sensor legs which is different than other cars. No idea why it's there unless it has something to do with how the Sevcon perceives motor speed. So, my question is: What is the purpose of the resistor and if I remove how will that affect the speed sensor signal to the controller? Thanks for any input. |
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04-17-2018, 10:47 AM | #2 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Motor Speed Control Issue
I would guess the 10kΩ resistor is a "pull-up" resistor for the sensor output.
Are You sure the Alltrax is setup for the correct number of magnet poles? It may be as simple as you have it set for a 8-pole magnet but the motor has a 4-pole magnet. |
04-18-2018, 10:23 AM | #3 |
Not Yet Wild
Join Date: Dec 2017
Posts: 71
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Re: Motor Speed Control Issue
Thanks for the response.
The setting is for 8 poles. Did try the 4 pole setting and it did indeed cut the speed in half. The motor is 8 pole according to the drawing. The resistor seems to be unique to the Sevcon controller as the tech told me it's not used on any of the other cars or on other D&D motors but we left it in place simply because it was there but buried in the original part of the wire harness. I was hoping to find out exactly what the resistor is used for before just cutting it out. The cars performance is great as is but I don't know what, if any, other controller functions use the speed input and might be adversely affected by an erroneously input signal. |
04-18-2018, 01:17 PM | #4 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Motor Speed Control Issue
If the resistor is between the Sensor output and the Sensor positive power wire, it is not needed as the Alltrax Controller has that built in.
The main concern would be reduced speed sensor life by forcing the Hal effect sensor to drain more current then needed (internal and external resistors current). |
04-19-2018, 12:20 PM | #5 |
How Can I Help?
Join Date: Oct 2009
Location: SW Wisc & West Central, FL
Posts: 1,383
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Re: Motor Speed Control Issue
Sergio is correct on the 10K resistor. It's a pullup for the controller to be able to reference.
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04-23-2018, 01:25 PM | #6 | |
Not Yet Wild
Join Date: Dec 2017
Posts: 71
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Re: Motor Speed Control Issue
Quote:
Thanks again for all your assistance. |
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04-23-2018, 01:29 PM | #7 |
How Can I Help?
Join Date: Oct 2009
Location: SW Wisc & West Central, FL
Posts: 1,383
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Re: Motor Speed Control Issue
Indicated motor speed that controller sees is NOT ground speed. Its a percentage calculation that we only look at to make sure the encoder reads a signal and is going up or down with vehicle speed
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