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Unread 02-05-2016, 11:50 PM   #1
Getting Wild
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Location: Seattle,WA /Sebastian,FL
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Default add speed sensor to motor?

Is it possible to add a speed sensor to and AMD7124 (beast) motor?
It is not required for controlling the motor but data collection?
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Unread 02-06-2016, 04:36 AM   #2
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Tomberlin
 
Join Date: Oct 2015
Location: MN
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Default Re: add speed sensor to motor?

Is the shaft accessible for drilling or tapping?

If it is, then it should be a simple project.

I can put you in touch with someone who does it. He may even have a kit.

He has been working with me on speedometer/tach kits.
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Unread 02-06-2016, 07:55 AM   #3
Getting Wild
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Default Re: add speed sensor to motor?

Definitely yes. Please send the information!!!!


Some how after my calcs, my system was only supposed to run 15-20mph. But I am getting 30+mph. see signature for details. Yes, I did the calculation but 60V into AMD7124, does not give me ~2800rpm with my setup.
I have verified the model on the sticker off the motor, that it is the correct model.


So as a test electrical engineer, I am going to instrument the motor to see what I am really getting.

Either everybody who labels the motor as 36V=1600rpm/48V=2300rpm is incorrect, or the motor is built incorrectly, ie. wrong configuration.
Stock motor it would only run 13-14mph at 36V with FLA batteries.

I should be able to simply assume from specification on the AMD motor, approx. double 36V/1600rpm to 60V = ~2800rpm

I know, I know what happens when you ASSUME....
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Unread 02-06-2016, 08:34 AM   #4
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Yamaha
 
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Default Re: add speed sensor to motor?

A series motor will run at much higher than rated RPM if the load is less than the load where it is specified. It will run away and blow up if you have no load. This is because the field reduces as the current drops which decreases the BEMF which allows the motor to run faster on a given voltage. I would recommend a speed sensor if you can add one.
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Unread 02-06-2016, 10:25 AM   #5
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Default Re: add speed sensor to motor?

Quote:
Originally Posted by rottie View Post
Definitely yes. Please send the information!!!!


Some how after my calcs, my system was only supposed to run 15-20mph. But I am getting 30+mph. see signature for details. Yes, I did the calculation but 60V into AMD7124, does not give me ~2800rpm with my setup.
I have verified the model on the sticker off the motor, that it is the correct model.


So as a test electrical engineer, I am going to instrument the motor to see what I am really getting.

Either everybody who labels the motor as 36V=1600rpm/48V=2300rpm is incorrect, or the motor is built incorrectly, ie. wrong configuration.
Stock motor it would only run 13-14mph at 36V with FLA batteries.

I should be able to simply assume from specification on the AMD motor, approx. double 36V/1600rpm to 60V = ~2800rpm

I know, I know what happens when you ASSUME....
What you are looking at is the incomplete Non-Peak HP rating.

The complete Non-Peak HP rating is:

8.0HP @1600 @36V
11.4HP @2300 @48V

Since HP = RPM X Torque / 5252, the motor is generating roughly 26ft/lb of torque in both instances (Specifically: 36V = 26.26 and 48V =26.03)

The motor will accelerate (increase in RPM) until the torque it generates equals the mechanical load imposed on it, and your cart's mechanical load is obviously less the 26ft/lb, the motor will spin faster than 1600RPM at 36V or faster than 2300 at 48V, and faster than whatever RPM the motor will produce 26ft/lb of torque at 60V.

If you ran that motor and controller and tires at 36V or 48V and know the top speed, you can estimate the top speed at 60V by the ratio of the voltage increase. It will be roughly linear. Also, use the 100% SoC pack voltage rather than the nominal 36V or 48V since the 60V is true pack voltage rather than nominal.

And the specs also state:

13-15 at 36V
16-18 at 48V

These speeds are for 18" tires. With 20.5" tires the speeds will be about 14% greater, less some speed loss due to the taller tires being harder to turn.


FWIW: With 20.5" tires and 12.44:1 gears, at 30.0 MPH, your motor is spinning at 6,119 RPM.

You may want to check with AMD for the Max recommended RPM for a AMD7124, but as a general rule of thumb, 6,500 RPM is max (31.9 MPH with your setup) and it probably isn't prudent to spin it over 7,000 RPM routinely (34.3 MPH with your tires and gears)

BTW: Your 20.5" tires spin 16.4 times per MPH and your final drive ratio is 14.564:1, so if you know the cart's speed, you can crunch the numbers to get motor RPM.

Last edited by JohnnieB; 02-06-2016 at 10:30 AM.. Reason: added info
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Unread 02-06-2016, 10:29 PM   #6
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Default Re: add speed sensor to motor?

Well, I did get a full charge this morning and gave it another run, 32MPH at 67Vdc, way too fast and is really squirrely with the steering.

So I am going to either limit the throttle voltage thru Firmware (remapping throttle position) or cut pack voltage in half by reconfigure the batteries to 8S8P (~33.6V at 240AH). Also, if I reconfigure the batteries from 16S4P to 8S8P, then my BMS issue goes away for too high of pack voltage.

another possibility is buy one more module and have 11S6P for ~46V at 180Ah, but will still have high rpm issues.
I am open for ideas.......
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Unread 02-07-2016, 08:35 AM   #7
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Default Re: add speed sensor to motor?

To start with, I would limit your throttle or amps. Since you don't have a speed sensor, you can't just dial the max motor RPM like I can with my Alltrax.
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Unread 02-07-2016, 09:44 AM   #8
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Default Re: add speed sensor to motor?

Quote:
Originally Posted by rottie View Post
Well, I did get a full charge this morning and gave it another run, 32MPH at 67Vdc, way too fast and is really squirrely with the steering.

So I am going to either limit the throttle voltage thru Firmware (remapping throttle position) or cut pack voltage in half by reconfigure the batteries to 8S8P (~33.6V at 240AH). Also, if I reconfigure the batteries from 16S4P to 8S8P, then my BMS issue goes away for too high of pack voltage.

another possibility is buy one more module and have 11S6P for ~46V at 180Ah, but will still have high rpm issues.
I am open for ideas.......
Cart speed = RPM times Final Drive ratio; And RPM is proportional to Voltage.

So if 67V yields 32MPH, re-configuring the battery pack for 33.6V will give you about 16MPH and 46V will be about 22MPH.

As for Motor RPM, with your 20.5" tires and 12.44:1 gears:
32MPH = 6527RPM
22MPH = 4488RPM
16MPH = 3264RPM

You might be pushing your motor's RPM envelope a wee bit at 32MPH, but not at all at 22MPH.

Remapping the throttle position might reduce the top speed, but it may also gut the low end performance.
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Unread 02-07-2016, 03:32 PM   #9
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Default Re: add speed sensor to motor?

I wouldn't reconfigure your pack. You might want to consider going down to 14 cells and save the other two for a rainy day (or sell them). Then you would have no problems with the Orion JR BMS and you would get plenty of top speed still. Your series motor will generate lots of low end torque for good hole shots.
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Unread 02-07-2016, 07:34 PM   #10
Getting Wild
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Default Re: add speed sensor to motor?

That is pushing it at 6500+ rpm. not good for long term reliability. Thanks for the calcs.

After thinking more last night and today, doing other projects i.e. adding 120VAC 20amp power plug by cart, adding hangars to wall for hanging shovels, rakes, swept floor from all of the metal shaving/chips/dirt/leaves, etc. I decided it was not good idea to reconfigure batteries to 8S8P (lower voltage) as the main contactor and reversing contactor are rated at 64V and probably would not work well at 30V, so I just went with throttle remap (for speed) for now and will try that out.

Ok, I have remapped the throttle (speed) and uploaded tonight. I will give it a test tomorrow.


Today, when I had it in reverse, I hit the throttle pretty hard accidentally and barked the tires. Now set reverse speed to 25% instead of 50%.


PS:
The dog can no longer keep up with the cart..... :)
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