Can the MP4 be programmed to travel below 100 RPM?

[WheelWalker]

Hi,
I'm doing agricultural research and we've used two 20" Magic Pie 4's on the front of a field-vehicle (see attached photo). Each wheel is operated and powered independently by a 48V battery.

Even with the wheels set to the lowest maximum RPM, 100, the vehicle operates at ~6mph, a light jog. Those speeds affect the resolution of the images that we can take and make consistent operation more difficult. I would love to know if there's a way to alter the settings to make the wheels operate at slower speeds.

It seems like most of the folks on the message board are speed demons. I had a hard time finding anyone asking if they could possibly go SLOWER.

Thank you for your time,
WheelWalker
 

[Bikemad]

Hi andto the forum.

I don't think that altering the settings will achieve the slow speeds you are wanting, but reducing the acceleration should improve the sudden start up.

I don't think the MP4 with the vector controller was the best for your application. You would have been better off using MPIIIs  instead of MP4s because the Vector controllers are not ideal for very slow speeds.

I have placed a video on YouTube showing the difference in the slow speed capability between the MP4 and a much earlier MPII (and also the earliest and latest Smart Pies) and you can see the big difference between the newer Vector "Sine wave" controllers and the older "Square wave" controllers.

I'm not sure how much difference the battery voltage makes to the slow speed, but I was only using a 29.6V LiPo pack, so the minimum speed with your 48V battery might be slightly faster than mine.

The MP4 runs at about 1 revolution every 2 seconds (60/2=30 rpm) whereas the older MPII takes around 23 seconds to complete 1 revolution (60/23=2.61 rpm), which indicates that the slowest speed of the MP4 is around 11.5 times faster than the MPII.

Unfortunately my MPIII is not in use at the moment so I was unable to test it, but I would expect it to be very similar to the MPII regarding the slow speed capability.

It might be possible to use the older MPIII controllers in your motors instead of the newer vector controllers, but the wiring connections for the Hall sensors and Phase wires are definitely different and would need to be changed:



I know that the MP4 controller does not work properly in the MPIII motor but I think it should work ok the other way around (using an MPIII controller in the MP4 motor)

I think the wheelchair hubmotors would have been a much better choice for your particular application.

Alan
 

[Morgen 3Eman]

I read your message, and it would seem you have a problem that may be approached from a different direction.  It seems to me that you are going too fast for what you want to achieve.  Can you fit a smaller rim and tire to slow down the rate of advance?

A couple of years ago I wanted wider tires on my 20" MP3, and JB welded a pair of rims to the casting.  Perhaps a variation on such an arrangement would work for you.  I have no idea what the diameter of the hub motor itself is, but it looks like a 12" rim would fit, and that would slow the speed considerably. Maybe get rid of the rubber tire entirely?  fit a wheel barrow tire to the motor and join them with expanding foam to transmit the torque?  The low speed will reduce the effect of mis-centering….

Or, how about setting up a time delay relay to send out a drive signal for one rotation, then stop for some small time before doing it again?  If your project has a micro controller involved, it would be easy to include a similar function in an Arduino type device….


Maybe you should go get a beer and think like a crazy old fool for while….

By the way, what are you working to achieve? 

Let us know what you come up with, please.

[Morgen 3Eman]

My eyeball says a 12" tire will stretch fit over the hub motor…  OK, they are old eyes, but they have lots of practice:)  That would drop your speed by around a third— is 4 kliks OK?

Or, since the speed and load are so low, just cut the 20" tire  and staple join it to the proper length.   Hell, Gorilla tape would probably be good enough to join the ends. 

TTFN,
Dennis

[Lewis Balentine]

I know that the MP4 controller does not work properly in the MPIII motor but I think it should work ok the other way around (using an MPIII controller in the MP4 motor)

It does not seem that room is a problem in this application. If all else fails an external controller might allow a little more 'finesse'. That has been done before with the Smart Pie.
https://lollandster.wordpress.com/2012/12/25/modifying-the-smartpie/
 

I have placed a video on YouTube showing the difference in the slow speed capability between the MP4 and a much earlier MPII (and also the earliest and latest Smart Pies) and you can see the big difference between the newer Vector "Sine wave" controllers and the older "Square wave" controllers....Alan

That explains a lot.
My SP4 from a dead stop does not seem to 'kick in' until I am half way across an intersection (four lanes).

Edit:
Well have reread the URL posted above I note the reason for the external controller was a two second throttle delay.
... with an extra 20-25 pounds of hardware to get moving that is a bit of a safety issue.

[Bikemad]

My SP4 from a dead stop does not seem to 'kick in' until I am half way across an intersection (four lanes).

I experienced a similar problem when I tested a revised version of the SP4 controller. I had the Acceleration set at 100% and with the wheel raised off the ground it was unbelievably slow to respond to full throttle and took over 12 seconds to reach maximum rpm on 32V and 27 seconds on 54V.

The long delay was caused by using the earlier programming software with the later "revised" controller.

When I reprogrammed the controller using the "revised" programming software the motor was then much too responsive and I could not pull away on loose surfaces without spinning the front wheel.

The original controller and original software only allowed 5 different values of 1, 2, 3, 4 or 5 to be stored as the acceleration parameter and these equated to 20%, 40%, 60%, 80% and 100%.
The revised controller and revised software allows 101 values of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. right up to 100 (or presumably the hexadecimal equivalent) to be stored as the acceleration parameter and these directly equate to 0 - 100%.
If you use the old software, it stores 100% as a value of 5, but the later controllers will interpret a value of 5 to be 5% not 100%.

The Vector controllers produce an almost instant response to the throttle movement when the Acceleration is set to 100%. I have the Acceleration setting at 80% or less on both of my vector controllers to enable safe acceleration without either wheel spinning the front mounted Smart Pie 4 or flipping over backwards on the "Wheelie Machine" with the rear mounted Magic Pie 4:

 

It sounds like you have been using the wrong (earlier) software, in which case, I suggest you try resetting the Acceleration level using the revised software and see if it makes any difference to your motor's response time. 

Alan
 

[Lewis Balentine]

Thank you Alan.
I will try that but I have no luck with the laptop windows XP and this software so I have to remove the wheel and take it to my desktop.
Might be a few days.