New Quadracycle build - underpowered - how to fix?

[Mad-about-it]

Just recently completed building the quadracycle from plans bought from here: https://americanspeedster.com/about/our-quadricycles/side-kick-i/

Golden Motor CA recommended the wrong size motor for my build. I want it to be able to get me and my wife up small hills. I bought from them the 20" rear Magic Pie Edge and the lifepo 36v battery. Well, the battery did not make it through customs. I was already thinking it was not going to have enough power, so I upgraded the battery. Golden Motor CA sourced a battery locally for me - a 48v 15ah battery. I have the Edge on the right rear, but it does not have enough power to get us up small hills.

I guess my options to fix this would be:

- Buy the Magic Pie 5 and replace the Edge with the 5
- Buy another Edge kit and put on left rear with 6 speed freewheel. So would have 2 Edge wheels on the ground, but still just the one battery.

Of those two options, which would provide the most power to get up small hills and how would each setup affect the performance of the battery?  Is there a better third option I should consider? Thank you for any insight.

[Bikemad]

Hi andto the forum.

As a quadricycle is basically a heavier version of two single bikes it seems sensible to have two motors and two batteries like you would for two single bikes.

Upgrading to a single Magic Pie 5 will not be as powerful as a Pair of Magic Pie Edge motors, so adding an additional Magic Pie Edge would seem to be the cheaper and more powerful upgrade out of the two options.
However, your existing battery would need to be capable of supplying at least 45 Amps continuous current to power both motors under full load on steep hills, but most 48V 15Ah packs will probably have a maximum continuous output of ~30 Amps, therefore an additional battery pack will probably be required to enable each motor to produce maximum power under heavy load conditions.

A more expensive option would be to fit a mid drive motor that could be used in conjunction with the lowest gear ratio for maximum torque at slow speeds. This would be fitted in addition to the existing Magic Pie edge, but on the other non-motorised side to help even up the power distribution. Unfortunately, an addition battery is probably going to be required with this option as well.

Alan
 

[Mad-about-it]

Okay. So if I don't plan to upgrade the battery right now, would that make the Magic Pie 5 the better option? It would definitely offer me quite a bit more power than I have now with the single Magic Pie edge, correct?

Here is the designer of the quadricycle running a single Magic Pie from about 10 years ago... https://www.youtube.com/watch?v=bS2p3yqYb-I&lc=UgzcMK1iR1AzkTN6wMR4AaABAg

[Bikemad]

The torque produced by a motor is typically in relation to the current being drawn, and the Magic Pie 5 is set by default to draw a maximum battery current of 25A, which is approximately 20% more than the 21A for the Magic Pie Edge.

In addition to this, as the Magic Pie 5 is a larger diameter motor than the Magic Pie Edge, therefore it should produce about 11% more torque for the same current draw.
If my figures are correct, a single Magic Pie 5 drawing 25 Amps of current should theoretically produce about 22.2% more torque than a single Magic Pie Edge drawing just 21 Amps.

Unfortunately, there are no dynamometer test figures available for these motors showing the torque produced relative to the current draw at very low rpm, so it is impossible to say what the difference in torque would be between a single Magic Pie @ 25 Amps compared to a pair of Magic Pie Edge motors drawing the same combined 25 Amps (12.5 Amps each) at very low speed. 

I would expect a pair of Magic Pie Edge motors running at half load to be more efficient than a single Magic Pie 5 motor running at full load, and this increase in efficiency could probably increase the available range using the same single battery by as much as 9~10%.

However, if you really need the absolute maximum torque for climbing steep hills, a Pair of Magic Pie 5 motors and dual batteries to enable maximum current to be used continuously would be a better option, or even four motors, one on each wheel:



Alan