[mikesheiman]

Video at
https://www.facebook.com/spectra.ce/videos/10155815129587445/


I've been working on a trike, but I can't figure out why performance is so low per amperage used.

It is running off 6 MAXX29 lead acid batteries for a 72v system. I have it geared with a 16 and 60 tooth sprocket for 3.75 gear reduction and am using R15 tires. I am also using 2/0 gauge wire and an Alltrax SR72500 motor controller.


When I limited the controller to 175 amps at the battery, 225 at the motor, I could not get it above 50 mph and it barely accelerates above 45 mph. Also performance under 15 mph or so is terrible, perhaps due to lack of a gearbox and a lower gear.

This frustrates me as the following 72v Geo Metro with the exact same motor (ME1003, brushed) apparently needs only about 100-120 amps to hit 50-55 mph (http://www.johnsavesenergy.com/GeoEV2.html).

Curious from a technical and aerodynamics perspective (final shape is in the video), any clue what I'm doing badly that could account for a hatchback getting better efficiency than my at least attempted as streamlined trike?

 

[dain254]

Just in my own experience you need way more amperage to accelerate. Amps=Torque. When I was using the lead acid set of batteries and the same motor in my trike I used every bit of amperage my 450A alltrax would kick out. Even then.. acceleration was still not great. I didn't click the link but I assume the Geo guy was using a gearbox to drastically increase his torque at low speeds then shifting as he got moving.

 

[madderscience]

It may not be one big thing, it may be many little things.

wheel/tire alignment? tire inflation? brake drag? How well does this thing roll?

What type of motor? What is the expected torque/rpm curve at 72v? Maybe its running out of torque due to relatively low voltage.

How did you decide on gear ratio? If the motor is too small, you may need a higher ratio. Too big, and you may need a lower one.

If its a brushed DC motor, is it timed right?

Is the controller connected to an adequate heat sink?

Is the controller misconfigured insofar as minimum battery voltage?

How bad do the batteries sag under load?

etc, etc.