Electric go kart with two ebike motors

Hello from Derbyshire, England

A couple years ago I built a small electric go kart for my two young sons to use. It has a single rear 500w hub motor and two front wheels. Its great fun and goes fast on the flat (22mph) even with me on board. As my boys are only 4 and 6yrs old I have fitted a mechanical stop on the thumb throttle to limit speed to around 10mph.


The place where we use the go kart has some hills and the hub motor just hasn’t got the torque to get up some of them, especially as the boys are getting older. So my plan is to use some electric motor I have to build a new ‘hill climbing’ 4 wheeled go kart. The mechanical side of design is sorted (20 years as a mechanical engineer) but I need some assistance from you fine people with the electrical elements

I already have two of these motor kits (450w 36v Unite)
http://www.aliexpress.com/item/MY1018-450W-36V-gear-brush-motor-with-Motor-Controller-and-Twist-Throttle-DIY-Electric-Bicycle-Kit/1808574078.html

The plan is to build a four wheeled go kart with two motors, each driving its own rear wheel.
At max throttle position I want to have a max speed of 10mph and an optional second speed limit of 5mph, so my youngest son can use it safely.

Questions:
What’s the best way to run two identical controllers and motors off one throttle?

The max speed of the gokart can be fixed by matching the drive sprockets to the max rpm of the motor, but how can I electronically limit the throttle so that full throttle position only gives half speed of the motors?

If I want forward & reverse what is the best way to switch the power to the motors? These switches look like they would work for one motor but ideally I’d like to have one switch that controls the forward/reverse of both motors
http://www.aliexpress.com/store/product/30A-0-110V-DC-forward-backward-and-stop-reverse-switch-Electric-tricycle-inverted-switch-severing-controller/1209624_2053846286.html

Thanks in advance for your help !

I won't really solve your questions, but just throw a small light.

- What’s the best way to run two identical controllers and motors off one throttle?

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Same configured controllers, same configured motors, one battery and one thumb throttle wired to both controllers, I think is as easy as it looks, but maybe someone has anything to say

- can I electronically limit the throttle so that full throttle position only gives half speed of the motors?

Click to expand...

usually basic chinese controllers has by default a connector for a "3 speed switch" 50%, 100% and 120%. It can be configured from factory to limit each position as you want.

A CA can do this better.

- If I want forward & reverse what is the best way to switch the power to the motors?.

Click to expand...

the same thing as "3 speed switch" controllers has by default reverse conector by default, it just exchange phase communication.

I'm sure others will be so better specific.

cheers

you build two of my lebowski controllers, connect your throttle to one of them and wire up the CAN bus for the controllers to share the throttle info. Then to speed
limit you can adjust the setting for maximum (electrical)rpm.

hey, welcome, brilliant built, congrats!
With respect to your concern
(- What’s the best way to run two identical controllers and motors off one throttle?) I would answer like "Nobuo"
- can I electronically limit the throttle so that full throttle position only gives half speed of the motors?
I would mention "throttle tamer" sold by Zombies (which has a set of trim pot for adjustement, one being related to the Max output voltage of the throttle
Note that this device as 1 throttle input for 2 throttle output
http://greyborgusa.com/product/throttle-tamer/

I think those motors are brushed, making this project a lot simpler. you only need 1 controller and either parallel or series the motors. Needless to say parallel doubles the amps and series allows each motor full voltage. I could be wrong but Unite makes brush motors for Ezip type bicycles. Very powerful little gear motors especially when run @36 volts.
otherDoc

Thanks for the replies.
Yes these motors are brushed.

The controllers don't have connectors for a 2 or 3 speed switch or for reversing the motors.

I was hoping to set up the 'two speed mode' by splicing in 2nd signal wire from the throttle that switches over by a toggle switch or key switch. This 2nd signal wire would have resistors in it to limit the signal voltage by 50%.
So in full speed mode a full twist of the throttle would give max volts. Then in 'half speed' mode a full twist of the throttle would give 50% of the volts.

PS:
What do you mean by

A CA can do this better.

Click to expand...

A Cycle Analyst will let you precise control for Amps output

With brushed motors it will be easier to use a single controller and put the motors either in series or parallel. You could even make a switch for this that could do both, giving a two-speed range. The switch needs to handle the full motor current, so while it sounds easy, finding a hefty enough switch could be a challenge. Alternately, you could use Anderson connectors and a jumper to make reconfiguring the motor wiring relatively quick but not as handy as a switch.

The speed of a controller can be limited in a number of ways. The CA or Throttle tamer circuits would both work. Even simpler would be to place a resistor divider on the output of the throttle, which you could adjust. This could be activated by a switch or you could just put a knob on the pot and dial it.

Reverse requires a switch or relay between the controller and the motor. You need a DPDT configuration for reversing. You want to make sure the switch doesn't get activated while the motors are running. This would be bad. This switch needs to handle full motor current as well, so needs a high amp rating. Since we (hopefully) never operate the switch under power, the contact ratings could probably be pushed a bit. For example, you could probably get away with running 30A through a 20A rated switch.