Scorpion XL Speed Controllers

[widow_twanky]

Just interested in the maximum number of the 24V 150W gold motors you could run off each side of a Scorpion XL speed controller?

Also, are there any potential problems with running more than one motor from each side of the speed controller (Differences in speed due to tolerences etc)

Andy

[jamesb]

Scorpion XL Speed Controllers

If you run them in parallel, you can in theory run more motors than you have weight for, but the controller will still current limit the same, so if you have one motor per side, at 24v you will see about 35amps per motor maximum, use 2 per side, and each motor will get 18amps max, use 4 per side and each gets 9 amps.
Basically, you can get as much power from 2 motors as you will from 4, but 4 are heavier.
Email me if you need more detailed explainations.

[psychostorm]

Scorpion XL Speed Controllers

Bit like asking how long a piece of string should be(using the same fibres), when what you really to do with it is pull a car...

Well assuming were in hunky dory land, the maths would work out at:
(35A*24V)/150W = 840W/150W = 5.6 motors a side.

But as James correctly points out, it doesnt work that way. In praticality, those 5 motors arent going to move the machine, just like the 5mm wide 12ft long string aint gonna pull the car.

Your drive chain causes more current to be used per motor and the speed controller has a current (and therefore power) limit it can provide to the motors.

So the more motors added, the lower the fraction of current they can use. As math:

Current limit / Number of motors = Average current per motor

Or using Jamess examples: 35A/1 motor= 35A, 35A/2 motors= 18A and 35A/3 motors= 9A.

Since the controller has this power limit, that becomes the power limit for the entire machine. You could add as many motors or batteries as you like, you arent going to get any more energy.

[woody]

Scorpion XL Speed Controllers

The total current drawn by a bot is a function of the mass to be moved and the gear ratio used to obtain your required top speed / acceleration.

Example:-
A 13.5kg ( 30lb ) bot geared for 10 mph that will accelerate to its top speed in 4 metres will require a total power of 480 watts ...this would equate to 40 amps @ 12v.

Divide the total amps required by the number of motors to get an amps value for each motor.

http://architeuthis-dux.org/torquecalc.asphttp://architeuthis-dux.org/torquecalc.asp

A Harbour Freight motor should be a fair representation of std cordless drill and is the motor I picked to provide the guesstimation above.