Motors with an earth

ive got a problem with my featherweight robot which ive been building, because the 2 drive motors and wheels are each from 2 electric scooters, i didnt know this untill i found out but each motor used to use the scooters chassis as an earth which was fine until i put both motors into a steel chassis and now i cannot operate them at the same time because of the fact that they each end up using the chassis as an earth if i connect one motor to the speed controler it works fine but i cant use both, does anyone have any ideas how to get around this problem? thanks

Use 2 speedos, I think, but you should wait for answers from an expert

have you had the motor apart to see if there are any obvious connection between the case and the brushes for example?

if your not electrically minded.. you could try insulating the motor from the chassis- i.e. mount it on polycarbonate instead of steal :)

Sounds like the old days, with wiper motors...

if he mounted the motor to say polycarb then wouldnt you need to use plastic gears or chain to insulate it that way too. not sure if it applies from the armature onwards but a thought.

unless the complete drive unit was seperate from the chassis mounted on say poly. that might work

Any chance of a pic of the motors Calum?

IF there are two wires coming out of the motor and one is attached to the casing...simply detach the wire from the motor casing.

swan- i know what you mean, it would work if he was using belts though, which i think alot of the aussies do with those scooter motors :).. but its still better practise, as woody said to look at the motors carefully.. there is normally a wire bolted or soldered to the case some were. cut it..

Calum.. i had this problem with one of my first robots.. even though i thought i un-earthed the motors.. what speed controllers are you using? I used electronize 15amp CPU controllers and wiper motors.. i found that when the heatsink of the controller touched the chassis it would have similar effects to what you describe. Are the controllers your using insulated from the chassis aswell?

the speed controller is insulated from the chassis, ive taken 1 motor apart and theres no earthwire connecting to the inside of the case so i guess its from the motor shaft then it goes through the case of the motor -is it called a motor shaft??

ill put a picture of the robot so far as my profile pic so anyone can see the motors and the way they are mounted. and yes the welding isnt great at the minute.....

would using 2 speedcontrollers work? which ben read mentioned?? if not it looks like ill be making the motor brackets out of poly and yes there are 2 wires coming out of each motor.

ive got 2 take a smaller pic so it will go on the profile this may take a while...

(Message edited by calumco on August 27, 2008)

it wont allow me to change my pic although it is within the allowed size if anyone wants one youll have to ask

try saving the picture as a jpeg and cutting it down on paint.. its what i do..

Ive received you email and picture.

Calum

Your motors dont appear to have a built in earth to the chassis.
You simply want TWO seperate speed controllers or one DUAL controller.

Ive added you on Messenger should you wish to chat.


(Message edited by woody on August 27, 2008)

the speed controller ive been testing the robot out on is a dual one, which because of the motors using an earth( 4 volts--- which i tested using a multimetre) it only allows one motor to operate at a time,

i think if i was to get 2 seperate speed controllers like woody mentioned above i think that should work because they would be both using an earth but they would be on a seperate circuit does that seem like it would work???

but if not ill have to make the motor brackets out of poly

The motors have two wires and I can see no reason for the scooter motors having an extra internal connection to their casing.
Did the donor scooter have an earth wire from the battery to the chassis?
If not Id suggest that the motor armatures have a fault ... did the windings look a little cooked in the motor you took apart?


(Message edited by woody on August 30, 2008)

hi, there wasnt an earthwire from the battery to the chassis, and as for the motors windings i think they were fine i cant remember anything looking damaged ,ill have to have another look.

it works!!!!!!!!!! ive wired it all up again and for some reason it now works with the dual speed controller that i have, but i need to get a better one as it is ment for combat robots up to 6 kg.

calum, sounds like you had a loose wire or somthing shorting on the chassis.. go through all your wires and connectos etc and check for no stray cables or scratched wire insulation..