Milkfloat - 4 Wheel driven cabac type

[Oscvol]

Just a general question about a milkfloats I've always wondered - why do most of the 4 Wheel driven cabacs make that weird variable moaning acceleration/whirring sound when the float starts up?

What part of the motor is it which causes this? are these variable electric types of motors expensive?

Thankyou

Vol

 

[itsmoked]

Sorry,, What! is a milkfloat?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Have you never heard of Google, Keith???

http://www.milkfloats.org.uk/picindex.html

Vol,

I think the noise is likely to be caused by some form of PWM controller which is the basis of the variable speed operation. It isn't really part of the motor but a piece of power electronics between the battery and the motor which converts the fixed battery voltage to a variable voltage to the motor with relatively low losses, thus conserving precious battery energy.


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Goo-what?

Ah an English vehicle name... I should've known. Here we have something that could NEVER float being called a 'float'.


I do agree with Scotty, Oscvol. The way they chop up the current to the motor occurs in the human audible sound region. It can often be louder at starting speeds. It is the windings vibrating. They usually will vibrate at a fixed frequency but there may be more current involved at the slow/starting speed and so it is more noticeable then.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Oscvol]

Cheers guys!

I browsed the internet for sound samples and could not find any easily. However I found this link with the exact sound of the milkfloat I mean that someone has recorded!

http://www.freewebs.com/milkfloats/milkfloatsounds.htm

It's the acceleration thingy. I would love to find out what electronics these vehicles use!

 

[itsmoked]

Yep that is a fixed frequency, pulse width modulation (PWM) controlled motor.

On that site they mention another five pedal position control that doesn't make the noise. In that case they are either using resistors to drop voltage, (highly wasteful), or they are lead switching the motor or the batteries. That would be hooking them up in different groupings to use them all always but in different voltage patterns. This is how all diesel-electric locomotives used to operate and why there are 8 specific power settings.

The 5 settings leads me to believe they are using the resistor method as I believe the other method might be more likely to create an even number of settings.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[itsmoked]

By the way;
You don't need to see a float just go to your local golf course and look at the golf carts, or look at any electric wheelchair, or electric people moving chair, or any electric man-lift, or any electric forklift, or your local electric auto club, (DC cars only). They all use the same exact technique.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Oscvol]

Thanks for the help guys! I find these components+motors fascinating, being the PWM type with the variable ramp. I know for sure though that the battery to drive these vehicles are huge (infact they are the lead type battery) and occupy the under platform carrier.

It's not just floats that use this method so that is correct. But before now I always found it fascinating that these things can go so far on just one charge, so it's wired up and engineered nicely. I always guessed that the initial load would probably be alot heavier than the ideal speed - because they do seem heavy vehicles to start indeed - and there is a heck of a weight to carry.

I've seen some pedal cycles now emply electric motors (except they are fixed) so the motor would gain RPM in a gradual process. I would love to see more electric vehicles out and about though.

 

[TheFloater]

Hello guys! I just found this thread through a Google search, and just wanted to add that these old milk float controllers actually use a combination of frequency and pulse-width modulation to control the motor speed. As they move off, you hear the frequency of the "moan" rise and then fall, before stopping completely as maximum speed is reached and the motor is effectively running on pure DC. Modern controllers in things like golf carts are pure PWM.
Before these chopper controllers became the norm, speed control on milk floats was nothing more than an array of resistors and a set of contactors to switch in varying resistances. My own milk float has this arrangement.
Take a look at

http://www.milkfloats.org.uk/documents/

- there is a maintenance manual for a "Sevcon" SCR motor controller which explains the theory of operation.
Hope this is useful