# Powering a DC car vacuum cleaner with a brushless motor for better performance?

I'm making a self autonomous vacuum cleaning robot for a project and I need a vacuum cleaning mechanism to install on the robot. The problem I'm having is with figuring out how to make the vacuuming system powerful enough to be impressive and be practical enough for mounting it on top of the robot chassis.

I pulled apart a car vacuum cleaner and found it had nothing much inside and just a motor which pulled 5A at 12V. So what I concluded was that the main thing here is the velocity of the motor which is what produces the air pressure, so if the velocity were increased it would become better, right?

I had an idea to use a brushless DC motor (like the ones in RC helicopters) in place of the present one as the brushless ones have much higher RPMs. Would this be a good idea or is there a flaw in this theory somewhere? And also please do share any other ideas you might have to achieve the aforementioned goal of effective vacuuming.

• Will the fan/impeller cope with the higher RPM or will it disintegrate / vibrate to destruction? – John U Aug 14 '14 at 9:37
• Would that be such a problem? i mean brushless motors do drive propellers so won't it be kinda the same? – Hameem Aug 14 '14 at 20:07
• OK, if you fit the wheels off a delivery van to a Ferrari and then drive it at 200mph, would you expect the tyres to survive? If the tyres weren't balanced above ~70mph and wobbled like hell, would you expect the Ferrari to get damaged from the vibrations? The two halves (motor & impeller) need to be matched. If you drive an impeller too fast it will cavitate and cease to move any air at all. It will have an optimum speed, and I'd hope that the current motor is moving it at about that speed already. – John U Aug 15 '14 at 8:09

Speed $\times$ torque $\times$ 2$\pi$ is power in watts.

Speed is in revs per second and torque is in newton.metres.

This basically translates to....

For a given power input to a motor, if you have higher speed you CANNOT generate the same torque compared to a lower speed motor.

Dragging debris from a carpet requires the right ratio of RPM and suction - suction depends on RPM and the available torque from the motor. Arbitrarily running at a faster speed does not mean better cleaning efficiency.

Do not ask me what the right ratio is for carpets - it's certainly going to be different for other surfaces. I can say this... more power = better suction.

A higher RPM will help, but you can also play with the impeller size, number of blades, and the angle of attack of those blades. Having a tight seal on the entire vacuum system will also make more difference than you think, because even small leaks around fittings will lower your pressure a surprising amount. As long as your impeller is decently balanced, you shouldn't have too much of a problem with vibration.

If you want more details, there's some good information out there on this kind of design for wind turbines like this: http://winds-energy.blogspot.com/2009/04/effect-of-blade-number-on-aerodynamic.html

• This answer does not discuss torque or motor power and implies that i could vacuum anything with a fan motor. -1. – Sean Boddy Mar 13 '15 at 1:52