Miniflyer

Hi guys,

i have a bit of an awkward question concerning electric motors, but i feel the car guys will be the best to know. We are running a pump on a Speed 400 4,8V (22000rpm, 4600rpm/V) with a 6V max power supply.

Load, power supply and controller cannot be changed, but output needs to be increased quite a bit. So basically i am looking for a "drop-in" brushed tuning motor to replace the 400. Size and weight is no matter, so a 480/500/600 class motor will be fine also. I'm just looking for more torque and rpm from the same 6V max....

Any ideas? I'm not really getting anywhere with the "17x2" type designations often used in car tuning motors....

Best regards
Hank

Slo-V Flyer

What do you mean by not getting anywhere with 17x2 designations? As in the motor didn't work for you or you don't know what it means?

In case you don't, 17x2 means 17 turns, and 2 or double winds (more smoother torque band than a single wind).
The lower the turns, the higher the rpm and more amp draw in order to create the same given torque.

So for torque maybe you want a "stock" 540 sized motor, 27 turns, sealed end-bell type, maybe even a cheap Tamiya silver can motor, or you want a 19 turn motor for more rpm.

Or for a lot of torque, but low rpm, you want 55 turn lathe motors, those are used in rock crawlers and have lots of torque and use less current, but need volts to run at high rpm.

Though most of those motors I mentioned are made to run on 7.2 volts, they will still work on 6v, but obviously just not as fast.

Does that answer your question?

Access

It is an impossible problem.

You are not going to get a major increase in mechanical power (torque * rpm) without a major increase in load (electrical power). Short of going with a much more efficient motor, it's a problem you can't solve in reality. Larger motors may be slightly more efficient than smaller ones, but a brushed motor is a brushed motor, you aren't going to find one that is 20% more efficent than what you are using right now.

If you must try start with somewhere around a 13-turn make sure to gear it appropiately. It will provide more torque (than your speed-400) but you'll also draw more current (higher load) where you stated 'load, power supply, and controller cannot be changed'. Be careful b'cos unless the power supply is current-limited, you will draw more current and you might exceed it's power rating.

Miniflyer

By saying "Load is the same" i meant to say that nothing in the pump will be changed, the mechanical design is to remain unchanged.

I have a pump here that will deliver around 700-800ml (close to 1/4 gal.) per minute without having to create pressure. When pressure is needed (5bar=72psi), the delivery rate goes down to about 500ml. What i need is a pump that will deliver the 800ml in a 72psi/5bar situation, so basically i need a motor that will either

a) spin the pump faster in a no-load situation (e.g. delivering 1100ml per minute with no pressure), so that the flow-drop will put me near the 800 when pressure is applied

or
b) spin the pump with less rpm loss when pressure is built up.

So what i need is to increase either the rpm, the torque or even both at given Voltage (higher amp draw is acceptable).

A "stock 540" seems to turn around 17000rpm @ 7,4V, putting me near 11000rpm @5V. The speed 400 will be spinning beyond 22000rpm at that voltage....more than twice that. The motor might be more powerful, but it will not deliver the same power output under the given circumstances.....

The explanation of winds and turns was excellent, but it still does not supply me with numbers for rpm constants and idle rpms....nor does the manufacturer who makes those type of motors.

Thanks for the responses :-)

best regards
hank

Access

That's why I suggested starting with a 13-turn, 13-turn will give you a decent tradeoff of torque and rpm, kinda the fewest turns you would want to use for an off-road truck setup. Normally I'd go with a reedy quad mag (as a basher) very reliable, dependable motor, but that isn't going to give you the rpms you want.

The problem is these motors tend to be quite picky when it comes to gearing, and running it with the wrong gearing, too high / too low is going to kill your motor. In your case, you can't really adjust the load or even the voltage, so it's kinda just trial and error and you might ruin a few motors before you find one that works. This isn't a normal car/truck application (a pump), and these motors are spec'ed for cars/trucks so it's not an easy question to answer, will probably involve some trial and error on your part. Another good starting point might the traxxas motor that goes with the XL-5, into the XL-5 rustler/bandit/'pede, pretty sure those are 11-turn and they shouldn't be too expensive, should run a long time before needing replacement.

Slo-V Flyer

The Traxxas motor Access is talking about is the Titan 12t motor, i.e. 12 turns. is a 550 sized sealed endbell silver can, and inexpensive compared to the other lower turn rebuild-able motors mentioned above. It has lots more torque, but again, a little on the slow side. I'm not sure what kind of gearing options are available to you, but you'd want to gear something like that with a taller pinion to get the rpm you need. Unless you are using the motors for a direct drive kind of pump that has no gear reduction?

Miniflyer

The pump is a direct drive, i have no gear whatsoever. That is why i'm trying to "beat" the 22000rpm @ 4,8V of the speed.

I've also found a supplier who gives some engine data to calculate with (rpm constant, resistance, idle amps etc...). Judging from the numbers i'll probably end up around 10x2. I'll order a set of motors in that range and see what i can do with them....

Thanks a bunch
best regards
hank