Using winch motor for weapon drive?

[BrentwoodSchoolRoboteers]

Hi again, hope this is not a stupid question.

Trying to locate some relatively powerful motors for driving the spinner and have so far been stuck between the cheap (but not very powerful) motors you can buy on eBay for £60 for 1000w and the expensive 10hp motors that start from £500 upwards.

Trying to find something in-between.

Although I have not found any standalone motors for sale I have noticed that you can buy 24v winches for between 1-200 pounds that look to be approximately 3kw. This could then be stripped down to get the motor.

Does anyone see any flaws in using these for a weapon?

Thanks

[shakesc]

Why not go for a brushless?

Having bought a winch to strip down for the gearbox those things are really heavy and mine had the pinion ground directly on the shaft that doesnt help converting the motor

[cmalton]

+1 for brushless DC motors

Big Dave 3 is entirely brushless motor driven, and while the speed controllers for high current brushless motors can be hard to sort out, there are suppliers out there. Brushless provides a healthy level of torque and ability to move stuff.

There are people who will swear by brushed DC motors (the sort you connect a voltage across and they spin), and they're not bad. Everyone has their own opinions though - and I don't think we (ARC) would ever consider brushed motors now we've got our head around brushless ones.

[BrentwoodSchoolRoboteers]

Brushless controllers are very expensive from what I can see. When you say heavy how much are we talking. Motors are heavy at the best of times!

Thanks.

[cmalton]

I'll get Rob from ARC to reply tomorrow with the weight saving/increase in power we got by going brushless - but it was quite significant.

[overkill]

The cheap winch motors will be very hard to convert. As Chris mentioned, the shaft usually has a gear or a spline cut into it and on all the gearboxes I have seen, the front face of the motor is part of the gearbox. It would take some ugly hacking to make the motor a standalone unit.

[typhoon_driver]

"Brushless provides a healthy level of torque and ability to move stuff."

For drums or objects with low moments of inertia yes but for larger discs with high moments of inertia the raw torque generated by a brushed motor can't be matched with brushless.

With brushed you generally pay a lot for the motor and can use a relatively cheap solenoid to give you on off control. Brushless tends to have cheaper motors but the control works out to be the expensive part.

Right now I just don't see brushless having the reliability in the arena when compared to a brushed spinner set up.

[overkill]

As long as you don't go cheap, brushless is highly reliable - I have boxes of burnt out Mag motors and have only lost one brushless weapon motor in three years. I disagree with low torque statement too; pick the right motor and the right gearing and a brushless motor will provide all the torque you need for a large diameter weapon.

[typhoon_driver]

Are those in heavyweight spinner setups or featherweight spinner setups? The former is a nightmare to get right with brushless. The latter is easy as most hobby gear is perfectly sized for it all.

[overkill]

Feather and light weights, but I also have a brushless Etek that does the same job as the brushed versions - except there are no brushes to shatter .

[R9000]

I thought the low startup torque was only because of it being difficult to monitor back EMF until the motor's up to speed - surely sensored brushless should have no problem?

[overkill]

That's correct; I see a big difference in the start up performance of sensored VS sensorless motors in the same conditions. It also depends of the ESC, some brands seem to have smarter firmware to handle sensorless start-up. IMHO, most ground-based ESCs are designed for higher RPM motors that are run flat out. They don't need low speed control and sensors, so asking them to do low speed fine control in bots is not ideal.

[emisnug]

Brushless controllers are very expensive from what I can see. When you say heavy how much are we talking. Motors are heavy at the best of times!

Thanks.

In terms of weight saving, we're getting 4.5ishKw constant power (under load) for a motor weight of 1.25Kg (Slightly less now that I've chopped the excess shaft off of the end).

In comparison, a similar brushed motor (ME0708, which is admittedly the first 4.5ish KW constant motor I found on google) is 12.7Kg.

However, as Gary says, for the first couple of seconds, the raw torque generated by a brushed motor is far superior, but after those first couple of seconds (as low as .5s), it's a dead heat. For anything with a larger moment of inertia, it will be slower to spin up, but not by much - as soon as it breaks that moment of inertia, the brushless can pull more power and dump a bit more torque, so can spin up to speed perhaps 1-3 seconds slower than a brushed. Other roboteers, feel free to correct me.

Brushless motors are also more efficient in general, and don't really require servicing. The PWM curves, as Chris will tell you, are fun to deal with.

[daveimi]

It helps me to think of brushed and brushless and diesel and petrol respectively.

[Ellis]

Sensorless brushless motors are only efficient if your ESC is decent. Otherwise they can be shockingly inefficient at low speeds.