Simple on-off switch damages motor brushes?

Maybe.

No.

If you apply full voltage to the motor before it gets to full speed, _and_ its not designed for it, then that damages it.

Without knowing more about the motor, do what the drill does: if the drill has some fancy controller, then see if you can't just use the drill's fancy controller. If the drill just has a switch, then you can probably (well, maybe) just use a switch.

When you stall the motor in the drill, that has the same effect as stalling the motor in your push stick. The only real difference that I can see is that with the push stick you may overload the motor for longer.

I am converting a DeWalt 18 V right angle drill into a push stick for in-line skating. If I use a simple on-off switch instead of the controller, will that damage the motor brushes? Would a bypass capacitor help (just guessing)?

If the motor has to work hard before getting to full speed, that damages it?

This is not a big deal, I probably will go ahead with a momentary on-off switch, but wondering if I should buy a capacitor at the same time.

Thanks. The motor is designed to work at full voltage. If you supply full load to the motor at startup it will work harder.

It would be like pulling the drill trigger all the way each time.

Tom

Maybe. The current drawn while stalled can be vastly higher than the normal operating current (e.g. I have a small 12V bench drill nominally rated at 2A with a stall current of over 100A). If the motor is going to take significantly longer to spin up than it does in its intended role as a drill, you're probably going to need current limiting.

If you hard-start the motor, don't forget to add the following line to the user manual:

"Grab ankles before operating switch."

-- Cheers, James Arthur

Maybe I should not have asked the second question. All I really need to know is whether a simple on-off switch will do. At the moment, I am going with a controller.

FWIW...

It is going to be a stick held by hand, sort of like a stick they use for very small boats in shallow water. The pressure against the ground is readily controlled. There does not have to be massive pressure against the motor on startup, especially not if I get up to speed (in low gear, only somewhere around 6 mph) before putting the wheel on the ground.

I might use a cuff against my left back thigh. That cuff will stick out from the stick at thigh level (of course). In experimentation with an earlier (way too heavy) more powerful model, it was stable enough with the pushing force at thigh level or even lower. Using a thigh cuff will allow effortlessly pushing the wheel into the ground, without a lot of static weight on the wheel. As the wheel gets closer to my center of balance, the stick angle becomes steeper and the wheel is pushed into the ground by the counterforce of my thigh.

I plan to put the battery on the top end of the stick, as a counterbalance when carrying the thing. That is partly due to lack of freewheeling. But carrying the push stick instead of rolling it along behind when not in use might be advantageous, if it is light enough. Going up curbs with the 30+ pound version was a rough process that tended to break the thing.

Maybe I should not have asked the second question. All I really need to know is whether a simple on-off switch will do. At the moment, I am going with a controller.

FWIW...

It is going to be a stick held by hand, sort of like a stick they use for very small boats in shallow water. The pressure against the ground is readily controlled. There does not have to be massive pressure against the motor on startup, especially not if I get up to speed (in low gear, only somewhere around 6 mph) before putting the wheel on the ground.

I might use a cuff against my left back thigh. That cuff will stick out from the stick at thigh level (of course). In experimentation with an earlier (way too heavy) more powerful model, it was stable enough with the pushing force at thigh level or even lower. Using a thigh cuff will allow effortlessly pushing the wheel into the ground, without a lot of static weight on the wheel. As the wheel gets closer to my center of balance, the stick angle becomes steeper and the wheel is pushed into the ground by the counterforce of my thigh.

I plan to put the battery on the top end of the stick, as a counterbalance when carrying the thing. That is partly due to lack of freewheeling. But carrying the push stick instead of rolling it along behind when not in use might be advantageous, if it is light enough. Going up curbs with the 30+ pound version was a rough process that tended to break the thing.

With the method you are describing I'll bet you won't be utilizing the speed controller function. You will be at full speed all the time. Controlling the ground pressure is a better idea imo.

Tom

Just use a mechanical solenoid to actuate the existing switch, and nothing more is needed.

What may damage the brushes is current (I2R losses).

The basic equation for an electric motor is:

current = (feed voltage - back EMF) / circuit resistance

The back EMF is proportional to the RPM of the motor. The torque of the motor is proportional to the current.

The brushes may be overloaded if you're requesting more torque than the motor is dimensioned to supply. You may need some kind of current limiting.

Tom Biasi wrote: (at least according to my newsreader)

You don't want an on-off switch for that. Switch on, you'll either lay a patch of whatever the tire is made of, or you'll get dumped on your face. Why can't you salvage the trigger from the drill, and klooge up some kewl belt-mounted throttle thingie?

Have Fun! Rich

The inline skating push stick weighs in at a lean 6.3 pounds. The DeWalt 18 V motor is small but surprisingly powerful. I sort of messed up the right angle drill controller, currently using another controller from a standard DeWalt 18 V drill, it seems to work. The wheel is a 125 mm Razor scooter wheel, it is hard but small and light. Not good for rough terrain, but that is usually avoided. The push stick is unwieldy and unnecessarily stressful when held by hand against the ground. Will attach a hook to the stick that will press against my rear thigh. And the controller needs to be attached properly so that the stick can be held and the controller used with one hand. Then to determine how long one

Much of the problem with abrupt starting could be in theory eliminated by a clutch that is included with most cordless drills. Unfortunately, the DeWalt right angle drill happens not to include a clutch. However, it is small and light, and the chuck can be hacked and ground so that the skate/scooter wheel is secured right on the chuck extremely close to the large right angle gear bearing. The wheel being so close to the bearing, hopefully the unusual torque will not prematurely destroy the bearing and the right angle gear.

In short, the damn thing works, yea.

FWIW. Further comment is posted in the inline skating group.

Thanks to the replies.

That's because you are posting in the wrong place, Babbler, but the idea that you can use a computer for anything is stunning.

Not if I get up to speed first, Babbler.

After some practice with the prototype, the speed control works okay. I am pleasantly surprised that this 18 V right angle drill has the power to push me on skates, even up annoyingly steep hills in low gear. And the batteries last long enough.

I figured out how to prevent the automatic braking mechanism when the trigger is released. Someone on UseNet suggested using a rubber band to help depress the trigger. Coincidently, the automatic braking appears to be a switch when the trigger is completely released. By using a rubber band to slightly depress the trigger, that also prevents the trigger from completely releasing and it stops the automatic braking. I still remove the wheel from the ground when coasting, but the automatic braking instantly stopped the wheel and might have eventually stripped the gears.