Simple on-off switch damages motor brushes?

[John Doe]

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.

 

[Tom Biasi]

"John Doe" wrote in message

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

 

[Nobody]

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?

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.

 

[John Doe]

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

"Grab ankles before operating switch."

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.

 

[Tom Biasi]

"John Doe" wrote in message

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

"Grab ankles before operating switch."

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.

-- Cheers, James Arthur

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

 

[TheQuickBrownFox]

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.

 

[Tauno Voipio]

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.

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.

 

[Rich Grise]

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

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.

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

 

[John Doe]

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
18 V XRP battery lasts. Using lithium-ion, later, the weight will
be reduced.

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.

 

[John Doe]

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

Thanks to the replies.

 

[John Doe]

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

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

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.

Not if I get up to speed first, Babbler.
--

 

[John Doe]

"John Doe" wrote in message

With the method you are describing I'll bet you won't be
utilizing the speed controller function.

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.