pdp1@EARTHLINK.NET on thu 3 jul 03
Were I to build an electric Wheel from scratch...I'd look
into some smallish to medium smallish 'used' variable output
hydraulic pump and 'motor' and work that into the design...
It would solve all these Mechanical vexations as for torque,
speed controll, (would be 'quiet') and certainly no more
difficult to do...
Phil
lasvegas
----- Original Message -----
From: "Michael Wendt"
To:
Sent: Thursday, July 03, 2003 3:53 PM
Subject: Re: Potters Wheel Mechanics
> Early Skutt wheels used spring loaded variable pitch
sheaves to vary the
> speed by changing the ratio between the motor and the
wheel head. They used
> constant speed AC motors. Step pulleys will work but are
cumbersome and
> don't provide the ideal speed a DC motor can
> Modern wheels use permanent magnet DC motors which are now
very cheap (I
> bought a 3/4 hp one last week for $59.00 brand new in the
box). Speed
> control schemes for these don't use rheostats. Instead,
they use electronic
> circuits that switch the power on for a brief instant if
low speed is wanted
> or a longer duration if more speed and power are wanted.
This switching is
> every cycle so the motor runs smoothly. Often, feedback
sensing circuits
> are built in to increase the power to the motor if a load
is applied. Two
> schemes I am familiar with can be employed, either a Triac
or a Silicon
> controlled rectifier. Shimpo now offers a brushless DC
drive and these
> probably use some scheme to electronically replace the
mechanical switching
> the old commutator does on brush type DC motors.
> I always include a separate full wave bridge rectifier
circuit in the wheels
> I build to assure they can be run plugged directly into a
wall outlet
> without a controller for people who want a single speed
wheel.
> Regards,
> Michael Wendt
> Wendt Pottery
> 2729 Clearwater Avenue
> Lewiston, Idaho 83501
> 1-208-746-3724
> wendtpottery.com
>
>
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Runyan,Jacob on thu 3 jul 03
Hello All,
I have a question regarding potters wheels. There was
recently a submission asking about gear/belt drive...my
question is how does belt drive work. Is there speed
controlled DC motor?
Further, are there any wheels that use a constant speed AC
motor but then change the speed by changing pulley
diameters or by driving off from a cone?
I am looking at building my own wheel, just because that's
the way I am (hobby machinist). I would however like to
know what technology is being used as of now in regards to
speed control.
Thanks,
Jacob Runyan
Eric B on thu 3 jul 03
my best guess (as a non-mechanic) is that a typical electric, belt-driven
wheel has its speed modulated by controlling the current going to the motor, such
as a reostat (spelling) somewhere in the mechanical part of the wheel the
potter uses to control speed, e.g., the foot pedal.
Eric
Roger Korn on thu 3 jul 03
Runyan,Jacob wrote:
>Hello All,
>
>I have a question regarding potters wheels. There was
>recently a submission asking about gear/belt drive...my
>question is how does belt drive work. Is there speed
>controlled DC motor?
>
This is the usual technology.
>
>Further, are there any wheels that use a constant speed AC
>motor but then change the speed by changing pulley
>diameters
>
The old Skutt (ca. 1962) wheels used this.
>or by driving off from a cone?
>
Shimpo and Amaco
>
>I am looking at building my own wheel, just because that's
>the way I am (hobby machinist). I would however like to
>know what technology is being used as of now in regards to
>speed control.
>
>Thanks,
>
>Jacob Runyan
>
Hope this helps,
Roger
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>
Michael Wendt on thu 3 jul 03
Early Skutt wheels used spring loaded variable pitch sheaves to vary the
speed by changing the ratio between the motor and the wheel head. They used
constant speed AC motors. Step pulleys will work but are cumbersome and
don't provide the ideal speed a DC motor can
Modern wheels use permanent magnet DC motors which are now very cheap (I
bought a 3/4 hp one last week for $59.00 brand new in the box). Speed
control schemes for these don't use rheostats. Instead, they use electronic
circuits that switch the power on for a brief instant if low speed is wanted
or a longer duration if more speed and power are wanted. This switching is
every cycle so the motor runs smoothly. Often, feedback sensing circuits
are built in to increase the power to the motor if a load is applied. Two
schemes I am familiar with can be employed, either a Triac or a Silicon
controlled rectifier. Shimpo now offers a brushless DC drive and these
probably use some scheme to electronically replace the mechanical switching
the old commutator does on brush type DC motors.
I always include a separate full wave bridge rectifier circuit in the wheels
I build to assure they can be run plugged directly into a wall outlet
without a controller for people who want a single speed wheel.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Avenue
Lewiston, Idaho 83501
1-208-746-3724
wendtpottery.com
David Malicky on sun 6 jul 03
I built one from "scratch" last winter. Here's what I found out:
MOTORS AND DRIVES
DC
A DC motor and speed control is easiest. For low buck, use the parts from an
old motorized treadmill--this also ensures the motor and controller are
matched. Else, you can find DC motors and speed controls on ebay but you'll
need to match their voltage and HP. There are two types of DC controls: SCR
(silicon controlled rectifier, common and lower $), and PWM (pulse width
modulation, fairly new, expensive, but better low end torque). With DC, high
HP motors (3/4HP-1.5HP) are needed to provide the low speed torque.
AC w/ VFD
The AC equivalent to DC is to use an AC motor and a Variable Frequency Drive
(aka "inverter"). Expensive, tho.
AC w/ transmissions
These are appealing, as you probably know, since 120V single speed AC motors in
the 1/3-1/2HP range are very common and typically $10 used. The HP is much
lower than w/ DC since the transmission multiplies the torque at low speed.
1) Multiple pulleys: as noted, only a few speeds, and a (dis)engagement system
is needed. Awkward but cheap. 4-step pulleys are at www.mcmaster.com.
2) Cone-drives: the traditional Shimpo approach, done DIY by another clay-
arter, Vince Pitelka (search for his posts). There are two approaches: a) a
small rubber ring on a jackshaft which then drives the wheel by a pair of
pulleys; b) a large rubber ring (12"-14") direct drive to the wheel. The
latter approach is well-suited to using a car wheel/hub/bearing (see below).
3) Zero-max: this is an industrial transmission that varies output speed from 0-
400rpm (for 1650 input). On ebay they go for $30-$50 for one with reasonable
torque capacity. See www.zero-max.com/products/drives/torque.asp Most of
the zero-max drives on ebay are low torque, so you'll have to look a while. I
got a model Y41 for $40 and built my wheel using it with a 1/3HP motor. It has
60in-lb capacity which turned out to be more than enough for me. The downside
to the Zero-max is vibration--not too bad, but not nearly as smooth as DC.
WHEELHEAD AND BEARINGS
1) Buy the Brent wheelhead with integral bearings and shaft. By far the
easiest. $70 for the wheelhead, and $110 for the wheelhead + bearings/shaft.
2) Wheel bearing, spindle, hub, and wheel from a junked car (fill the wheel
with plaster or cement). This is the approach of Jolyon Hofsed:
www.ceramicsmonthly.org/mustreads/wheel.asp
I have not tried this "transmission", but I am guessing it would be hard to
control the speed steadily. But, if one changed the rubber plug to a cone, and
then riveted some reinforced rubber tubing (split down the middle) to the
inside rim of the wheel, you have a cone-drive system (option "b", above) half-
way done. Durability is a question and entirely dependent on how well the
rubber can be fastened to rim. Also need to get the contact point to the cone
consistent (speed fluctuations), which might be hard.
3) Front wheel bearing/spindle/hub from a FWD/4WD car. Mate this to a
wheelhead of your choice. The main advantage is that you can drive from below
and separate the motor/tranny from the clay. The cartridge bearing needs to be
kept together (easiest with the original CV joint). I took this approach with
my Zero-max tranny, and got the car parts for free from a collision shop
(unlikely to get the CV, tho).
Overall advice:
1) If I were doing it again for low $ and effort, I'd use a DC motor and
controller from an old treadmill, mated to the Hofsted wheel head/bearing via
belt drive.
2) For a nicer wheel at higher $, use the Brent wheelhead/bearing/shaft instead
of the Hofsted design, mated to the treadmill motor via belt drive.
3) To find AC motors, car parts, etc. at low $, go to a "metal recycling" yard
(or collision shop). Avoid auto junkyards if you want to keep the cost down.
4) For pulleys, belts, and hardware at reasonable $, go to mcmaster.com.
Best of luck!
David in Lawrence, KS
--------------------------------------------------------------------------------
>
> I have a question regarding potters wheels. There was
> recently a submission asking about gear/belt drive...my
> question is how does belt drive work. Is there speed
> controlled DC motor?
>
> Further, are there any wheels that use a constant speed AC
> motor but then change the speed by changing pulley
> diameters or by driving off from a cone?
>
> I am looking at building my own wheel, just because that's
> the way I am (hobby machinist). I would however like to
> know what technology is being used as of now in regards to
> speed control.
>
> Thanks,
>
> Jacob Runyan
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