Rotary Viscometer almost finished

Well, it’s been a long road but I’m almost at the finish line in terms of the majority of development. All of the parts are mostly made and I’ll begin programming very soon, most of which has been done already or figured out in advance.
Firstly, I started with the board. I had to build it from scratch because I’m not certain of they’ll want more features or different ones, also I simply don’t have the funds to get the printed boards made, those will fit in the top of the unit below the LCD and reflection switch.


viscometer test board with lcd display
viscometer test board with lcd display

Viscometer, assembled on base
Viscometer, assembled on base

So, after this I spent the entire weekend building the parts required to make the rest of the unit. I opened up a few of the tolerances and had to make some changes simply to allow for better fitting afterward. The unit would have been impossible to assemble otherwise 🙂

Viscometer with sensor in hand
Viscometer with sensor in hand

I have to say, I’m satisfied with the results thus far. The bearing holding the sensor together could be a bit better though. This week I’m going to have to program the unit and hopefully this long saga will be over. Well, at least when I make the 15 units it will be.

Viscometer Project, coming along…

I thought I would have nothing to post but I do I guess. I’ve felt the need to really expedite this project now that I am starting a business. I have done a few of the mechanical things associated with it after a major redesign. Today I have completed the design of the board and despite it’s sloppiness, I’m happy it’s done. Now to get it made.


Viscometer Board 3D View
Viscometer Board 3D View

Viscometer Board traces
Viscometer Board traces


Like I state in the description, I used the autorouter on this image, I may revise many of the traces so that ripple can be eliminated from IC’s by bringing the caps closer electrically to Gnd and Vcc. This week I hope to finish the machining side of the device, I’ll have to wait for bolts from Fastenal to arrive but it’ll be worth the wait. Here are some shots of the parts so far, note that the main block is made of phenolic, I love this material since it looks kind of like wood but is reasonably machinable.

Machining the block
Machining the block

Phenolic Block Finished
Phenolic Block Finished

Coming along, main block and holders finished
Coming along, main block and holders finished


Just for the record, here is the list of, well electrical features:

  1. 16 key Keypad for data entry, mostly for calibration.
  2. 16×2 LCD display for seeing alarms and viscometer output.
  3. 24V motor, PWM driven with TIP102
  4. Light interrupted sensors for top and bottom
  5. provisions for temperature sensing
  6. RS-485 Out
  7. Provision for an external RS-232 board, if needed
  8. TVS’ed to the hilt, hopefully this will prevent funny stuff from happening.

Anyways, let’s hope she all works out in the end.

Rotational Viscometer design proceeding apace

It’s been a while since I’ve worked at full steam on the viscometer project. Though now a long way from it’s DIY roots I am making this new version from mostly Aluminum, Phenolic, Nylon and Low Density PolyEthylene. I had to scrap the last version since it would have been too difficult to actually assemble, this one is a little different in it’s overall size and assembly.


Of course it isn’t finished yet as it doesn’t have the screen and top switch attached as well as the outer shell. Perhaps I’ll start making it this week sometime.

Viscometer Ver.(Eleventy Billion Jillion) a la rotational

Well, this has a been a long few days of work. I have created the ideal rotary viscometer in both terms of price and repeatability. Now, this idea is nothing new but I’m simply happy that it works. I guess it’d be prudent to go in to how it works…

How it works:

The concept is simple. you have a shaft that is separated by a spring, in this case two plastic cups connected by a ball bearing with rods sticking out one side. This shaft is driven by a small gear motor and a set of paddles is attached to the other end. While this is rotating, the difference in the driven and the resisted side is measured with some form of instrument be it a hall effect sensor or a slot type optical transducer.


Viscometer and stand
Viscometer and stand


What I used:

Well, as far as materials are concerned, for the prototype I used blocks of polyethylene to support both the motor and the shafts. The material has pretty low friction properties at low loads and thus I used it as the bearing on the bottom. The actual difference mechanism is made from a high density plastic. I would probably use this material again as it’s light, rugged and easy to machine. For the real unit, I may still use this plastic as it is more than strong enough and it’s easy to machine.

As for the drive I used a design similar to the older designs with PWM motor output, serial output, keyboard input, LCD out and 2 channels of input. This is all controlled with a PIC18F2620 which is more than enough for it’s needs.

The motor itself is a Hsiang Neng gearmotor running at 12 volts. It’s a piece of shit but that’s not important at this stage of the game.


Motor and sensor
Motor and sensor


So, finally, a desired feature list:

1. RS-485 Out
2. KU and Cp out
3. Multi-fluid calibration, this feature allows the user to select fluids of any KU value and calibrate the unit by entering them in.
4. Easy to use menus. Too often have I seen automation stuff that’s unintuitive. This hould be easy for the operator to understand and easy for the people to use.
5. Speed selection, so that you can use under-powered motors.

Anyways, here’s a gallery of some of the pictures of what could be a DIY stormer viscometer.

Working on the new rotary viscometer

Been working on a new version of the rotary viscometer, after many design changes, the result is this. A rotary viscometer bridged with a rotary reaction strain gage. Guess it’ll work. Here are some pictures.

I’d say a bit more but I’ll wait until the design is a little more fleshed out, and of course, remember that this design isn’t finished since the motor at the back obviously doesn’t float in mid-air.

Rotary Strain Gage update

Well, it’s been a little while since the last update, I suppose I should have stated something sooner. So far, the device seems to work but now I have mechanical problems. Friction on the top is preventing the load from being sensed at the paddles. Plus, the strain gages, I believe, are placed improperly. While it looks as though one side gets compressed and the other side gets stretched, I am thinking that this is not the case.
Unfortunately what that means is that the strain gages are counteracting each other, thus the voltage difference is too small to detect effectively.

Gonna design a new one with only two strain gages.


Viscometer Rotary Strain Gage update

It hasn’t been long since my last update about this thing but I’ve made some progress as far as making the unit into a single board. I simply used the AD7705B as I suspected it work work great for this application. I’ve been playing around with reducing the amount of noise coming from the sensor but random fields are causing the ad7705 to produce strange numbers, even when my hand just gets close to the unit. Here are some pictures of the unit.


Messy ugly board for rotary strain gage
Messy ugly board for rotary strain gage

Rotary Strain Gage being tested
Rotary Strain Gage being tested

Thus far it seems to work though, at least when tested with a multimeter. Sadly though, it seems impossible to test it with the oscilloscope because it uses the same ground as the power supply, damnit!

The Rotary Torque Sensor… continued

Well, so far, so good. That’s all I can say at the moment. The rotary gage is operational, though it hasn’t had brushes made for it and it seems to output a reasonable amount of voltage difference based on displacement.

Here’s what it looks like so far:

The rotary strain sensor
The rotary strain sensor

I’ve put it through its paces thus far and I can see a 10mV difference when I move the sides, that’s good enough. Soon I’ll see if it works with the stuff attached.