Results 18 to 31 of 31
06-12-2013, 07:40 PM #18
But isn't this a great idea to pass the time with?
To answer some earlier questions - from what I can come up with...
RM1605 ball screw to move 5 inches per second would require a screw rpm of 1524.
Torgue required to move say against a 100lb force, would be 0.37Nm or 3.3lbs*in or 524oz*in - stepper motors around 640oz*in would be Nema 34 in size and cost about $80 or so. One in particular is 1.8 degrees per step, so 200 steps per rotation. To get 5 inches/sec would need 304800 steps per minute or 5080 steps per second. This is eminently achievable. The only thing is whether this will give sufficient resolution on the load cell. If not, then we need to half-step or microstep.
Another thing I envisage is a calibrate menu item maybe under utilities with a pin number. Allows the tensioner to pull at specific points within your usual tension, say from 18 to 30 lbs - pulls at one tension like 18, then allows you to key in what your tension meter says, then do 20 etc. After doing this for the required range - ask if you want to save this and replace the current calibration. Assuming we have an accurate tension meter.
06-12-2013, 07:45 PM #19
My earlier calculations were for direct drive where the stepper motor is directly coupled to the ball screw. If we use a gear or pulley system, we can reduce the torgue requirements of the motor allowing us to use a smaller one.
06-13-2013, 06:50 AM #20
Yes in that this is a great challenge/project and no in that I'd probably prefer to pass the time hitting some shuttles.
Don't let me put you off though, if this is something you are determined to do, you certainly have my support! But if this is intended as a blueprint for others with little electronics knowledge to DIY at home, imho it's probably cheaper and far less hassle to pay someone like Kwun to string it for them!
06-13-2013, 01:51 PM #21
if it is something that end up functioning better than what is available and can be made at a reasonable price, it will be worth it for both the spirit of DIY and sharing.
i guess we are just engineers at heart.
06-13-2013, 01:53 PM #22
how noisy would it be if we were to use stepper motor? one of the thing i don't like about the wise is how noisy it is. putting it next to the ES5Protech makes it sound like a freight train.
06-14-2013, 04:09 AM #23
06-14-2013, 07:24 AM #24
Just spitballing here, but why not use a motor to drive a chain? Or go all out and do a worm-wheel on a toothrack?
If you're going to rebuild a wise, just buy a wise
06-14-2013, 09:06 AM #25
Incidentally, how much travel does the wise have? I.e. if you press the button, how far will it move before it will return to the home position. The Eagnas Plus 8000 has only about 5.5 inches of travel.
06-14-2013, 09:18 PM #26
Im not sure if ball screws = lead screws, but thats what many hobbiests use for linear motion on diy cnc.
06-14-2013, 10:39 PM #27
06-15-2013, 12:29 AM #28
06-15-2013, 06:43 AM #29
Yes, we could use lead screws instead. The friction is generally higher because it is a sliding friction than a rolling friction. Cost wise - yes, it is cheaper, also the lower accuracy is quite acceptable because we don't need to obtain positional accuracy. It has a higher wear rate than ball screws, but then ball screws need to maintain lubrication - although I think in our situation, this is essentially maintenance free.
I think ball screws would still be better since they are designed to move against high loads. In our case, if we want to do tennis stringing, we need to pull against a load of up to 100lbs. It would however be sufficient to use lead screws for the prototype to confirm the proof of concept. The design change to accommodate ball screws if needed should not be too difficult.
06-15-2013, 09:04 AM #30
I have just been doing some off the shelf costings on leadscrews, drive rails, bearings, supports, stepper motor and controller to suit a tension head with about 200mm travel and maximum tension to 20Kg would be around $200-220 including the load cell. Now this is without the electronics, microswitches, display, chassis and framework etc.
This is for a 10mm diameter drive system using a smaller stepper motor that would be suitable to build as a prototype. Makes the Wise quite reasonable, doesn't it. Estimate the steel framework, machining to mount the rails, then the electronics with microcontroller and 4 line backlit lcd display, and keypad would be an extra $200 or so. This is bare bones, without a housing - since I have no experience with housings other than sheet metal or basic folded plastics.
To use ball screws, would add about $150. To go to higher tension, say to 100lbs, would be an additional $100. Oh, I forgot the power supply to drive all of this, would be something like $70 or so.
08-12-2013, 09:21 PM #31
How about the diablo and gripper is below racquet height when untensioned, but then raises itself during tensioning? This allows 360 rotation but then allows the string to be pulled horizontal from the grommet, reducing friction.
The gripper could be lower than the diablo, like some machines - meaning that the diablo is the highest part of the tension head. Occasionally the handle will just touch the gripper when I am rotating the turntable, means I need to raise the turntable another fraction, or lower the gripper.