View Full Version : Chatter cheap lead screw and servo motor suppilers?
09-13-2011, 03:03 AM
A friend of mine is looking to make some tv lift cabinets and entertainment centers.Through some brief research I see many over priced options.Some use linear actuators and gas shocks which have a poor duty cycle.I'm looking into using a lead screw design for a robust system.If you know any place to get parts or info toward the mechanics of the would be system.That would be excellent.With this project Id love to use one of parallax's MCU's for expandability.Ideally the lift would be capable of a 200lb. Lift. The lift should lift the Tv or box 30 inches.Also looking at ir remote control.
Your thought or comments pls.
Phil Pilgrim (PhiPi)
09-13-2011, 03:21 AM
For one-off projects, the surplus dealers, like H&R (http://www.herbach.com/), offer some outstanding bargains. But, once you go into production, you're pretty much stick with places like Stock Drive Products (http://www.sdp-si.com/) and others of that ilk who sell new components.
09-13-2011, 04:22 AM
Thanks Phil,always a pleasure.
09-13-2011, 05:58 PM
No question for me, I'd use Enco for the screws and nuts
The stock a LOT of stuff and have extremely good prices.
Aside from that, THK (believe it or not) has self contained, low cost actuator they call the CRES Rod actuator. I dunno if you could build an actuator for the cost of these. The CRES 500 develops 490N (110#) force each at 15mm (5/8") per second. Every one I've seen was 12V, but there's an "Option" for voltage..... "Option" probably means more expensive.
EDIT: Actually, the THK units are 130mm (5") max stroke, so I guess that won't be of much good, would it? Oh well. They are still neat.
Aside from that, I've gutted a trailer jack before and had surprisingly good luck with that. Driving the shaft is easy this way :)
09-13-2011, 07:16 PM
I'll check them out too,thanks spiral
09-14-2011, 03:01 AM
Why not try an "electric jack"? Basically a DC motor driving a thread and siscer lift. You'd probably find them in varying quality (depending where they are made) at any good automotive parts store and I'd expect them to be more reasonably priced compared to the other things you've been looking at. These are DC and built for the automative environment able to lift far more than you need. And for how you plan to use them they should be way over engineered (5X) thus have pretty good repeatability and longevity. You may have to rebuild the siscer portion to get a higher lift, but it certainly would be a start on the concept. They should come with switch based control (up and down) which should prevent the need from building a PWM controlled H-bridge, though that could be cool as you could adjust the ramp up and ramp down times to make it more sexy (and you can vary the up/down time to either be linear or accelerated based on what you want). Then implement some limit switches for maximum limits (I'd normally have 2 for each direction and have them over different types (one detecting near limit, the other cutting motor power when exceeding limit) to avoid catastrauphic failure, as well as over current detection (in case of limit or obstruction)). As these are designed for cars, then it will run on +12V but will suck a lot of current. Though you may be able to replace the motor with a lower power geared motor as your lift is lower. Of course as these things are designed to move 1+tonn, then you need to really look at the safety of the solution in the design, human beings are inherently fragile in design compared to electric jacks, and children with their little hands are very likely to have them go where you least expect. Best to avoid damaging anyone by limiting access within the design. Maybe place the electronic item to lift on a wooden or metal block with very narrow clearences in the cabinet to avoid a "standard" finger from fitting within the hole. The really fun part is - if you are driving it with a prop you could have a callibration setting on initial build to determine the current in the lift/lower, then add a few percent to alarm on an obstruction (finger/hand/arm). Of course also add in over temperature sensing too (avoid overheating/fire/etc).
I could imagine you'd have the electronic device sit on a raising plaform within a channel, the lift would never push the platform above the table surface (flush) and thus avoid the potential for someone getting their hands into the lift mechanism without accessing the service panel. Of course the electronic unit being lifted (flat panel TV) would electrical connections (power, signals) and would need those to connections in the base, have to be run in looms etc to ensure they bend and don't rip, snag, have the correct bend raduis for minimum wear of the conductors, etc. and can handle the expected number of raising/lowering. Just in case a cable gets a breakdown in insulation (leading to the potential worst case scenario of power connected to signal or just loose power wires randomly touching things and leading to a life/safety issue, you'd want to have them in separate channels, flexible plastic conduit of some kind. Also you probably want to cleanly drop and apply power to the electronic unit being lifted to prevent it operating while being raised or lowering. Dependent on the design you may also want a wooden flap (same as the table surface) to spring back in place when the unit is down but clear when the unit is rising - though you can do this mechanically, depending on the clearences it could be a very sexy design indeed.
You could certainly control all of this nicely with a prop, and depending on your build skills some of the Parallax products (you may want to look into their H-Bridge to see if it can handle the expected current).
At the end of the day, as long as it's quiet, and does the job reliably the user doesn't need to know you've placed an automotive part in the base of the unit :-)
Sounds like fun - let us know how you go.
09-14-2011, 03:56 AM
well for starters we orderd a couple of these the other day.(havent recieved them yet).They appear to be in limited supply.So we will definatley need an alternative.You couldnt beat the price?Compared to others.The design also looks similar to what Ive envisioned.There are many options Ive put some thought into it its a simple task.Up,Down-Quietly,Repeat. Off any universal remote.Which Im not sure how to do.The use of pulleys and springs depending on what your doing.I looked at a scissor jack the length of the screw was equall to the height basically....... I wanna look some more.Ill be back.
09-14-2011, 03:59 AM
omg.. this is perfect. I think .Any thoughts.
They are not perfect.there is only 25 inches of travel and the lead screw looks like a fine thread.
09-14-2011, 04:04 AM
Alternatively I've also seen fun stuff done in the past with threaded rod (buy it from your local HW store) driven by motors, a cheap way of doing linear positioning. I've seen them in brass and galvo, I'd assume you could also get them in staneless steel for a price. Your travel would then be dependent on the length of rod (and how much bend your vertical weight would apply to the rod - hence diameter of the rod is important). Though the lift strength would be dependent on the thickness of the thread (and all of the weight is effectively only held by a couple of threads within the nut, hence likely to rip/damage the thread under load), and they are likely to wear with friction (molybdenum grease would be essential). It's unlikely they'd be reliable, would likely bend, etc. Potentially if you know someone with a lathe you could custom make a heavier unit from a wider diameter piece of steel, but it would be heavy and harder to turn. Or a tight spiral grove cut to the outside of a wide diameter steel pipe (but the issue would be building the corresponsing nut and driving the rotation (cog) and bearings etc). making it very hard to achieve.
Another alternative is to look at CNC parts, but I don't think they are designed to push what you are trying to lift without damage. And they are more expensive.
Another horizontal positioning system I've seen work very effectively is a looped cord (imagine a bow) with a single turn around a wheel driven by a motor, as the motor turns the wheel it moves down the bow. Potentially you could use this as a vertical solution but with more robust parts, though this would be a challenge best met with chains and a sproket (think of something bigger than a bicycle chain and sproket (or multiple in parallel (share the load on both sides)), the smaller the sproket the lower the torque - but still would be considerable and would definitely need to be a geared motor, and would need some kind of electromagetic locking pin / latch when you get to where you need to go. You'd also need to consider some kind of cluched break (electric clutch which disengages the break when power is applied) in case power is lost during the lift to stop it from just crashing to the bottom (thus destroying the beautiful piece of electronics you were trying to show off in the lift). Parts from an old bicycle may provide the inspiration. You can buy on e-Bay electric bike conversion motors/kits to apply to the standard sprokets. Examples can be found here;
Again all of the safety concerns from the previous post must be applied here as well. They'd still all need limit switches (both near and end of limit cut outs), over temperature and over current. etc.
09-14-2011, 04:08 AM
What about this one?
Again, it's only an example - and it was the first one the came back from a google images search for the keyword "electric jack"
09-14-2011, 01:03 PM
I didn't even know there was such a thing as an electric jack. On a positive note, there's everything you need for $40!