Anyone know of a power drill (mains would be OK) that can be mounted in a 43mm mounting collar and be set up to run at a fixed rate - something like 60 to 120 RPM - rather than one which slows down too much under load?
If not, I guess I'll have to buy a variable-speed drill that is powerful enough not to be overly affected as load is applied. That would be OK as long as it does not have to be hand-held to regulate the speed but I thought you guys might know of one which could be set to turn with a constant rotational speed.
No direct help to you but years ago I built a 'plug in' drill speed controller project (possibly from ETI or some such) that was fantastic at load / power regulation. A built it for a mate so he could use a 9" angle grinder as a car buffing mop and apparently he is still using it, many many years later). The good thing about it in that role was that you set the speed on the box itself so you couldn't accidentally take it overspeed.
You could take a drill down to where it was doing about 60 rpm but if you tried to stop the chuck it would take the skin off yer hand. ;-(
I don't think I've ever come across a mains drill with such good regulation but then I've not bought any expensive ones.
Cheers, T i m
p.s. I started to gather the components to build a model train speed controller where it would (apparently) cut the power if you tried to push the train faster and keep the same speed up and down any gradients. ;-)
Problem can be with that - I've done the same - is the motor fan runs too slow to cool it when it is taking a lot of load. If the load is low, you might get away with it.
Better to use a fundamentally lower speed motor like and induction type, and gearing.
Understood ... and in the case of my mate using a big angle grinder as a polishing mop, I don't think it was under anything like the load it might have been, had it been at full power (even proportionally).
I've heard of those but couldn't think how they could work unless they had a way to measure how fast the drill was turning. They seem to claim to work merely by sensing the power drawn.
I've been looking at that but it would be expensive. A good solution from a local engineering firm using parts off the shelf would be £220+VAT for a fixed-speed 100 RPM solution (including the motor). The variable-speed solution was £320+ VAT.
You would need some kind of servo to do that. I had a drill speed controller I think from a North London kit provider that sounds similar to the one you mention. Probably based on a similar design. However it was not a servo it merely monitored current and had a feedback loop a bit like on cheap cassette decks but in this case had it controlling the switching point for an scr somehow. all a bit of a black art at the time. Brian
You'll certainly be OK varying the speed of a mains drill by a reasonable amount. But most two speed ones will run at about 800 rpm of the low gear, so controlling it electronically down to 100 or so may lead to overheating.
Which is what I found with an ordinary drill in a pillar attachment.
Yes indeed. A theoretically perfect motor with zero resistance windings would run at a constant speed at any load for any given voltage. But because of resistance, current in the windings reduces the effective voltage. A speed controller can monitor the current, and increase the voltage applied to the moter to compensate. The controller acts like the negative value of the motor's resistance.
However the motor will be dissipating more at higher load, and there will be no slowing down to warn the user of possible burn-out!
One option would simply be one with massive torque, so that the amount of slowing is negligible for most likely loads. If you started with a "mixer" drill, and drove it into an external reduction box, then the drill can run fast (say 700 - 800 rpm) and get proper cooling) and there would be masses of torque available to minimise the effects of load.
Other than that, it will be difficult to achieve more without some kind of feedback based speed controller.
It didn't quite fail. The smell made me switch off before termination. ;-)
A cordless drill, of course, runs at a much lower speed, and the type of motor less prone to overheating than a universal mains one. Ones without batteries are worth next to zero. Perhaps building a PS for one of those would be a cost effective route? Modify the speed control to an external pot?
Surprised no-one else has said it yet, but you are not really providing enough information.
When you say "load", do you mean pure torque, or is the load something like that in a cement mixer, varying in the course of a single revolution.
Is the "thing being rotated" in its own bearings, or is it being supported from the chuck. If so, is it horizontal or vertical, what does it weigh, what moment is it applying to the chuck.
How long do you need it to run, are there a lot of starts and stops, is there a significant "start up" load?
If you actually described *what you are trying to do* it would be so much easier to advise.
Sorry, I was trying not to bore people with details, especially as we already discussed it a while ago, but I don't mind explaining. The idea is as follows.
The drill will be mounted vertically and, from below, turn a horizontal
18mm-thick, 9"-diameter wooden disc. It in turn, will push and pull an arm which will push and pull the sled on the soil sifter I mentioned here previously. So the hip bone will be connected to the foot bone. ;-)
Here's the photo of it:
formatting link
Amazing how green the grass is, there. It's dry and mainly the colour of straw at the moment!
Anyway, the table part will have a hole in it. The drill is to be mounted below the table facing up through the hole. The disc and the rest of the mechanism will be above.
Now, to those of your questions which I can answer, the "load" will vary only as earth and stones are placed in the sled and fall through. The chuck will provide the main support though I can add small wheels to help stabilise the disc, as needed. Start up load would be low.
I guess a common-or-garden mains-powered drill will work as long as it is strong enough and can be set to run at the right speed - a relatively low ~100 RPM. That's the key requirement. But drill manufacturers tend only to report their no-load speeds. Hence, me asking if you could recommend a drill that could be left to run at around that speed.
I should say the only place I could think of to look at a range of power drills was B&Q so I just went over to a nearby store. Many of the mains drills had a lock button and a small wheel on the trigger. I presume I could use that approximately to set a fixed speed but I could not find out what speeds were supported.
I /suspect/ any such drill which is strong enough would be fine and could be set and left to run at between 90 and 120 RPM - so I am probably worrying unnecessarily. But it would, of course, be costly and/or a pain to buy one then find out it could not do the job. Hence, guidance appreciated.
As I said to someone, I costed that at a few hundred pounds with the exact number depending on the solution chosen. That's a lot to spend on a solution to just one problem. And it would get limited use.
For about half the money of an induction-motor solution I could buy a very serious drill and reuse it many times and in many different ways.
Thanks, I had not made the connection to the soil sifter.
My concern now, as earlier, is that your home made crank may not be particularly stiff or efficient, so you will end up with losses and may find that while, say, a 750 watt variable speed drill may work with no load, you will find that it won't sift much soil.
I have a fairly typical Ryobi which has, as you describe, a locking button and a speed dial on the trigger. I have a small mortar / plaster mixer and the Ryobi drives that OK at something like 60 to 100 rpm.
The speed dial is continuously variable, it certainly runs down below 60 rpm but the torque drops off rapidly with speed.
But I still think, for your job, I would start with something like the geared motor from a small electric cement mixer, and would have designed and built the reciprocating mechanism first, and then built the sieve on to that.
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