Power Transmission Capability of Mower Variable Speed Drives

Talking about variable speed drives in another context I got to wondering what the power transmission capability of the infinitely variable speed drives fitted to many self propelled mowers is. If the transmission capability and reliable lifetime is adequate such drives might be a relatively inexpensive solution to the problem of replacing a two speed motor. VFD drives are effective but low speed power loss is inevitable so an oversize motor is needed to compensate so things can get expensive.

For example my Hayter Harrier 56 has a neat double variable pully arrangement bolted on underneath giving a seamless speed change from very slow walk to about as fast as I want to go. My guess is that its capable of transmitting at least 1 HP which would make it potentially useful for machine drives. I imagine there are larger ones. Judging by mine belt life in a mower is approaching 1,000 hours. A bit on the short side for workshop use but not completely unreasonable. Probably get an easier life on a tool and last longer.

The Hayter unit is under £40 new so probably looking in the region of £75 for a complete installation after buying the other bits'n bobs needed for a nice job. .

Well it's what Hardinge use to change spindle speed so they must work, Small Boxford mill also has the same arrangement as does my wood lathe.

Is there any other gearing in teh drive train or straight off the engine as that would determine what the slowest speed would be.

Edited By JasonB on 10/07/2016 13:07:15

The only issue is that the speed range is probably not great, say 3 or 4:1, while you probably want at least 10:1 or ideally 15:1 for a lathe, so you will still have to do some pulley/back gear changes.

Neil.

Whee. Neil really believes in picking up the ball and running with it. Using a simple mower drive unit to produce a "proper" wide range machine drive system seems far to ambitious and way beyond anything I was wondering about.

I was thinking in terms of an affordable way to replace a defunct or non VFD or rotary phase converter friendly two-speed three phase motor with a standard single speed three or even single phase one. Anything over 2 to 1 speed range will do as the main speed range changes can be handled by the machines standard equipment. So long as the device works OK in suitable fast or slow positions it will be fine. Any use as a true varidrive being a bonus.

Many of the old machine tool 2 speed motors have non-standard, in modern terms at least, frame sizes, mounting hole positions and shaft lengths. Some even have special drive splines machined on the shaft. So direct motor replacement gets rather fraught. Especially when they were originaly magiced through a too small access door into the base of the main casting. Popping a pair of plummer blocks in for a countershaft where the old motor was and running a two belt drive from an external motor via the varispeed unit could be much simpler.

Industrial standard wide range reeves drives are very effective an long lived. I have three between my machines. But anything of that quality will be expensive and needs to be engineered in. No comparison with simply hanging a £40 gizmo from the mower parts shop off a suitable bracket and running a pair of belts.

Many automatic scooters have similar drive systems which certainly would take the power. But they would need considerable engineering effort to install. Replacing the automatic speed change with a manual system probably isn't as easy as might be hoped and the varidrive components will be integrated with the rest of the scooter so new shafts, bearings and other gubbins would be essential. Maybe the effort in engineering a scooter drive to cover the speed range of the physically huge three speed motors fitted to many full size British 1950's - 60's era machines with a standard single speed motor would be worth it if your motor has died. Allegedly re-winding one of those monsters is a sucks teeth "thousand pound to you guv" sort of job. All too often they are hung on the end of a similarly monster multispeed gearbox. In my book worth a fair bit of engineering effort not to have to put one of those units back in!

Clive

It certainly looks an interesting idea, Clive

... and the price is right.

Must go searching for an exploded diagram, and some dimensions.

Thanks

MichaelG.

Both Raglan lathes and mills had about a (claimed) 6.5 ratio, so say 6:1 with the variable speed pulleys. Selecting back gear on the lathe can be a pain, but then gives another approx 7 1/2 speed reduction. On top of that I have a VFD fitted on mine (lathe has a 415V three phase motor, so no real option) and all that makes speed selection nooo problem at all! Far better than changing belts on pulleys! One of the (several) reasons why Raglans were so much superior (and costly) than a my Ford!

Scooter systems might be troublesome? Don't want the lathe spindle speed to change with load?

My experience with me 30mph limited scooter was to run below 30mph in town I had to shut down the throttle and when out on the open road just held the grip fully round maxed out to 30mph flat out on the level, could get it up to 35 going down a hill but could only hold 24 mph up the same hill.

Now it would seem to me that a problem with scooter vari-drives is that to control and maintain a fixed output speed (mph) you need to control input speed (engine rpm) and even the output speed drops changes with gradient changes so it would seem that to maintain a fixed spindle speed one would have to vary the motor input speed to keep up with the changes of the load applied to the spindle (cutting load).

So by having to control motor speed all the time to keep up with an ever changing load one would need a load sensing speed control to control the drive motor speed - or have I got this badly wrong

MichaelG

Here is the Hayter variator pulley unit :- **LINK** . It can be found rather cheaper on E-Bay.

Lower diagram here :- **LINK** is an exploded view of the mower under-deck components et al showing where it lives in the drive line.

not done it yet, Dod

Provided the automatic drive control gubbins have been removed and the system properly converted to manual control there is no inherent reason why a drive using re-purposed scooter components should suffer speed variation under load.  For constant drive ratio the pulley openings merely need to remain fixed after the control mechanism is set. That said I suspect that a shop made system will be better behaved if you simply change between fixed speed settings rather than try for true varispeed. The control mechanics of the Reeves drives on my Bridgeport 2J2, Smart & Brown 1024 and Startight bandsaw look simple enough but I'll bet there are some resonation gremlins just waiting to pounce at the right speed(s) if you don't get some apparently trivial detail of the engineering right.

Clive.

Edited By Clive Foster on 10/07/2016 21:15:38

Edited By Clive Foster on 10/07/2016 21:15:56

Ah, you propose to emasculate the poor drive thingy.

Michael, my wood lathe has 10 detents on the speed change lever which like you say gives 10 set speeds rather than fully variable although it is possible to leave the lever between detents. Hardinge have similar at a price.

It will still suffer spead change depending on load but no more than a similar setup with 10 different pullies and a motor that can be stalled if you push your luck.

.

All very interesting, Jason ... but you credit me with things I did not say.

Thanks anyway.

MichaelG

I thought that was what you were suggesting?

"if you simply change between fixed speed settings rather than try for true varispeed. "

Clive wrote that ...

You usd to be able to get a DRO with a constant surface speed arrangement such that as the diameter became less the spindle speed increased. Much more useful

What happened when the diameter approached zero? Always flat out?

Certainly good in some instances, but not for all situations, for sure!