Electric Rototiller Details -- Review, Comments, etc.

Phil Timmons · May 29, 2021

NOTE to MODS: The following images are from a Yanmar Operator's Manual. I think this is considered "Fair Use," as we are discussing the various technical merits of equipment -- and not re-publishing documents. If this a violation of TractorByNet TOS, please delete. This full manual is also directly available from Yanmar, as a download PDF at https://www.yanmar.com/media/en_vn/2016/operationmanual/manual_RH170_RH190_en.pdf
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Looking at some other samples . . . .

Images below show the details of a Yanmar 6 tine (as opposed to 4 Tine, like most of this discussion) per Mounting Plate Rototiller. It is interesting in that it appears to have a larger diameter mounting plate (allowing deeper soil penetration), and a method of aligning the various tine plate mounting with an index "small hole" method.

It is also showing higher RPM on both the PTO and final shaft drive -- maybe making this easier for Electric Motor use.

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Phil Timmons · Jun 2, 2021

My next look-ahead is the Chain Drive. (this is the musing of an Electrical Guy wandering deep into Mechanical -- so please correct me if you see errors or cautions)

I guess I noted that I have some surplus 5 HP 1200 RPM Motor(s) for this.

Nuisance on that RPM (1200) is it is a 6-pole, and somewhat unusual motor. I sort of prefer "common parts, only" or what in industry we call COTS (Commercial Off-the-Shelf).

For a COTS easy match and replace -- 1800 RPM (4 Pole) and 3600 RPM (2 Pole) are the common available choices.

But I want the lowest RPM available, without getting too weird, as that allows me to use the least step down on the Gear or Chain Drive Ratios -- so 1200 RPM it is.

I am swagging that a 5 HP will handle this, as that is not untypical of a small (2 foot) garden tiller, and most PTO (wider) rototillers rate their HP required at around 5 HP per foot.

If this were a Gasoline Engine Rototiller and had a 5 HP Gasoline motor, it only really hits that HP at some high RPM, and a Tractor Mounted PTO is not generally running at its Max HP either.

Meanwhile, these Electric Motors are hell-for-stout, Industrial, full service rated for VFDs. (Variable Frequency Drive -- will go into those details on a future post). Just saying that to justify a maybe too small of motor – but I never tend to have as an issue with Electric Motors.

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So. Going Mechanical. This link and images are public domain from the American Chain Association (yeah, who knew there was such a thing?) for Chain and Sprocket HP and RPM ratings. Here is the link to full design manual >>> https://mpta.org/wp-content/uploads/2016/05/Power-Ratings-122001R1.pdf

The ratio I would like to go down from the Electric Motor (1200 RPM Max) down to the Rototiller Drive Shaft (400 RPM Max) is about 3 rotations to 1. The ideal smallest sprockets are cheapest – which would be 11 teeth on the Motor shaft, and about 33 on the Rototiller shaft. But that will be hard to match shaft diameters, so more likely it will be 15 on the motor, and 45 on the Rototiller shaft.

Next part is “Service Factor.” Table 1. I am calling this at the match of Electric Motor (center column) and Moderate Shock (middle row) which gives us 1.3 Multiplier for a single row chain.

So that is 5 HP x 1.3 = 6.5 HP

I am thinking the Single Row #50 Chain from the charts is what to use, as I go through this.

I could use a double #40, and that may be cheaper, but likely more complex.

And it looks like it needs to be in an oil bath at the bottom of the chain path.

The 50 HP chart below is for telling us the HP rating of various #50 Chain on various sprockets at various RPM – and we will want to stay with rating more than our 6.5 HP Load

So that is showing:

1200 RPM for the Motor Shaft, with possible sprockets (in practice, under load it will "slip" to about 1125 to 1150 RPM)
and
300 RPM for the Rototiller Drive Shaft, with its possible sprockets. (in practice, the VFD will allow both the motor and drive shaft to go slower, but it also reduces the input HP to the system)

Details from the Design Manual:
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