How do I guestimate MPH at PTO speed rather than engine rated speed?

[LouNY]

how did they put out fertilizer on old tractors without a speedo?

Most fertilizer spreaders are / were ground driven. If we apply fertilizer using the supplied spreader cart form the fertilizer plant the apron chain is gear driven from the wheels and a chart is consulted for the tons per acre. The pro only drives the spinner on those carts.
The older grain drills and planters are also ground driven with various sprockets and chain configurations for the pounds or tons per acre.

I am going to assume that the original poster is planning to apply fertilizer using a 3 point broadcast spinner spreader.
That being all the simple math suggestions are correct to get his speed.
You will find quite the variance in flow rate between different fertilizers in those spreaders, as well as differing flow rated depending on how full the spreader is,
then add in the difficultly in maintaining the proper spacing and overlap to manage the non uniform spread characteristics of that type of spreader.
He will be having fun.
Good Luck

 

[sixdogs]

I'm the OP on this and spread a fair amount of fertilizer in the fall that's at different speeds and changing application rates. I use a "wagtail" 3pt Vicon pendulum spreader. If the ground firms up I need to spread 275 lbs per acre over 8 acres at 4.3 MPH on a 30' center on Monday and will use the math approach to see where things go.

Farmer495--no decal on tractor although I have seen them in the olden days. Might be a requirement in Canada.

All the math was very helpful and thank you.

pmsmechanic--a bicycle speedometer is a brilliant idea I plan to look into.

 

[jmc]

To me, this has been a more interesting thread than most, simply because of the clinical nature of the responses.

 

[sixdogs]

Most fertilizer spreaders are / were ground driven. If we apply fertilizer using the supplied spreader cart form the fertilizer plant the apron chain is gear driven from the wheels and a chart is consulted for the tons per acre. The pro only drives the spinner on those carts.
The older grain drills and planters are also ground driven with various sprockets and chain configurations for the pounds or tons per acre.

I am going to assume that the original poster is planning to apply fertilizer using a 3 point broadcast spinner spreader.
That being all the simple math suggestions are correct to get his speed.
You will find quite the variance in flow rate between different fertilizers in those spreaders, as well as differing flow rated depending on how full the spreader is,
then add in the difficultly in maintaining the proper spacing and overlap to manage the non uniform spread characteristics of that type of spreader.
He will be having fun.
Good Luck

You would be surprised how accurate modern spreaders are. They are pricy but very accurate, allow an even flow regardless of hopper contents and there are charts showing various fertilizer blend drops at various ground speeds. When I do my part, I can put down 275 lb per acre, or whatever rate I want and it's pretty much on the money. I figure in a 5% or sometimes more overage (error) rate for problems like terrain or things that foul my numbers.

 

[sixdogs]

This is not an original idea. Someone on TBN used this to add a pto speed indicator to his pto on the tractor.

Buy a cheap bicycle speedometer and calibrate it to the wheel size on your tractor. I did this because I wanted to be able to return to the same speed after turning around on the end of a garden while rototilling a large garden. I also do other work where being able to return to the same speed is convenient.

The first bicycle speedometer I bought was a wireless one. The signal wouldn't transmit through my fender so I bought a wired one.

Any greater detail or explanation on this? Any pics? What brand name speedo did you buy? Any difficulties or problems you solved?

 

[pmsmechanic]

Any greater detail or explanation on this? Any pics? What brand name speedo did you buy? Any difficulties or problems you solved?

Ok so lets start with the pto setup. The way I remember it he used a hose clamp to attach the magnet onto the pto shaft. He built a bracket to attach the speed sensor where it needed to be so that the magnet would activate it while rotating. He calibrated it so that 54.0 kms/hour indicated was 540 pto rpm. I don't remember all the details of the calibration but it wasn't difficult to do as you have quite a range of calibration numbers in the speedometer to work with. The article was on TBN here so you should be able to find it if you want to.

In my case I read about the above idea and said that since bicycle tires and compact utility tractor tires are roughly the same diameter I should have no trouble using a bicycle speedo on my tractor. I had the wireless unit working when I held it beside the tire but like I said I couldn't get it to read through my fiberglass fender so I bought a hard wired one. I believe part of the problem was that I had the magnet mounted near the center of the inside of the wheel as I wanted to minimize the chance of mud on the tire removing the unit for me.

I'm pretty handy at fabricating so mounting everything was just a matter of spending the time to do it. I haven't mounted the wired one yet as spring came along and I just haven't made the job a priority.

I don't remember which units I bought. I just searched on Amazon until I found what I was looking for. They come loaded with many features but I just wanted numbers that were large enough to see. Semi waterproof was also a requirement. Wireless ones are plentiful. I had to look a bit harder for a wired one. I paid around $10 - $15 CAD.

 

[sixdogs]

OK, I'm the OP on this and need to have my math double checked. In my example, I have an L4300 Kubota that has a rated engine speed of 2600 RPM and a 540 PTO speed of 2473 RPM.

So, if the gear tractor is the same throughout it's range, I could divide 2473 by 2600 to get 95.115. That is, the PTO engine speed is 95.115% of the rated speed.

Now, the book says the tractor is going 4.3 MPH in 5th gear. So, 4.3 MPH times the 95.115% of the engine to PTO RPM ratio equals 4.09 MPH.

This sounds right to me and is easy math. What do you say? All I need to remember is that factor and I'm good to go as applications change? Correct?

 

[pmsmechanic]

I did the math a different way and came up with essentially the same answer.

2600 rpm = 4.3 mph
2473 rpm = x mph

2473 x 4.3 divided by 2600 = 4.08 mph. That's close enough to your answer in my books.

 

[sixdogs]

I did the math a different way and came up with essentially the same answer.

2600 rpm = 4.3 mph
2473 rpm = x mph

2473 x 4.3 divided by 2600 = 4.08 mph. That's close enough to your answer in my books.

The numbers are exactly the same since I rounded up. It's close enough for government work.
Thank you very much for your help.

 

[CobyRupert]

Your math seems ok, but
what is "engine rated speed"?

Seems like a meaningless phrase (or only has meaning in these days of sealed fuel pumps). What ever the meaning, it's a pretty useless term. Just look at the confusion it's causing here. Any ground speed chart should be based on (calibrated at) the engine rpm that matches 540 PTO rpm.