I have one of these and have been testing the speed of all my PF motors especially M motors I am using for my latest MOC to try and match a pair of steering motors. 

Does anyone know where I can find instructions how to use it as I am getting all sorts of weird RPM readings way above Lego stated RPM.

25 minutes ago, Doug72 said:

testing the speed of all my PF motors especially M motors I am using for my latest MOC to try and match a pair of steering motors.

Did you try that trick with the differential between two motors? You can use it to find out which motor is faster/slower than the other. Or if they are the same speed.
About instructions...I know there is some videos with them on YT. Maybe someone who has the Speed Comp will be able to tell you more details.

Most probably, You have to set somewhere some coeficient (gear ratio)

3 hours ago, Doug72 said:

all sorts of weird RPM readings way above Lego stated RPM

What readings are you getting for which motors? Are they at least consistent when you test the same motor a second time?

I've got a speed computer right here an could do some tests to verify your measurements if you want to

[Edit:] Do you have a way to measure the operating voltage? What power source are you using?

Edited January 5, 20187 yr by schraubedrin

4 hours ago, Doug72 said:

I am getting all sorts of weird RPM readings way above Lego stated RPM.

Have you tried comparing them to @Philo's motor chart?

I have a brand new set sealed in box, but right now I am in another city. Hopefully, I will make a review and scan instructions if there is any:)

5 hours ago, Doug72 said:

...

Does anyone know where I can find instructions how to use it as I am getting all sorts of weird RPM readings way above Lego stated RPM.

The instructions for the speed computer set 5206 and how to use the settings can be found here:

http://letsbuilditagain.com/instructions/5206/

The weird PRM readings result from the inaccuracy in the system itself. It´s not reliable at all and that´s why I have sold mine again.

Just now, Limga said:

I have a brand new set sealed in box, but right now I am in another city. Hopefully, I will make a review and scan instructions if there is any:)

Thanks, I look forward to reading your review. Mine is a hand me down from grandson who got a Technic which contained it, can,t recall set number, but it had Control centre in it, which I also have.

Took me long enough to figure how to open the battery compartment to replace the battery !

Doug.!

Just now, brunojj1 said:

inaccuracy in the system itself. It´s not reliable at all

I actually found it to be quite reliable under the right circumstances.

The refresh rate is quite slow, so the maximum reading should be dismissed.
As it measures in 200 rpm steps, it's useful to gear it up for measuring slow speeds.

Measuring continually, constant turning PF Motors is exactly the right use-case. Although I'd advise to gear it up 1:3 for an XL-motor

Yea... I agree with others....... it really matters how much the motors differ in speed.  If it is less than 10%, I would say that it may just be inherent differences between the motors, which we all know exists.  I made a post about this last summer addressing this. 

 

Differences of less than 10% should not be huge problems as the resistance the slower motor receives (when hard-coupled) really is no different than the resistance of just working against friction when placed in a model in the first place. 

 

21 hours ago, brunojj1 said:

The instructions for the speed computer set 5206 and how to use the settings can be found here:

http://letsbuilditagain.com/instructions/5206/

The weird PRM readings result from the inaccuracy in the system itself. It´s not reliable at all and that´s why I have sold mine again.

Sorry missed your post. Thanks for the instructions. Will study & test again.

Doug

On 05/01/2018 at 10:12 AM, Milan said:

Did you try that trick with the differential between two motors? You can use it to find out which motor is faster/slower than the other. Or if they are the same speed.
About instructions...I know there is some videos with them on YT. Maybe someone who has the Speed Comp will be able to tell you more details.

Thanks for the tip, now tried and easy to find out which motor is slower.

4 hours ago, Doug72 said:

Thanks for the tip, now tried and easy to find out which motor is slower.

I don't have speed computer, so i used this differential method once, when i had to use two M motors coupled together. It worked great.

Probably not worth opening a new topic for another question about the speed computer. My version was pretty accurate so far but now it started to show much higher RPM values than it should be. The cable is getting old and the cover peeling, I was trying to take the unit apart to see if I can replace the cable but I got stuck. All I can remove is the battery cover, no visible screws or anything found. Did anyone manage to take this apart or anyone encountered the issue with the false RPM values?

@kbalage I have 3 of these, all show some decay on the wires, i do not think they where ever made with the better type of insulation, so i guess that is normal, mine aren't that bad, just some minor cracks, but handling them can make it worse fast.

One of those started to show the same issue as yours and i had the same idea, fix the sensor and replace the wire, but i started with opening the sensor end, since that is the part i suspected to be faulty, inside that are very flimsy contact rods which are pushed together by a camshaft which i managed to line up correctly again (a contact had to be very slightly bent inwards). These thin contacts can also be pushed together by a shock or by vibrations, that is why it is so unreliable. But the very thin strips of metal had the wires directly soldered onto them and then wedged snugly in the plastic,that is not very easy to solder (i am a welder but i can solder.. but this small makes me reconsider) especially when i saw the computer end, which seemingly needs to be pried open indeed, my best guess is, 2 flat sharp objects inserted at the diagonal line where the grey meets the yellow, but since i got it working and was already hesitant to replace the wire, i never tried to open one..

maybe try to open the sensor,(push in 4 tabs, inside the studs on top, and on the bottom) take out the contacts, put shrink wrap for electrical wire over the entire length of the cable,it might help.. 

 

 

Edited June 9, 20186 yr by Marxpek

@Marxpek thank you very much for your instructions, apparently I had exactly the same issue as yourself. Managed to take apart the sensor part, bent the contact rod a little bit and now it works like a charm :)

@kbalage im glad you got it working again. The contact points just bend over time and use is my conclusion here. 

If you decide to ever try to open the computer side, could you take pictures please? I would be interested (to replace the wires).

I will do the same when i get a malfuntion in one of them of course.

@Marxpek I'm glad that it's working now, don't want to break it  If something goes wrong again and I have to open the computer part I'll take pictures of course 

I had the same issue with the wires, so I had to replace it. It was not an easy fix, as I had to break it to open the computer bart, as it is glued or welded. Also you need to make sure you buy a similar diameter wire. I managed to glue it back, and it is working now as it should.