Electric Pre-Rotator

wolfy

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Ah yep I was about to watch that tonight.
On your rotor head why do you have 3 gears between the pre rotator shaft and the Bendix? You have the same direction rotation and what appears to be the same speed output as the input, maybe hard to tell from the pictures though.

wolfy
 

JETLAG03

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@DarDow101 post 161 do you have any further data on the pre-rotator, motor and gearing? On the video they suggest reaching 300rrpm(y)
 

Jazzenjohn

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You may want to reconsider your reduction ratio.
 

Jazzenjohn

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From your vantage point what do you estimate the ratio is and what would you estimate the ratio should be?
Your current reduction is 12-1 like Jeff says. 108/9=12. Pretty much the same as every Wunderlich ring gear/ Bendix system out there. As far as your system, It appears to me you are using an Ampflow motor A28-400 and you've said previously you are using it at 36 volts. There are a few variations of the motor, so I'm assuming you are using the most common. At 36 volts I'd experiment with ratios between 2.5-1 and 3.5-1 . The 3.5-1 might limit max RRPM in favor of a faster spin-up time and lower demand on the motor and batteries. 2.5-1 might get a bit higher max RRPM with the trade-off of higher current demand, especially when starting up and running it at full blast. Running it as is will put a huge demand on your batteries and wiring. Be careful when you start experimenting as you have a very powerful system. The RPM's you are seeing now will not be possible with blades on.
Are you using a servo tester for control?
 

Jazzenjohn

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The easiest way to add some reduction would be with a chain and sprocket between the motor and the shaft going to the head. Chain and sprockets are very inexpensive and allow for fast and easy sprocket changes to try out different ratios. You can get the sprockets at Surplus Center for a couple dollars already bored out with the appropriate key. #35 chain is what most people use. It is no problem using a chain in this situation because it doesn't run in flight. Make a plate that bolts to the end of the motor and has a bearing for the driven sprocket. You'll just have to work out how to attach the driven sprocket to the shaft. You can see how Mike is doing it in this pic. He used a piece of angle instead of a flat plate bolted to the motor to mount his speed control.
 

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Resasi

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It would seem that Wing Commander Wallis incorporated a Sturmey Archer 3 speed gearing in his pre rotation set up, but very little is published about this.

This was in post No 8 by Dinoa on this thread.

In the PDF diagram I suspect the gearing in question may be No 35 which is described as a 'commercial epicyclic gearbox'.

Wallis prerotator.png

wallis-gyro4-flight-mag-pdf.1036898

And how it works,

 
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Jazzenjohn

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@ Leigh, I've heard Wing Commander Wallis used a 3 speed hub for a reduction on some of his gyros. I don't see it as useful in this case as it would weigh and cost more, and be more difficult to set up, but I can see it being very useful in a different application.

@ Dar, Mike is Mike Vadney, he doesn't get on the forum much. I'll ask him for additional pics if you want. Adding a chain and sprocket shouldn't cost very much at all. Be very cautious testing, it will cost less to add that than to replace batteries or other electrical components...
 

Resasi

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@ Leigh, I've heard Wing Commander Wallis used a 3 speed hub for a reduction on some of his gyros. I don't see it as useful in this case as it would weigh and cost more, and be more difficult to set up, but I can see it being very useful in a different application.
I must admit I wasn’t sure how it was utilised John, and he seems to have been the only person I knew of who had used it.
 

mvadney

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Two more pics from the newer gyro. This one has all of the components up in the head. 37Volts and some where around 150-170 rpm. The batteries are easily removed from their box down below against the fuel cell.
 

wolfy

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Thanks John,
So far the electrical side of testing has gone well. No overload issues with run time under load, no major heat issues and the battery pack seems up to the job. I monitor the heat issues with 2 temp sensors (batteries and fuse blocks) also a hand held temp gun and they are way under temp from maximum safe temps so far. My goal is to get to 220+Rrpm and should that happen than I will have met that goal. The battery pack is from a Kobalt 40V ( actual 42V ) outdoor yard equipment (Chainsaw,mower,etc) and I have to commend it's performance. Recharge time is under 1/2 hr. for a full charge. I plan to add a on board charge circuit so it will charge via a switch when needed.
Dar, you may have said before but if not do you know amp hour rating of your battery?

wolfy
 

AirCommandPilot

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At one point it showed 201 Rrpm on the digital tach used to monitor the rpm and then shut it off once it reached a predetermined rpm.
I will video my next runs with the tach shown for reference.
I'd have to agree with Wolfy, looks to be less than 100 rpm. You might want to verify the settings on the rotor tach. If you get creative, you can take the video and do some math with the frame rate.
 

Resasi

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I appreciate at this stage you are testing from a standing start, it will probably be very much more efficient/quicker up to max rrpm if given a good boost by hand on the intial start up.

But I imagine that is how it would be utilised?

The electric prerotator that Nickolas sold me for the Hornet certainly needed initial movement before engagement.

IMG_0862.jpeg
 

Brian Jackson

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I did a quick "tempo" match of the 2'nd video using the Tap Tempo feature of my digital audio workstation at each blade pass. I got 182 bpm. Dividing this by 2 = 91 RRPM at its fastest point midway in video. Is your tach measuring double the actual RPM?
 

Brian Jackson

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No not that I know of. I have tested the tach against a hand held unit and they pretty much sync up. It is likely it was very momentary at 200 Rrpm and I have another opportunity to show it again tomorrow @ 200 Rrpm since I am convinced I will achieve that rpm and more. I do appreciate everyone's considerations as to the rpm's. :D(y)
Anxious to see this succeed. As for the RRPM, I can only measure what I can see in the video. For quick reference, 180 RRPM would be indicated by 6 blade tip passes per second. Currently I'm counting around 3 or so, which is why I asked. Still impressive and I will be following your development with interest.
 

Jean Claude

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About 150 rpm according my chrono
 

Jazzenjohn

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What controller did he use? do u know the specs of his system. I tested my system again today and I am going to increase the amp hours of the battery from 40v 2.5ah to 40v 5ah. I am temped to try the 80v 2.5ah Kobalt's. what do you think?
Mike has used the Vyper ESC and is currently using one similar to what you have now. I don't believe the ESC is your limitation Dar. I believe the current capacity of your batteries is the main problem. You could switch from 2.5ah to 5ah, or hook up another 40v 2.5ah in parallel with the batteries you have now which would double the current available. Adding the first stage of reduction will be helpful too. I can't see the wiring to know if there is a problem with that. You might need to bump up the 50 amp fuse to a 100 amp slow blow if you do the battery upgrade. You might even need to remove it if it's tripping often. I think going to 80 volts would cause more problems than it would solve.
 

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DD, would you mind putting the dogs in the backyard during testing ? Hate to see one of them injured.
Brian
 

Jazzenjohn

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If you are certain you want to go with the cylindrical cells, the weak link is the current capacity of the pack/cells which is basically solved by stacking pack/cells in parallel like the Tesla car does. There is another weak link in the chain, the internal pack wiring itself. Those aren't meant to do the massive current your system demands and the internal wiring and connectors could be the next problem waiting to come up. I have no experience with using cylindrical cells in something like this. I'm certain it can be made to work, but the cost and time necessary to get it to work may be more than you want to handle. If you are going to buy new packs, I think you'll have better luck by switching to a high current R/C battery pack made for high demands. I've used both LiPo and LiFe packs with success. I usually use those with the high current XT-90 connectors although other types can be used. You'll need to get a charger for them. I'd look for a pack of about 5 ah with a 50c rating, XT-90 connectors, and I'd carefully check the ESC documentation to see the maximum voltage it can take. The nominal voltage of the pack is just that, they can often get peak charged and have a higher voltage which can damage the ESC. The batteries will run about $150+. You'll need to get a decent charger for them for another $80 or so. I'd also put the reduction in for another $30. The "c" rating is how much current the pack can deliver. They may give a very short term number like 10 seconds and a lower number for a more sustained output. Basically multiply the "c" number by the packs ah rating 5ah*50c=250 amps peak the pack can deliver.
 
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