INTRODUCING: the "Roto Damper"

Making some progress on mine...
http://www.youtube.com/watch?v=gSsdeluVXz0&feature=share&list=UUZjU7IQffBb-999MYgHAnTg

Well, it is ready for a trial run this weekend. I had to model a new smoker interface to match my current UDS setup. I also want to use a panel mount connector of some sort for the servo and fan, so I can close up the wiring cavity.

Anyway, here it is in all its glory.

I'm a little confused by the bends, does your UDS draw air from the bottom? Most pics I see of drum smokers take the air in from the side... Do you have any pics of your smoker?
...now I see why you wanted a cover on the wiring cavity, I never really expected the roto damper to be run inverted like that.

Well, it isn't likely to stay in this configuration. This is the way I had it set up for the ball damper so gravity was working for me.

When I built the UDS, I ran the pipe up the side so I could adjust the valve without standing on my head. I left it there when I added the fan for the heatermeter so it was off the ground and wouldn't get kicked. I will probably remove the outer elbow so the damper mounts horizontally. I just need to grab some parts to do that.

I built up a roto damper last night with a Tower Pro MG90s servo that I bought "slow boat from China" style from Ebay, previously I had been using the same Tower Pro servo's purchased through Amazon. I had figured/hoped they all would be the same but right away I started noticing some differences...

The first thing I noticed was the Ebay servo fits into the roto damper part a little looser than the Amazon servo. The Amazon servo fits a little tight, the Ebay servo fits a little loose, they both work fine so no biggie there. The second thing I noticed is the horn from the Amazon servo will not fit on the Ebay servo, the shaft on the Ebay servo is bigger. The good news is both horns fit into the roto damper part just fine, so no biggie here either. The final thing I noticed is when I assembled the roto damper the screw didn't pull the two parts together tightly like the servos from Amazon do. This is a problem, cause the parts need to mate closely otherwise you have no valve! I decided the easiest remedy for the situation was to put a shim under the servo, a brief brainstorming session yielded the idea to wrap a rubber band around the part of the servo that mates with the roto damper to act as a shim/spacer. This worked well, the rubber band held onto the servo making installation easy and did provide the offset needed to make the parts mate tightly, so problem resolved pretty simply....

I set out to inspect the two servos and try to find a difference I can see with the naked eye. I noticed on the label of the Amazon servo the brand "Tower Pro" is written in a larger font and the model MG90s is shown in a smaller font, on the servo from Ebay the model MG90s was shown in a larger font than the brand name "Tower Pro". I took a picture of them side by side to show the difference:


You can kinda see in the picture how the shaft on the servo on the right sticks out further, it is also bigger around. I also noticed that the shaft will pull out of the servo on the right a bit if force is applied, you can see the entire gear mechanism inside the servo move when pressure is applied. I am not sure if this is just variance in batches of servo's or perhaps one of the two are bootleg items. Due to the slop in the shaft on the Ebay servo I was first inclined to assume the Amazon servo was genuine and the Ebay servo may be bootleg. However, during calibration of the roto damper with the Ebay servo (which is indeed different than the calibration settings that worked for the Amazon servo) I noticed the Ebay servo seems to move with more power and settle into the proper place with much less chattering than the servo from Amazon. I also noticed the servo from Ebay seemed to have a slightly greater range of motion than the one from Amazon. So I am up in the air as to which one may be "genuine", though after overcoming the physical differences between the two I think the unit from Ebay moves with more authority, and having a larger shaft perhaps it is a more sturdy unit.

In order to compensate for the difference I threw together a fitted shim (also shown in picture) that can be used to compensate for the physical difference between the two. I figured I would document the issue here for anyone who may be working with these servo's and/or building a roto damper in the future.....

From what I've read online, pretty much all budget servos are knock-offs of knock-offs.

The MG90S units I purchased have a purple label and white lettering.

Haha knockoffs of knockoffs is about right. My servo was a little too big for the rotodamper too so I shimmed it with teeny piece of neoprene foam. Mine all have the purple stickers I think and make a little chattering noise every few minutes (which I thought might have been heatermeter sending a poorly-timed pulse but may be the servo itself). I guess we have to design for the smallest servo we find and then larger variants can just shave or shim!

Bryan Mayland said:

Haha knockoffs of knockoffs is about right. My servo was a little too big for the rotodamper too so I shimmed it with teeny piece of neoprene foam. Mine all have the purple stickers I think and make a little chattering noise every few minutes (which I thought might have been heatermeter sending a poorly-timed pulse but may be the servo itself). I guess we have to design for the smallest servo we find and then larger variants can just shave or shim!

Click to expand...

Yah, I had a bit of chattering with the first roto damper(s) I built and figured the same, although this is the servo I left powered on outside since fall. It lived through a solid week of rain, then the freeze, since then it has lived through extended severe cold weather and major snow and is still working. So I can't really complain.
With this new servo (shown on right in picture) I am getting very little to no chattering. I stepped the roto damper from 100-0 in one percent increments and it made every single step accurately without chattering. It moves with more autority and accuracy it seems, although I haven't given it the beat down that I put the first Amazon servo's through yet.

When I designed the Roto Damper I based the design around the standard HM blower. With the blower output size being the limiting factor both the valve opening and the output size are closely matched to the blower output. (when the blower is attached the blower output size is the limiting factor for air flow) I've experimented with larger blowers myself for high heat pizza cooks, but thought it best to tailor my first design to the standard HM blower that most HM builders are using.

This spring I set out to design a second roto damper which is based on higher air flow for natural draft and larger blowers. I printed my first prototype of the High Draft Roto-Damper last night, codename "BatMan":




This damper is designed to maximize the natural air flow for Kamado grills. The valve itself opens much larger and is symmetrical, and the output cap is funneled toward the output which is the 1" conduit connector (like Bryan posted about using on his Roto Damper). The conduit connector will easily attach to a metal plate for mounting to your grill. The unit is designed to have a lower profile so it sticks out less without needing a right angle.

This is just the first draft and is far from complete. It is intended to run wide open (without the restriction of the HM blower) to maximize the natural draft of a Kamado grill. I am tossing around several ideas to attach a blower to the unit that can either be removed after the pit is stoked to temp, or perhaps rotated out of the way instead. I will also be adding the wiring cavity for a CAT5 jack and some probe jacks in future revisions.

This unit will not "replace" the roto damper, they both excel in different areas. The original Roto Damper seals off incredibly well and can open a very tiny bit for low flow low and slow cooking. This High Flow Roto Damper can open wide and is more suitable for natural draft operation and higher flow with larger blowers.

I will post further details as the project develops...

Correct me if I'm wrong, but didn't you have the same size connecting tube on the original RD? If so, unless your valve opening was smaller than a 3/4" to 7/8" diameter circle (which I doubt), then you aren't really accomplishing much with the new design except for removing the fan. In fact, all you've really done is cut the resolution of the valve by 50% by creating the "batman" opening. If you really want to improve convective flow for a bigger smoker, you gotta increase the ID of the connecting pipe and have that CSA propagated through the valve in the shortest distance possible.

No, the output connector is larger on this new damper, almost twice the size, as is the opening inside the valve. The opening in the original roto damper is the same as the output of the HM blower, the opening in the new damper is about twice that size. Furthermore, the new damper has a more direct symmetrical air flow that is funneled into the output to provide a more aerodynamic design. Yes the resolution of the valve is decreased by the symmetrical design, but the smallest opening size will still be small enough to control the pit for low and slow cooking IMHO, tests will be forthcoming on that. The major difference being this valve is designed for unrestricted convection flow while the original roto damper was designed around the HM blower and forced air flow.

As for increasing the ID of the connecting pipe, I can make the output as large as I want (this new valve is larger around than the original Roto Damper, 70mm instead of 60mm), the size of the vent opening on most kamado's is the limiting factor. I checked out a large BGE at Ace and I think this 1" conduit connector may be about as big around as I can go. The 1.25" conduit connector is quite large and MUCH longer than the 1" conduit connector.

As for the overall size, the limiting factor on this is the servo, which forces me to make the body of the valve at least large enough to fit the servo in there....

RalphTrimble said:

No, the output connector is larger on this new damper, almost twice the size, as is the opening inside the valve. The opening in the original roto damper is the same as the output of the HM blower, the opening in the new damper is about twice that size. Furthermore, the new damper has a more direct symmetrical air flow that is funneled into the output to provide a more aerodynamic design. Yes the resolution of the valve is decreased by the symmetrical design, but the smallest opening size will still be small enough to control the pit for low and slow cooking IMHO, tests will be forthcoming on that. The major difference being this valve is designed for unrestricted convection flow while the original roto damper was designed around the HM blower and forced air flow.

As for increasing the ID of the connecting pipe, I can make the output as large as I want (this new valve is larger around than the original Roto Damper, 70mm instead of 60mm), the size of the vent opening on most kamado's is the limiting factor. I checked out a large BGE at Ace and I think this 1" conduit connector may be about as big around as I can go. The 1.25" conduit connector is quite large and MUCH longer than the 1" conduit connector.

As for the overall size, the limiting factor on this is the servo, which forces me to make the body of the valve at least large enough to fit the servo in there....

Click to expand...

I have about the same kind of damper and think your connector will probably work. My damper runs between 10 and 20% to maintain temp. I have a much larger opening to cooker but since damper runs under 20% it is not needed. I have used it about 6 times now and it works perfect. I think you will miss having a fan, my fan only runs to bring my egg up to temp then it is damper controlled from then on. I think you could make a middle section to mount an inline muffin fan as I have. I've posted pictures before of this thing but not the internals, so maybe this will help picture what I'm talking about. A printed version would be much nicer than what I hobbled together!

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Ralph, I was referring to the connector from the grill to the damper. I thought you were using the same diameter connection. Regardless, it doesn't make as difference really how big your valve opening is (as long as it's bigger than the ID of the connecting pipe) because you will ultimately be limited by the ID of the connecting pipe. I have a large BGE and you easily have about 2" or so of clearance. In terms of the trade off of a longer pipe with bigger ID or shorter pipe with smaller ID, you have to calculate the diff in resistance. Given the inverse square dependence on radius vs. linear dependence on length, I would imagine that the bigger ID tube will win unless it's ridiculously long.

Dan, I like the in-line fan. It's similar to a design I've been using for the past couple of months. I went through many iterations and ultimately scrapped the axial fan for a rotated blower because I didn't like the airflow that I got with the axial fan. It's not surprising given they aren't designed for such applications. Here is what I ultimately came up with:

Like I said Tom, the conduit connector I am using on the new damper is about twice the diameter of the one used on the original roto damper, it may look the same but its not. I looked at even larger connectors but they got REALLY large (and long), and the nut was rather large as well so I worried about it fitting into the vent of a Kamado. That said, this new design is similar to the roto damper in that I can just print a different cap for a different grill interface, so if I want to go larger no biggie. The new valve is bigger around than the roto damper but it is actually about half as tall (the printed parts) so it will stick out from the grill much less without a right angle.
I do agree with you on the axial fans, when restricted in a tunnel their output is less than impressive, blowers do blow better...

I set out the other day to design a new damper that would allow more unobstructed natural convection air flow through an opening larger than the HM blower. Initially I decided to modify the roto damper valve by enlarging the opening and making it symmetrical (an opening on both sides), I posted pics of the first draft of that valve the other day. While this was a promising direction to pursue I decided to think outside the box and not let success with the roto damper get in the way of progress. So I took my original design goals and added to it the need for a larger unobstructed opening and a lower profile and came up with something different.

The result of this fresh take on things is my new prototype damper design, the best name I can come up with so far is the "Chopper Damper". I took the basic idea of the roto valve but decided to use it a bit differently.

Here is a picture of the parts for the new valve:


When the holes on the top and bottom parts align the valve is wide open, when the top "chopper" rotates the solid side up the valve is closed.

Here is a picture of the valve assembled and closed:


Here is a picture of the valve assembled and opened:


As you can see, when this valve is open there is a very direct and wide open path for convection air flow to the grill. I integrated the blower into the unit to assist in the initial stoking of the fire, just slide the cover in place and the blower is in control. At this point the air flow will be roughly equal to the original roto damper (with the opening of the blower being the limiting factor), once the pit is stoked to temp just slide off the cover and the damper is now wide open for convection air flow.

Here is a picture of the valve with the cover in place to engage the blower:


The valve seals off fairly well, but the roto damper still reigns supreme as the tightest valve so far, with the single opening on the round surface the roto damper seals off really tight. This new valve seals off pretty well, about as good as the double sided high flow roto valve I made a few days ago, and I am confident it seals off well enough to control the pit.

I need to make a new grill adapter for this valve (since the output is larger than what I am using now) and do some testing before I call this a success. Time will tell if this will be as successful as the roto damper, the way it is designed puts a little more stress on the servo since the position of the blower puts a little weight on the unit the servo has to move. I also have to wait and see if the parts start to warp and loosen up the valve over time before I call this concept a winner. I'm hopeful this design will stand the test of time and be my new go-to high flow damper design...

Working on a heatermeter build now, and really like the idea of a damper. Is it possible to buy any of these? (I don't have access to a 3d printer).

Email inquiries to: rotodamper AT hotmail.com

I did my first test with the Chopper Damper last night, I'm happy to report that the servo seems to be capable of moving the mass of the chopper and blower without a problem. It worked awesome for a high heat cook, had no problems hitting 600 degrees fast, and backing down to 350 degrees and back up again (all without the blower active at all). Temperature response in the upper temp range was nice and swift as was recovery from lid open. I had no problems with overshoot or lowering temps in the higher temperature range.

I started out with a large pile of coals cause I was shooting for high heat, though I initially tried to land on 225 degrees I had some overshoot on the low setpoints. Not sure yet if this was just a function of the size of the fire, or perhaps the large opening has a hard time providing the trickle of air needed for low and slow cooking. I will try a low and slow with an appropriate size fire later this week and see how it works out, if it still struggles I have some ideas that should fix it up so it works as well for low and slow as it does for high heat cooking.

All in all I am pretty happy with how it worked out, seems like another promising adventure into grater dampering...

Just received my Rotodamper. I am very impressed! This was about a 1/4 load of lump in my 18" Kamado Joe. The initial line not being straight was me screwing with the fan trying to attach it. Later on, I realized that the temp wasn't going to drop as quick as I wanted it to, I raised it to 350 and gave it a shot. All in all, good enough for me!

Your graph looks awesome! Seems to be holding steady on your setpoint pretty good... Looks like you were able to drop about 20 degrees from 300 in 10-15 minutes, that's not too bad with a hot ceramic grill. You can use the "choke and burp" method to drop the pit temp about as rapidly as it can go by having the roto damper closed and setting the top vent barely open (or completely closed if your grill leaks a bit), then after a few minutes open the lid to let out the heat and resume normal operation at the lower setpoint. It works for me, but you gotta get to know your grill and how it responds and work from there... but you gotta be careful not to completely choke out the fire..... At any rate, happy smoking!