# Roll control with a reaction wheel

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#### alexzogh

##### Well-Known Member
I've been working on a set of rollerons for roll control over the last month with limited success. Yesterday, while catching up on the latest bps.space video's, he mentioned and showed using a reaction wheel. Starts the discussion at 5:05

Has anyone else tried this? I briefly toyed with the idea of a control moment gyroscope, but this seems much cleaner.

#### QBrandt

##### Member
Roll control was the objective of the Midwest High Power Rocketry Competition a few years ago.
Two launches were required. On the first, the objective was to minimize the rocket's roll between burnout and deployment. On the second, the objective was to direct a fixed camera to cardinal directions by rolling the rocket.

A lot of teams (including mine) used reaction wheels. Most of the rest used control surfaces. One used a cold gas expansion system that I don't remember much about. (Rollerons were not allowed because they are not an active system.)
There weren't any complete successes, probably because tuning something like this requires a lot of flights beyond the timeline and budget of college teams.

If you want to make a system like these, it might be worth reaching out to Gary Stroick (President/Owner of OffWeGo Rocketry, one of the runners of the competition), he probably has all of the teams' reports.
The basic approach we took was to design a rocket with a ballpark payload mass for the motor/wheel/battery/etc., then determine the roll moment of inertia. From that, an assumed initial roll (1.5 Hz IIRC) and a chosen roll acceleration (be able to turn 90 degrees in 1 second, IIRC) we sized an electric motor and reaction wheel. Then a lot of iteration (Change in mass changes MoI of rocket, changes required MoI of wheel, etc.). After it was built, there was a fair amount of PID tuning and ground testing.

#### alexzogh

##### Well-Known Member
Thanks for the note. I've started the hunt for information, although I suspect it might just be easier to build one from scratch.

#### Bob Touch

##### Active Member
TRF Supporter
Hello everyone. I have recently joined this forum and enjoyed copying the mail. My hobbies started with rockets about forty years ago then on to RC planes and helicopters. Miss the fun I had with rockets and started building again and joined a local rocket club. My question and I don't know if its been tried or may be a legal issue but why can't I put a RC rudder control on rockets?

#### dhbarr

##### Amateur Professional
Hello everyone. I have recently joined this forum and enjoyed copying the mail. My hobbies started with rockets about forty years ago then on to RC planes and helicopters. Miss the fun I had with rockets and started building again and joined a local rocket club. My question and I don't know if its been tried or may be a legal issue but why can't I put a RC rudder control on rockets?
Welcome! You totally can, check out
https://www.rocketryforum.com/forums/rocket-boosted-gliders.44/

#### Bob Touch

##### Active Member
TRF Supporter
Wow, way cool. I did not realize how well the two co-mingle. Now I'm picturing working hidden cargo bay with a micro glider, A space shuttle replica.

#### Culprit

##### Well-Known Member
TRF Supporter
Here's a YouTube video I stumbled across a few weeks ago. The video is 24 minutes and slow to get started for guys who already know the underlying physics at play, but by the end of the video he walks you through building his own reaction control wheels and flying a drone with them.

Also, BPS Space has the next two Sprint videos out with reaction control wheels. Good stuff!

#### Bob Touch

##### Active Member
TRF Supporter
Being a RC helicopter pilot for years. I relied on a small electronic gyro for stable flight. I would like to know if anybody tried to implement that with control surfaces for stable or predictable flight. I think not being designed for that amount of G's may be a problem and should I scrap the idea.

#### JimJarvis50

##### Well-Known Member
Being a RC helicopter pilot for years. I relied on a small electronic gyro for stable flight. I would like to know if anybody tried to implement that with control surfaces for stable or predictable flight. I think not being designed for that amount of G's may be a problem and should I scrap the idea.
I've done quite a few flights using a vertical stabilization module. It uses gyros and canard control surfaces to acheive vertical flight. There are perhaps a dozen videos (search youtube for "Jiminaus50") and there is a thread here:

Jim

##### Well-Known Member
i wonder if you could rotate a balanced ebay somehow. You're already carrying that mass so you get the effect without adding a wheel.

#### Culprit

##### Well-Known Member
TRF Supporter
i wonder if you could rotate a balanced ebay somehow. You're already carrying that mass so you get the effect without adding a wheel.
You would need slip rings out to the ejection charges, and altimeters that are barometric only. An altimeter with a MEMS gyro(s) or accelerometer(s) probably wouldn't respond well. Interesting idea. On a design that needs significant nose weight, you could use that mass.

#### alexzogh

##### Well-Known Member
Ok,

Finished designing version .5. I went the easy route, a gravity 6 DOF arduino shield for with downloadable libraries and integrated motor drivers all for $19 bucks. - https://www.dfrobot.com/product-788.html what a crazy time to be alive...$19 bucks!

I decided not to print the reaction wheel, and went with an old tedco gyroscope toy I found in the basement. They can be purchased new fairly cheap https://www.amazon.com/Original-TEDCO-Gyroscope-Nostalgic-Pak/dp/B00000IU7S

I'm a little worried the PID loop seems to over compensate when I turn it by hand, I'll dust off my Kalman filter algorithm optimization skills a bit.

I'll post it up in the 3d section when I get to version 1.

#### jderimig

If you are only using 1 reaction wheel to control the roll axis, be aware that the gyroscopic effect reaction to a moment applied to the other 2 axes if your reaction wheel is "spun up". A lateral force will result in a moment perpendicular to that force in the other axis. The result is could be a serious precession motion of the rocket.

My dynamics is a little rusty but if you have one reaction wheel you may need active correction on the other 2 axes also...

#### alexzogh

##### Well-Known Member
John, you are correct - the vector properties of the gyroscopic effect will effect yaw as well as roll, but it won't be much as the wheel will be up to speed well before liftoff. When I was researching multi axis attitude control when you are dampening or compensating for a misalignment of a fin, there 0 probability the misalignment is only in one axis, thus a larger issue is the axis will be inertia coupled. If I compensate for roll, it will reorient the misalignment in pitch and yaw as well, which will then effect roll again. I'm going with the assumption that I will be putting the fins on as straight as I can, and I am relying on the the aerodynamic forces on the fins for yaw and pitch to be an order of magnitude stronger then the biasing the momentum wheel may produce.

Found a good book on the subject which I was able to ”rent” long enough to type up the Matlab model - https://play.google.com/store/books...&rdid=book-2IFj1UBaEqsC&rdot=1&source=gbs_atb

Then again, this is all theory I could have wrong. That's the fun of this hobby!

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