mud's RC motor reduction unit/MTB bike build

[mud2005]

Hi all, I've finally made some good progress on building a reduction unit for my 3210. Here's a couple pics...View attachment 1
It's not quite finished yet, as you can see. I still need to cut the shaft and grind some flats. The reason I made the pieces so long on the ends it to attach mounting brackets. All the slots and the bearing holes were cut on a milling machine.
I was very happy when the bearings fit perfectly snug in the bored holes and fit flush with the surface. My last unit was made w/o the mill and the bearing holes were a bit sloppy.
I was also very pleased when I slid the shaft through the first bearing and it slid right through the second bearing. Nothing like the precision of a milling machine
Anyway, I just wanted to give a preview and let you guys know I hope to be able to sell a couple of these soon. I thinkin the price will be somewhere between $100-$150 depending on the unit.
First though I need to finish this one up, mount it, and wail on it a bit to see how it holds up

-mud2005

 

[Timma2500]

Hi all, I've finally made some good progress on building a reduction unit for my 3210. Here's a couple pics...View attachment 1
It's not quite finished yet, as you can see. I still need to cut the shaft and grind some flats. The reason I made the pieces so long on the ends it to attach mounting brackets. All the slots and the bearing holes were cut on a milling machine.
I was very happy when the bearings fit perfectly snug in the bored holes and fit flush with the surface. My last unit was made w/o the mill and the bearing holes were a bit sloppy.
I was also very pleased when I slid the shaft through the first bearing and it slid right through the second bearing. Nothing like the precision of a milling machine
Anyway, I just wanted to give a preview and let you guys know I hope to be able to sell a couple of these soon. I thinkin the price will be somewhere between $100-$150 depending on the unit.
First though I need to finish this one up, mount it, and wail on it a bit to see how it holds up

-mud2005

Looking great mud! Keep the pics comin! What reduction ratio are you going to run / kv of the Astro?

Paul

 

[mud2005]

Thanks Paul, the astro is a 10 turn and the reduction is 15t - 50t or 3.33 : 1.
I used 5mm pitch HTD pulleys.
The aluminium pieces are 3/8" thick and bolted together with 1/4" stainless bolts through nylon spacers. I threaded the aluminium so the bolts don't need nuts.
I'm going to mount this on my bike soon and then I'll have some more pics and details

 

[liveforphysics]

The loading between the two plates won't be compressive (which the nylon would take well), but rather sheer as the system is put under load. This means you will be loading the tip of an outside edge on the nylon spacers. For not much more work, you could cut a little chunk to fit onto the edge of the two pieces, drill, tap, counter sink, and fit 4 machine screws into it. This would add a ton of stability to the nylon spaced version, or you could do this to each side, and forget the nylon spacers.

 

[recumpence]

Looks good, Mud.

The primary belt is 9mm wide (3/8 inch). You will get good efficiency with that setup. Your torque will be limited, though. You really need a 15mm wide belt to extract the full potential out of your design. You should, also, go with an aluminum motor pulley. The plastic will skip more easily.

That being said, it looks very good! I have a nearly identical drive sitting on my bench from my R&D 15 months ago.

Like minds..................

Matt

 

[mud2005]

The loading between the two plates won't be compressive (which the nylon would take well), but rather sheer as the system is put under load. This means you will be loading the tip of an outside edge on the nylon spacers. For not much more work, you could cut a little chunk to fit onto the edge of the two pieces, drill, tap, counter sink, and fit 4 machine screws into it. This would add a ton of stability to the nylon spaced version, or you could do this to each side, and forget the nylon spacers.

great advice, I'm going to look into adding a piece on that edge right away. Thanks Luke

Looks good, Mud.

The primary belt is 9mm wide (3/8 inch). You will get good efficiency with that setup. Your torque will be limited, though. You really need a 15mm wide belt to extract the full potential out of your design. You should, also, go with an aluminum motor pulley. The plastic will skip more easily.

That being said, it looks very good! I have a nearly identical drive sitting on my bench from my R&D 15 months ago.

Like minds..................

Matt

more great advice, I used the plastic pulley to save $, but an aluminium would be better. I'm thinking about trying 8mm pitch belt also. Hope you don't mind me trying to sell these once their done. The Shumaker drive is worlds nicer I was just trying to make something a bit more affordable. Not trying to steal your business. You were here first so just let me know if I'm out of line in any way.
Thanks Matt

 

[dontsendbubbamail]

That is a nice design I was thinking of doing a similar design but without the spacers and use a rack mounting similar to my build three. Does anyone see any problems with not spacing the plates apart?

Bubbba

 

[recumpence]

Go right ahead and make drives. That is fine.

The best thing is variety. The problem with only ONE design in the market is eveything is limited to that one setup. Look at Microsoft. :?

Matt

 

[liveforphysics]

That is a nice design I was thinking of doing a similar design but without the spacers and use a rack mounting similar to my build three. Does anyone see any problems with not spacing the plates apart?

Bubbba

If you don't space the plates, shear loading between the bearing holding plates goes up, and the amount of shaft lateral free play goes up.

For example, 2" spaced apart bearings will provide 4x the rigidity of 1" spaced bearings. However, if 1" is enough to not break, than it's fine.

IMO, when it comes to anything involving a belt or chain, there is no such thing as too much rigidity, but too little rigidity is very easy to wind up with.

Inadequate rigidity in the form of shaft-flex, bearing wiggle, bearing mounting plate motion and flex etc etc, it all results in belts slipping and wearing, and a host of other problems that nobody wants to have to deal with in a drive. It's honestly pretty tough to get something solid enough to hold lots of power without needing to result to an excessively large and power robbing belt. Matt played with this enough to kinda find that sweet spot between weight and drag vs reliability and power handling. If you want to make something with similar ability, it's going to require similar rigidity to Matt's drive IMO, or you will need to band-aid fix it with excessive belt width.

Just my $0.02, and for lower powered applications, I'm sure you can get away with anything, so my advise is mainly directed towards someone looking to get the full potential from that big HXT motor.

 

[enoob]

IMO, when it comes to anything involving a belt or chain, there is no such thing as too much rigidity, but too little rigidity is very easy to wind up with.

its amazing what can feel rock solid but still flex under load, specially when already preloaded for belt/chain tension. Ive got a late model snowmobile and there were alot of teething problems with drive belts blowing prematurely untill some folks rigged up helmut cams for a ride and saw the tower holding the secondary pulley flexing and causing misalignment.

overbuild as much as your weight limit will allow.

 

[mud2005]

The problem with only ONE design in the market is eveything is limited to that one setup. Look at Microsoft. :?

great example, been a Linux user since 2003 only use MS when I need to play grand theft auto

there is no such thing as too much rigidity, but too little rigidity is very easy to wind up with.

overbuild as much as your weight limit will allow.

good points, my next version is going to be similar but more sturdy thanks guys

 

[MitchJi]

Hi Mud,

If you don't space the plates, shear loading between the bearing holding plates goes up, and the amount of shaft lateral free play goes up.

For example, 2" spaced apart bearings will provide 4x the rigidity of 1" spaced bearings. However, if 1" is enough to not break, than it's fine.

there is no such thing as too much rigidity, but too little rigidity is very easy to wind up with.

[

]overbuild as much as your weight limit will allow.

good points, my next version is going to be similar but more sturdy thanks guys

Why not use square or rectangular aluminum tubing (as wide as necessary) for the section that requires spaced plates, then bolt on a plate that will hang out the end for the motor which only requires one plate? That should be stronger and only require drilling holes for the shaft as opposed to cutting spacers etc..

If you mount the plate to the tubing with slots for the mounts the entire plate could slide for belt tension so the only changes required for any motor would be the motor mount holes.

 

[mud2005]

actually I was thinking I may get a thicker piece of aluminium and just mill a section thinner for the motor. Then put the shaft through the thick part. Couldn't be stronger than that, but it will be a bit heavier.

 

[mud2005]

I thought about it a bit and came up with a new design which will be stronger.
This is a rough 3d image not at all to scale and no sprockets pictured. It's pretty simple just a solid piece of aluminium attached to a piece of aluminium angle.
The shaft will be supported better and also the angle makes it easier to attach a mounting bracket to the bottom
I'm thinkin #25 chain instead of belt and 1/2" shaft instead of 8mm. That should make a nearly bulletproof drive I hope

 

[Thud]

Mud,
You are starting to sound like Me!
I will design & redesign & tweek & re-tweek untill I have gone full circle & arive at the original design. :lol:
It is an easy trap to fall into,
I am working on accepting the short comings of a particular design & saying "this is what you get ofr XXX amount of $$" anything beyond that will be negotailble.
I am interested to see if you can find structural "Angle aluminum" that is square on the inside as you have drawn. most have some "draft" in them from my experiance. (Unless you plan to bolt together plate?) The main reason for belts on the primary is for noise reduction. Them chains kinda hiss on small sprockets cranking at 9500+ rpm motor speeds.
Sorry to have so much negitive input, you are doing great & as Matt said, we need some more designs out there.
hope I saved you some time.

 

[recumpence]

There are aluminum angles without draft. But, they are not as common.

I agree about the chain. But, that being said, the chain can be less costly (less costly than large aluminum pulleys) and really strong.

It all depends on what you are looking for.

I like the idea of the flat bottom, though. It does make for better mounting options.

Matt

 

[mud2005]

I am interested to see if you can find structural "Angle aluminum" that is square on the inside as you have drawn. most have some "draft" in them from my experiance. (Unless you plan to bolt together plate?) The main reason for belts on the primary is for noise reduction. Them chains kinda hiss on small sprockets cranking at 9500+ rpm motor speeds.

The angle aluminium I get does have a "draft" I just didn't draw it. I plan to file the edge off the solid piece so it clears the draft.

Not sure yet if I'm going to go with chain or belt. At first I'll be running a 3210 10turn at 24V cause that's what I have so the rpm won't be as high. I'd like to try both and compare the noise.

There are aluminum angles without draft. But, they are not as common.

If you have a link to some I'd totally appreciate it. I get angle locally or at onlinemetals.com and they only have the angle w/ draft in 6061

 

[e-motion]

Try these guys:

http://www.mcmaster.com/#aluminum/=4xjn68

 

[mud2005]

thanks e-motion, but mcmaster only has the 6063 aluminum that has 90 degree angles. The 6061 is rounded just like at onlinemetals.

 

[Miles]

Why do you not want to use 6063, mud?

 

[mud2005]

quote from onlinemetals

its strength is significantly less (roughly half the strength of 6061)

plus it only comes in thickness up to 1/4" AFAIK

 

[Miles]

Tensile strength isn't really a factor for this, I would have thought..... the tensile modulus doesn't vary by more than a gnat's whisker. But if you can't get it in the right thickness, that's a problem...

 

[mud2005]

good point Miles, I'm using 3/8" thick 6061 angle and it's probably massive overkill. Oh well, as long as I'm going to overbuild this one I may as well go crazy.

 

[Miles]

Just for the record.......

Comparing the two alloys at T6 temper:

6063 Yield strength 214 MPa;... Tensile modulus 68.9

6061 Yield strength 276 MPa;... Tensile modulus 68.9

I think they may have been comparing the two alloys at different tempers in your quote?

Anyway, as you can see, there's no difference in stiffness showing.

 

[MitchJi]

Hi Mud,

I thought about it a bit and came up with a new design which will be stronger.
This is a rough 3d image not at all to scale and no sprockets pictured. It's pretty simple just a solid piece of aluminium attached to a piece of aluminium angle.
The shaft will be supported better and also the angle makes it easier to attach a mounting bracket to the bottom
I'm thinkin #25 chain instead of belt and 1/2" shaft instead of 8mm. That should make a nearly bulletproof drive I hope

Why not use square tubing instead of solid for the shaft? Probably cheaper, defintely lighter and more than strong enough, especially since it will be bolted or welded to the angle. If you are lucky the corners might be rounded enough to fit into the angle without grinding.

Why not use belts for 8150's and smaller? I think the sprockets and pulleys are pretty much interchangeable.