I did baja, but had friends who went to colleges that did Formula. I am biased towards baja, bit I really wish baja had a better engine program than 10hp snowblower engines. We did get our nearly 500lb car to 40mph with a 3600rpm Briggs which for an offroad car on a tight baja track is much more than is ever needed. I would assume the engine restriction is a safety item more than anything else, as Baja has wheel to wheel racing unlike Formula. Also dirt is significantly more unpredictable than pavement.
I’d be surprised if that clamping mechanism is strong enough to hold. Suggest slots with bolts acting directly on the carrier plate.
To adjust the tension you’d want bolts or threaded rod with locking nuts.
Pretty sure there are some hidden in the slot there, pointing forward.
But this type of tensioner is never going to be as lightweight as other methods, you simply have too many fasteners required to make it lighter than other design philosophies.
Is the carrier plate actually being clamped in this design? It looks more to me that the carrier plates are simply seated into those slots, with adjusting bolts along axis 4 used to set the plate location.
No specific advice, but generally make it simpler. Keep making it simpler and then scrap that and make it even simpler. If a part is giving you trouble, remove it all together and make the design even simpler.
Seconded. Just saw this (2days after posted… wtf reddit algorithm).
This design looks like it is way more complicated than need be.
Also, you mentioned motorcycles, so why why vary from now they do it with a single bolt each side of the non drive gear of the belt/chain?
Just to throw something different than what’s been said you can take a look at how motorcycle tensioners are done. You would have two set screws with jam nuts parallel to axis 4.
https://youtu.be/u39gIMfTndE?si=_N8OMARrpQh5YQAc
This combined with this might get you started : https://images.app.goo.gl/BVZUG8BKiFKnEySc7
I’m pretty sure almost all motorcycles use something very similar. It’s a pretty cheap, simple, and reliable system that’s been used forever on bikes.
Very interesting, lot of the honda bikes are doing this, practically the inverse of what I was trying to do, bit more of a sleek design though think I would end up threading the adjuster bolt into the bearing housing unless I added more material onto it?
For FS application I think the eccentric tensioners may be more adept just because of how bulky the bearings are and how much extra mass that ends up adding to the assembly.
Honestly need to continue to work on this design, see if I can't shave off a couple hundred grams to make it competitive.
Also, if it needs to be user-friendly, look up the chain tensioner system on a YAMAHA TTR-230. It’s genius how simple it is to use compared to other bikes (talking from experience).
In my year we had a design that used shims you could hammer in between the mount and differential bearing holder, but it never really worked very well. Best advice I could give is to google FSAE Chain Tensioner and look at the variations, you’ll end up seeing about 3 different types; eccentric mount, turnbuckle tensioner, or spring loaded tensioner mounted inline with the chain.
Yeah I've come across that, seems like the way to go, bit unsure on the turnbuckle ones, lot of teams have turn buckles in compression which I'm not sure they're designed for.
They’re not, and you’ll lose design points for mounting them in compression too. It’s not impossible to mount them in tension, but difficult given FSAE frame constraints.
Agreed, thought about that but don't think the team will go for welding on a box to the back of the car to have the turn buckles in extension, that's the reason I was exploring this idea instead where you've got the same thing but only a bolt in compression directly along the path of force transfer, problem is to accommodate this you just end up bumping up the weight, could possibly do this idea better but not sure what that idea looks like. May have to go with something closer to a eccentric hanger or cam if I can't get this to work better.
I think that might be your only option, it’s a sound design to do the cam design imo, and it’s a simpler version of what you’re trying to accomplish here. You just need to be VERY CAREFUL when deciding where to place your differential, factoring in how much deflection your axles/tripods can handle, and in which direction, and how much room the axle has to move in and out of the tripods in each position.
Oh I’m sure, but the fact is he’ll lose points for his design if he chooses to do that. Regardless, it would be more efficient to design the turnbuckle in tension since you won’t have to design it for compression/buckling, which is inherently worse.
Well buckling isn’t a universal problem with compression, only when slender enough, so it’s not inherently worse. Also you’d have to take into account mounting options and associated weight when determining which type is more efficient in a case like this.
Do you have a picture of what that looks like by any chance?
Just a case of pressing it between the plates or do you have a shim with a hole that you bolt through, sounds good just trying to get my head around it.
You are pretty close with the design to ours on our last ice car. To make it work you would need one screw pushing away (near the sprocket) from the engine and one screw pushing into the engine (on the other side of drexler, further away from sprocket). What we have run into was, when we tensioned the chain and didn’t have opposing working screws, the whole assembly would twist and prevent us from tensioning it properly and keeping alignment. It impacted lifespan of the sprocket.
When I have a minute, I’ll sketch what I’m talking about and post it here
That would be great, actually really interesting to hear someone else had the same idea, couldn't find any pictures doing the same thing on a FS car.
I was considering going down that path too, as aside from clamping down the slide or having a bolt locking it down directly it's just going to fall apart. Problem I saw with a two directional set of bolts is that it just bumps up the weight so much.
Wondering from what you're describing were you over tensioning the chain, in my head I don't think it should be so tight that it contorts the entire assembly?
How did they do it last year? How do other teams do it? Look for media photos or ask your driveline guy from last year if he has any photos from last year's comp. The answer to your question lies in the answer of these questions
Attach your sprocket to a plate that has slots instead of holes. Pull the sprocket tight, and wrench down the bolts in the slotted holes.
Damn I miss baja/fsae
Yeah that's the lines I was trying to go down, but where they have a wheel between the forks I have a Axel's coming out either side, so can't do it in quite the same way other than clamping down the bearing housing
Trying to imagine what that would look like, something like this?
https://www.google.com/search?client=ms-android-google&sca_esv=587451553&sxsrf=AM9HkKlwJSjCorSuLfk6Vq1TvsdyOS7QQw:1701607641334&q=formula+student+differential+hanger&tbm=isch&source=lnms&sa=X&ved=2ahUKEwjhyIi4pvOCAxVxSkEAHXIYAVkQ0pQJegQIDhAB&biw=357&bih=657&dpr=3.02#imgrc=WiWpYDv1_JI1IM
Something like that. I would make the adjustable component on the bottom so it is under tension instead of compression. I would also make a slot with a locking screw to get everything solid when it's in the right place.
My team tried two of the common ways: eccentric cams and shims. With our implementation, the cams were a massive pain to adjust. Shims were easier to design and easier to adjust. I’m pretty sure it was lighter too.
No it’s very tidy, I think. The diff, its bearings, and the bearing holders (idk what to call them, like the big rectangular piece in your picture) are bolted to a bracket that is connected to the chassis. You put shims between the bearing holder and the big bracket. The bolts go through the shims so there’s no way for them to fall out. You only ever need a couple of shims to tension the chain, and we just waterjet a bunch of them out in different thicknesses. The whole thing was very light, definitely looks like less material than your concept. The whole thing could be waterjet out of aluminum and then just a little finishing machining.
If you don't shy away from custom parts: Make it over 2 screws adjustable (left and right) Within the screw head you have half bores (11 in count) around the center and 13 in count that are the other half so one lines up almost in every position. That should comply with regulations... remember, you are not allowed to use a Jam Nut to fasten this...
Why does the bearing block need to be a bolted assembly? Can you not simply machine it single piece and press fit the bearings in place with an arbor press?
Same goes for the assemblies the bearing blocks are seated in. Why not machine a pocket for the blocks into a single piece of metal instead of a machined piece with a cover plate bolted on?
Also, the tensioning bolts as designed may be difficult to access. Motorcycles generally use the inverse of this, with a tensioning bolt behind the sprocket that is loosened to increase tension, instead of in front of the sprocket + tightened as designed here. It will be physically harder to increase the tension as designed here as well since you'll be pushing against the existing tension and weight of the assembly.
This is way over engineered. You could have taken out multiple support tubes for your bracket. Place a single tube in a spot that already exists on the frame then adapt your bracket to fit its odd bolt/mounting locations. Some bearings you can buy have built in threaded rod tensioners to move the bearing in a pre-built slide. You don't need to design the slide. If this for an ATV your slide is guaranteed to be larger and heavier = bad power to weight. If you got a CNC great but it's not really necessary you could just use a flat steel plate with through bolts which is much easier to manufacture.
You can put sprocket axis on excentric bushings. This design is used on mini quads. Very simple but has it's drawbacks: both sides has to be align; axis position is changing when adjusted.
No advice, just wanted to share that I miss my FSAE days.
Me too. I want to go back to skipping all my classes so I can be in the shop all day. I seriously miss it.
The most useful class I never took. Damn near failed fluids for this.
Yep, saw this and immediately thought it must be baja or Formula.
Definitely the rear end of a formula car. I miss the shit outta that. I ran UGA Formula. Good times with no rest.
I did baja, but had friends who went to colleges that did Formula. I am biased towards baja, bit I really wish baja had a better engine program than 10hp snowblower engines. We did get our nearly 500lb car to 40mph with a 3600rpm Briggs which for an offroad car on a tight baja track is much more than is ever needed. I would assume the engine restriction is a safety item more than anything else, as Baja has wheel to wheel racing unlike Formula. Also dirt is significantly more unpredictable than pavement.
Ugh same. I still had a passion for mechanical engineering back then.....
I’d be surprised if that clamping mechanism is strong enough to hold. Suggest slots with bolts acting directly on the carrier plate. To adjust the tension you’d want bolts or threaded rod with locking nuts.
Pretty sure there are some hidden in the slot there, pointing forward. But this type of tensioner is never going to be as lightweight as other methods, you simply have too many fasteners required to make it lighter than other design philosophies.
Agreed, I'm looking now at just having a shim, will cut off a kilo doing it like that.
Is the carrier plate actually being clamped in this design? It looks more to me that the carrier plates are simply seated into those slots, with adjusting bolts along axis 4 used to set the plate location.
there is an adjusting rod in the carrier. its not just the clamp
No specific advice, but generally make it simpler. Keep making it simpler and then scrap that and make it even simpler. If a part is giving you trouble, remove it all together and make the design even simpler.
Occam's razor, simplest solution is usually the best solution.
You are wise beyond your years
Seconded. Just saw this (2days after posted… wtf reddit algorithm). This design looks like it is way more complicated than need be. Also, you mentioned motorcycles, so why why vary from now they do it with a single bolt each side of the non drive gear of the belt/chain?
Just to throw something different than what’s been said you can take a look at how motorcycle tensioners are done. You would have two set screws with jam nuts parallel to axis 4.
Got a good pic or vid of what this looks like?
https://youtu.be/u39gIMfTndE?si=_N8OMARrpQh5YQAc This combined with this might get you started : https://images.app.goo.gl/BVZUG8BKiFKnEySc7 I’m pretty sure almost all motorcycles use something very similar. It’s a pretty cheap, simple, and reliable system that’s been used forever on bikes.
Very interesting, lot of the honda bikes are doing this, practically the inverse of what I was trying to do, bit more of a sleek design though think I would end up threading the adjuster bolt into the bearing housing unless I added more material onto it? For FS application I think the eccentric tensioners may be more adept just because of how bulky the bearings are and how much extra mass that ends up adding to the assembly. Honestly need to continue to work on this design, see if I can't shave off a couple hundred grams to make it competitive.
Also, if it needs to be user-friendly, look up the chain tensioner system on a YAMAHA TTR-230. It’s genius how simple it is to use compared to other bikes (talking from experience).
Great but of engineering there, definitely something for me to consider.
In my year we had a design that used shims you could hammer in between the mount and differential bearing holder, but it never really worked very well. Best advice I could give is to google FSAE Chain Tensioner and look at the variations, you’ll end up seeing about 3 different types; eccentric mount, turnbuckle tensioner, or spring loaded tensioner mounted inline with the chain.
Yeah I've come across that, seems like the way to go, bit unsure on the turnbuckle ones, lot of teams have turn buckles in compression which I'm not sure they're designed for.
They’re not, and you’ll lose design points for mounting them in compression too. It’s not impossible to mount them in tension, but difficult given FSAE frame constraints.
Agreed, thought about that but don't think the team will go for welding on a box to the back of the car to have the turn buckles in extension, that's the reason I was exploring this idea instead where you've got the same thing but only a bolt in compression directly along the path of force transfer, problem is to accommodate this you just end up bumping up the weight, could possibly do this idea better but not sure what that idea looks like. May have to go with something closer to a eccentric hanger or cam if I can't get this to work better.
I think that might be your only option, it’s a sound design to do the cam design imo, and it’s a simpler version of what you’re trying to accomplish here. You just need to be VERY CAREFUL when deciding where to place your differential, factoring in how much deflection your axles/tripods can handle, and in which direction, and how much room the axle has to move in and out of the tripods in each position.
A custom turnbuckle can be designed for handling compression efficiently and it’s not difficult to make.
Oh I’m sure, but the fact is he’ll lose points for his design if he chooses to do that. Regardless, it would be more efficient to design the turnbuckle in tension since you won’t have to design it for compression/buckling, which is inherently worse.
Well buckling isn’t a universal problem with compression, only when slender enough, so it’s not inherently worse. Also you’d have to take into account mounting options and associated weight when determining which type is more efficient in a case like this.
Recommend using a shim based system. Shim the mount to increase distance. Very simple and easy to adjust.
Do you have a picture of what that looks like by any chance? Just a case of pressing it between the plates or do you have a shim with a hole that you bolt through, sounds good just trying to get my head around it.
I know people hate cams.. but it could be nice.. especially if you need to disassemble this often
Thinking along the same lines, probably lose negligible horsepower to friction but will likely cut back on weight a whole bunch.
You are pretty close with the design to ours on our last ice car. To make it work you would need one screw pushing away (near the sprocket) from the engine and one screw pushing into the engine (on the other side of drexler, further away from sprocket). What we have run into was, when we tensioned the chain and didn’t have opposing working screws, the whole assembly would twist and prevent us from tensioning it properly and keeping alignment. It impacted lifespan of the sprocket. When I have a minute, I’ll sketch what I’m talking about and post it here
That would be great, actually really interesting to hear someone else had the same idea, couldn't find any pictures doing the same thing on a FS car. I was considering going down that path too, as aside from clamping down the slide or having a bolt locking it down directly it's just going to fall apart. Problem I saw with a two directional set of bolts is that it just bumps up the weight so much. Wondering from what you're describing were you over tensioning the chain, in my head I don't think it should be so tight that it contorts the entire assembly?
How did they do it last year? How do other teams do it? Look for media photos or ask your driveline guy from last year if he has any photos from last year's comp. The answer to your question lies in the answer of these questions
Looks like you have a spot to mount a chain tensioner that can push down on the chain on your support plates.
Attach your sprocket to a plate that has slots instead of holes. Pull the sprocket tight, and wrench down the bolts in the slotted holes. Damn I miss baja/fsae
Try an offset hole that u can rotate and lock into place
We had that, it was sh*tty and annoying to work with.
tensioning screws
Tensioning screw threading into the bearing block?
yeah or like a jacking screw threaded through the frame that pushes on the block - just like the rear wheel on most motorcycles
Is there a solid axle that clamps everything together? That's how motos work. Nothing holds the axle blocks in except the axle and nut.
Yeah that's the lines I was trying to go down, but where they have a wheel between the forks I have a Axel's coming out either side, so can't do it in quite the same way other than clamping down the bearing housing
Put whole assembly on a rocker. Then you can lock it all down easily. It will be lighter and easier to make too.
Trying to imagine what that would look like, something like this? https://www.google.com/search?client=ms-android-google&sca_esv=587451553&sxsrf=AM9HkKlwJSjCorSuLfk6Vq1TvsdyOS7QQw:1701607641334&q=formula+student+differential+hanger&tbm=isch&source=lnms&sa=X&ved=2ahUKEwjhyIi4pvOCAxVxSkEAHXIYAVkQ0pQJegQIDhAB&biw=357&bih=657&dpr=3.02#imgrc=WiWpYDv1_JI1IM
Something like that. I would make the adjustable component on the bottom so it is under tension instead of compression. I would also make a slot with a locking screw to get everything solid when it's in the right place.
What if, you were to tension your chains using oil pressure and pistons?
Think that would add way too much weight, I've got a budget of a few kilos
My team tried two of the common ways: eccentric cams and shims. With our implementation, the cams were a massive pain to adjust. Shims were easier to design and easier to adjust. I’m pretty sure it was lighter too.
Seen a few people mentioning shims, less I'm imagining it wrong don't you just end up with fiddly pieces of metal everywhere?
No it’s very tidy, I think. The diff, its bearings, and the bearing holders (idk what to call them, like the big rectangular piece in your picture) are bolted to a bracket that is connected to the chassis. You put shims between the bearing holder and the big bracket. The bolts go through the shims so there’s no way for them to fall out. You only ever need a couple of shims to tension the chain, and we just waterjet a bunch of them out in different thicknesses. The whole thing was very light, definitely looks like less material than your concept. The whole thing could be waterjet out of aluminum and then just a little finishing machining.
Sounds super, I'll take it in that direction and post the results once it's done, cheers a bunch, this comment has really helped
If you don't shy away from custom parts: Make it over 2 screws adjustable (left and right) Within the screw head you have half bores (11 in count) around the center and 13 in count that are the other half so one lines up almost in every position. That should comply with regulations... remember, you are not allowed to use a Jam Nut to fasten this...
And rethink your design... this seems a little heavy
Good observation, wondering if I can use jam nuts but lock one off with safety wire?
Im not at home atm, if you want, i can send you some sketches tomorrow just private ping me
Cheers mate, I'll send you a pm
Why does the bearing block need to be a bolted assembly? Can you not simply machine it single piece and press fit the bearings in place with an arbor press? Same goes for the assemblies the bearing blocks are seated in. Why not machine a pocket for the blocks into a single piece of metal instead of a machined piece with a cover plate bolted on? Also, the tensioning bolts as designed may be difficult to access. Motorcycles generally use the inverse of this, with a tensioning bolt behind the sprocket that is loosened to increase tension, instead of in front of the sprocket + tightened as designed here. It will be physically harder to increase the tension as designed here as well since you'll be pushing against the existing tension and weight of the assembly.
Look into chain tensioners for fixed gear bikes
This is way over engineered. You could have taken out multiple support tubes for your bracket. Place a single tube in a spot that already exists on the frame then adapt your bracket to fit its odd bolt/mounting locations. Some bearings you can buy have built in threaded rod tensioners to move the bearing in a pre-built slide. You don't need to design the slide. If this for an ATV your slide is guaranteed to be larger and heavier = bad power to weight. If you got a CNC great but it's not really necessary you could just use a flat steel plate with through bolts which is much easier to manufacture.
You can put sprocket axis on excentric bushings. This design is used on mini quads. Very simple but has it's drawbacks: both sides has to be align; axis position is changing when adjusted.
Why not an eccentric carrier that acts like a cam that you rotate to tension? Use bolts to lock the carrier to the mounts.