My RC Mid Drive with Single Stage Reduction
- Thread starter FZBob
- Start date
I was organizing my VESC motor files and noticed that I never tried different parameters on the orange motor after switching from 3S to 4S. I decided to try increasing the current limit a bit.
I have been running 48 Amp Motor and 40 Amp Battery current limits for the last 8 months. I have seen a max of about 525 watts, and 35 Amps on the wattmeter, and it has run very well.
I tried 55 Motor, 40 Battery, and it ran really well, with a max of 616 watts up the driveway hill. Max Amps recorded on the wattmeter was 40, which is the first time I have actually reached the battery limit. It felt really powerful. However, at very low RPM and full throttle, I could get a bit of cogging.
I tried 53 Amps Motor, 40 Amp battery. This also ran really well, with a max of 575 watts up the driveway. I saw 39 Amps max. I didn't notice the cogging, so I decided to keep these values.
Since the power increased, I decided to try a 10T motor sprocket instead of the 9T. This felt good on the driveway test.
With the higher gearing the crank spun pretty fast on the stand so I decided to set an ERPM limit. I tried 8400 ERPM, but I could spin to the point where the power dropped off. A nice soft decrease when I pedaled like crazy. I went with 9500 ERPM, which worked well. With this motor, max motor RPM = max ERPM/7, and power begins to reduce at 80% of that.
I took it for my usual ride, and maintained a quick pace (it was getting dark). My time was 16% faster than usual, (and used 16% more watt hours), but it felt pretty easy on my legs. I checked the motor periodically, and it never got more than slightly warm. I may have noticed a slight tendency to spin a bit fast, but I'm not sure. The 10T sprocket may have been a bit quieter and smoother than the 9T.
This may mean that for guys that are lighter than me (almost everyone...), there are more gearing options. Possibly an 80T chain ring for more ground clearance with a 9T on the motor. Or possibly a 10T on the motor for smoother and quieter operation.
I have been running 48 Amp Motor and 40 Amp Battery current limits for the last 8 months. I have seen a max of about 525 watts, and 35 Amps on the wattmeter, and it has run very well.
I tried 55 Motor, 40 Battery, and it ran really well, with a max of 616 watts up the driveway hill. Max Amps recorded on the wattmeter was 40, which is the first time I have actually reached the battery limit. It felt really powerful. However, at very low RPM and full throttle, I could get a bit of cogging.
I tried 53 Amps Motor, 40 Amp battery. This also ran really well, with a max of 575 watts up the driveway. I saw 39 Amps max. I didn't notice the cogging, so I decided to keep these values.
Since the power increased, I decided to try a 10T motor sprocket instead of the 9T. This felt good on the driveway test.
With the higher gearing the crank spun pretty fast on the stand so I decided to set an ERPM limit. I tried 8400 ERPM, but I could spin to the point where the power dropped off. A nice soft decrease when I pedaled like crazy. I went with 9500 ERPM, which worked well. With this motor, max motor RPM = max ERPM/7, and power begins to reduce at 80% of that.
I took it for my usual ride, and maintained a quick pace (it was getting dark). My time was 16% faster than usual, (and used 16% more watt hours), but it felt pretty easy on my legs. I checked the motor periodically, and it never got more than slightly warm. I may have noticed a slight tendency to spin a bit fast, but I'm not sure. The 10T sprocket may have been a bit quieter and smoother than the 9T.
This may mean that for guys that are lighter than me (almost everyone...), there are more gearing options. Possibly an 80T chain ring for more ground clearance with a 9T on the motor. Or possibly a 10T on the motor for smoother and quieter operation.
FzBob,
Those are all promising results, it seems you are correct that there might be more room for improvement tweaking ratios and controller settings!
As for my build, I’ve ordered all of the components and some have come in. Currently I’m waiting on motor, vesc and batteries.
My 90t sprocket after some investigation will need to be milled on one face, it’s just to thick to allow the chain to fully engage in the teeth. Oh well, it’s not a big deal, just adds another setup.
As for my motor mount, I had something fairly elaborate that would also house the vesc (using the mount as a heatsink) and batteries but decided to put that on the back burner and go with this simple mount instead.
I’ll be moving forward with a Kepler inspired vesc/arduino/battery all in one bottle solution (at least for testing).
I’m seriously considering cutting an 80t for testing based on your new findings! We’ll see if I find the time.
Those are all promising results, it seems you are correct that there might be more room for improvement tweaking ratios and controller settings!
As for my build, I’ve ordered all of the components and some have come in. Currently I’m waiting on motor, vesc and batteries.
My 90t sprocket after some investigation will need to be milled on one face, it’s just to thick to allow the chain to fully engage in the teeth. Oh well, it’s not a big deal, just adds another setup.
As for my motor mount, I had something fairly elaborate that would also house the vesc (using the mount as a heatsink) and batteries but decided to put that on the back burner and go with this simple mount instead.
I’ll be moving forward with a Kepler inspired vesc/arduino/battery all in one bottle solution (at least for testing).
I’m seriously considering cutting an 80t for testing based on your new findings! We’ll see if I find the time.
I would stay with 90t and go bigger on motor sprocket. The 9t makes noise and is really rough. I am just dreaming of a smooth belt drive.
I seem to have some issues with the chain getting slack and climbing on top of the 90t chainwheel teeths. My chainwheel is not concentric and on heavy loads it seems that something is not stiff enough and the chain slack increases. I am thinking of a chain tensioner but it could be possible that a well made chainwheel will fix the issue.
NateTN would you be able to make a spare chainwheel for me ?
In the meantime i got this switch:
It's rated at 100amps in chinese SI units. I'll try to measure the voltage drop at 20-30amps. It could be even good.
I seem to have some issues with the chain getting slack and climbing on top of the 90t chainwheel teeths. My chainwheel is not concentric and on heavy loads it seems that something is not stiff enough and the chain slack increases. I am thinking of a chain tensioner but it could be possible that a well made chainwheel will fix the issue.
NateTN would you be able to make a spare chainwheel for me ?
In the meantime i got this switch:
It's rated at 100amps in chinese SI units. I'll try to measure the voltage drop at 20-30amps. It could be even good.
How far out of concentric is your chainwheel? I just took a look at mine, and it has less than 1/2 mm run out. I still have tight and loose spots, but have never had any chain skip issues.fixvid said:
When I first did the conversion I bought a Shimano crank arm. The four sprocket mounting holes were drilled about 1 mm out of concentric. I used a round file and elongated the holes in the correct direction. At least in my case, once I centered the sprocket and tightened it, it didn't move, even with elongated holes.
Are you using the 3D printed angle mount? If so, I wonder if the front face is flexing. The tension in the chain can easily exceed 175 Lb and just a small amount of flex will cause a lot of chain slack. If you grab the top and bottom chain runs and squeeze them together hard, you may be able to put enough tension on the chain to track down the flex. If the front face is flexing, could you try a metal doubler on the front of the mount, like 4-5mm aluminum, or 2mm steel? Even some 1" diameter washers might help distribute the load.
That's a really nice looking mount! Water Jet?NateTN said:
How thick is it? I wonder about twisting due to 175 lb of chain tension offset from the mount face. Any chance of a bit of FEA? Might be interesting to get a feel for twist of the mount front face vs chain tension. I wasn't sure, so I just overbuilt using a big chunk of 1/4" aluminum angle.
FZBob said:
I would say like 1-2mm, but .. i was looking at the chainwheel and it is not true anymore. I wonder if it deformed because of the high spot. Yesterday i was pretty problem free, but my power is limited to 20/30amps batt/motor. I will try some wide washers also.
After a few rides i would say that if you treat this system as a pedal asist it will be satisfying enough. For serious stand alone drive it needs improvements:
- the first would be a freewheel crank. Sometimes i stop pedaling but my finger is still pulling the accelerator or im in a low gear and sudenly pull the trigger without my legs realizing that it will be a lot of rpm at the crank. Nasty sensation
- transmission tuning. A belt drive for a smooth and silent operation or a bigger sprocket on motor but then a two stage reduction would be needed.
Beside this the system is working pretty well, i can cruise at 27kmh with low effort and low battery consumption. It just takes some time to get there
. For more power i really have to stiffen up everyhting. Well, it's just not at the same level of performance as shimano E8000 drive, yet.Just to prevent unrealistic expectations, I would not recommend this system for stand alone use. The motor (running at low RPM) does not make a lot of power, and if the power was increased substantially, the drive system might become a weak link. I tried it, and it was underpowered.fixvid said:After a few rides i would say that if you treat this system as a pedal asist it will be satisfying enough. For serious stand alone drive it needs improvements:
- the first would be a freewheel crank. Sometimes i stop pedaling but my finger is still pulling the accelerator or im in a low gear and sudenly pull the trigger without my legs realizing that it will be a lot of rpm at the crank. Nasty sensation
- transmission tuning. A belt drive for a smooth and silent operation or a bigger sprocket on motor but then a two stage reduction would be needed.
Beside this the system is working pretty well, i can cruise at 27kmh with low effort and low battery consumption. It just takes some time to get there
I did run a freewheel crank very briefly last year using parts laying around from my old Cyclone build. If you would like to try that, Sickbikeparts.com sells Freewheel cranks, a Freewheel Spider, and a Heavy Duty front freewheel. In the pics below, I made my own spider. Functionally, it worked fine. It probably added almost a pound as compared to my existing crankset. If you are running a square taper bottom bracket, it would probably add about 1/2lb (the freewheel is 211 gm). Running stand alone, without pedaling, it was underpowered.
My experience with belt drive on this build. https://endless-sphere.com/forums/viewtopic.php?f=28&t=97490&hilit=fzbob
TLDR: For me, the chain has been trouble free with minimal effort. It slaps around a bit, but has never once skipped or come off. I just don't think about it.
I put a lot more effort in the belt, and it was never happy. The constraints of size and reduction required for this build were just too much. The 12 tooth motor pulley was just too small (it was a bit of a long shot). It seemed unforgiving of pulley concentricity, and wanted a lot of tension. I never made it past testing in my driveway. It skipped a lot.
FzBob
This mount was just something I tossed together real quick in cad because the water jet was available, so no analysis, it is 0.125 6061-t6.
I tossed it on to have a look and it seems like all should work well, if it fails I’ll probably just move ahead with my original mount design.
Again, this is only for testing.
All in all, it doesn’t appear to be visually intrusive, with a water bottle battery in front of it I think it will blend in well. Not hidden but when moving hopefully unnoticeable.
This mount was just something I tossed together real quick in cad because the water jet was available, so no analysis, it is 0.125 6061-t6.
I tossed it on to have a look and it seems like all should work well, if it fails I’ll probably just move ahead with my original mount design.
Again, this is only for testing.
All in all, it doesn’t appear to be visually intrusive, with a water bottle battery in front of it I think it will blend in well. Not hidden but when moving hopefully unnoticeable.
This is a great thread! I fought this gearing problem for a long long time and finally purchased a Tangent Ascent Gearbox for my bike and designed a single chain routing system with an on off switch on the chain just like Rocky Mountain did. I was lucky and got an older gearbox that you can remove the Astroflight motor to swap it for a smaller motor.
Changing batteries, voltages and amps is pretty easy with a Cycle Analyst. The key is in the reduction gear. Any way you can do it and not use a huge gear on the crank is better. The huge gears are always an issue for me because they take away ground clearance.
Here is a picture of my gear setup. I wish someone else made small gearboxes that worked with high rpm motors. I think there will be a huge market for this in the future for climbing assistance. When Dave said he was not going to offer smaller motors anymore I started designing one and was going to call it the Climber, Clibr, Klimbr, or Klimber, etc. It would use a 3205 motor with a planetary gear reduction then using a 16 tooth freewheel and a 32 tooth ring gear. All with 1 chain, not 2. Maybe Dave will make us some gearboxes if we ask him nicely?
Changing batteries, voltages and amps is pretty easy with a Cycle Analyst. The key is in the reduction gear. Any way you can do it and not use a huge gear on the crank is better. The huge gears are always an issue for me because they take away ground clearance.
Here is a picture of my gear setup. I wish someone else made small gearboxes that worked with high rpm motors. I think there will be a huge market for this in the future for climbing assistance. When Dave said he was not going to offer smaller motors anymore I started designing one and was going to call it the Climber, Clibr, Klimbr, or Klimber, etc. It would use a 3205 motor with a planetary gear reduction then using a 16 tooth freewheel and a 32 tooth ring gear. All with 1 chain, not 2. Maybe Dave will make us some gearboxes if we ask him nicely?
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Namahs,
I appreciate your input but the Tangent drive is in a completely different realm. The drive everyone is developing in this thread conforms to a design scope of simplicity, minimal assist, low weight and cost effectiveness.
The Tangent Drive can produce 12x the power (maybe even more)!
Also, just the motor and gear box weigh in at almost twice (8lbs vs 4.5lbs) as much as the complete drive (motor, motor mount, chainring, chain, vesc, battery, wiring etc) I'm assembling.
I will say, I also have contemplated a very compact low power motor/gearbox combo, it would just be cost prohibitive in comparison.
I appreciate your input but the Tangent drive is in a completely different realm. The drive everyone is developing in this thread conforms to a design scope of simplicity, minimal assist, low weight and cost effectiveness.
The Tangent Drive can produce 12x the power (maybe even more)!
Also, just the motor and gear box weigh in at almost twice (8lbs vs 4.5lbs) as much as the complete drive (motor, motor mount, chainring, chain, vesc, battery, wiring etc) I'm assembling.
I will say, I also have contemplated a very compact low power motor/gearbox combo, it would just be cost prohibitive in comparison.
Grantmac
10 kW
I think using primary tensioner pressure as a control method has a lot going for it if you can find a way to measure it accurately and have the tensioner respond quickly.
Strain gauges are a fairly simple and economical sensor after all.
Strain gauges are a fairly simple and economical sensor after all.
Thanks for the pics. That looks really good. I'm starting to think about converting my primary bike ('2013 Giant Trance 29er), as it's not getting much use now. I'm looking at everyone's motor mount ideas. I'm reluctant to drill holes in the frame of my good bike like I did on my original project. At this point, I'm leaning toward a plastic pillow block setup, similar to what you and fixvid did.NateTN said:
Back when I did the Cyclone kit, I built a pair of these motor mounts out of aluminum.
Probably over designed. They were very heavy, 150 gm each, and the complete mount was 500 gm. Also, a pain to machine, as my mill is not CNC.
I left about a 1.5mm gap all around and filled it with Silicone sealer to keep it from moving, and maybe absorb a tiny bit of vibration.
NateTN said:
I think its still still the lightest option to use without the huge chainring hanging down under your bottom bracket. I thought I read that was a problem that other people were having. Its not very cost effective though, thats true. The concept is really nice though, if the same style gearbox was put on a 3205 or smaller motor that would be the best!
namahs said:
Well, I did some testing yesterday, I changed the motor pulley from 9t to 10t and the smoothness did improve but performance was reduced.
That was just a change in reduction from 10:1 to 9:1. Under heavy acceleration I could still feel the sprocket teeth in pedal and the performance dropped significantly.
I think the solution would be a small planetary gearbox with a reduction of let's say 3:1. Then we could increase the motor sprocket to 12t or more and drop the crank chainWheel to 80t or less. That would yield to a reduction of around 20:1. This would open up new levels of performance and smoothness.
My makita cordless drill has a small planetary gearbox and I think it has like 90nm of torque. So I cannot see why we couldn't implement such a lightweight solution.
I'm wondering if efficiency is increased with a higher reduction. FZBob what's your take on this ? I think a high reduction uses less amps and more volts and less amps means better efficiency for a brushless motor. Am i right ?
With the 10t sprocket i had to pedal like crazy to get more power from the motor.
stan.distortion
1 kW
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One of the skateboard belt drive reduction kits would probably be a good option for low weight primary reduction, attach the sprocket in place of the skate wheel and most of the work is done (idler bearings + shaft, motor mount with slots for belt tensioning). Alternatively there are plenty of belt drive idler reduction pulleys on ebay complete with bearings that would be fairly easy to use but that would mean mounting a belt drive on the crank. That would add a lot to the cost if such a large timing belt pulley has to be bought in and would still take a fair bit of work to mount but if you have access to a 3d printer it's probably worth considering. Planetary primary reduction would be nice but belt would be the lower weight option.
Fixvid - I was kinda hoping someone would raise the subject of drill planetry's. My new Hitachi battery drill is very compact and light (Hikoki in some markets) and has a whopping 130NM of torque with a speed of 0-500 rpm. The torque is very real, as a fencing contractor I run 65mm (2 1/2") self feeding wood bits, and this drill is the first one I've had that would definitely break your wrist/arm without the large extension handle
stan.distortion
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tentman said:
That's a brushless model? I've a big version of one of the older brushed hitachis and same thing, completely replaced corded drills for anything other than high rpm and that's only because the cordless doesn't have a high gear, plenty of power there. Kind of surprised gutted brushless cordless drills aren't commonly used with conversions, the "body only" version prices are pretty low compared with hub motors etc. even for the top name brands. I think inertia would be a big issue in this case, takes a lot of force to get the motor spinning so would likely need a freewheel so the motor is only assisting and the output shaft would have to have a support bearing for the side loads, all I've stripped have only a bronze or plastic bush in there.
Sounds like there are some really good gearing ideas here. Maybe someone with a 3D printer could print up a housing for a drill motor/planetary...
Before I did the single stage reduction, I looked at drill motor planetaries, RC gearboxes, and anything else I could find. I also laid out multiple designs of plain gearboxes. Gears, bearings, shafts, etc are available from McMaster Carr relatively inexpensively.
First pic - A small piece of my gearbox sketch pad. A bunch of design studies...
Latest layout. Box is sized to allow for swapping several ratios.
If anyone is interested in building something like this, let me know. The design in the last picture is not fully detailed, but it would not take much to clean it up. The box machining is not complex, anyone with a mill & a boring bar could do it. It will probably need a freewheel on the gearbox output.
I never got over the motivational threshold to actually build a gearbox, as it adds weight and complication, and I don't need the extra power.
Also, I got busy with other projects...
In any case, if we want to look at gearboxes or other multi-stage reduction, let's consider starting a different thread...
Before I did the single stage reduction, I looked at drill motor planetaries, RC gearboxes, and anything else I could find. I also laid out multiple designs of plain gearboxes. Gears, bearings, shafts, etc are available from McMaster Carr relatively inexpensively.
First pic - A small piece of my gearbox sketch pad. A bunch of design studies...
Latest layout. Box is sized to allow for swapping several ratios.
If anyone is interested in building something like this, let me know. The design in the last picture is not fully detailed, but it would not take much to clean it up. The box machining is not complex, anyone with a mill & a boring bar could do it. It will probably need a freewheel on the gearbox output.
I never got over the motivational threshold to actually build a gearbox, as it adds weight and complication, and I don't need the extra power.
Also, I got busy with other projects...
In any case, if we want to look at gearboxes or other multi-stage reduction, let's consider starting a different thread...
RC type motors will definitely produce more power with more reduction. They like to rev. The D5035 120KV motor is near the lower edge of it's operational envelope with only 10:1 reduction. If you had 30:1 reduction and 12S, you would make at least 3X the power. (not exactly a direct answer to your question...). With regard to true motor efficiency, (power out/power in) my motor stays cold to the touch, so I think it's operating fairly efficiently. (still not a direct answer...)fixvid said:
Have you tried raising your current limits to around 48 motor and 40 battery? If your motor current is still set to 30, I suspect that might be limiting your power. I didn't run the 10T sprocket until I raised the motor current to 53 Amp.
Do you have an amp meter? I'm curious what current you typically run, and what max current you see.
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