Dave's 80:1 RC mid drive kit build log

[www.recumbents.com]

A Davinci drive unit isn't quiet either, no high RPM system will be. If you want quiet get a direct drive hub motor. When I'm passing people or cops I just let off the throttle and pedal. I like how the Tangent drive sounds.

Warren.

 

[tangentdave]

my hard earned money

still in early development

Completely agree, I do the same thing. I know the kit's not cheap, I know the chance you're taking, doing my best to make sure it exceeds expectations. Time will show.

If this kit was even 400 miles away from me somewhere in the U.K i would be banging at Dave's front door demanding a test drive

Thanks. This forum is entirely too nice and mature for the internet. I'll get the new design out the door and into the hands of riders ASAP.

-dave

 

[LiFeCycle]

Hi Dave

Wow! This is the mid drive I have been waiting for! Thanks for your efforts to design a no-compromise system.

I am 100% in the market for one of these. My only question is the chainring. I currently run a BBS02 with a 48 tooth chainring, and I do max out 48/11 from time to time, so I would want at least a 48, probably a 52 tooth chainring for this system. Are you able to supply a 52 tooth as part of your ready-to-go kit?

The recent developments with switching the chainring to the outside and the vibration damping are super exciting as well. If I ordered a unit now, would it include these changes? Or is there old stock you need to clear out first?

Thanks, feel free to PM me re the purchase. Really looking forward to testing this beast out.

 

[tangentdave]

The spider is what determines the chainring bolt pattern and we can use either 4x104 or 5x110. I'm making the spiders in-house now too so no more waterjet crap. I haven't been supplying the bike sprocket, only the 32t stainless motor chainring. The 4x104 was chosen to be standard because of the narrow-wide MTB sprockets. If you want/need the 5x110 road sprockets, I can accommodate with the spider and 5x110 stainless chainring.

All units will include all the changes I mentioned. The previous customer units will slowly be replaced to bring everybody to the same.

 

[LiFeCycle]

Thanks for the info. That sounds great, I'd love to get a complete kit with the 5x110 spider then.

 

[Nathan]

You have no idea what you are talking about. A 3220 is 92% efficient while the cycle is around 80%. That means a 3220 can produce over twice the power of the cyclone per pound of weight. I have run 8kw continuously through a 3220 without any problems (10 kw with fan cooling).

That's not the point I was making, I was saying that 3210 continuous power rating and weight is similar to a standard 48v 1680w cyclone motor like others have said

Compared to a 3210 the cyclone motor should be more powerful. It weighs 2kg compared to ~1kg for the astro.

and then if you force air cool the cyclone it will be similar continuous power to a NON air cooled 3220 i.e 4-5kw continous, I never said compared to an aircooled 3220, reason being is the cyclone is so cheap you could set that up fan cooled motor for like $250 usd whereas just the standard 3220 astro is $695 usd alone ! so u would have no spare money in the kitty. And being aircooled the cyclone would never get above 80c magnet danger zone and run at lower winding temps hence ~ 4-5% higher efficiency than a non aircooled astro. hence bang for buck for the watt, weight and efficiency and continuous power rating of the astro motor is expensive for what it is.

 

[bunya]

The kit looks awesome Dave, great to see your progress, its also funny how the sounds is somewhat like a two stroke. Strange question, if some people wanted reduced sound would it be possible to incorporate software with a current ripple that phases out the cyloidal drive harmonics? Could be a cool development, I imagine the noise is associated with a torque ripple on the output too.

In relation to the cyclone kit which I have, I don't think its fair to compare the two... In response to Nathan, from modelling, my CY650-1200 motor is at best 65% efficient at ~60amps, so to get comparable output power say 2kW the Cyclone would need 3.07kW input compared to 2.33kW from the Astro, it would need to dissipate 1070W of heat vs only 233W from the Astro. The power output is obviously comparable for peak (2kW) but continuous power is a different story. I'm in the process of getting better data, so I'll post it up on it's own thread when I'm done...

 

[tangentdave]

There is a bit of research on reducing harmonics in cycloidal drives- most of it revolves around manufacturing tolerances within the gearset for the application. This part isn't as simple as reducing tolerances to zero, the tolerances need to be in the right place and the right direction, with an eye towards how you're gonna make each component and that process's limitations. Half a hair width makes a big difference. I too imagine after enough time programming a fancy controller we could optimize the current profile for the drive. A few papers show a reduction in secondary harmonics and wear when the motor/controller is optimized but they take all take different approaches and almost nobody spins a cycloidal reducer as fast as we are- we're kinda sorta in new-ish territory. Most cycloidal reducers are enormously tough and heavy, used in industrial and earthmover applications where huge output torque is required; RPM is not really a consideration. It is a good idea Bunya, it's on the radar.

I think it's kinda funny the drive resembles a 2-stroke sound. It's like a full circle, back to old crappy technology we used to race with. I'm nostalgic for the smell of 2-stroke oil, but gawd what a pain. And obnoxious.

-dave

 

[LiFeCycle]

Hello Dave and other owners of this kit.
How do you feel about the 3210 motor versus the 3215 and 3220?
Per astroflight,

Motor				Typical Power Range 		Length (inches)
Astro 3210		 2,000 to 3,000 watts		2.2
Astro 3215		 3,000 to 4,500 watts		2.7
Astro 3220	 	4,000 to 6,000 watts		3.2

I would have thought it would be worth an extra 1/2" to add a few more hp.
Would the transmission handle it? Or would it be too wide to be practical? Just wondering why you chose what you did, and whether you think you'll stick with a 3210, or probably upgrade to 3215 or 20. Cheers

 

[tangentdave]

LiFeCycle- the difference in motors is really the application. What I mean is, for a given 50V motor wind, about 200Kv, the 3210, 3215 and 3220 make equivalent torque per amp, there's no free lunch. We're running the 3210 limited to 60A (HV80 is limiting here) which gives us a calculated 200ft-lbs of crank torque, which is what you're really after. An equivalent 3220 would still need about 60A to make 200ft-lbs. This is a lot of torque. As other users have noted, in average situations with this much power, you don't use the lower 5 gears of the cassette anymore, more torque probably won't help riding in the low speed regime.

The 3215 and 3220 are very much motorcycle territory. The extra current capacity in these motors means we can reduce the reduction ratio, increase the current and still have 200ft-lbs of torque but at a higher RPM. If we swap the 16t motor freewheel for an 18, 20 or 22t, we can have an overall motor->crankset ratio of 71:1, 64:1 or 58:1.

3210 7turn 80:1 375in/oz = 53A ->156ft-lbs continuous @130RPM (50V)
3210 5turn 71:1 562in/oz = 75A -> 208ft-lbs continuous @ 143RPM (50V)
3220 3turn 64:1 750in/oz = 125A -> 249ft-lbs continuous @ 176RPM (50V)
3320 4turn 58:1 750in/oz = 91A -> 226ft-lbs continuous @ 146RPM (50V)

There's math involved, double check me.

Basically, the larger motors add value above 40kph, otherwise there just isn't enough load on the bike to need the larger currents.

-dave

 

[Nathan]

In relation to the cyclone kit which I have, I don't think its fair to compare the two... In response to Nathan, from modelling, my CY650-1200 motor is at best 65% efficient at ~60amps, so to get comparable output power say 2kW the Cyclone would need 3.07kW input compared to 2.33kW from the Astro, it would need to dissipate 1070W of heat vs only 233W from the Astro. The power output is obviously comparable for peak (2kW) but continuous power is a different story. I'm in the process of getting better data, so I'll post it up on it's own thread when I'm done...

Where did you measure the cyclone efficiency was that at the wheels ? As it will be different if you measure at the wheels vs after the gearbox vs at the motor shaft as every stage has losses. So you need to be careful to measure at the same spot when comparing to something else. On other threads Chupa measure with dyno the cyclone motor efficiency to be 83% @ 3kw at the motor and they list on their website 90+% at the motor.
https://endless-sphere.com/forums/viewtopic.php?f=28&t=68648

I checked efficiency of the motor on the stand and saw 83% at the mechanical power of 3.2 kw.

Hence the gearbox makes a big difference to efficiency as cyclone has very efficient single stage planetary with strait cut gears, how and where did you measure 65% was that with a dyno at the wheels?

Another factor when comparing is that the Tangent motor has twice the gearbox reduction 80:1 to the cranks vs cyclone so you would most probably expect twice the gearbox efficiency losses when you compare the cyclone and the tangent at the wheels . So even though the motor may be slightly more efficient the gear reduction has twice the losses due to twice the reduction at the wheels is where to compare it.

Has anyone measured the efficiency of the Tangent astro motor at the cranks or at the wheels to see how efficient the whole motor and reduction is ?

 

[tangentdave]

the motor may be slightly more efficient the gear reduction has twice the losses due to twice the reduction

This isn't true. Tangent uses a single stage cycloidal arrangement optimized for speed and efficiency. Look back a few pages, you'll see at 10kRPM the Cycle Analyst shows a loss of about 150W when the gearbox is unloaded. I know it doesn't mean much without a actual measurement, but think about this. If the motor gives us 3000W, the gearbox uses 150W, that leaves 2850W for the freewheel, or 95% of what we put into it. At 10,000RPM.

I know from experience the motor is what is heating the unit when I run it hard. The heat comes from the motor side, the chain side of the drive runs cooler until everything is equalized. The Astro is 90%+ efficient, so... A quick googling of cycloidal gearing will show their efficiency, and that's not including my improvements. Super hard 4140 steel, advanced lubrication, optimized contact angles, beneficial leverage arms and enormous bearings all make a difference.

Cyclone setups work well and they're cheap. Less cars, more ebikes!


-dave

 

[jk1]

you'll see at 10kRPM the Cycle Analyst shows a loss of about 150W when the gearbox is unloaded. I know it doesn't mean much without a actual measurement, but think about this. If the motor gives us 3000W, the gearbox uses 150W, that leaves 2850W for the freewheel, or 95% of what we put into it. At 10,000RPM.

This assumes the gearbox losses are the same no load vs full load , which is not the case as under load their is a lot more frictional drag of the gear, with no load all you are doing is turning the gearbox bearings.... . Also it is true that losses are higher the higher the gear reduction as again their is more frictional load related losses. The only way to measure it accurately is with a dyno on the rear wheel i.e what is the output power at what input power.

 

[tangentdave]

This assumes the gearbox losses are the same no load vs full load

True true. My gearbox has 3-4 planetary teeth engaged with the ring gear at any time, and there's 2 planets. The planets have 12 points of contact with the output carrier at a diameter almost equal to the gear teeth. There is very little sliding contact in the Tangent gearbox, I estimate about 0.15mm per planet/ring tooth engagement, far less than any traditional spur gear allows. Here's a scientific equation I came up with:

very little sliding + large contact area * optimized geometry = runs cooler than the Astro Flight

The scientific literature on calculating cycloidal efficiencies is waay complex and I think they make too many assumptions or their equations are tailored for the particular reduction unit they're testing. Several trends do shine through, hence this awesome piece of hardware. A dyno would be cool, maybe when there's enough money and time. For now we've got to rely on user testing, and people are getting as good Wh/mi as about any other setup (with the fun of insane power on tap).

-dave

 

[morati]

This looks like it could be the lightweight machine I've been looking for. Awesome job Sir!

 

[Archer]

Ok call me spoiled but we need video from users of the tangent drive.Any takers?

 

[tangentdave]

Totally my bad, I'm in the middle of making the next bunch. I think it was worth re-doing most of the parts again to get these improvements in. I'll have more time and a better ride shortly.

The cheapo gopro is here, time to take a break and go for a ride o(^▽^)o

 

[Ralith]

On the subject of chainrings, I like the 38t narrow-wide (from RaceFace) I'm running as it gives me enough leverage to still pedal up a hill if I'm inclined to. I only wish it came in a nice hard steel. Limits your top speed on a flat to under ~50kph, but a larger motor freewheel could address that if you really want to go that fast. For myself, I'm perpetually conflicted between "speed is awesome" and being relieved I don't have the temptation towards that level of danger. Only time I've topped out on the road was this one time I found myself trying to keep pace in traffic on a major road, which was a terrible idea in the first place (blame Google routing in an unfamiliar area).

Speaking of a larger motor freewheel, I'm beginning to wonder if that might be the way to go to enable powered use of a wider range of the bike's gears, thereby reducing concentrated wear and making a wide cassette more useful. I like pedaling along, but doing that while simultaneously pegging the throttle isn't really necessary. This comes to mind as my 11t rear sprocket has started skipping under power.

All units will include all the changes I mentioned. The previous customer units will slowly be replaced to bring everybody to the same.

Awesome! This is really generous of you.

 

[tangentdave]

Reducing the overall ratio, I'm thinking the same. An 18t motor freewheel would put us at 70:1, 145 crank RPM. The motor could push each gear 15% farther than the 16t and use the lower gears a touch more. Maybe it's nicer to have the motor outrun the pedals, have more headroom in each gear.

That 11t cog is pretty small, especially to turn a bicycle wheel. I haven't skipped the chain on the 12t, so maybe we should gear for your same current top speed but in the 13t to be safe (and give ourselves two speeds of overdrive...)

 

[rodgah]

Reducing the overall ratio, I'm thinking the same. An 18t motor freewheel would put us at 70:1, 145 crank RPM. The motor could push each gear 15% farther than the 16t and use the lower gears a touch more. Maybe it's nicer to have the motor outrun the pedals, have more headroom in each gear.

That 11t cog is pretty small, especially to turn a bicycle wheel. I haven't skipped the chain on the 12t, so maybe we should gear for your same current top speed but in the 13t to be safe (and give ourselves two speeds of overdrive...)

with the small amount of playing I've had on 'thru the derailleur' drive bikes I have realised that if I made one for myself I wouldn't try to match the peak motor rpm to peak cadence.....you have a throttle after all. Instead give more headroom to the lower gears so you can climb those ridiculous hills in the big cogs and use the throttle to gain synergy while pedalling. Remove or don't use the really low tooth cogs....problem soldered

 

[Nathan]

with the small amount of playing I've had on 'thru the derailleur' drive bikes I have realised that if I made one for myself I wouldn't try to match the peak motor rpm to peak cadence.....you have a throttle after all. Instead give more headroom to the lower gears so you can climb those ridiculous hills in the big cogs and use the throttle to gain synergy while pedalling. Remove or don't use the really low tooth cogs....problem soldered

Yeah I agree why match peak power rpm to peak cadence RPM ? this means you severely limit your top speed and or put too much load on the small 11T rear cog. Also what difference does adding 200w peddling continuous to a 2000w continuous motor make to top speed or efficiency... not much ..

ALso Dave can you list on your website what the total weight of your kit, as it only shows the motor and brackets weight being 3.23 kg, i.e including chain wheels, controller, BB and throttles etc, i.e Total kit weight is what most people compare and some have to have very heavy chainwheels like the BBSHD 1000W http://electric-fatbike.com/2015/11/04/bbshd-first-impressions-meh/

BBBS HD1000w
•12lb 12 oz 68mm drive unit 5.509kg
•13lb 1oz 100mm drive unit 5.95kg
•558g crap ass 46T steel chainring (did I mention yet how much I hate this thing?)
•102g for each ebrake
= So total kit weight for BBSHD 68mm BB is = 6.169 kg what is the total weight of all parts of Tangent with a 68mm BB ?

 

[tangentdave]

My design intent has been the largest reduction possible to reduce current demands; I don't want to carry more battery. That said, I do want about two seconds longer in each gear under hard acceleration. And when you're really on the power, you can't pedal very well anyway. Good thing we can change our overall ratio so easily by swapping the freewheel, we can try out different ratios for different builds.

1300g are what the BB, spider, sprocket, 54 links of chain, threaded crank arms and White HD freewheel weigh. The website pics are the weight you would add to your bike, I assume your bike has a BB and crank arms already (did omit the freewheel/chain/sprocket for the pic).

Headed to the plating shop Monday, hopefully have this batch back by end of the week.

 

[Nathan]

1300g are what the BB, spider, sprocket, 54 links of chain, threaded crank arms and White HD freewheel weigh. The website pics are the weight you would add to your bike, I assume your bike has a BB and crank arms already (did omit the freewheel/chain/sprocket for the pic).

ALso Dave can you list on your website what the total weight of your kit, as it only shows the motor and brackets weight being 3.23 kg,

So the total kit weight of everything with the 3210 motor ( excluding throttle) is =3.23+ 1.3 = 4.53 kg, which is quite light compared to the BBSHD which is 6.169 kg and is less power 1kw continuous.

 

[morati]

Reducing the overall ratio, I'm thinking the same. An 18t motor freewheel would put us at 70:1, 145 crank RPM. The motor could push each gear 15% farther than the 16t and use the lower gears a touch more. Maybe it's nicer to have the motor outrun the pedals, have more headroom in each gear.

That 11t cog is pretty small, especially to turn a bicycle wheel. I haven't skipped the chain on the 12t, so maybe we should gear for your same current top speed but in the 13t to be safe (and give ourselves two speeds of overdrive...)

Really like the idea of switching to the 18t freewheel. Do you think you might make the switch on your kits Dave?

 

[tangentdave]

I'm shipping this round of customer kits with the 18t left-hand drive ACS freewheel. It's a better freewheel than the ACS southpaw for our application, but still no sealed bearing yet (trials freewheels won't work, the ratchet mechanism needs to be reversed). Joostj is getting a 22t since his pedals are only for show. ACS makes left hand drive freewheels in 16, 18, 20 and 22t. I've also integrated Grin Tech's inline shunt with the kit, simplifying the electronics even further.

This is a custom mount shape for a medium size Intense Tracer 29 which will be fitted inside the triangle. The motor chain now sits about 4mm off the mount plate now, reducing the sideways pull by 10x over the previous outer position. Flex and twist are non-issues. The 3/32" motor chain is super straight 'cause of the new spider and White HD freewheel and its kept tight by the ball bearing mounted tensioner. You can see the rubber motor mounts as the black interface between the housing and the mount plate (they're actually NinjaFlex right now). The first pic shows the adjustable metal strap used to hold the poly cushion against the downtube or seat tube. The black units are at another shop being anodized and colored optical black, pics to follow soon.

-dave